Study On Crack Propagation Mechanism Of Rock Mass In Low Permeability Reservoir

The mechanism of crack propagation for hydraulic fracturing is widely used in many engineering such as exploitation of oil, shale gas, coal-bed gas, and Slope, dam, tunnel, nuclear waste repository, chamber under water pressure. This paper study the mechanism of crack growth in low permeability reservoir rock whether it has water flooding or not. In the process of the water pressure, The Initiation, expansion, evolution of crack in low permeability reservoir rock lead to rock macro-structure and micro-structure changes, That cause the redistribution of rock stress field and changes of the rock permeability. The seepage flow field redistribution due to changes in the structure of rock permeability. The essence of hydraulic fracturing crack propagation mechanism is complex process that the change of rock micro-structure alter the mechanical characteristics of rock mass macro-structure. Both from the macro or micro perspective, Study on the crack propagation mechanism of rock mass play an important role in petroleum Engineering and rock engineering.1) Firstly. In this paper, the crack propagation law of rock fracture is studied by using ARAMIS system. Through the use of ARAMIS system, the rock crack spot and surface strain was obtained. Then, comparing the RFPA2D numerical analysis results and experimental results verify the reliability of the RFPA2D numerical software.2) Secondly, based on Mohr-Coulom failure criterion and rock fracture theory, this paper establish single prefabricated fissure rock model and double parallel prefabricated fissures rock model under no consideration of water. For the study about different single prefabricated fissure dips of rock, the paper investigated the rock fissure initiation, propagation mechanism with different single fissure dips, and the single fissure morphology influence on the mechanical properties of rock was analyzed. For the research about double parallel prefabricated fissure angles and rock bridge inclination of rock specimens.the paper analyzed the fissures initiation, propagation mechanism under different double fissures morphology, the fissure and rock bridge dips influence on the mechanical properties of rock was analyzed. Besides, the paper investigated the influence of different fissure dips and different rock bridge dips on the rock bridge transfixion.3) At last, considering fluid solid coupling and rock micro damage characteristics, the paper establish numerical model of low permeability reservoir rock with a single natural cracks and double parallel natural fractures based on seepage-stress damage coupling theory, the mechanism that hydraulic fracture activates natural fissures was studied.The research results of this paper can provide a theoretical basis for guarantee the stability and safety of rock engineering that has jointed, cracks and other defects, and production optimization of petroleum engineering.