Gas Reservoirs In China Research Articles

Differential pressure power generation in UGS: Operational optimization model and its implications for carbon emission reduction

Underground Gas Storage (UGS) is an important facility for natural gas peak adjustment and ensuring the balance between energy supply and demand. The daily gas injection and production capacity of large UGS can reach several hundred million or even billions of cubic meters, and the energy consumed by the injection and production equipment is not to be underestimated, which also contains a large amount of pressure energy that can be utilized for power generation. In this context, the optimization of low-carbon operation of UGS is of great practical significance in engineering. In this study, an innovative UGS system operation optimization method is proposed to integrate a natural gas differential pressure generator set in the UGS system. Considering the complex interconnections among multiple storage areas, multiple wells and wellsites, and the hydro-thermodynamic constraints during the operation of injection and production pipeline network, and with the objective of minimizing the carbon emission, the UGS integrated with Differential Pressure Power Generation System (UGSIDPPGS) is established. In order to solve this complex model, this paper designs an optimization solution framework based on variational assignment, which effectively avoids the problem of falling into inferior solutions during the solution process. The optimization model is applied to the case study of a large-scale depleted gas reservoir in China, and the optimal operation schemes under three scenarios are successfully obtained. The results show that the UGSIDPPGS optimization model, not only effectively utilizes the pressure energy, generates up to 56.908 × 106 kW h per month, and reduces the CO2 emission by 56,738 tons, but also achieves the low-carbon and economic operation of the UGS. In conclusion, the operation strategy proposed in this study is of great value for optimizing the operation of UGS, and provides practical guidance and suggestions for the low carbon and environmental protection of UGS and the utilization of new energy sources.

A data-driven dual-optimization hybrid machine learning model for predicting carbon dioxide trapping efficiency in saline aquifers: Application in carbon capture and storage

Geological carbon sequestration (GCS) is a promising method to reduce global carbon emissions. To better understand the CO2 trapping mechanism, the CO2 sequestration process was simulated through a physics-based reservoir simulator, and the residual trapping (RTI) and solubility trapping (STI) efficiencies were analyzed. Through the experiments, a database containing 4543 data points with reservoir physical parameters and rock properties was established. In this study, a kernel extreme learning machine (KELM) model based on variational mode decomposition (VMD) and dung beetle optimization optimizer (DBO) was proposed to perform the prediction task. Through the VMD, the original data sequences were decomposed and combined, and the obtained subsequences were executed modeling prediction and reconstruction respectively. The reliability of the prediction model was confirmed to be greater than 97.71% through domain analysis. In addition, it was applied to a tight gas reservoir in China in to confirm its validity in field applications. Comparative results indicated a high agreement between the prediction results and the simulation results, suggesting that the proposed method can complement numerical simulations and help users understand the application of machine learning in carbon capture and storage (CCS).

A Comprehensive Review on the Geological Uniqueness and Enrichment Regularity of Shale Gas Reservoirs in China

This paper reviews the geological uniqueness and enrichment regularity of shale gas reservoirs in China, analyzes the patterns of shale gas formation under different geological backgrounds, discusses the main controlling factors affecting the enrichment of shale gas, and proposes potential directions for future exploration and development of shale gas. The study shows that the patterns of shale gas formation in China are diverse and are jointly controlled by multiple factors such as sedimentary environment, diagenesis, and later tectonic movements.

Review about evaluation methods of recoverable reserves of deep water drive gas reservoirs in China

It has been widely accepted that China is one of the biggest natural gas consumers. Related to the imports of LNG, China stands in a very uncomfortable situation. Most domestic gas reservoirs fall within deep water drive gas reservoirs inordinately, which has entered the production depletion stage. Accurate estimation of SEC recoverable reserves of deep water drive gas reservoirs is of great significance for gas consumption planning and peak shaving. The existing calculation methods of recoverable reserves mainly consist of static methods and dynamic methods. In the early stage of exploration and development, the volumetric method has often been utilized to calculate the recoverable reserves. With the continuous development of gas reservoirs, the main methods for evaluation are dynamic methods, including the successive subtraction of production method, water drive curve method, prediction model method, attenuation curve method, improved virtual curve method, and material balance method for deep gas reservoirs.

