| Traditional hydraulic fracturing technology has some shortcomings such as fracturing fluid pollution,hydration of clay minerals and simple fracturing network in unconventional oil and gas reservoir development.Exploring new methods and technologies of hydrofracturing is a hot and difficult problem in the field of unconventional oil and gas exploitation and rock mechanics.In this paper,a set of rock true triaxial anhydraulic/gas fracturing test system developed by ourselves is used to conduct a series of Rock Hydraulic fracturing,gas permeability fracturing and gas pulse fracturing tests under true triaxial conditions.The propagation and evolution of fracture network in rocks under different true triaxial stress conditions and different fracturing modes are studied in depth.Combining with theoretical analysis and numerical simulation,the mechanism of rock hydraulic fracture and gas fracture under true triaxial condition is discussed.The main achievements of this paper are as follows:(1)A series of rock true triaxial hydraulic fracturing,gas permeability fracturing and pulsed gas fracturing tests were carried out by using a self-developed rock true triaxial hydraulic and gas fracturing test system.The variation law of water/gas injection pressure during rock fracturing and the characteristics of initiation pressure,under different in-situ stress and fracturing modes were obtained.(2)Acoustic emission monitoring technology is used to monitor and analyze the whole process of Rock Hydraulic and gas fracturing in real time.The law and characteristic parameters of acoustic emission activity in rock induced by hydraulic and gas fracturing under true triaxial condition are obtained,and the differences of micro-fracture evolution characteristics in samples under different fracturing modes are revealed.(3)The CT scanning tests of rock samples after hydraulic and gas fracturing were carried out,and a series of reconstructed images of the spatial geometry and distribution of cracks in rock samples were obtained.The effects of different true triaxial stress conditions and different fracture modes on the expansion pattern and evolution characteristics of cracks in rock were revealed.(4)Based on Rock Hydraulic and gas fracturing test results,three-dimensional numerical model of true triaxial hydraulic and gas fracturing under impermeable conditions and two-dimensional seepage-stress coupling theoretical analysis model under permeable conditions are established,and rock fracture expansion model considering impulse gas action is established.the mechanism of Rock Hydraulic and gas-induced fracture initiation and expansion is preliminarily discussed. |
PDF Full Text Request