Different scales of fractures affect the reservoir quality in tight sandstone. There are more studies on macroscopic tectonic fractures but less on bedding fractures and microfractures. The control factors of multi-scale fractures are unclear. In this paper, we analyzed the types and controls of fractures in the second member of the Xinchang region in Western Sichuan. We use core and outcrops observations, imaging logging, scanning energy spectra, and rock slices. Natural fractures can be classified into tectonic, bedding, and microscopic types. The tectonic fractures are mainly low- to medium-angle tensile fractures. The bedding fractures are nearly horizontally distributed along the bedding surface, including parallel, dark mineral interface, and carbonaceous fragments interface bedding fractures. The microfractures develop intra-grain, edge-grain, and inter-grain types. The intra-grain microfractures are inside quartz or feldspar grains, whereas inter-grain types penetrate multiple grains with larger extension lengths. The tectonic fractures are related to the stress, grain size, mineral component, argillaceous content, and lithologic thickness. Parallel bedding fractures are controlled by the coupling of water depth and flow velocity. Bedding fractures at the interface are controlled by rock component. The microfractures are controlled by the length-width axis ratio of the grain, grain element content, and brittleness index. Fractures of different scales form a three-dimensional fracture system that has a substantial impact on the gas production.Tight sandstone gas is an unconventional natural resource dominated by low-porosity and low-permeability reservoirs with porosity less than 10% and air permeability less than 1 × 10–3 μm2 [1-4]. It has been discovered in many basins in China [5-8] and accounts for a relatively large proportion of the gas production, such as in the Ordos, Sichuan, Junggar, and Tarim basins [9-16]. The Xinchang gas field in the Sichuan Basin was first discovered in 1988. The exploration progress was slow owing to the insufficient understanding of geological and fracking processes. After 2,000 years, a few exploration wells were drilled in close to the fracture system, and gas production was increased [17-21]. Exploration showed that the fractures play an important role in controlling the gas production of the Xinchang gas field. However, the distribution of fractures in this zone is complex with different fracture geneses, scales, and occurrences. Nevertheless, there is a lack of the systematic understanding of fractures.Tectonic fractures in tight sandstones have been extensively studied [22, 23]. The factors affecting them include the stress heterogeneity in different tectonic zones [24-31] and lithologic heterogeneity [32-34]. Sedimentation controls differences in the lithology and layer thickness, and heterogeneity in the mineral composition and structure of reservoirs influence fracture development [35-40]. Bedding
{"title":"Controls of Multi-Scale Fractures in Tight Sandstones: A Case Study in the Second Member of Xujiahe Formation in Xinchang Area, Western Sichuan Depression","authors":"Junwei Zhao, Yingtao Yang, Gongyang Chen, Xiaoli Zheng, Senlin Yin, Lei Tian","doi":"10.2113/2024/lithosphere_2023_343","DOIUrl":"https://doi.org/10.2113/2024/lithosphere_2023_343","url":null,"abstract":"Different scales of fractures affect the reservoir quality in tight sandstone. There are more studies on macroscopic tectonic fractures but less on bedding fractures and microfractures. The control factors of multi-scale fractures are unclear. In this paper, we analyzed the types and controls of fractures in the second member of the Xinchang region in Western Sichuan. We use core and outcrops observations, imaging logging, scanning energy spectra, and rock slices. Natural fractures can be classified into tectonic, bedding, and microscopic types. The tectonic fractures are mainly low- to medium-angle tensile fractures. The bedding fractures are nearly horizontally distributed along the bedding surface, including parallel, dark mineral interface, and carbonaceous fragments interface bedding fractures. The microfractures develop intra-grain, edge-grain, and inter-grain types. The intra-grain microfractures are inside quartz or feldspar grains, whereas inter-grain types penetrate multiple grains with larger extension lengths. The tectonic fractures are related to the stress, grain size, mineral component, argillaceous content, and lithologic thickness. Parallel bedding fractures are controlled by the coupling of water depth and flow velocity. Bedding fractures at the interface are controlled by rock component. The microfractures are controlled by the length-width axis ratio of the grain, grain element content, and brittleness index. Fractures of different scales form a three-dimensional fracture system that has a substantial impact on the gas production.Tight sandstone gas is an unconventional natural resource dominated by low-porosity and low-permeability reservoirs with porosity less than 10% and air permeability less than 1 × 10–3 μm2 [1-4]. It has been discovered in many basins in China [5-8] and accounts for a relatively large proportion of the gas production, such as in the Ordos, Sichuan, Junggar, and Tarim basins [9-16]. The Xinchang gas field in the Sichuan Basin was first discovered in 1988. The exploration progress was slow owing to the insufficient understanding of geological and fracking processes. After 2,000 years, a few exploration wells were drilled in close to the fracture system, and gas production was increased [17-21]. Exploration showed that the fractures play an important role in controlling the gas production of the Xinchang gas field. However, the distribution of fractures in this zone is complex with different fracture geneses, scales, and occurrences. Nevertheless, there is a lack of the systematic understanding of fractures.Tectonic fractures in tight sandstones have been extensively studied [22, 23]. The factors affecting them include the stress heterogeneity in different tectonic zones [24-31] and lithologic heterogeneity [32-34]. Sedimentation controls differences in the lithology and layer thickness, and heterogeneity in the mineral composition and structure of reservoirs influence fracture development [35-40]. Bedding","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":"15 1","pages":""},"PeriodicalIF":2.4,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140017254","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-12DOI: 10.2113/2024/lithosphere_2023_317
Zeqi Zhu, Xiancheng Mei, Jianhe Li, Qian Sheng
In order to study the initiation mechanism of rocks under hydromechanical coupling, hydromechanical coupling triaxial tests and acoustic emission tests were carried out on basalt in the Xiluodu hydropower station dam site area in southwestern China. The test results indicate that the basalt displays typical hard brittle behavior, and its peak strength increases as confining pressure rises. Conversely, the peak strength decreases gradually as the initial water pressure increases, which leads to decreased hardness. Meanwhile, tensile failure is the main crack initiation mode under hydromechanical coupling action. During the stable crack growth stage, tensile failure is predominant, complemented by shear failure, with failures mainly occurring in the rock middle position. Contrary to this, during the unstable stage, the rock failure is mainly due to shear failure. The critical pore water pressure failure criterion of rock crack initiation under hydromechanical coupling conditions is derived based on the test results and introduced into the numerical simulation. The hydromechanical coupling failure process and pore water pressure distribution law of basalt are analyzed, and the rationality of the critical pore water pressure failure criterion is verified. These findings are significant for understanding the rock failure process under hydromechanical coupling action and provide a valuable reference for future research.Hydroelectric engineering projects often involve structures such as underground power stations, water diversion tunnels, and sloping dam foundations, which are subjected to the combined action of high-ground stress and strong osmotic pressure. Therefore, research on the mechanical properties of rocks or rock masses under hydromechanical coupling has become a pressing issue in geotechnical engineering. Several scholars, including Song et al. [1], Zhu et al. [2], Yu et al. [3], Xu et al. [4], Wang et al. [5], and Wang et al. [6], have conducted hydromechanical coupling triaxial tests on limestone [1-3], sandstone [4-6], and granite [7, 8] to investigate the relationship between rock permeability, stress, strain, and pore water pressure. They have discussed the influence of pore water pressure on rock strength characteristics, deformation laws, and damage evolution. Moreover, Li et al. [9], Zhao [10], and Guo et al. [11] have employed acoustic emission (AE) signals to analyze the AE characteristics during the process of rock cracking under hydromechanical coupling.The aforementioned research has extensively demonstrated that hydromechanical coupling induces pore water pressure within the internal cracks of a rock, which significantly impacts the cracking process [12, 13]. Once the pore water pressure attains a critical level, it instigates the inception, expansion, and penetration of rock cracks, commonly referred to as hydromechanical fracturing [14]. This phenomenon is a significant factor that causes a range of engineering disasters, inc
