Geofluids最新文献

Qadri, Hamza Azam, Ali Wahid, Numair Ahmed Siddiqui, Syed Haroon Ali, Ahmed Abd El Aal, Amirul Qhalis Bin Abu Rashid, and Mohd Najib Bin Temizi. “Prospect Analysis of Paleocene Coalbed Methane: A Case Study of Hangu Formation, Trans-Indus Ranges, Pakistan.” Geofluids 2022, no. 1 (2022): 8313048, https://doi.org/10.1155/2022/8313048.

The authors wish to correct the acknowledgement statement as follows, to acknowledge the support from Group Research and Technology (GR&T):

The authors would like to thank Universiti Teknologi PETRONAS, Malaysia, for the lab analysis and technical support at the Geoscience Department and research fund YUTP-FRG 1/2021 015LC0-363. We would also like to thank GR&T (Cost Centre: 015MDO-068) for some laboratory analysis support. Moreover, special thanks are due to the Makarwal Collieries Limited, Pakistan, for allowing access to their mines and to conduct this research work. The laboratory facilitation provided by the Center of Coal Technology, Punjab University, Pakistan, and Centralized Resource Laboratory (CRL), University of Peshawar, Pakistan, are also highly appreciated.

As GR&T is a commercial entity, the Conflict of Interest statement is therefore also corrected as follows:

Support for laboratory analysis was provided by GR&T. The authors declare no other conflicts of interest associated with this study.

The Dengying Formation within Pengtan 1 well area in the Sichuan Basin is a vital gas reservoir for exploration and development. The reservoir is situated in a complex fault block structure characterized by multistage fault evolution, leading to a complicated distribution of tectonic fractures crucial for the accumulation and migration of oil and gas. This study establishes a geological model to describe the fault patterns observed in the region and conducts numerical simulations of the paleotectonic stress field. Moreover, we combine rock fracture criteria and strain and surface energy theories to predict tectonic fractures quantitatively. Our findings indicate that the tectonic fractures in the study area predominantly consist of shear fractures, with primary development of low-angle and oblique fractures and, to a lesser extent, high-angle fractures. These fractures generally exhibit trends in the north–northwest (NNW), northeast (NE), nearly east–west (EW), and nearly south–north (SN) directions. Most fractures formed during the Yanshanian–Himalayan period are identified as effective fractures. The maximum and minimum principal stress values recorded for the Himalayan period of tectonic activity were 150–180 and 120–150 MPa, respectively. Faults significantly influence the distribution of tectonic stress, and stress concentration usually occurs near the fault. A significant correlation exists between tectonic stress and burial depth, exhibiting lower stress levels at shallower depths. In addition, the linear density of fractures gradually decreases from the fault core to its periphery and further decreases to areas far away from the fault. In these three regions, fractures mainly develop in the order of high angle, oblique, and low angle. This study enhances our understanding of the fracture dynamics within the Dengying Formation, contributing valuable insights into the region’s geomechanical properties and potential hydrocarbon exploitation strategies.

The northern Shanxi mining region, a pivotal coal-rich area in China, is characterized by substantial reserves of shallow coal seams and distinctive geological mining conditions that exacerbate overburden rock fissure development. This study delves into the mechanisms governing overburden damage and fissure evolution in shallow coal seams using the theoretical frameworks of key strata and mining subsidence, augmented by numerical simulation methodologies. It also examines the impact on ground fissure morphology and propagation. Additionally, this paper investigates the prediction of water-conducting fracture zone heights in shallow coal seams. This paper’s findings reveal a sequential dynamic process in overburden rocks during mining: microfissure initiation, key stratum rupture, fissure aggregation, and fissure coalescence. Leveraging a long short-term memory (LSTM) model, this paper develops a prediction model for water-conducting fracture zone heights in shallow coal seams, achieving high accuracy with a mean squared error (MSE) of 2.29, a mean absolute error (MAE) of 1.22, and an average relative error of 2.51%. These results contribute scientific insights for mitigating ground fissure disasters and facilitating ecological restoration in the context of intensive shallow coal seam mining in northern Shanxi. Furthermore, they hold substantial scientific merit in advancing the theories of mining subsidence and stratum control in mining engineering.

