Natural Gas Industry B最新文献

The Sulige tight sandstone gas reservoir is marked by low permeability, intricate pore structures, and notable lateral heterogeneity, making it difficult to predict the productivity of fractured horizontal wells in the reservoir. In this study, a productivity prediction model for fractured horizontal wells is developed based on the characteristics of the Sulige gas reservoir, including its high start-up pressure gradient, strong stress sensitivity, obvious non-Darcy flow, and typical slippage and diffusion effects. This new model fully accounts for each hydraulic fracture in the horizontal wells based on the superposition principle and Green's function. This model facilitates efficient productivity calculations and enables rapid quantitative analysis of the influencing factors specific to horizontal wells with hydraulic fractures, fully integrating the specific characteristics of the Sulige gas field. The accuracy of this model is tested against field data from Wells LX1 and LX2 in the Sulige field, indicating good agreement between the predicted values and field data. Well LX2 is used as a case study to analyze the influences of geological and engineering factors on well productivity. The following conclusions are drawn: 1) Well productivity is notably influenced by the start-up pressure gradient and stress sensitivity, with a minor impact from non-Darcy effects. 2) Productivity linearly decreases with increased hydraulic fracture spacing. 3) Productivity increases, and the increment rate gradually decreases, with increases in the length and conductivity of the hydraulic fractures. This model provides valuable guidance on predicting productivity in tight sandstone gas reservoirs, such as that of the Sulige gas field.

To improve the drill pipe fracture failure phenomenon in deflecting drills with ultra-short radius flexible drill pipes, this study establishes a mechanical model of a deflecting drill with an ultra-short radius flexible drill pipe, numerically simulates the mechanical characteristics of the flexible drill pipe under the conventional drilling process using the finite element analysis method, performs mechanical performance tests on the flexible drill pipe, and optimizes and improves its structure. The results show that, with the gradual increase in the bending angle of the flexible drill pipe unit section, the upper drilling pressure of the flexible drill pipe unit section decreases rapidly and its friction increases approximately linearly. The tensile strength of the optimized ultra-short radius flexible drill pipe is increased by 24.7%, and the minimum threshold of its torsional strength is doubled. This effectively improves the overall strength of the ultra-short radius flexible drill pipe and provides a theoretical basis for downhole drilling stability studies of flexible drill pipes.

The complex network of fractures formed by randomly distributed natural fractures in hot-dry rocks (HDRs) complicates the heat transfer regularity of injected fluid. On the basis of the fracture network, exploring the characteristics of the fluid flow and heat transfer as influenced by different parameters helps enable efficient resource extraction and effectively promotes the construction of diversified energy utilization structures. Accordingly, accounting for the effect of the thermal shock on the evolution of the permeability of the rock matrix, a thermo-hydro-mechanical (THM) coupling model is developed to analyze the influences of fracture network characteristics on the heat extraction performance of HDRs. In addition, a large-scale injection and production physical simulation experiment is performed using a newly developed, in-house, large-scale true triaxial experimental system. The corresponding numerical model is established and validated. The good agreement between the numerical and experimental results verifies the reliability and accuracy of the proposed THM model. Subsequently, a two-dimensional model is established under complex fracture network conditions, taking, as a research object, the natural fracture characteristics of HDR in the Qinghai Gonghe Basin in combination with the regional geological information. The effects of different parameters, including the production well location, rock matrix permeability, injection rate, initial fracture width, and number of fractures, on the production temperature and heat extraction performance are systematically analyzed. The results indicate that an increase in the number of fractures, the distance between the injection well and the production well, or the width of the initial fractures leads to an improved heat extraction performance. The number of fractures increased from 11 horizontal fractures and 22 high-angle fractures to 35 horizontal fractures and 70 high-angle fractures, with a 20% increase in heat extraction rate. While the influence of the rock matrix permeability is not highly significant, it cannot be ignored. It is crucial to select an injection rate that is neither too low nor too high, taking into consideration economic factors.

During the development of carbonate reservoirs, the risk of bottom water invasion is a frequent concern. Pore-scale simulation methods are commonly acknowledged as effective tools for investigating the dynamics involved in water invasion mechanisms. Despite extensive research on gas-water two-phase flow, few studies have investigated reservoirs with interlayers, which can remarkably affect assessments of water invasion. Three models were designed to study the effects of different interlayer distributions on flow behavior. A mathematical model based on the volume of fluid (VOF) method was employed to describe variations in water saturation. The four primary influencing factors (interlayer distribution, gravity, pressure difference, and wettability) were studied based on simulations. The accuracy of the model was validated through comparisons with microfluidic visualization experiments. Compared to the model without interlayers, the models with semi-permeable and semi-sealed interlayers reduced the risk of water invasion, resulting in slower upward water saturation rates and delayed water breakthrough times. Neglecting gravity would introduce errors of up to 5.6% in water saturation and 24.2% in water breakthrough time for the models with interlayers. Controlling the pressure difference within 1.5 MPa/100 m would effectively reduce the produced water-gas ratio and delay the water breakthrough time. The water invasion behavior in the models with interlayers was highly sensitive to contact angles in the range of 50°–60°, while its effect on the model without interlayers was relatively small. Field-scale water invasion dynamics with examples from the Yuanba (YB) gas field in the Sichuan Basin, China, were consistent with the pore-scale simulation results. This work provides fundamental support for and valuable insights into the development of similar gas reservoirs, offering a strong foundation for future endeavors in this field.