{"title":"Experimental and Numerical Investigation of Rock Failure Process under Hydromechanical Coupling Action","authors":"Zeqi Zhu, Xiancheng Mei, Jianhe Li, Qian Sheng","doi":"10.2113/2024/lithosphere_2023_317","DOIUrl":"https://doi.org/10.2113/2024/lithosphere_2023_317","url":null,"abstract":"In order to study the initiation mechanism of rocks under hydromechanical coupling, hydromechanical coupling triaxial tests and acoustic emission tests were carried out on basalt in the Xiluodu hydropower station dam site area in southwestern China. The test results indicate that the basalt displays typical hard brittle behavior, and its peak strength increases as confining pressure rises. Conversely, the peak strength decreases gradually as the initial water pressure increases, which leads to decreased hardness. Meanwhile, tensile failure is the main crack initiation mode under hydromechanical coupling action. During the stable crack growth stage, tensile failure is predominant, complemented by shear failure, with failures mainly occurring in the rock middle position. Contrary to this, during the unstable stage, the rock failure is mainly due to shear failure. The critical pore water pressure failure criterion of rock crack initiation under hydromechanical coupling conditions is derived based on the test results and introduced into the numerical simulation. The hydromechanical coupling failure process and pore water pressure distribution law of basalt are analyzed, and the rationality of the critical pore water pressure failure criterion is verified. These findings are significant for understanding the rock failure process under hydromechanical coupling action and provide a valuable reference for future research.Hydroelectric engineering projects often involve structures such as underground power stations, water diversion tunnels, and sloping dam foundations, which are subjected to the combined action of high-ground stress and strong osmotic pressure. Therefore, research on the mechanical properties of rocks or rock masses under hydromechanical coupling has become a pressing issue in geotechnical engineering. Several scholars, including Song et al. [1], Zhu et al. [2], Yu et al. [3], Xu et al. [4], Wang et al. [5], and Wang et al. [6], have conducted hydromechanical coupling triaxial tests on limestone [1-3], sandstone [4-6], and granite [7, 8] to investigate the relationship between rock permeability, stress, strain, and pore water pressure. They have discussed the influence of pore water pressure on rock strength characteristics, deformation laws, and damage evolution. Moreover, Li et al. [9], Zhao [10], and Guo et al. [11] have employed acoustic emission (AE) signals to analyze the AE characteristics during the process of rock cracking under hydromechanical coupling.The aforementioned research has extensively demonstrated that hydromechanical coupling induces pore water pressure within the internal cracks of a rock, which significantly impacts the cracking process [12, 13]. Once the pore water pressure attains a critical level, it instigates the inception, expansion, and penetration of rock cracks, commonly referred to as hydromechanical fracturing [14]. This phenomenon is a significant factor that causes a range of engineering disasters, inc","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":"10 1","pages":""},"PeriodicalIF":2.4,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139553739","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-12DOI: 10.2113/2024/lithosphere_2023_288
Junwu Du, Qingxiang Huang
Aiming at investigating the strong roof weighting when the large height mining face is nearing the main withdrawal roadway, the 52,304 working face (WF) nearly through the main withdrawal roadway mining in a colliery of Shendong coalfield was taken as the research background. The ground pressure, roof structure, and superposition effect of stress in the last mining stage were studied by field measurement, physical simulation, and numerical calculations. The obtained results demonstrated that the main roof formed the “long step voussoir beam” structure under the influence of the main withdrawal roadway. The superposition effect of the front abutment pressure of the WF and the concentrated stress of the main withdrawal roadway caused the stress asymmetrical distribution on the two sides -level hard rock straof the main withdrawal roadway, and the stability of the pillar on the mining side decreases. The initial average periodic weighting interval was 20.7 m. While the WF approaches the main withdrawal roadway, the pillar near the WF of the main withdrawal roadway collapsed, the main roof was broken ahead of the WF, and the actual roof control distance of support and the periodic weighting interval increased by 2.56 and 1.26 times the normal state, respectively. Consequently, the “static load” of the immediate roof and the “dynamic load” of the sliding unsteadiness of the long step voussoir beam increased. The structural model of the “long step voussoir beam” under the superposition of “static and dynamic load” was established concerning those results, and an expression was proposed to compute the support resistance. Meanwhile, the mechanism of strong roof weighting was revealed when the WF was nearly through the main withdrawal roadway. The research conclusion is expected to provide a guideline for the safe withdrawal of the large-height mining faces under similar conditions.To increase the withdrawal speed and yield efficacy of the working face (WF) and avoid the tense connection between face mining and entry driving, predriving double withdrawal roadway is widely used in coal mines to reinforce the withdrawal operation [1]. In this scheme, the main and auxiliary withdrawal roadways are advance driven at the stop-mining line of the WF. After the primary withdrawal roadway is connected with the WF, the reinforcements are withdrawn through the connecting entry between the primary and secondary withdrawal roadways. Consequently, the withdrawal speed of the WF increases 3–5 times compared with the traditional methods, thereby increasing the production rate and improving the mining efficiency [2, 3]. Although this method has remarkable advantages, it has some shortcomings, including low mining speed in the last mining stage, concentrated mining-induced stress field, and high roof pressure [4]. More specifically, the superposition effect of the lateral and front abutment pressure of the main withdrawal roadway and the WF near the main withdrawal roadway