Drilling has shown that there is significant overpressure throughout the Jurassic in the central Junggar Basin and that the maximum pressure coefficient exceeds 2.0. The pore pressure in the central Junggar Basin was jointly predicted by combining a number of methods, such as the Eaton, Bowers, and equilibrium depth methods based on logging data, with the D_C method and Fillippone formula approach based on drilling and seismic interval velocity data, respectively. The findings indicate that, among the logging-based prediction methods, the Bowers method prediction of the pore pressure may more closely match the pore pressure. Based on seismic layer velocity data, the Fillippone approach can more precisely predict the change in section pressure by simulating pressure in space. The full forecast results show that two overpressure systems formed in the Jurassic system at Mbr. 1 (Badaowan) and Mbr. 3 (Xishanyao). The transfer of overpressured fluid also resulted in the development of localized overpressure in the Mbr. 2 (Sangonghe) and Mbr. 4 (Toutunhe) formations, which serve as transition zones of overpressure. The top interface of the overpressure section shows an increasing trend in burial depth from the deep concave to the slope region. The overpressure section also demonstrates outstanding low acoustic velocity characteristics. The Jurassic’s anomalous overpressure intensity decreased from the southwest to the northeast, and the overpressure gradient served as a dynamic mechanism for petroleum migration and accumulation.

The hydrocarbon-bearing property of a reservoir is a crucial index for its evaluation. Although various evaluation methods based on well-logging data can reasonably interpret the hydrocarbon-bearing property of most reservoirs, these methods often exhibit significant randomness and ambiguity. This is due to various external influences, making it challenging to quickly and accurately evaluate the hydrocarbon-bearing property of a reservoir. To address this issue, this study investigates the identification of hydrocarbon-bearing properties in reservoirs based on well-logging data and machine learning techniques. Initially, 1731 sets of well-logging data with hydrocarbon-bearing property identification result labels from 356 wells in the Shahejie Formation of the Bohai Bay Basin’s Qikou Sag were collected. The distribution of different hydrocarbon-bearing property categories was analyzed on three types of well-logging data: gas logging, quantitative fluorescence logging, and Rock-Eval pyrolysis. Subsequently, seven model inputs were formed by combining these three types of well-logging data, and their performance was evaluated in combination with three machine learning techniques: K-nearest neighbor, random forest, and artificial neural networks. The influence of different inputs and models on classification performance was compared. Lastly, the importance of each input feature was analyzed. The results showed that the combination of quantitative fluorescence logging and Rock-Eval pyrolysis as inputs with the random forest model could achieve the best classification performance, with a macro F1 score of 95.36%. This suggests that this method has sufficient precision for the identification of hydrocarbon-bearing property categories in formations, providing a more efficient classification method for the hydrocarbon-bearing property of reservoirs compared to manual identification.

During the excavation of the shaft, the inlet air temperature undergoes seasonal variations and is influenced by geothermal effects and air compression heat. Merely augmenting the inlet air volume fails to mitigate the extreme temperatures encountered at the deep working face. Consequently, the implementation of refrigeration and cooling technologies becomes imperative to manage the heat-induced issues. To address the high-temperature challenge during shaft excavation at the Sanshandao Gold Mine, a ventilation system model was developed utilizing Fluent simulation software. This model facilitated the prediction of the temperature field dynamics at the working face, taking into account project progression and seasonal shifts. Through a comprehensive analysis of factors encompassing cooling capacity deterioration, energy consumption for cooling, and the installation and maintenance requirements of refrigeration units across various systems, a surface-based centralized refrigeration system was devised. Furthermore, a simulation analysis was conducted to evaluate the refrigeration technology, offering valuable technical insights for the calculation of cooling capacity, as well as the selection and application of appropriate refrigeration systems. The results indicated that subsequent to excavating the shaft to a depth of 1600 m, the working face temperature fluctuated with seasonal variations but consistently remained above 28°C. At a depth of 1800 m, the temperature peaked, reaching a maximum of 40.19°C. Following the implementation of the surface centralized refrigeration system, with an inlet air volume of 22.6 m³/s and an inlet air temperature maintained below 10°C, the working face temperature was effectively reduced to below 27°C. This study presents a comprehensive suite of refrigeration and cooling methodologies, encompassing temperature field prediction, refrigeration parameter calculation, simulation analysis of cooling performance, refrigeration system design, and their application in deep shaft excavation. These methods provide a technical foundation for mitigating heat-induced damage in deep shafts.