Geothermal resources have a very broad development prospect owing to their clean nature; accurate evaluation of their potential is an important basis for the realization of fine zoning and large-scale efficient development. Here, a geothermal evaluation system is established based on reservoir, cap-rock, transportation-system, heat-source, and water-source data. The entropy weight Technique Order Preference by Similarity to an Ideal Solution (TOPSIS) and Analytic Hierarchy Process - Technique Order Preference by Similarity to an Ideal Solution (AHP-TOPSIS) methods are used to evaluate geothermal resources in Eryuan County, and the evaluation results are superimposed with equal weights, and combined with the Moran index, to determine the geothermal exploration potential. Our results show that geothermal resources in Eryuan County are abundant, being concentrated in Liantie Township, Qiaohou Town, junction of Sanying and Cibihu towns, and junction of Fengyu and Yousuo towns. The Moran index indicates that there is significant geothermal accumulation, with high geothermal values mainly distributed around the water system. Three types of geothermal models are established based on control factors. The first one is controlled by the combination of reservoir and cap rock, while the second one is controlled by heat source and the third one is controlled by the combination of reservoir and cap rock and heat source. The junctions of Sanying and Cibihu towns, and Fengyu and Yousuo towns, are evaluated to have high geothermal potential, and these may become the next favorable directions for geothermal exploration in Eryuan County.

The Lower Cretaceous Bashijiqike Formation, which is an important gas exploration target in the Kuqa Depression, Tarim Basin, China, is an excellent case illustrating the diagenesis and reservoir property variations of tight sandstone with burial depths ranging from 3500 m to 8000 m. Thus, integrated approaches incorporating thin-section petrographic characterization, mineral morphology and identification, X-ray diffraction analysis, reservoir property tests, and fluid inclusion analysis were applied to investigate the diagenesis and reservoir property variations of Bashijiqike sandstone with different burial depths. The main findings of this study were as follows. (1) Diagenesis of the Bashijiqike sandstone with a burial depth of less than 5000 m was mainly characterized by kaolinite, colloidal quartz, euhedral quartz, and the dissolution of feldspar, whereas diagenesis of the sandstone with a burial depth of more than 5000 m was primarily distinguished by albite, dolomite, calcite, illite, and chlorite. (2) The porosity and permeability rapidly decreased as the burial depth increased within the range of less than 5000 m, while they slowly decreased as the burial depth increased within the range of more than 5000 m, indicating that the reservoir properties have a nonlinear correlation with the burial depths ranging from 3500 m to 8000 m. (3) During the late stage of the Himalayan movement, the enhanced compaction of Bashijiqike sandstone with the increased burial depth resulted in a decrease in the number of intergranular pores, whereas the dissolution of feldspar and quartz led to the formation of secondary pores. Taken together, the findings of this study indicate that the Himalayan movement after the Neogene resulted in burial depth variations with regard to the studied sandstone, which represents the key controlling factor for both its diagenesis and its reservoir properties.

As an important component of the exploration and evaluation of geothermal resources, the formation model has unique formation and distribution rule in different regions. Reliable geological models need to be established to help in temperature prediction, favorable area selection, and drilling design studies prior to the development of geothermal resources. This paper provides an integrated approach for analyzing the formation models of geothermal resources by combining geological studies and the wide-field electromagnetic method. The resistivity profile is converted into a geologic profile by analyzing the fault distribution, stratigraphic lithology, magmatic rock development, and signal changes of the profile. Comprehensively analyzing the geological elements including the heat sources, water sources, thermal reservoirs, transport conditions, cap rock, and preservation conditions, we investigate the matching relationship of the geological elements on the geologic profile and establish a formation model of the geothermal resources. This approach avoids the respective limitations of geological and geophysical methods, and the formation model established by this approach is comprehensive, intuitive, and accurate and can provide support for the development of geothermal resources.

Thermal storage has not yet been classified in a unified way. By analyzing the factors of thermal storage and the interactions of fluids, spaces, and solids, this study proposes a three-level classification scheme based on fluid–space–solid thermal storage and dissects the main thermal storage types in the Eryuan, Midu, and Lancang areas of Yunnan Province. The results show that the hydrothermal-karst-carbonate reservoirs of the lower Devonian Kanglang Formation, Carboniferous, and Lower Permian are the main reservoirs in the Eryuan area, the hydrothermal-fracture-carbonate reservoirs are Carboniferous and Lower Permian in the Midu area, and the hydrothermal-fracture-metamorphic reservoirs of the Manlai and Huimin formations are the main reservoirs in the Lancang area. These reservoirs are characterized by high porosity and permeability, high thermal conductivity, high thermal diffusivity, and high specific heat capacity. The classification scheme is systematic, comprehensive, and unified, is capable of conveying multiple information points, and provides a new method for geological exploration personnel to analyze the thermal storage characteristics.

Hydraulic fracturing has become the main technology for the efficient development of geothermal energy in hot dry rock (HDR), however, few studies on the propagation behavior and mechanism of HDR hydraulic fractures under high-temperature conditions have investigated. In this paper, a large-size high-temperature true triaxial hydraulic fracturing physical modeling apparatus is designed, and hydraulic fracturing experiments with it are performed to investigate the fracture initiation and propagation behavior in natural granite samples collected from Gonghe Basin, the first HDR site in China. The experimental results show that the designed high-temperature apparatus provides a constant-temperature condition during the whole hydraulic fracturing process and the maximum temperature can reach 600 °C, showing its ability to simulate realistic temperatures and pressures in both ultra-deep and HDR formations. Although the tensile strength of the rock samples remains almost unchanged at a temperature of 200 °C, the cooling effects of the fracturing fluid in high-temperature rock can induce the formation of microfractures and significantly reduce the rock strength, thus lowering the breakdown pressure and increasing the complexity of the hydraulic fracture morphology. Compared with traditional oil and gas reservoirs, the hydraulic fractures in HDR are rougher and the specific surface area of a single fracture is larger, which can be helpful for heat extraction. This study provides a basis for understanding hydraulic fracture geometries and field construction design in HDRs.