在这种情况下，采空区一侧煤柱的集中应力为10.0 MPa，是正常情况下的2.5倍。当距离为 2.0 m 时，WF 的前墩压力传递到主回风巷道的煤柱壁上，峰值应力达到 11.5 MPa，WF 的应力场发生超前叠加。分析结果表明，当 WF 接近主回风巷道时，前方支护压力与主回风巷道集中应力的叠加效应显著，导致采掘侧煤柱完全垮塌。物理模拟和数值计算表明，当 WF 接近主回风巷道时，前方支护压力和主回风巷道集中应力的叠加效应显著，主回风巷道 WF 附近的煤柱垮落，WF 前方主顶板破碎。在这种情况下，WF 的风险最大。考虑到主回风巷道对 WF 的影响，WF 的顶板控制距离和周期加权间隔都有所增加。因此，主顶板呈现出 "长台阶伏梁 "结构。此外，直接顶板的 "静载荷 "和 "长台阶伏溜梁 "结构的 "动载荷 "都有所增加，由液压动力支架承担。为进一步研究末采阶段强采压的作用机理，根据物理模拟和数值计算得出的基本结论，针对大采高工作面顶板的结构特点，建立了 "静、动荷载 "叠加下的 "长台阶伏梁 "结构模型，如图 8 所示，其中 h1 和 h 分别表示直接顶和主顶板的厚度。其中，h1 和 h 分别表示直接顶和主顶板的厚度，M 和 N 分别表示主顶板的关键块体，ω θ 分别表示块体的旋转角度。此外，b 是相应的台阶高度。A、C 和 B 代表关键砌块的铰接点。T 是水平挤压力。RM 和 W 分别为支撑所承受的动荷载和静荷载。R1 为开采侧支柱的残余加固力。R0 为煤矸石对关键块 N 的加固反力，P 为液压动力支架的工作阻力。参照 "伏流梁 "结构的应力分析方法[27]，由于岩块转角挤压面的高度较小，破碎关键块接触面的高度可以忽略不计。因此，WF 接近主要回撤巷道时的关键块模型可简化如下（图 9）：其中，l 表示 WF 通过主要回撤巷道前的平均周期加权间隔；lz 为 WF 接近主要回撤巷道时周期加权间隔的增加长度；h 为主要顶板厚度。P1 和 P2 分别是关键区块 M 和 N 的重量及其承受的荷载。此外，QA 和 QB 分别代表铰链接头 A 和 B 处的剪力。在 C 点，关键块 M 由关键块 N 加固，而关键块 N 则由掘进巷道中的塌落矸石加固。根据关键块的平衡特性，关键块 M 在 C 点的力矩总和为 0，可用数学公式表示如下：此外，沿关键块垂直方向的结果力如公式（5）所示。将公式（1）、（3）、（4）和（5）合并可得到以下表达式：根据 "S-R "稳定性理论[28]，除非满足以下不等式，否则该结构容易发生滑动失稳：其中 P1 为关键块 M 所承受的荷载，可通过以下表达式计算得出：根据 Terzaghi 的土压力理论，荷载传递系数的计算公式为。 最后，揭示了WF接近主要回撤巷道时顶板冒落和支架破碎的机理。根据物理模拟，52304 大采高工作面在无主要回撤巷道影响的情况下，主要顶板冒落形成 "阶梯伏梁 "结构，主要顶板关键块体的平均塌落角和旋转角分别为 65°和 5°。在主撤退巷道影响前，平均周期配重间隔为 20.7 m，平均支护工作阻力为 17540 kN，WF 前承压力和主撤退巷道集中应力的叠加效应导致支柱完全倒塌。同时，主顶板在 WF 前方塌陷，形成 "长台阶伏梁 "结构。因此，支护的实际顶板控制距为正常状态下的 2.56 倍，周期加权间隔为正常状态下的 1.26 倍。在此基础上，建立了 "静、动载荷 "叠加下的 "长台阶溜子梁 "结构模型，并推导出了液压动力支架在 WF 接近主撤退巷道时的合理工作阻力表达式。最后，揭示了当 WF 接近主撤退巷道时顶板冒落和支架破碎的机理。本文有望为类似条件下大采高回采工作面的安全回撤提供指导。本文收录了主要相关数据，相应作者将根据合理要求提供其他相关数据。作者声明，本文的发表不存在利益冲突。我们感谢国家自然科学基金、陕西省自然科学基础研究计划、煤炭资源精细勘查与智能开发国家重点实验室对本研究的支持。感谢学术编辑和匿名审稿人提出的善意建议和宝贵意见。
{"title":"Investigating the Mechanism of Strong Roof Weighting and Support Resistance Near Main Withdrawal Roadway in Large-Height Mining Face","authors":"Junwu Du, Qingxiang Huang","doi":"10.2113/2024/lithosphere_2023_288","DOIUrl":"https://doi.org/10.2113/2024/lithosphere_2023_288","url":null,"abstract":"Aiming at investigating the strong roof weighting when the large height mining face is nearing the main withdrawal roadway, the 52,304 working face (WF) nearly through the main withdrawal roadway mining in a colliery of Shendong coalfield was taken as the research background. The ground pressure, roof structure, and superposition effect of stress in the last mining stage were studied by field measurement, physical simulation, and numerical calculations. The obtained results demonstrated that the main roof formed the “long step voussoir beam” structure under the influence of the main withdrawal roadway. The superposition effect of the front abutment pressure of the WF and the concentrated stress of the main withdrawal roadway caused the stress asymmetrical distribution on the two sides -level hard rock straof the main withdrawal roadway, and the stability of the pillar on the mining side decreases. The initial average periodic weighting interval was 20.7 m. While the WF approaches the main withdrawal roadway, the pillar near the WF of the main withdrawal roadway collapsed, the main roof was broken ahead of the WF, and the actual roof control distance of support and the periodic weighting interval increased by 2.56 and 1.26 times the normal state, respectively. Consequently, the “static load” of the immediate roof and the “dynamic load” of the sliding unsteadiness of the long step voussoir beam increased. The structural model of the “long step voussoir beam” under the superposition of “static and dynamic load” was established concerning those results, and an expression was proposed to compute the support resistance. Meanwhile, the mechanism of strong roof weighting was revealed when the WF was nearly through the main withdrawal roadway. The research conclusion is expected to provide a guideline for the safe withdrawal of the large-height mining faces under similar conditions.To increase the withdrawal speed and yield efficacy of the working face (WF) and avoid the tense connection between face mining and entry driving, predriving double withdrawal roadway is widely used in coal mines to reinforce the withdrawal operation [1]. In this scheme, the main and auxiliary withdrawal roadways are advance driven at the stop-mining line of the WF. After the primary withdrawal roadway is connected with the WF, the reinforcements are withdrawn through the connecting entry between the primary and secondary withdrawal roadways. Consequently, the withdrawal speed of the WF increases 3–5 times compared with the traditional methods, thereby increasing the production rate and improving the mining efficiency [2, 3]. Although this method has remarkable advantages, it has some shortcomings, including low mining speed in the last mining stage, concentrated mining-induced stress field, and high roof pressure [4]. More specifically, the superposition effect of the lateral and front abutment pressure of the main withdrawal roadway and the WF near the main withdrawal roadway","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":"35 1","pages":""},"PeriodicalIF":2.4,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139758627","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-12DOI: 10.2113/2024/lithosphere_2023_173
Yanzhong Liang, Bailu Teng, Wanjing Luo
Hydraulic fracturing stimulation, which improves matrix permeability and reduces production costs, has been extensively used in the exploitation of multilayer reservoirs. However, little research on the production dynamic characteristics of vertically fractured wells in stratified reservoirs has been done in the literature. The influence of flux variation along the fracture on the pressure transient behavior has been ignored in these previous works. Therefore, this paper introduces a novel semi-analytical model for fractured wells in multilayer reservoirs, in which the finite difference method is used to characterize fluid flow in the fracture and the Green’s function method is used to characterize fluid flow in the matrix. With the aid of the model, the production dynamic characteristics of fractured wells in multilayer reservoirs can be readily investigated. In addition, based on the assumption of nonuniform flux distribution along the fracture, we successfully recognize four flow regimes occurring in the pressure drop and pressure derivative curves. Following that, the influences of several parameters on the pressure dynamics and layered flux contribution are studied. The calculation results indicate that a larger storability ratio, as well as a larger permeability ratio, can increase the values of the pressure drop and the pressure derivative; the greater the fracture height, the greater the fluid flow into each layer of the fracture. During the production of this model, increasing the fracture conductivity can reduce the pressure drop and pressure derivative, which means lower flow resistance in the fracture.With the growing dependence on fossil energy, deep and ultra-deep areas have steadily evolved into the next main potentials of resource exploration and development. Recently, China has consistently discovered a huge number of deep-layer reservoirs, such as the Puguang, Tahe, Shunbei, and Anyue oilfields, showing great resource potentialities and considerable economic benefits [1]. Considering the influence of the complex sedimentary environment, most deep reservoirs are composed of several layers with different stratigraphic characteristics. Commingling production is commonly adopted to increase producing profit for stratified reservoirs in oil and gas fields [2]. Given this, extensive literature was related to the pressure dynamics of a vertical well in stratified reservoirs [3-6]. Rahman and Mattar [7] derived a new analytical solution for the commingled-layered reservoir with unequal initial pressures in the Laplace domain. Onwunyili and Onyekonwu [8] developed a coupled model that can more accurately simulate the commingled production behavior of multilayer reservoirs. Shi et al. [9] investigated the impact of the vertical inhomogeneous closed boundary radii on pressure transient behaviors of the multilayered commingled reservoir. These previous researches give us a basic understanding of the production dynamic characteristics for th
