Experimental Study of True Triaxial High Pressure Subcritical Water Impact Fracturing

Abstract

A new fluid alternative to slick water for fracturing shale gas can reduce the waste of water resources and improve the extraction efficiency. For the new fracturing technology, the experiments of different release pressures under pre-injection and for pre-injection were conducted by using the self-designed true triaxial experimental system, and the pressure pulse curves were obtained to analyze the fracturing principle. The experimental results showed that: (1) the pressure rise curve in the reactor can be divided into five steps: initial reaction stage, linear pressure rise stage, rate slowdown stage, instantaneous pressure release stage and residual pressure stage;(2) Pre-filling mode fracturing requires smaller expansion ratio, weaker pressure degradation, resulting in better fracturing effect;(3) The increase in initial fracture length leads to an increase in the pressure required to extend the fracture, and high-pressure subcritical water impact fracturing achieved fracture extension by a lower fluid pressure;(4) The fractal dimension has a strong linear relationship with fracture complexity, which is a new option to evaluate the fracturing effect.