Unconventional Resources最新文献

This research endeavors to characterize the primary factors that influence the formation of Ordovician karst caves in the Keping area of China. A 3D digital model of the cave structure and fracture sets was generated using an Unmanned Aerial Vehicle (UAV). The characterization of fracture and cavity development involved the examination of thin sections, fluid inclusion testing, and the analysis of C and O isotopes. Key parameters controlling karst development were identified through the application of multiple linear regressions and statistical analysis. The Ordovician limestone karst cave exhibited four distinct fracture sets. Set 1 consisted of partially filled fractures with a sub-horizontal orientation and a striking direction of SEE, interpreted to have formed during the Middle-Late Caledonian orogeny. Set 2 comprised inclined tensile-shear fractures with a striking direction of NEE, likely formed during the Early Hercynian orogeny. Set 3 included fully filled conjugate shear fractures with variable orientations, which developed during the Indo-Yanshanian orogeny. Set 4 comprised high-angle shear fractures with striking directions of NNE 20–40° and NEE 60–80°, formed during the Himalayan orogeny. Two stages of cave filling deposition were identified. Stage I coincided with the Middle-Late Caledonian Set 1 fractures and can be attributed to the circulation of freshwater fluid. Stage II occurred concurrently with the Early Hercynian Set 2 fractures and can be attributed to deep hydrothermal fluid circulation. The karst caves are interconnected and aligned along a fault zone. The Ordovician limestone possesses high permeability, which facilitates karst development. The lithologies in the Aksu area play a crucial role in cavity formation and dissolution. The development of cavities is influenced by the combined patterns of the fracture system, with larger fault and fracture zones resulting in larger cave sizes. As one moves away from the fault zone, limestone dissolution decreases, resulting in less pronounced karst development.

The interactions between aqueous solutions, gases, and minerals dictate the extent of issues such as scaling, degassing, and corrosion, which have a major impact on the performance of a vast number of industrial applications (e.g., geothermal plants, oil and gas production facilities, natural gas storage in saline aquifers, flue gas scrubbing, carbon sequestration, etc.). Among the different software programs available for aqueous chemistry calculations, Phreeqc and Reaktoro were tested and validated against a wide dataset of gas solubility measurements. For the datasets considered, the two programs essentially led to the same outcome with only a few discrepancies observed. Yet, the agreement between the models and experimental data was greatly affected by the selected database. The models implemented in Phreeqc and Reaktoro were also compared with the experimental bubble point pressure of fluids sampled at several geothermal wells. The satisfactory performance of both Phreeqc and Reaktoro for describing different chemical systems at a wide range of pressures and temperatures showcases their versatility and practicality for assisting in the design and optimization of various processes relevant to the energy transition (e.g., geothermal exploitation, CO₂/H₂ transport and storage).

Casing deformation seriously affects the fracturing progress and stimulation effect of shale gas reservoirs. Considering casing deformations in fractured deep shale gas wells in the Luzhou block of southern Sichuan Basin, the influences of micro-structure, natural fractures, frequent layer penetration during drilling, cementing quality, borehole enlargement and fracturing operation on casing deformation were systematically analyzed. The results show that the occurrence rate of casing deformation is 51 % and 66.3 % respectively in areas with micro-structure and frequent layer penetration, the overlap rate of casing deformation points and natural fracture points is only 22 %, the proportion corresponding to good cementing quality is only 36.5 %, borehole enlargement/shrinking universally exists, and the fracturing intensity and scale are generally large before casing deformation. It is concluded that casing deformation is closely related to micro-structure, layer penetration and lithologic mutation surface, and controlled by well diameter, frequent layer penetration, cementing quality, micro-structure and natural fractures in a descending order of influence degree. Accordingly, a multi-factor weighting evaluation method and the vertical well trajectory, well quality and well stimulation classification criteria were built to realize the prediction, prevention and control of casing deformation in deep shale gas wells in the Luzhou block, demonstrating effectively improvement in stimulation effect.

The difference in porous structure significantly impacts the CH₄ adsorption capacity in the coalbed methane (CBM) reservoir. Herein, a series of experiments, including maceral and mineral test, N₂ adsorption/desorption, proximate analysis, are conducted for 8 coal samples collected from 5 basins, to compare the effect of coal composition, moisture content, and ash yield on pore structures of various sizes. Subsequently, the comprehensive analysis of the above factors on CBM adsorption capacity is explored via the results of CH₄ isothermal adsorption experiments. The results show that the vitrinite in the organic macerals has the greatest influence on the pore content of different sizes, followed by the exinite, and the inertinite has a minor influence. The mineral content has a positive effect on the micropores and macropores, while it could weaken the content of mesopores. The rising moisture content will reduce the content of micropores and macropores while promoting mesopores. Besides, the microporous specific surface area slightly rises with increased ash yields, while the proportion of mesoporous specific surface area decreases due to mineral filling. The ash yield has little effect on the macropores. Due to the integrated effect of moisture and ash, the influence on CH₄ adsorption capacity varies from pores with different sizes. The content of micropores and macropores promotes adsorption capacity, while mesopores have an inhibitory effect. Observations here could benefit the understanding of the interaction of coal with methane.