{"title":"Production Dynamic Characteristic of Fractured Wells in Multilayer Reservoirs Considering the Effect of Non-Uniform Flux Distribution","authors":"Yanzhong Liang, Bailu Teng, Wanjing Luo","doi":"10.2113/2024/lithosphere_2023_173","DOIUrl":"https://doi.org/10.2113/2024/lithosphere_2023_173","url":null,"abstract":"Hydraulic fracturing stimulation, which improves matrix permeability and reduces production costs, has been extensively used in the exploitation of multilayer reservoirs. However, little research on the production dynamic characteristics of vertically fractured wells in stratified reservoirs has been done in the literature. The influence of flux variation along the fracture on the pressure transient behavior has been ignored in these previous works. Therefore, this paper introduces a novel semi-analytical model for fractured wells in multilayer reservoirs, in which the finite difference method is used to characterize fluid flow in the fracture and the Green’s function method is used to characterize fluid flow in the matrix. With the aid of the model, the production dynamic characteristics of fractured wells in multilayer reservoirs can be readily investigated. In addition, based on the assumption of nonuniform flux distribution along the fracture, we successfully recognize four flow regimes occurring in the pressure drop and pressure derivative curves. Following that, the influences of several parameters on the pressure dynamics and layered flux contribution are studied. The calculation results indicate that a larger storability ratio, as well as a larger permeability ratio, can increase the values of the pressure drop and the pressure derivative; the greater the fracture height, the greater the fluid flow into each layer of the fracture. During the production of this model, increasing the fracture conductivity can reduce the pressure drop and pressure derivative, which means lower flow resistance in the fracture.With the growing dependence on fossil energy, deep and ultra-deep areas have steadily evolved into the next main potentials of resource exploration and development. Recently, China has consistently discovered a huge number of deep-layer reservoirs, such as the Puguang, Tahe, Shunbei, and Anyue oilfields, showing great resource potentialities and considerable economic benefits [1]. Considering the influence of the complex sedimentary environment, most deep reservoirs are composed of several layers with different stratigraphic characteristics. Commingling production is commonly adopted to increase producing profit for stratified reservoirs in oil and gas fields [2]. Given this, extensive literature was related to the pressure dynamics of a vertical well in stratified reservoirs [3-6]. Rahman and Mattar [7] derived a new analytical solution for the commingled-layered reservoir with unequal initial pressures in the Laplace domain. Onwunyili and Onyekonwu [8] developed a coupled model that can more accurately simulate the commingled production behavior of multilayer reservoirs. Shi et al. [9] investigated the impact of the vertical inhomogeneous closed boundary radii on pressure transient behaviors of the multilayered commingled reservoir. These previous researches give us a basic understanding of the production dynamic characteristics for th","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":"28 1","pages":""},"PeriodicalIF":2.4,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140151178","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hydraulic fracturing is a crucial technology for enhancing the recovery of oil and gas from unconventional reservoirs. Accurately describing fracture morphology is essential for accurately predicting production dynamics. This article proposes a new fracture inversion model based on dynamic data-driven methods, which is different from the conventional linear elastic fracture mechanics model. This method eliminates the need to consider complex mechanical mechanisms, resulting in faster simulation speeds. In the model, the fracture morphology is constrained by combining microseismic data and fracturing construction data, and the fracture tip propagation domain is introduced to characterize the multi-directionality of fracture propagation. The simulated fracture exhibits a multi-branch fracture network morphology, aligning more closely with geological understanding. In addition, the influence of microseismic signal intensity on the direction of fracture propagation is considered in this study. The general stochastic approximation (GSA) algorithm is employed to optimize the direction of fracture propagation. The proposed method is applied to both the single-stage fracturing model and the whole well fracturing model. The research findings indicate that in the single-stage fracturing model, the inverted fracture morphology aligns closely with the microseismic data, with a fitting rate of the fracturing construction curve exceeding 95%, and a microseismic data fitting rate exceeding 93%. In the whole well fracturing model, a total of 18 sections were inverted. The fitting rate between the overall fracture morphology and the microseismic data reached 90%. The simulation only took 5 minutes, demonstrating high computational efficiency and meeting the needs of large-scale engineering fracture simulation. This method can effectively support geological modeling and production dynamic prediction.The world has abundant shale gas reservoir resources; however, due to the influence of reservoir rock properties, its development poses significant challenges [1-4]. Hydraulic fracturing technology can effectively enhance the physical properties of reservoirs and form complex fracture networks within the reservoir, thereby promoting oil and gas production [5-7]. In order to assess the development impact of shale gas reservoirs and devise appropriate development plans, it is necessary to establish a numerical model that is specific to the shale gas reservoir in question. Accurately describing the post-fracturing fracture morphology is crucial for model construction and subsequent flow simulations, as it is a key factor in ensuring the accuracy of model calculation results [8]. Moreover, the morphology of fractures post-fracturing is often highly complex, characterized by a network structure of fractures [9, 10]. Many existing fracture propagation models only consider a simplified quasi-three-dimensional or three-dimensional straight fracture structure. However, these mo
{"title":"Data-Driven Dynamic Inversion Method for Complex Fractures in Unconventional Reservoirs","authors":"Ruixue Jia, Xiaoming Li, Xiaoyong Ma, Liang Zhu, Yangdong Guo, Xiaoping Song, Pingde Wang, Jiantao Wang","doi":"10.2113/2024/lithosphere_2023_347","DOIUrl":"https://doi.org/10.2113/2024/lithosphere_2023_347","url":null,"abstract":"Hydraulic fracturing is a crucial technology for enhancing the recovery of oil and gas from unconventional reservoirs. Accurately describing fracture morphology is essential for accurately predicting production dynamics. This article proposes a new fracture inversion model based on dynamic data-driven methods, which is different from the conventional linear elastic fracture mechanics model. This method eliminates the need to consider complex mechanical mechanisms, resulting in faster simulation speeds. In the model, the fracture morphology is constrained by combining microseismic data and fracturing construction data, and the fracture tip propagation domain is introduced to characterize the multi-directionality of fracture propagation. The simulated fracture exhibits a multi-branch fracture network morphology, aligning more closely with geological understanding. In addition, the influence of microseismic signal intensity on the direction of fracture propagation is considered in this study. The general stochastic approximation (GSA) algorithm is employed to optimize the direction of fracture propagation. The proposed method is applied to both the single-stage fracturing model and the whole well fracturing model. The research findings indicate that in the single-stage fracturing model, the inverted fracture morphology aligns closely with the microseismic data, with a fitting rate of the fracturing construction curve exceeding 95%, and a microseismic data fitting rate exceeding 93%. In the whole well fracturing model, a total of 18 sections were inverted. The fitting rate between the overall fracture morphology and the microseismic data reached 90%. The simulation only took 5 minutes, demonstrating high computational efficiency and meeting the needs of large-scale engineering fracture simulation. This method can effectively support geological modeling and production dynamic prediction.The world has abundant shale gas reservoir resources; however, due to the influence of reservoir rock properties, its development poses significant challenges [1-4]. Hydraulic fracturing technology can effectively enhance the physical properties of reservoirs and form complex fracture networks within the reservoir, thereby promoting oil and gas production [5-7]. In order to assess the development impact of shale gas reservoirs and devise appropriate development plans, it is necessary to establish a numerical model that is specific to the shale gas reservoir in question. Accurately describing the post-fracturing fracture morphology is crucial for model construction and subsequent flow simulations, as it is a key factor in ensuring the accuracy of model calculation results [8]. Moreover, the morphology of fractures post-fracturing is often highly complex, characterized by a network structure of fractures [9, 10]. Many existing fracture propagation models only consider a simplified quasi-three-dimensional or three-dimensional straight fracture structure. However, these mo","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":"179 1","pages":""},"PeriodicalIF":2.4,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140313388","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-12DOI: 10.2113/2024/lithosphere_2023_103