Rapid assessment of water phase trapping on gas permeability reduction in typical tight gas reservoirs in China

Water phase trapping (WPT) is one of the primary formation damage issues which can cause a steep drop in tight gas production. This paper presented a rapid assessment of the damage potential of WPT in Daniudi, Nanpu 5th, and Keshen 9th tight gas reservoirs involving shallow to ultra-deep layers in China. Typical core samples of the three tight gas reservoirs were selected to perform water imbibition and drainage experiments to mimic the WPT occurrence. After that, the damage degree to core gas permeability induced by WPT was evaluated. Results showed that, for a 16-h vertical water imbibition experiment, the core samples of Daniudi gas reservoir experienced the fastest water imbibition process while the core samples of Keshen 9th gas reservoir established the highest water saturation. After water removal, the ranges of damage degree to core gas permeability induced by the incremental water saturation were 36.07%–78.13%, 36.06%–56.21%, and 61.00%–76.30% in Daniudi, Nanpu 5th, and Keshen 9th tight gas reservoirs, respectively. It found that with the increasing formation depth, tight gas reservoirs can suffer greater damage from WPT not only because of the decline in rock permeability but also the salting out of high salinity formation water. In general, it holds that strong water capillary imbibition phenomenon, low water removal capacity, and high gas permeability damage degree are found to be the striking features of WPT potential on these typical tight gas reservoirs in China.

Saturation Height Modelling for Tight Sandstone Reservoirs with Gas Diffusion Dynamics Taken into Account

Interpreting and predicting the saturation of tight sandstone gas reservoirs are the key task to improve the reservoir development. The role of gas diffusion dynamics is stronger than that of buoyancy during the gas accumulation of tight sandstone reservoirs. In this study, a saturation height model that takes gas diffusion dynamics into account is proposed, which can complement logging saturation interpretation and provide a better practice in saturation prediction. Taking the study of the Sulige tight sandstone gas reservoir in China as an example, the saturation height model compares the controlling factors and uncertainties affecting the saturation distribution, characterizes the complex gas-water distribution, and determines the lower gas charging limits. This study concludes that the configuration between gas diffusion dynamics and reservoir capillary pressure controls the distribution of saturation. The buoyancy effect only serves to improve the saturation at regional uplifts with good petrophysical properties. The different saturation characteristics in the central, western, and eastern parts of the Sulige gas field are precisely caused by the different configurations of source rock quality and reservoir quality. This study provides a key reference for static model and development deployment.

Pore connectivity and microfracture characteristics of Longmaxi shale in the Fuling gas field: Insights from mercury intrusion capillary pressure analysis

Assessing the connectivity of pores and the characteristics of microfractures is essential for comprehending gas migration mechanisms and effectively implementing development strategies in deep shale gas plays. The Fuling gas field, a prominent shale gas reservoir in China, holds promise for deep shale development. This requires a better understanding of variations in pore connectivity among shale samples from different depths of the Fuling gas field. To achieve this goal, this study employs innovative methodologies based on mercury intrusion capillary pressure (MICP), a recognized technique for evaluating material pore structures. In this research, we conducted MICP tests on shale samples of varying sizes to examine variations in pore structure and quantify inaccessible pores. Additionally, repeated MICP tests were performed on the same sample to investigate the spatial distribution of residual mercury and distinguish different pore types associated with flow conduits and storage spaces. Furthermore, a directional MICP experiment was carried out to quantitatively characterize the degree of pore development and anisotropy of microfractures by considering the direction of mercury intruding the sample (parallel or perpendicular to lamination). Our findings revealed that deep shale samples exhibited a higher proportion of inaccessible pores compared to mid-deep ones. Regarding accessible pores, a greater proportion of connected pores was observed in the deep shale samples, while the mid-deep shale samples exhibited a lower proportion. The results from the directional MICP experiment indicated that samples with anisotropy in mercury intrusion volume possessed finer and denser microfractures. However, no evidence was found to correlate the ratio of dead-end and connected pores with sample anisotropy. Overall, this study presents a novel approach for experimentally evaluating pore connectivity and microfracture characteristics in shale reservoirs using MICP. The outcomes contribute to enhancing our understanding of shale gas migration mechanisms, particularly in deep ultra-low-permeability reservoirs, and hold significant implications for future developments in the field.