There is an abundance of tight gas resources in narrow channel sand-bodies from the Jurassic Shaximiao Formation of the Jinqiu gas field in the central Sichuan Basin of China. The architecture of sand group in the study area is undefined, and the spatial distribution of channel sand-bodies is unclear. The complex and inhomogeneous sandstones have a significant impact on the reservoir’s physical properties and the fluid mobility of the reservoir. In this study, data from drilling cores, logs, seismic, and experiment testing were used to investigate the spatial distribution of sand group architecture and the channel types. There are five channel genetic types, including the multiphase superimposed type, deeply incised type, abandoned type, progradational superimposed type, and normal single genetic type. Based on the channel genetic types, the ratio of sandstone and mudstone, the ratio of width to depth, the connectivity ratio of sand-bodies, and the production dynamic characteristics, the channel sand-body connectivity is defined into three types. The connected sand-bodies occur in the multiphase superimposed and deeply incised types of channels, with an average connectivity ratio of 83%, a ratio of sandstone and mudstone larger than 0.9, and a ratio of width and depth larger than 40. Based on the association of sandstone and mudstone and rhythmic structure, the sand group architecture can be divided into three types, including (A) uniform-grain-sequence pure sandstone architecture, (B) positive-grain-sequence thick sandstone and thin mudstone architecture, and (C) positive-grain-sequence thick mudstone and thin sandstone architecture. There is a high content of natural gas in Types A and B of sandstones, with a daily gas production of 29.16 × 10⁴–47.6 × 10⁴ m³/day and pressure coefficients of 0.72–1.08. The sand group architecture of the study area is mainly controlled by the channel sinuosity and the ratio of accommodation and sediment supply, and Types A and B of sand group architectures occur with large channel sinuosity of 1.14–1.36 and a large ratio of accommodation and sediment supply of 0.61–2.92. Based on the connectivity degree of channel sand-bodies, the sand group architectures, and production data, the channels of the study area can be divided into three types. Type I channels mainly occur in Sand Groups 6, 8, and 9, and Type II and Type III channels occur in Sand Groups 6 and 7 in the western and southern parts of the study area. The technology of fine characterization for channel sand-bodies on the basis of human–computer interaction and seismic attributes is proposed, and geological modelling of the spatial distribution of sand group architectures and channel types is established. The research results achieve a theoretical breakthrough in the characterization of the sand-body structure of tight sandstone reservoirs in narrow river channels and assist in the efficient exploration and development o

China’s shale gas has undergone nearly 20 years of exploration; unconventional oil and gas geological evaluation theories and research methods have been greatly enriched, but how to quickly, conveniently, and accurately identify the sweet spots of shale gas is still puzzling many researchers. This study focuses on the black shale of the Wufeng–Longmaxi Formation in the southeastern edge of the Sichuan Basin; lithofacies classification, the relationship between lithofacies and depositional environments, and the correlation between lithofacies and shale gas–bearing capacity are discussed. At last, we have established the lithofacies classification criteria; the Wufeng–Longmaxi Formation deposited eight types of lithofacies, which the paleoenvironment during deposition evolved gradually from anaerobic environment to oxygen-poor and oxygen-rich environment. The black high-carbon and high-silicon shale lithofacies and the black carbon-rich and silicon-rich shale lithofacies are rich in organic matter, and they were deposited in high primary productivity, low terrigenous detritus input, and euxinic environment. The black medium-carbon medium-silica shale lithofacies and the black medium-carbon and high-silica shale lithofacies contain organic matter, which are deposited in medium primary productivity, middle terrigenous detritus input, and oxygen-poor and low hydrodynamic environment. The gray–black low-carbon low-silicon clay-rich shale lithofacies, the gray low-carbon and high-silicon shale lithofacies, and the gray–white low-carbon and silicon-rich shale lithofacies are poor in organic matter, which are deposited in a transitional environment of low primary productivity and oxygen poor–oxygen rich. In the analysis of the relationship between organic matter–rich black shale facies and sedimentary environment, it is shown that the enrichment of organic matter is positively correlated with the oxidation–reduction discrimination indicators Ni/Co, U/Th ratio of ancient oceans, and the evaluation indicators Ba_bio and Ba/Al ratios of primary productivity. Only under the favorable sedimentary geochemical conditions and good preservation conditions can deposit lithofacies sections (zones). Based on the optimization of shale gas dessert section and the drilling of horizontal wells, the optimization of favorable black shale lithofacies types and the classification of shale gas dessert section are the key to shale gas exploration. The shale gas–bearing capacity is closely related to lithofacies. Black carbon-rich silicon-rich shale lithofacies and black high-carbon high-silicon shale lithofacies have the best gas-bearing capacity and are favorable lithofacies.