Jing Ba, Jinyi Min, Lin Zhang, José M. Carcione
The nonlinear characteristics of the rock transport properties (permeability and electrical conductivity in this study) as a function of stress are closely related to the geometry of the pore space, which consists of stiff pores, microcracks, or microfractures. We consider two behaviors of the pore space, one linear and the other exponential, related to the stiff pores and microfractures, respectively, where the relation between stress and strain can be described by the Two-Part Hooke’s Model. With this model, the relations between porosity, transport properties, and effective stress (confining minus pore pressure) can be obtained and validated with the experimental data of four tight sandstones collected from the Shaximiao Formation of Sichuan Basin, southwest China. The agreement is good. At low effective stresses, the closure of cracks is the main mechanism affecting the transport properties, whose behavior is similar in terms of their parameters. Subsequently, experimental data of nine tight sandstones from the Yanchang Formation, collected from the Ordos Basin, west China, are employed to confirm the previous results, indicating that the fluid and electrical current follow the same path in the pore space.Reservoir rocks have pores, cracks, or microfractures and are generally heterogeneous [1-4]. The deformation under loading is different in stiff pores and microfractures, which affects the elastic and transport properties, especially in low-permeability rocks. Since cracks provide a permeability path for the flow of reservoir fluids [5-9], understanding of the relationships between the transport properties and effective stress is important for detecting and monitoring reservoir fluids.Previous studies revealed that the exponential function describes the behavior of permeability and conductivity as a function of effective stress [10-20]. However, an important point is to describe the behavior of the sharp decrease of these transport properties when the effective stress increases at low values, especially for low-permeability rocks [21, 22]. The power law has also been adopted to describe such variation [23-27]. For instance, Jones and Owens [28] and Walsh [29] reformulated the expression of power law. On the other hand, Kaselow and Shapiro [30] applied a four-parameter exponential equation to analyze the electrical conductivity as a function of the effective pressure.The closure of cracks with increasing effective stress leads to lower porosity, and permeability or electrical conductivity shows a similar behavior. The transport properties as a function of porosity can be studied with a power law [31, 32] or by analyzing experimental data [21]. Archie [33] established an empirical relation between the formation factor (the ratio between bulk resistivity and that of water) and porosity. Subsequently, some researchers investigated the relationships between electrical conductivity and porosity [34, 35], clay content [36-38], crack radii, aspect r
{"title":"Effects of Stress on Transport Properties in Fractured Porous Rocks","authors":"Jing Ba, Jinyi Min, Lin Zhang, José M. Carcione","doi":"10.2113/2024/lithosphere_2023_103","DOIUrl":"https://doi.org/10.2113/2024/lithosphere_2023_103","url":null,"abstract":"The nonlinear characteristics of the rock transport properties (permeability and electrical conductivity in this study) as a function of stress are closely related to the geometry of the pore space, which consists of stiff pores, microcracks, or microfractures. We consider two behaviors of the pore space, one linear and the other exponential, related to the stiff pores and microfractures, respectively, where the relation between stress and strain can be described by the Two-Part Hooke’s Model. With this model, the relations between porosity, transport properties, and effective stress (confining minus pore pressure) can be obtained and validated with the experimental data of four tight sandstones collected from the Shaximiao Formation of Sichuan Basin, southwest China. The agreement is good. At low effective stresses, the closure of cracks is the main mechanism affecting the transport properties, whose behavior is similar in terms of their parameters. Subsequently, experimental data of nine tight sandstones from the Yanchang Formation, collected from the Ordos Basin, west China, are employed to confirm the previous results, indicating that the fluid and electrical current follow the same path in the pore space.Reservoir rocks have pores, cracks, or microfractures and are generally heterogeneous [1-4]. The deformation under loading is different in stiff pores and microfractures, which affects the elastic and transport properties, especially in low-permeability rocks. Since cracks provide a permeability path for the flow of reservoir fluids [5-9], understanding of the relationships between the transport properties and effective stress is important for detecting and monitoring reservoir fluids.Previous studies revealed that the exponential function describes the behavior of permeability and conductivity as a function of effective stress [10-20]. However, an important point is to describe the behavior of the sharp decrease of these transport properties when the effective stress increases at low values, especially for low-permeability rocks [21, 22]. The power law has also been adopted to describe such variation [23-27]. For instance, Jones and Owens [28] and Walsh [29] reformulated the expression of power law. On the other hand, Kaselow and Shapiro [30] applied a four-parameter exponential equation to analyze the electrical conductivity as a function of the effective pressure.The closure of cracks with increasing effective stress leads to lower porosity, and permeability or electrical conductivity shows a similar behavior. The transport properties as a function of porosity can be studied with a power law [31, 32] or by analyzing experimental data [21]. Archie [33] established an empirical relation between the formation factor (the ratio between bulk resistivity and that of water) and porosity. Subsequently, some researchers investigated the relationships between electrical conductivity and porosity [34, 35], clay content [36-38], crack radii, aspect r","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":"66 1","pages":""},"PeriodicalIF":2.4,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139589747","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-12DOI: 10.2113/2024/lithosphere_2023_193
Hu Wang, Peisheng Luo, Yi Liang, Dongming Li, Kaijin Li, Lin Deng, Lichun Chen