Feasibility of hydrogen storage in depleted shale gas reservoir: A numerical investigation

Due to the low operation cost, high containment security, and large storage capacity, depleted shale gas reservoirs are considered as promising options for large-scale hydrogen storage. However, its feasibility has not been systematically examined yet. It is still unknown about whether the deliverability (injection/withdrawal) capacity could meet the energy supply/demand and how the depletion time, cushion gas selection, injection/withdrawal strategy will influence the performance of this scenario.Therefore, we present a numerical compositional modelling investigation on hydrogen storage in a partially depleted Fuling shale gas reservoir in China. The results demonstrated that: 1) a high injection/withdrawal capacity could be achieved through a single shale play pad in the area of interest as approximately 5.4 × 108 Sm3 hydrogen could be stored and 3 × 108 Sm3 could be recovered in each cycle (equal to 0.54 TWh of power output). 2) CH4 production is inhibited once hydrogen storage project is performed, an early depletion time could significantly reduce CH4 production but slightly improve H2 withdrawal. 3) Cushion gas injection is beneficial to reducing H2 loss and enhancing 2.8% H2 recovery, while the main drawback of this operational measure is an increase in capital cost in gas separation due to lower H2 purity in the produced gas.This work demonstrates that shale gas reservoir is a promising candidate for hydrogen storage, which is beneficial to the implementation of large-scale hydrogen economy and the operation of hydrogen supply chain.

Analysis of Migration Characteristics of Supercritical CO2 and Mechanism of Oil and Gas Production in Condensate Gas Reservoirs

At present, circulating gas injection is the most effective development method for condensate gas reservoirs in China, but the phenomenon of dry gas overlap has seriously affected the development effect of circulating gas injection in condensate gas reservoirs, while CO2 injection is used to drive gas, which can make CO2 widely used in removing retrograde condensation of condensate gas reservoirs, improving the development effect of gas reservoirs. This paper by comparing the migration laws of injected dry gas and injected CO2 obtains that the dry gas with a smaller density flows to the upper space of the reservoir, while the CO2 with a larger density settles to the lower part. With the injection of CO2 into the reservoir, the content of CO2 in the crude oil increases, the volume of condensate oil expands significantly, and the flow capacity of condensate oil in the formation is improved. Injecting CO2 into the formation can reduce the viscosity of condensate. The mixture of CO2 injected into the formation and formation water is slightly acidic, which can dissolve some cement in the rock. With the increase of CO2 injection, the interfacial tension between oil and water will also increase, which is unfavorable for the stability of the oil-water system and is easy to emulsify. After demulsification, the viscosity will decrease and the condensate oil will flow more easily. The dissolved carbon dioxide in the water is in a weak acid state, which is easy to corrode and shed particles, improving the reservoir space and seepage conditions near the well. It will provide theoretical support for the effective development of a condensate gas reservoir.

Research on Dynamic Monitoring Technology for Dengsi Gas Reservoir in Gaoshiti Moxi Block

The fourth group gas reservoir in the Moxi platform edge zone of Anyue Gas Field is a super large carbonate gas reservoir with edge and bottom water in China. There is no mature development experience in this type of gas reservoir in China, and there is a lack of a systematic dynamic monitoring system. This article focuses on the challenges and key technical issues faced by gas reservoir dynamic monitoring work. Through active exploration, continuous improvement, and innovation of dynamic monitoring technology and analysis methods, a dynamic monitoring system suitable for the four groups of gas reservoirs with lights at the edge of the Moxi platform has been constructed. Five key dynamic monitoring technologies, including pressure and temperature dynamic monitoring technology, production capacity monitoring and evaluation technology, fluid property monitoring technology, water invasion monitoring and identification technology, and well connectivity monitoring and evaluation technology, have been developed for the four gas reservoirs in the Moxi platform edge zone. Scientific and reasonable development measures have been formulated to support the preparation of the overall water control plan for the gas reservoir, It has played a role in ensuring the scientific and efficient development of large-scale edge and bottom water carbonate gas reservoirs.

Micro-seismic monitoring using sparse planar array and a weak signal enhancement method

Abstract Traditional ground micro-seismic monitoring is performed by laying long survey lines. This is expensive and difficult to implement in complex mountainous areas and deep marine shale gas reservoirs in China. To address these challenges, this study proposes a ground micro-seismic monitoring method using a sparse planar array that offers greater flexibility in implementation. This study presents a weak signal enhancement method based on a broadband-array adaptive beamforming algorithm to improve the signal-to-noise ratio (SNR) of micro-seismic data collected by sparse planar arrays and to suppress coherent noise. The proposed method involves establishing a signal model for a broadband planar array, estimating the direction of arrival (DOA) of broadband signals using a grid search method, and setting constraint conditions and objective functions based on the DOA results. The optimal weight vector is then calculated by solving the objective function to obtain the desired signal and suppress noise. This study demonstrates that the proposed method effectively improved the SNR and suppressed coherent noise in synthetic and real data. It also highlights the effectiveness of the sparse planar array as a ground micro-seismic monitoring method and the adaptive broadband beamforming method as a practical weak signal enhancement technology.

