Research On The Evolution Mechanism And Numerical Simulation Of Thermally Induced Microcracks In Shale

In many fields,such as enhanced oil recovery,unconventional oil and gas and geothermal development,nuclear waste deep placement and so on,the thermal effect of rock mass will be involved.Temperature change and temperature gradient will produce thermal stress in rock mass,which will lead to the generation of thermal cracks.In these fields,the thermal cracking of shale will be involved,but at present,the thermal cracking of shale is the main problem Therefore,it is of great practical significance to study the formation mechanism of thermal induced cracks in shale reservoirs.In this paper,the shale indoor heating experiment and particle flow method are used to study the formation mechanism of thermal induced cracks in shale.It is found that it is difficult to produce obvious thermal induced cracks in shale matrix,and only a few intergranular and intragranular cracks and shrinkage cracks of organic matter appear locally.Based on the particle flow method,a shale particle flow model is constructed,which is highly consistent with the macro and micro characteristics of shale The systematic micro parameter calibration method based on shale particle flow model can effectively calibrate the micro parameters of shale particle flow mechanics model.The thermal mechanical coupling model of shale particle flow based on shale particle flow mechanics model is used to study the influence of heating mode,natural micro crack and in-situ stress on the evolution of thermal induced crack of shale.The results show that heating mode,natural micro-crack and in-situ stress have an important influence on the propagation of thermal induced cracks in shale.The propagation modes of thermal induced cracks are different under different heating modes.Under the overall heating mode,the thermal induced cracks only propagate along the bedding plane,while under the side heating mode and from the outside to the inside heating mode,there is a crack network communicating with the bedding In addition,the higher the in-situ stress is,the less the thermal cracks extend along the bedding plane,while the thermal cracks generated by shale matrix itself increase,and the higher the proportion of shear failure thermal cracks is.