Mechanical principles of the fluctuation injection based hydraulic fracturing to induce microseismic and its influence on the fracturing effect

The propagation of rock fractures created by hydraulic fracturing can induce natural microseismic. The stress’s redistribution range caused by the microseismic of the traditional hydraulic fracturing area is limited, and the seismic wave of low magnitude has limited effects, so they cannot excite the seismic in the farther reservoirs, which, to some extent, restricts the stimulation effect of hydraulic fracturing. In this regard, the idea of making use of the fluctuation injection based hydraulic fracturing to induce “microseismic” in a larger area was proposed in this paper. Firstly, the pressure vibration model for the wellbore unsteady flow in the process of the fluctuation injection based hydraulic fracturing was established according to the theory of fluid mechanics, and the bottom hole pressure’s vibration sources and the rocks’ damage and fracturing mechanisms of artificially induced “microseismic” were analyzed. Then, seismic source characteristics and mechanical principles of the “microseismic” induced artificially by the fluctuation injection based hydraulic fracturing were investigated, and the influential mechanisms of microseismic on the hydraulic fracturing effect were analyzed. It is indicated that the frequency of the source fracturing signal of the microseismic artificially induced by the fluctuation injection based hydraulic fracturing decreases with the increase of fracture length. As for the fractured reservoirs, the mechanical principle that the fluctuation injection based hydraulic fracturing induces microseismic by leading to rock fracturing is the shear glide of faults or natural fractures in reservoirs. As for the non-fractured reservoirs, however, it is the artificial seismic effect and damage-fracturing effect. In conclusion, the fluctuation injection based hydraulic fracturing can artificially induce “microseismic”, which can increase the “microfractures” in reservoirs and enlarge the sweep area of natural microseismic, so as to enhance the stimulation effect of fracturing.