Geological characteristics and models of fault-fold-fracture body in deep tight sandstone of the second member of Upper Triassic Xujiahe Formation in Xinchang structural belt of Sichuan Basin, SW China

In the second member of the Upper Triassic Xujiahe Formation (T3x2) in the Xinchang area, western Sichuan Basin, only a low percent of reserves has been recovered, and the geological model of gas reservoir sweet spot remains unclear. Based on a large number of core, field outcrop, test and logging-seismic data, the T3x2 gas reservoir in the Xinchang area is examined. The concept of fault-fold-fracture body (FFFB) is proposed, and its types are recognized. The main factors controlling fracture development are identified, and the geological models of FFFB are established. FFFB refers to faults, folds and associated fractures reservoirs. According to the characteristics and genesis, FFFBs can be divided into three types: fault-fracture body, fold-fracture body, and fault-fold body. In the hanging wall of the fault, the closer to the fault, the more developed the effective fractures; the greater the fold amplitude and the closer to the fold hinge plane, the more developed the effective fractures. Two types of geological models of FFFB are established: fault-fold fracture, and matrix storage and permeability. The former can be divided into two subtypes: network fracture, and single structural fracture, and the later can be divided into three subtypes: bedding fracture, low permeability pore, and extremely low permeability pore. The process for evaluating favorable FFFB zones was formed to define favorable development targets and support the well deployment for purpose of high production. The study results provide a reference for the exploration and development of deep tight sandstone oil and gas reservoirs in China.

In situ stress determination in isotropic and anisotropic rocks and its application to a naturally fractured reservoir

Anisotropies exist in many sedimentary rocks, particularly in naturally fractured reservoirs, causing horizontal stress anisotropies. Case studies indicate that when a rock formation contains high dip-angle fractures or contains horizontal factures (e.g. bedding planes), it has very distinguished horizontal stresses. In these cases, the conventional isotropic method for estimating horizontal stresses may give erroneous results. Using the theory of anisotropy, horizontal stresses in the vertical transverse isotropy (VTI) and horizontal transverse isotropy (HTI) models are derived for determining in situ stresses in naturally fractured rocks. Comparing with the isotropic model, the VTI model predicts a higher minimum or maximum horizontal stress, which is suitable for shales. In contrast, the HTI model gives a lower minimum stress than the isotropic model. A combined model based on the VTI and HTI models is proposed for estimating the minimum horizontal stress in a naturally fractured formation containing natural fractures with different dip angles. Measured data in the Xujiahe gas reservoir in China reveal that the minimum horizontal stresses and formation breakdown pressures decrease as the fracture dip angles increase, which is consistent to the derived HTI model. Natural fractures can result in a decrease of the minimum horizontal stress by up to 3 MPa/km and a reduction of the formation breakdown pressure by up to 10 MPa/km in the studied area. Combining the proposed anisotropic model to the measured data of natural fractures and horizontal stresses, the assessment of in situ stresses and their impact on hydraulic fracturing are proposed. Case study demonstrates that the proposed model gives a good prediction of the minimum horizontal stresses in the naturally fractured reservoir.

New insights into the evaluation criteria for high-quality deep marine shale gas reservoirs in the Longmaxi formation: Evidence from organic matter pore development characteristics

Porosity, total organic carbon content, brittle mineral content, and gas content are now the primary references for classifying and evaluating marine shale gas reservoirs in China. Is there a more effective and appropriate reservoir classification scheme for deep marine shale? The Longmaxi Formation in Luzhou, southern Sichuan Basin, China, is the main object of study. Quantitative analysis and modeling using data from field emission scanning electron microscopy, nitrogen adsorption, and logging were used to characterize organic matter (OM) pore multi-scale development and reveal the relationship between OM pore and the high-quality reservoirs. Microscopic and macroscopic indications from OM pores show that a large number of OM pores were developed in high-quality reservoirs. OM surface porosity occupancy of the high-quality reservoir in the Luzhou area was more than 60%. OM porosity occupancy was more than 50%. The nitrogen adsorption–desorption hysteresis loops demonstrate the development of bottleneck and wedge-shaped OM pores. Characterization of multi-scale pore structure by box dimension, pore volume and specific surface area. It is found that the key to the formation of high-quality reservoirs was the massive development of OM mesopores in siliceous shale and the relatively homogeneity structure, which was conducive to the enrichment and migration of shale gas. Furthermore, the improved model decreased the relative error in predicting the OM porosity by about 32.5%. The use of OM porosity occupancy for high-quality reservoir classification was better, and the results were consistent with geological understanding. OM porosity occupancy showed that the area from Lunanxi to Luzhou to Rongchang to Jiangjin was the key exploration area for high-quality reservoirs in southern Sichuan. This study is expected to provide a new idea for OM pore modeling analysis and deep marine shale gas reservoir classification.

