Synergistic Mechanism Of Temporary Plugging And Propping Technologies To SRV Fracturing In Gas Shales

China is rich in shale gas resources with recoverable reserves of 36.1×10¹²m³.The efficient exploration and development of gas shales has an important strategic significance to alleviate the current situation of energy shortage in China.At present,China’s annual shale gas production is about 150×10⁸m³,Sichuan Basin is the main shale gas production area in China.The field data shows that the poor efficiency in SRV fracturing when encounters with gas shales with poor frac-ability,large horizontal stress difference and few natural fractures development.Although large-scale fracturing can improve the efficiency of SRV fracturing,the technique of activating and communicating more micro fractures or unsupported fractures under the same scale is expected to provide a new idea to solve the problem.Based on the analysis of the relevant factors influencing on the efficiency of shale SRV fracturing,the research of"synergistic application of temporary plugging and propping technologies to SRV fracturing"is put forward.Through the comprehensive research of laboratory experiment,theoretical model and software simulation,the main research results are as follows:The insufficiency fracturing of micro-fractures would restrict the efficiency of SRV fracturing in gas shales.The simulated hydraulic fracturing test was conducted to quantitatively characterize the micro-fractures activated and communicated.It is considered that the micro-fracture is an important part of SRV network.However,the difference in horizontal stress is great,or the micro-fractures are unpropped,would effect on the efficiency of micro-fractures fracturing.Therefore,a new technical idea of synergistic application of temporary plugging and propping to SRV fracturing in gas shales is demonstrated.The application of the new technique would improve the ESRV in shale SRV fracturing,by fracturing more micro-fractures and propping micro-fractures.Since the removal of temporary plugging agent and the micro-propping,the multi-propped fractures with continuous gas supply were established to improve the efficiency of shale SRV fracturing.Moreover,the composite temporary plugging behavior of temporary plugging agent and proppant in the fracture and its mechanism are revealed.During the process of composite plugging,the hydration expansion,deformation,filling and adhesion of temporary plugging agent are accompanied.The rigid proppant plays a role in bridging of composite temporary plugging zone,and proppant with deformation and adhesion characteristics plays a role in improving the compactness and stability of composite temporary plugging zone.The effective closure stress and proppant placement have significantly impact on the micro-fracture conductivity.Based on the analysis of Hertz contact theory on the elastic deformation of the micro-fracture surface,the mechanism of micro-propping to strengthen the conductivity of micro-fracture is revealed.The significance of optimal placement concentration of micro proppants for production is put forward based on the research of laboratory experiment and theoretical model.Besides,the prediction model of potential failure of this technology in the application process was developed,including the critical permeability prediction model and the critical stress-bearing prediction model.The simulation of this technique based on the CFD-DEM method was carried out.Results show that the composite temporary plugging zone has good performance with high pressure bearing capacity and compactness.In summary,this thesis revealed the synergistic mechanism of temporary plugging and propping technologies to SRV fracturing.The mechanism of enhancing the conductivity of microfractures is explored,and the synergistic technology and theoretical method of temporary plugging and propping to shale SRV fracturing are formed.It is clear that the technology has theoretical and practical significance.