Microfracture density in fault damage zones can reflect spatial variability that decays in intensity as a function of distance from the fault, which is crucial in understanding the mechanical, seismological, and fluid-flow properties of the fault system. However, few studies explored the characteristics of fracture density between the two sides of active dip-slip faults due to rare field observations. Here, we measured and modeled microfractures across an active thrust fault associated with the 2008 Mw 7.9 Wenchuan earthquake in the Longmen Shan, eastern Tibetan Plateau. The results showed that the microfracture density at the Qingping site developed more intensely in the hanging wall than in the footwall for an exposed thrust fault, indicating an asymmetrical pattern. The hidden thrust fault at the Jushui site showed that microfractures developed more intensely in vertical planes in the hanging wall than in the footwall, whereas microfractures developed similarly in horizontal planes within the two sides, indicating a quasiasymmetrical pattern. Comparing the data at the two sites with computational modeling, we suggest that fault geometry might exert a first-order control of the asymmetrical microfracture density pattern, which is helpful for revealing different deformational behaviors of rock masses in the fault damage zones and better understanding the hanging-wall effect for evaluating seismic hazards on active thrust faults.A fault damage zone, expressed as a zone with numerous fractures surrounding a narrow fault core, has been considered to be related to coseismic loading and, therefore, has the potential to reveal the rock deformational mechanics and past earthquake rupture conditions [1-7]. Moreover, such a damage zone is expected to act as conduits, barriers, or combined conduit-barrier systems that play a fundamental role in crustal fluid flow [8-10]. Therefore, quantitative determination of characteristics of fractures in the fault damage zone is critical to understand the mechanical and seismological properties of the fault system.Geometrically, fracture density is one of the key parameters in evaluating the spatial variability that decays in intensity as a function of distance from the fault [11, 12]. Many studies have measured micro/mesofracture density on fault-perpendicular transects to show that fracture density decreases gradually away from the fault core, which can be simplified to fit either an exponential decay model [13] or a power law decay model [14, 15] in the fault damage zone. Moreover, previous studies have suggested that the characteristics of fracture density might be influenced by the amount of slip across the fault, the size of the fault, lithology, rupture processes, and movement history [8, 13, 16]. For example, Caine et al. [8] suggested that a wide damage zone may indicate the effect of more repeated seismic events with greater accumulative deformation than that of a narrow damage zone. Ostermeijer et al. [12]
{"title":"Asymmetrical Microfracture Density Across an Active Thrust Fault: Evidence from the Longmen Shan Fault, Eastern Tibet","authors":"Hu Wang, Peisheng Luo, Yi Liang, Dongming Li, Kaijin Li, Lin Deng, Lichun Chen","doi":"10.2113/2024/lithosphere_2023_193","DOIUrl":"https://doi.org/10.2113/2024/lithosphere_2023_193","url":null,"abstract":"Microfracture density in fault damage zones can reflect spatial variability that decays in intensity as a function of distance from the fault, which is crucial in understanding the mechanical, seismological, and fluid-flow properties of the fault system. However, few studies explored the characteristics of fracture density between the two sides of active dip-slip faults due to rare field observations. Here, we measured and modeled microfractures across an active thrust fault associated with the 2008 Mw 7.9 Wenchuan earthquake in the Longmen Shan, eastern Tibetan Plateau. The results showed that the microfracture density at the Qingping site developed more intensely in the hanging wall than in the footwall for an exposed thrust fault, indicating an asymmetrical pattern. The hidden thrust fault at the Jushui site showed that microfractures developed more intensely in vertical planes in the hanging wall than in the footwall, whereas microfractures developed similarly in horizontal planes within the two sides, indicating a quasiasymmetrical pattern. Comparing the data at the two sites with computational modeling, we suggest that fault geometry might exert a first-order control of the asymmetrical microfracture density pattern, which is helpful for revealing different deformational behaviors of rock masses in the fault damage zones and better understanding the hanging-wall effect for evaluating seismic hazards on active thrust faults.A fault damage zone, expressed as a zone with numerous fractures surrounding a narrow fault core, has been considered to be related to coseismic loading and, therefore, has the potential to reveal the rock deformational mechanics and past earthquake rupture conditions [1-7]. Moreover, such a damage zone is expected to act as conduits, barriers, or combined conduit-barrier systems that play a fundamental role in crustal fluid flow [8-10]. Therefore, quantitative determination of characteristics of fractures in the fault damage zone is critical to understand the mechanical and seismological properties of the fault system.Geometrically, fracture density is one of the key parameters in evaluating the spatial variability that decays in intensity as a function of distance from the fault [11, 12]. Many studies have measured micro/mesofracture density on fault-perpendicular transects to show that fracture density decreases gradually away from the fault core, which can be simplified to fit either an exponential decay model [13] or a power law decay model [14, 15] in the fault damage zone. Moreover, previous studies have suggested that the characteristics of fracture density might be influenced by the amount of slip across the fault, the size of the fault, lithology, rupture processes, and movement history [8, 13, 16]. For example, Caine et al. [8] suggested that a wide damage zone may indicate the effect of more repeated seismic events with greater accumulative deformation than that of a narrow damage zone. Ostermeijer et al. [12]","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":"32 1","pages":""},"PeriodicalIF":2.4,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139500784","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-12DOI: 10.2113/2024/lithosphere_2023_174
Kyra Hölzer, Reinhard Wolff, Ralf Hetzel, István Dunkl
The Eastern European Alps formed during two orogenic cycles, which took place in the Cretaceous and Cenozoic, respectively. In the Ötztal-Stubai Complex—a thrust sheet of Variscan basement and Permo-Mesozoic cover rocks—the record of the first (Eoalpine) orogeny is well preserved because during the second (Alpine) orogeny, the complex remained largely undeformed. Here, new zircon (U–Th)/He (ZHe) ages are presented, and thermokinematic modeling is applied to decipher the cooling and exhumation histories of the central part of the Ötztal-Stubai Complex since the Late Cretaceous. The ZHe ages from two elevation profiles increase over a vertical distance of 1500 m from 56 ± 3 to 69 ± 3 Ma (Stubaital) and from 50 ± 2 to 71 ± 4 Ma (Kaunertal), respectively. These ZHe ages and a few published zircon and apatite fission track ages were used for inverse thermokinematic modeling. The modeling results show that the age data are well reproduced with a three-phase exhumation history. The first phase with relatively fast exhumation (~250 m/Myr) during the Late Cretaceous ended at ~70 Ma and is interpreted to reflect the erosion of the Eoalpine mountain belt. As Late Cretaceous normal faults occur at the margins of the Ötztal-Stubai Complex, normal faulting may have also contributed to the exhumation of the study area. Subsequently, a long period with slow exhumation (<10 m/Myr) prevailed until ~16 Ma. This long-lasting phase of slow exhumation suggests a rather low topography with little relief in the Ötztal-Stubai Complex until the mid-Miocene, even though the Alpine orogeny had already begun in the Eocene with the subduction of the European continental margin. Accelerated exhumation since the mid-Miocene (~230 m/Myr) is interpreted to reflect the erosion of the mountain belt due to the development of high topography in front of the Adriatic indenter and repeated glaciations during the Quaternary.Mountain belts with thick continental crust, such as the European Alps, the Himalaya, or the North American Cordillera, are formed during long-lasting plate convergence with crustal shortening by nappe stacking and folding [1-3]. Due to the isostatic uplift of the thickened crust, the internal parts of such orogens become the locus of erosion, which removes material at the Earth’s surface and leads to the cooling and exhumation of metamorphic rocks [4, 5]. Apart from erosion, another important mechanism that may cause rock exhumation and cooling is normal faulting because tectonic slip along normal faults transports rocks in their footwalls toward the Earth’s surface [6-9].To quantify the cooling history of metamorphic rocks, it is necessary to determine the temperature conditions in rocks through time, which is possible by applying geochronological methods such as Sm/Nd, Rb/Sr, or Ar/Ar dating to minerals with different closure temperatures [10-12]. The final cooling in the upper crust from temperatures of ~250°C to ~60°C can be constrained with low-temperature ther