Shale gas production evaluation framework based on data-driven models

Increasing the production and utilization of shale gas is of great significance for building a clean and low-carbon energy system. Sharp decline of gas production has been widely observed in shale gas reservoirs. How to forecast shale gas production is still challenging due to complex fracture networks, dynamic fracture properties, frac hits, complicated multiphase flow, and multi-scale flow as well as data quality and uncertainty. This work develops an integrated framework for evaluating shale gas well production based on data-driven models. Firstly, a comprehensive dominated-factor system has been established, including geological, drilling, fracturing, and production factors. Data processing and visualization are required to ensure data quality and determine final data set. A shale gas production evaluation model is developed to evaluate shale gas production levels. Finally, the random forest algorithm is used to forecast shale gas production. The prediction accuracy of shale gas production level is higher than 95% based on the shale gas reservoirs in China. Forty-one wells are randomly selected to predict cumulative gas production using the optimal regression model. The proposed shale gas production evaluation framework overcomes too many assumptions of analytical or semi-analytical models and avoids huge computation cost and poor generalization for numerical modelling.

Architectural Element Analysis of Nonmarine Oil and Gas Reservoir in China, the Research History, Progress and Future Trend: A Review

Since Miall’s architectural element analysis (AEA) was introduced to China in 1986, the method has been widely applied to studying the heterogeneity of oil and gas reservoirs in China. The development history, research field, research progress, and potential limitations of AEA in China have been reviewed based on 601 Chinese documents retrieved from the China National Knowledge Infrastructure (CNKI) database and some English documents retrieved from various databases. The development of sedimentary AEA in China experienced four stages: (1) the conceptual and introduction stage (1985–1995), (2) the test and trial stage (1995–2005), (3) the popularization and application stage (2005–2015), and (4) the innovative stage (2015 to present). The research field covers all reservoir types of continental petroliferous basins in China. Papers published on AEA were distributed in the fields of (1) alluvial fan reservoirs, (2) braided channel reservoirs, (3) meandering channel reservoirs, (4) fan delta reservoirs, (5) braided river delta reservoirs, (6) shallow-water delta reservoirs, (7) large-scale delta reservoirs, (8) beach and bar reservoirs, and (9) lacustrine deepwater gravity flow reservoirs. Among all these fields, the architecture of alluvial fans, braided channels, meandering channels, braided river delta, and fan delta reservoirs was mainly researched. AEAs in China have made outstanding innovations in hierarchical sedimentary boundary surface classification, depositional architectural models, and quantitative reservoir architectural modeling. Combining the hierarchical AEA with geostatistical modeling, big data, and artificial intelligence technology and comprehensively using geology, geophysics, and production information to realize the hierarchical integrated reservoir architectural characterization are the development directions of the AEA in China and around the world.

Multiscale Pore Structure Evolution of Longmaxi Shale Induced by Acid Treatment

SummaryHydraulic fracturing to generate complex fracture networks is essential for shale reservoir development. However, the recovery of shale oil and gas is still low due to various engineering and geological factors. Acid treatment has been approved as a potential approach to enhance stimulated reservoir volume (SRV) by changing petrophysical and mechanical properties. Understanding the multiscale pore structure evolution behind the macro-performance change is critical in the application of acid treatment in shale reservoirs. In this study, cylindrical and powder shale samples from the Longmaxi formation are treated with 15 wt% hydrochloric acid (HCl) for 10 days. Before and after acid treatment, X-ray computed tomography (CT) and N2 adsorption techniques are used to characterize shale pore structure at microscale and nanoscale, respectively. Combined with the determination of variations in chemical compositions of shale samples and acid solutions, the mechanism of multiscale pore structure evolution induced by acid treatment is discussed. The N2 adsorption results uncover a considerable increase in volume and size of nanopores. All the nanopores increase in carbonate-rich shale, whereas the micropores and mesopores undergo a decrease in clay-rich shale. Reconstructed 3D CT images reveal the generation of large volumes of microscale pores and fractures, which leads to an increase in porosity of about 9%. The pore structure evolution in shale due to acid treatment is controlled by both mineralogy and microstructure. These findings demonstrate the promise of acid treatment for enhanced SRV and long-term productivity of shale oil and gas reservoirs in China.