The Chang 8 Member of the Yanchang Formation in southwest Ordos Basin is a typical faulted sandstone oil reservoir. The development characteristics of fractures have obvious controlling effect on the formation of sweet spots of tight reservoir. In this paper, taking the Chang 8 Member of the southwestern Ordos Basin as an example, the development characteristics and controlling factors of fractures in faulted sandstone oil reservoir are systematically studied. The results show that the faulted sandstone oil reservoirs in the study area are distributed along the main strike-slip faults. The fracture system includes vertical fractures and horizontal bedding fractures. The fracture surface of vertical fractures generally has good oil display, and mostly presented as oil spot and oil immersion level; however, the oil level of horizontal bedding fractures is usually presented as oil spot level. The development frequency of horizontal bedding fractures is 62.5 %, while that of vertical fractures is 37.5 %. The fractures are mainly developed in fine sandstone and a small amount of medium-grained sandstone and siltstone. The factors that affect the fracture development degree in faulted oil reservoir include the distance from main fault, sand thickness, lithology and structural location. For the Jinghe and Honghe Oilfields, the degree of fracture development decreases sharply when the distance from the main fault is greater than 1.25 km and 1.5 km, respectively. Single sand body thickness also controls the degree of fracture development. Single sand bodies with thickness within 6 m have more developed fractures, and the fracture development decreases sharply when the thickness exceeds 6 m. The sand body in the wing part of river channel is relatively thin with fine grain size and small compacted space, which is easy to break under tectonic activity. The fractures of the Chang 8 Member in the study area are mainly developed near the faults, the top of anticline and its wing part.

The Zigong area in southern Sichuan Basin is one of the key shale gas production areas in China, and the Longmaxi and Wufeng Formations within it are currently the key exploration and development layers. The present-day in-situ stress field has a significant impact on well trajectory deployment, horizontal well construction, hydraulic fracturing and other aspects. However, it has not been finely quantified in shale gas reservoirs of Zigong area, making it difficult to effectively guide development practice. Therefore, this study constructed a geomechanical model of the target layer in the Zigong area, quantitatively characterized the distribution of present-day in-situ stress, and explored its shale gas development effects. The results show that: (1) Based on the analysis of drilling induced fractures obtained from rock acoustic emission experiments and imaging logging interpretation, the dominant orientation of the maximum horizontal principal stress in the target layer is mainly NW-SE-trending; (2) The horizontal principal stress difference in the Layer S₁l^1-1−1 and Wufeng Formation is 5–30 MPa (the majority is 6–15 MPa) and 5–35 MPa (the majority is 6–18 MPa), respectively. Low stress difference values are mainly concentrated in the southeastern and northern parts. The overall prediction accuracy is high, with an error rate of less than 8% for the Layer S₁l^1-1−1 and less than 10% for the Wufeng Formation; (3) Based on rock acoustic emission experiments and finite element model simulation results, the study area is mainly under strike-slip stress faulting mechanism; (4) Due to the influence of the strike-slip faulting stress mechanism, when deploying horizontal wells in the area, priority should be given to selecting areas with low stress mechanism factor (A_φ) and low stress differences, to achieve better fracturing and transformation effects and reduce the risk of casing deformation and wellbore instability.

With many countries dependent on imported fuels, governments and industries are diversifying energy sources, including geothermal energy. Geothermal energy, derived from the Earth's internal heat, holds significant potential as a renewable energy source. The present work focuses on the geothermal resource estimation of the Uttarakhand region in India. Critical subsurface reservoir parameters for geothermal extraction and estimates of potential resources are reviewed through an analysis of geological formations, temperature gradients, and rock permeability. Various estimation methods, including surface heat flux, volume methods, and probabilistic methods, are discussed, with a particular emphasis on the Monte Carlo method. Assessment of the resource potential of the Uttarakhand geothermal system using available data estimates the resource potential of the Uttarakhand prospect, revealing an energy estimate of 1.26*10^15 J/kg (P50 case). Correspondingly, for the P90 and P10 scenarios, the estimated heat stands at 2.30*10^15 J/kg and 2.6*10^14 J/kg, respectively. However, successful exploitation requires a thorough understanding of subsurface reservoir parameters and careful resource estimation. This comprehensive analysis offers valuable insights for policymakers, researchers, and industry stakeholders interested in harnessing geothermal energy for sustainable development.

Decline-curve analysis and production forecasting are usually performed from a deterministic standpoint (point estimation). This approach does not quantify the uncertainty of the model's parameters and thus, the model's estimated ultimate recovery. In addition, decline-curve models do not consider the variations in the bottomhole flowing pressure, which can greatly impact the accuracy of the model's predictions. This work combines a new technique that incorporates variable bottomhole flowing pressure conditions into decline-curve models with Bayesian inference to improve the accuracy of production history-matches while quantifying the uncertainty of the model's parameters and its future production prediction. The method provides fast production history-matches and forecasts of shale gas wells (taking around 1 min per well) and it is more accurate than traditional decline-curve analysis for wells subject to variable bottomhole flowing pressure conditions while quantifying the uncertainty in the model's parameters and estimated ultimate recovery. The main contribution of this work is the illustration of a new method for probabilistic variable pressure decline-curve analysis. We present the application of this workflow for shale gas wells.

The use of hydrothermal geothermal methods in Enhanced Geothermal Systems (EGS) presents challenges like reduced thermal storage life and high external energy consumption. Due to its stable heat production time and lower external energy demand, CO₂ has the potential to be substituted for H₂O. The research zone for this study was chosen to be located in the HDR reservoir in the Gonghe Basin of Qinghai. A three-dimensional discrete fracture model based on a thermal-hydraulic-mechanical coupling method is established, where numerical simulations are conducted using COMSOL software. The discussion focuses on the comparison of heat production effects between H₂O-EGS and CO₂-EGS in different injection and extraction scenarios are discussed. The results indicate that by lowering the injection temperature and increasing the injection rate, the EGS net heat production rate can be increased, but it also accelerates the heat breakthrough time and shortens the reservoir life. Although CO₂-EGS has a lower heat extraction rate in the early stage of thermal recovery than H₂O-EGS, it has a longer stable heat production time and a more energy-efficient heat production process. Therefore, compared to H₂O-EGS, CO₂-EGS has more economic and social benefits.