{"title":"The Long-Lasting Exhumation History of the Ötztal-Stubai Complex (Eastern European Alps): New Constraints from Zircon (U–Th)/He Age-Elevation Profiles and Thermokinematic Modeling","authors":"Kyra Hölzer, Reinhard Wolff, Ralf Hetzel, István Dunkl","doi":"10.2113/2024/lithosphere_2023_174","DOIUrl":"https://doi.org/10.2113/2024/lithosphere_2023_174","url":null,"abstract":"The Eastern European Alps formed during two orogenic cycles, which took place in the Cretaceous and Cenozoic, respectively. In the Ötztal-Stubai Complex—a thrust sheet of Variscan basement and Permo-Mesozoic cover rocks—the record of the first (Eoalpine) orogeny is well preserved because during the second (Alpine) orogeny, the complex remained largely undeformed. Here, new zircon (U–Th)/He (ZHe) ages are presented, and thermokinematic modeling is applied to decipher the cooling and exhumation histories of the central part of the Ötztal-Stubai Complex since the Late Cretaceous. The ZHe ages from two elevation profiles increase over a vertical distance of 1500 m from 56 ± 3 to 69 ± 3 Ma (Stubaital) and from 50 ± 2 to 71 ± 4 Ma (Kaunertal), respectively. These ZHe ages and a few published zircon and apatite fission track ages were used for inverse thermokinematic modeling. The modeling results show that the age data are well reproduced with a three-phase exhumation history. The first phase with relatively fast exhumation (~250 m/Myr) during the Late Cretaceous ended at ~70 Ma and is interpreted to reflect the erosion of the Eoalpine mountain belt. As Late Cretaceous normal faults occur at the margins of the Ötztal-Stubai Complex, normal faulting may have also contributed to the exhumation of the study area. Subsequently, a long period with slow exhumation (<10 m/Myr) prevailed until ~16 Ma. This long-lasting phase of slow exhumation suggests a rather low topography with little relief in the Ötztal-Stubai Complex until the mid-Miocene, even though the Alpine orogeny had already begun in the Eocene with the subduction of the European continental margin. Accelerated exhumation since the mid-Miocene (~230 m/Myr) is interpreted to reflect the erosion of the mountain belt due to the development of high topography in front of the Adriatic indenter and repeated glaciations during the Quaternary.Mountain belts with thick continental crust, such as the European Alps, the Himalaya, or the North American Cordillera, are formed during long-lasting plate convergence with crustal shortening by nappe stacking and folding [1-3]. Due to the isostatic uplift of the thickened crust, the internal parts of such orogens become the locus of erosion, which removes material at the Earth’s surface and leads to the cooling and exhumation of metamorphic rocks [4, 5]. Apart from erosion, another important mechanism that may cause rock exhumation and cooling is normal faulting because tectonic slip along normal faults transports rocks in their footwalls toward the Earth’s surface [6-9].To quantify the cooling history of metamorphic rocks, it is necessary to determine the temperature conditions in rocks through time, which is possible by applying geochronological methods such as Sm/Nd, Rb/Sr, or Ar/Ar dating to minerals with different closure temperatures [10-12]. The final cooling in the upper crust from temperatures of ~250°C to ~60°C can be constrained with low-temperature ther","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":"57 1","pages":""},"PeriodicalIF":2.4,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139476961","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-12DOI: 10.2113/2024/lithosphere_2023_294
Shaojie Li, Lunju Zheng, Xiaowen Guo, Yuanjia Han
Organic carbon isotopic analysis is a significant approach for oil-source correlation, yet organic carbon isotopic behavior during oil expulsion from saline lacustrine source rocks is not well constrained, and this hinders its wide application for fingerprinting oils generated by saline lacustrine source rock. To resolve this puzzle, semiclosed hydrous pyrolysis was conducted on typical saline lacustrine source rocks from the Qianjiang Formation (type I kerogen) and Xingouzui Formation (type II kerogen) sampled in the Jianghan Basin, China, under high-temperature high-pressure conditions (T = 275℃–400℃; P = 65–125 MPa). Experimental results show that there is minor carbon isotopic fractionation (<3‰) between pyrolyzed and nonpyrolyzed retained oil fractions during the main oil generation/expulsion stage of both type I and II source rocks. Carbon isotopic fractionations between expelled and retained oil fractions are also minor (<2‰) during this stage. The δ13C values of retained and expelled oil fractions generated by the type I saline lacustrine source rock correlate positively with the degree of oil expulsion, whereas the influence of oil expulsion on the δ13C values of oil fractions generated by the type II source rock was not consistent. In addition, carbon isotopic analysis also unravels the mixing of oil-associated gases with different maturity levels and/or generated via different processes. Outcomes of this study demonstrate that oil expulsion from type I and II saline lacustrine source rocks cannot be able to result in large-degree carbon isotopic fractionation, indicating that carbon isotopic analysis is a feasible approach for conducting oil-source correlation works in saline lacustrine petroleum systems.Oil is generated through the thermal degradation of kerogen in hydrocarbon source rock and expelled after migrating within the source rock [1-3]. Oil migration within the source rock can be mainly through diffusion in organic matter networks, whole-phase flow, migration of a liquid-saturated gas phase, and so on [4-6]. Only portions of generated oils are expelled [7], and oil retained within source rocks is an important component of the rock. Besides the economic significance of retained oils (i.e., shale oil [8]), retained oil also has the ability to enhance the hydrocarbon-generating potential of source rocks because it has greater gas generation potential than overmature kerogen, especially for C2–C5 gaseous hydrocarbons [9-11].Fractionation of organic compound classes occurs during oil expulsion. In general, organic fractions with higher molecular weight and higher degrees of polarity are more likely to be retained in source rocks rather than being expelled out of rocks [12-14], and molecular fractionations within individual compound classes may not be substantial [15, 16]. Compared with polar compounds and aromatic hydrocarbons, paraffins are more readily to be expelled [14, 16, 17]. Therefore, the degree of oil expulsion has a si
{"title":"Carbon Isotopic Behavior During Hydrocarbon Expulsion in Semiclosed Hydrous Pyrolysis of Type I and Type II Saline Lacustrine Source Rocks in the Jianghan Basin, Central China","authors":"Shaojie Li, Lunju Zheng, Xiaowen Guo, Yuanjia Han","doi":"10.2113/2024/lithosphere_2023_294","DOIUrl":"https://doi.org/10.2113/2024/lithosphere_2023_294","url":null,"abstract":"Organic carbon isotopic analysis is a significant approach for oil-source correlation, yet organic carbon isotopic behavior during oil expulsion from saline lacustrine source rocks is not well constrained, and this hinders its wide application for fingerprinting oils generated by saline lacustrine source rock. To resolve this puzzle, semiclosed hydrous pyrolysis was conducted on typical saline lacustrine source rocks from the Qianjiang Formation (type I kerogen) and Xingouzui Formation (type II kerogen) sampled in the Jianghan Basin, China, under high-temperature high-pressure conditions (T = 275℃–400℃; P = 65–125 MPa). Experimental results show that there is minor carbon isotopic fractionation (<3‰) between pyrolyzed and nonpyrolyzed retained oil fractions during the main oil generation/expulsion stage of both type I and II source rocks. Carbon isotopic fractionations between expelled and retained oil fractions are also minor (<2‰) during this stage. The δ13C values of retained and expelled oil fractions generated by the type I saline lacustrine source rock correlate positively with the degree of oil expulsion, whereas the influence of oil expulsion on the δ13C values of oil fractions generated by the type II source rock was not consistent. In addition, carbon isotopic analysis also unravels the mixing of oil-associated gases with different