To thoroughly investigate the mechanisms behind coal and gas outbursts in folded structural areas, we conducted similarity simulation experiments using a custom-built apparatus designed to replicate these structures. The objective was to analyze the stress distribution characteristics of coal rock masses under horizontal structural stress within folded zones. The experimental outcomes reveal that, under horizontal loading, shear cracks progressively develop along layer directions within the anticline wing, anticline axis, and syncline axis, evolving continuously along the interlayer direction. In these folded structures, horizontal stress consistently remains compressive, with the highest compressive stress concentrations observed at the anticline axis, followed by the wings and turning points of the anticline, and the lowest in the syncline axis area. The stress coefficient (k) in the anticline axis reached values as high as 3.18, while the syncline axis exhibited much lower stress concentrations, with k values of 0.66. Vertically, the anticline axis and its wings primarily experience tensile stress, whereas the syncline and its wings mainly undergo vertical compressive stress. The anticline axis region, subjected to horizontal structural stress, tends to develop tension cracks, which adversely affect gas retention. The combination of horizontal tension and vertical tensile stress in this region reduces the risk of coal and gas outbursts. Conversely, the syncline axis area, experiencing triaxial compressive stress, exhibits a higher degree of stress concentration and superior gas sealing capacity, rendering it more vulnerable to coal and gas outbursts. These findings provide essential insights for refining coal mining methodologies in fold structures, particularly for addressing the safety challenges posed by coal and gas outbursts.

Rock masses characterized by X-type joints are prevalent in cold region rock engineering projects. A precise understanding of the mechanical mechanisms governing the fracture initiation strength of these jointed rock masses after experiencing freeze–thaw damage is paramount for ensuring the safety and stability of associated engineering structures. Leveraging the mutual constraint relationship between the displacements at the tips of intersecting joints under compressive shear conditions, a computational approach has been developed to determine the stress intensity factor at the tip of the main joint, taking into account the interference effects arising from both main and subjoints. Furthermore, the fine-grained defects within the rock mass are abstracted as elliptical microcracks, and deterioration equations for rock cohesion and fracture toughness under freeze–thaw cycling are derived using frost heave theory. Taking into account the mutual interference effects between main and subjoints, as well as the degradation of rock mechanical properties caused by freeze–thaw cycles, a computational approach for determining the initiation strength of X-type jointed rock masses has been developed. The validity of this method has been confirmed through rigorous model testing. The findings reveal that the wing cracks in X-type jointed rock masses predominantly propagate along the tips of the main joints, while the extension of subjoints is constrained. When the X-joints have the same inclination, the initiation strength of the subjoint exceeds that of the single-joint rock mass when its inclination is less than the main joint’s but is lower when the subjoint’s inclination exceeds that of the main joint. The interference effect between oppositely inclined intersecting joints enhances the initiation strength of the rock mass, with the maximum occurring when the subjoint is at an inclination of 120°. When the freezing time is less than 18 h and the temperature is below −16°C, variations in both time and temperature are more sensitive in affecting the initiation strength of the X-jointed rock mass. Rocks with a high elastic modulus and low tensile strength experience a greater rate of freeze–thaw damage, and brittle rocks are more susceptible to frost heaving failure.