Abstract To investigate the mechanism of super-critical CO2 saturation on the tensile properties of shale, shale specimens were saturated with Sc-CO2, and inert gas (Ar) was employed as control group. Brazilian splitting experiment with different layering inclinations (0°, 30°, 60°, 90°) showed that after Sc-CO2 saturation, the Brazilian splitting strength (BSS) and Brazilian splitting modulus (E) of shale were decreased by 11.9% and 5.7%, respectively. Regardless of any direction of stress loading, the bedding planes of shale had been damaged. The failure mode of shale transformed from single tensile to tensile-shear mixed failure after Sc-CO2 saturation and less energy was required for shale failure. The weakening of carbonate cementation made the bedding planes more prone to damage, and the number of shear cracks after Sc-CO2 saturation was twice as much. The X-ray diffractometer, scanning electronic microscope and nuclear magnetic resonance results showed that the increase of porosity caused by calcite dissolution and organic matter extraction was the fundamental reason for the deterioration of shale tensile properties. Furthermore, gas pressure made shale more compact, and also induced new cracks formation in the meanwhile. Therefore, after Ar saturation, E and BSS of shale were increased and decreased, respectively.
Abstract CO2 injections into shale reservoirs can enhance the recovery of oil and gas, while simultaneously sequestrating CO2. However, with the injection of CO2, the microstructure and mechanical properties alteration of shales caused by CO2/CO2-water exposure is should be noticed, which is of great importance to predicting the efficiency of CO2-enhanced shale oil/gas recovery and safety of CO2 sequestration in shale reservoirs. Therefore, this study clarifies the influence of sub/super-critica...
Last. Zhejun Pan(CSIRO: Commonwealth Scientific and Industrial Research Organisation)H-Index: 57
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Abstract Brittleness is an essential parameter in the evaluation of wellbore stability and hydraulic fracturing design of shale reservoirs. It is an inherent geomechanical property controlled by the mineral composition, sedimentary structure, and geological condition. However, traditional brittleness evaluation methods based on the elastic parameters and mineral composition analyses are limited by the anisotropic petrophysical behaviors of continental organic-rich shale. In this paper, we analyz...
Abstract Geological characteristics, geomechanical behavior and hydraulic fracture propagation mechanism in the Marcellus shale gas play are analyzed and compared with China’s Fuling shale play. Successful experiences in hydraulic fracturing and shale gas development in the Marcellus shale gas play are summarized, which might be applicable in other shale plays. The main factors contributing to the successful development of the Marcellus shale gas play include adoption of advanced drilling and co...
Abstract This study analyses the geological characteristics and development progress of unconventional gas in China, summarizes the development theories and technologies, discusses the prospects and challenges of unconventional gas development, and puts forward the future trends of development technologies. Various technologies of unconventional gas development are available in China. Shale gas development technologies include comprehensive geological evaluation, volume fracturing of cluster hor...
Abstract Shale permeability is very important for the prediction and evaluation of shale reservoir performance. In this paper, we review recent work on how shale permeability is affected by testing method, lithology, and fluid-rock interaction. Both the steady-state method and the pulse-decay method are used for shale permeability tests. However, the steady-state method is time-consuming, and the unsteady-state method may over-estimate permeability. Permeability is strongly affected by mesopores...
Abstract Hydraulic fracturing has been a successful stimulation method for enhancing recovery in very low permeability shale gas reservoirs. Proper modeling of multistage hydraulic fracturing in shale reservoirs requires an accurate representation of the pre-existing natural fractures in the shale. The objective of this study is to utilize a 3D discrete fracture network model to simulate hydraulic fracturing in five horizontal wells A-E in the Barnett Shale. Each horizontal well had 10 stages of...
Last. Yaoqing Hu(TUT: Taiyuan University of Technology)H-Index: 6
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Abstract This paper investigates variation in the failure behavior of shale in a ScCO2-immersion environment with different adsorption periods and layering orientations. Eight types of specimens are investigated, where the inclination of the layering to the applied force θ is 0°, 15°, 30°, 45°, 60°, 75°, 90°, and Divider type. The period of immersion ranges up to 60 days. The results indicate that after 60 days of ScCO2 adsorption, the Brazilian splitting strength (BSS), splitting modulus (E) an...
Abstract When fracturing a shale gas reservoir with supercritical CO2, the interaction between CO2 and shale will change the pore structure, thus affecting the mechanical properties of shale. To confirm the influencing mechanism of pore structure changes on mechanical properties, nuclear magnetic resonance, uniaxial compressive strength, and acoustic emission were performed on shale specimens from the Sichuan Basin before and after CO2 saturation. Results indicated that after CO2 saturation, the...
#1Yixiang Zhang(CAS: Chinese Academy of Sciences)H-Index: 4
#2Jianming He(CAS: Chinese Academy of Sciences)H-Index: 10
Last. Chong Lin(CAS: Chinese Academy of Sciences)H-Index: 5
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Abstract Hydraulic fracturing using freshwater as fracturing fluid is regularly employed in commercial shale gas or oil production. Many problems are brought by the fracturing fluid of water, such as water shortages, swelling of clay mineral, and the pollution of flow-back water. Replacement of water by supercritical CO2 (SC CO2) in the hydraulic fracturing treatment of shale reservoir has meaningful potential for the improvement of gas production. Hydraulic fracturing experiments, under differe...
Abstract A series of significant breakthroughs in exploring conventional and unconventional natural gas resources have been achieved in new strata and new domains. However, the quality of the increased reserves has declined with the entry of unconventional resources into the reserves sequence. Therefore, the potential of conventional and unconventional natural gas resources as well as important exploration regions of the remaining natural gas resources need to be clarified, and favorable directi...
Last. Xiang Ao(Chongqing University of Science and Technology)
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Abstract Using supercritical CO2 as fracturing medium to develop shale gas not only improve the stimulation effect of reservoir, but also reduce CO2 emissions. To optimise the flow of shale gas into a wellbore, it is important to understand the flow characteristics of gas in the shale fracture system after reservoir reconstruction. To date, no research has been conducted on the effect of supercritical CO2 on the flow characteristics of gas in shale fractures. Hence, in this study, experiments we...