maturity levels and/or generated via different processes. Outcomes of this study demonstrate that oil expulsion from type I and II saline lacustrine source rocks cannot be able to result in large-degree carbon isotopic fractionation, indicating that carbon isotopic analysis is a feasible approach for conducting oil-source correlation works in saline lacustrine petroleum systems.Oil is generated through the thermal degradation of kerogen in hydrocarbon source rock and expelled after migrating within the source rock [1-3]. Oil migration within the source rock can be mainly through diffusion in organic matter networks, whole-phase flow, migration of a liquid-saturated gas phase, and so on [4-6]. Only portions of generated oils are expelled [7], and oil retained within source rocks is an important component of the rock. Besides the economic significance of retained oils (i.e., shale oil [8]), retained oil also has the ability to enhance the hydrocarbon-generating potential of source rocks because it has greater gas generation potential than overmature kerogen, especially for C2–C5 gaseous hydrocarbons [9-11].Fractionation of organic compound classes occurs during oil expulsion. In general, organic fractions with higher molecular weight and higher degrees of polarity are more likely to be retained in source rocks rather than being expelled out of rocks [12-14], and molecular fractionations within individual compound classes may not be substantial [15, 16]. Compared with polar compounds and aromatic hydrocarbons, paraffins are more readily to be expelled [14, 16, 17]. Therefore, the degree of oil expulsion has a si","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":"19 1","pages":""},"PeriodicalIF":2.4,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139462814","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Jiangnan Orogenic Belt (JOB) evolved from the Yangtze and Cathaysia blocks through multi-stage oceanic-continental subduction, collisional orogeny, and intracontinental deformation, which is an important region to study the formation and evolution of the South China Continent (SCC). Magnetotelluric soundings were collected along a 520-km-long northwest (NW)-trending profile across the middle segment of the JOB to explore the possible remnants of ancient tectonic–magmatic processes beneath the central SCC by combining with the satellite gravity and magnetic data. The resistivity model reveals that the crust in the middle segment of the JOB and its adjacent area is characterized by high resistivity anomalies, while the uppermost mantle is characterized as medium resistivity anomalies and separated by several subvertical, lithospheric-scale conductors. Two trans-crust anomalies of high conductivity and low density beneath the Jiujiang–Shitai Buried fault (JSBF) and Jiangshan–Shaoxing fault (JSF) extend south-eastward to the lithosphere, which are attributed to the NW and southeast boundaries of the middle segment of the JOB. The imaged NW-trending of JSF reflects the tectonic process of the JOB subducting under the Cathaysia Block. Two lower-crustal conductors also imaged beneath the Jiuling area are interpreted as the partial melting of the lower crust, which may be related to the deep southeast subduction of the Paleo-south China Ocean during 970 to 860 Ma. In addition, the trans-lithosphere high conductivity adjacent to the ancient collisional zone of the Jinning period II (ACZII) is probably related to the asthenosphere upwelling caused by the soft collision between the Yangtze and Cathaysia Blocks, which triggered the contemporaneous magmatism in the Jiuling area. This work provides a new insight into the lithospheric evolution in SCC during the Neoproterozoic.The South China Continent (SCC) is located at the junction of the Paleo-Asian Ocean, Tethys, and Pacific tectonic domains, bordered by the North China Block to the north, the Indochina Block to the south, the Qinghai-Tibet Plateau to the west, and the West-Pacific Plate to the east [1] . Its present status comes from the composite evolution of multi-stage plate tectonics in the Paleo-south China Block, making it one of the most complex geological evolution history areas since the Neoproterozoic [2, 3]. The Jiangnan Orogenic Belt (JOB) in the middle of SCC is spread in a NE-NEE direction, with the Yangtze Block on the northwest (NW) and the Cathaysia Block on the southeast (Figure 1). This area records the collisional assembly of these two ancient microplates, which is of great significance for understanding the crustal accretion, tectonic evolution in the SCC, and the breakup of supercontinent Rodinia [4, 5].Previously proposed models for the tectonic evolution of the JOB include (1) plate subduction collision model [6, 7]; (2) plume model [8]; and (3) plate-rift model [9]. The first
{"title":"Lithospheric Conductivity Structure in the Middle Segment of the Jiangnan Orogenic Belt: Insights into Neoproterozoic Tectonic–Magmatic Processes","authors":"Jiayong Yan, Hui Chen, Juzhi Deng, Hui Yu, Yuexin You, Yidan Wen, Min Feng","doi":"10.2113/2024/lithosphere_2023_325","DOIUrl":"https://doi.org/10.2113/2024/lithosphere_2023_325","url":null,"abstract":"The Jiangnan Orogenic Belt (JOB) evolved from the Yangtze and Cathaysia blocks through multi-stage oceanic-continental subduction, collisional orogeny, and intracontinental deformation, which is an important region to study the formation and evolution of the South China Continent (SCC). Magnetotelluric soundings were collected along a 520-km-long northwest (NW)-trending profile across the middle segment of the JOB to explore the possible remnants of ancient tectonic–magmatic processes beneath the central SCC by combining with the satellite gravity and magnetic data. The resistivity model reveals that the crust in the middle segment of the JOB and its adjacent area is characterized by high resistivity anomalies, while the uppermost mantle is characterized as medium resistivity anomalies and separated by several subvertical, lithospheric-scale conductors. Two trans-crust anomalies of high conductivity and low density beneath the Jiujiang–Shitai Buried fault (JSBF) and Jiangshan–Shaoxing fault (JSF) extend south-eastward to the lithosphere, which are attributed to the NW and southeast boundaries of the middle segment of the JOB. The imaged NW-trending of JSF reflects the tectonic process of the JOB subducting under the Cathaysia Block. Two lower-crustal conductors also imaged beneath the Jiuling area are interpreted as the partial melting of the lower crust, which may be related to the deep southeast subduction of the Paleo-south China Ocean during 970 to 860 Ma. In addition, the trans-lithosphere high conductivity adjacent to the ancient collisional zone of the Jinning period II (ACZII) is probably related to the asthenosphere upwelling caused by the soft collision between the Yangtze and Cathaysia Blocks, which triggered the contemporaneous magmatism in the Jiuling area. This work provides a new insight into the lithospheric evolution in SCC during the Neoproterozoic.The South China Continent (SCC) is located at the junction of the Paleo-Asian Ocean, Tethys, and Pacific tectonic domains, bordered by the North China Block to the north, the Indochina Block to the south, the Qinghai-Tibet Plateau to the west, and the West-Pacific Plate to the east [1] . Its present status comes from the composite evolution of multi-stage plate tectonics in the Paleo-south China Block, making it one of the most complex geological evolution history areas since the Neoproterozoic [2, 3]. The Jiangnan Orogenic Belt (JOB) in the middle of SCC is spread in a NE-NEE direction, with the Yangtze Block on the northwest (NW) and the Cathaysia Block on the southeast (Figure 1). This area records the collisional assembly of these two ancient microplates, which is of great significance for understanding the crustal accretion, tectonic evolution in the SCC, and the breakup of supercontinent Rodinia [4, 5].Previously proposed models for the tectonic evolution of the JOB include (1) plate subduction collision model [6, 7]; (2) plume model [8]; and (3) plate-rift model [9]. The first ","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":"87 1","pages":""},"PeriodicalIF":2.4,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140036800","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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