Stratigraphic subdivision-based logging curves generation using neural random forests

Comprehensive logging curves are necessary for the accurate characterisation of unconventional hydrocarbon formations. However, the logging curves for some wells remain unavailable. Traditional methods of generating the missing logging curves (e.g. multiple regression techniques) have low accuracy, and it is difficult to represent the complex nonlinear relationships between the logging curves of unconventional reservoir using them. The neural random forest (NRF) is a new robust and fault-tolerant machine learning algorithm with high precision. Therefore, we used the NRF model to generate the missing logging curves of a shale gas reservoir in China for the first time. Specifically, four models for generating compensated neutrons, compressional slowness, gamma ray, and density curves were developed based on the NRF framework, incorporating stratigraphic subdivision information. Subsequently, considering the subnetwork connectivity characteristics of the NRF model, the joint and independent methods were separately used to train the model. Finally, the performance of the NRF model was evaluated by comparing it with neural network (NN) and random forest (RF) models. Results revealed that the NRF model achieved superior performance, with R2 > 0.85 on average. Compared to the NN and RF models, the NRF model demonstrated higher prediction accuracy. In addition, the prediction performance of the jointly trained NRF model was slightly superior to that of the independently trained NRF model. Moreover, stratigraphic subdivision information was proved to be important in reducing the model prediction errors and improving the accuracy by almost 20%. In summary, the proposed model provides a cost-effective method for generating the missing logging curves of horizontal wells in the shale gas reservoirs, which will further facilitate the exploration and development of unconventional reservoirs.

Progress and prospects of carbon dioxide capture, EOR-utilization and storage industrialization

Carbon dioxide capture, EOR-utilization and storage (CCUS-EOR) are the most practical and feasible large-scale carbon reduction technologies, and also the key technologies to greatly improve the recovery of low-permeability oil fields. This paper sorts out the main course of CCUS-EOR technological development abroad and its industrialization progress. The progress of CCUS-EOR technological research and field tests in China are summarized, the development status, problems and challenges of the entire industry chain of CO2 capture, transportation, oil displacement, and storage are analyzed. The results show a huge potential of the large-scale application of CCUS-EOR in China in terms of carbon emission reduction and oil production increase. At present, CCUS-EOR in China is in a critical stage of development, from field pilot tests to industrialization. Aiming at the feature of continental sedimentary oil and gas reservoirs in China, and giving full play to the advantages of the abundant reserves for CO2 flooding, huge underground storage space, surface infrastructure, and wide distribution of wellbore injection channels, by cooperating with carbon emission enterprises, critical technological research and demonstration project construction should be accelerated, including the capture of low-concentration CO2 at low-cost and on large-scale, supercritical CO2 long-distance transportation, greatly enhancing oil recovery and storage rate, and CO2 large-scale and safe storage. CCUS-EOR theoretical and technical standard system should be constructed for the whole industrial chain to support and promote the industrial scale application, leading the rapid and profitable development of CCUS-EOR emerging industrial chain with innovation.

Differences in micromechanical properties of shales from different depositional environment: A case study of Longmaxi marine shale and Yanchang continental shale using nanoindentation

An understanding of the mechanical properties of reservoir shale is of great significance for the efficient development of shale gas. Both marine and continental shale gas reservoirs in China have considerable development potential, but their different depositional environments may lead to substantial differences in their mechanical properties, which can result in production efficiency differences. In this study, nanoindentation, X-ray diffraction, backscattered electron imaging, and energy-dispersive X-ray spectroscopy were used to determine and analyze the mechanical properties and microtexture of marine and continental shale samples. The geogenesis of the microtexture of marine and continental shales and its influence on the mechanical properties were discussed. The results show that the elastic modulus of marine and continental shale samples are similar, but the hardness of latter is greater. The similar elastic modulus of the two shale samples may result from similar mineralogy. Due to differences in deposition and diagenesis, the marine shale sample forms a clay support matrix and the continental shale sample forms a rigid clastic support matrix, which results in lower hardness in the former and higher hardness in the latter. The low hardness of the shale with a clay support matrix indicates that it may be subject to more severe proppant embedment issue. The experimental results provide a useful reference for the development of these two types of shale gas reservoirs.