Seismic Respones To Fault Reactivation Induced By Hydraulic Fracturing In Coal Measures

Due to the complexity and diversity of the occurrence process of fault activation induced by water injection fracturing in coal measures,as well as the lack of monitoring methods,the recognition of activation and precursor information characteristics has been a difficult problem puzzling the academic community.The thesis focuses on the key scientific issue of "microseismic response law and stress loading,as well as the mutual feedback relationship between water injection fracturing and fault activation process induced by water injection fracturing",and the three key factors involved in "water injection fracturing,coal bearing strata,and faults".The theoretical analysis and experimental design of water injection fracturing induced fault activation,water injection fracturing induced fault activation experiment,and water injection induced fault activation experiment are carried out in sequence and engineering case validation of four main research contents,with a view to revealing the microseismic response law of fault activation induced by water injection fracturing in coal measures.Based on the Mohr Coulomb effective stress principle,the critical stress conditions for the slip of prefabricated section specimens and the stress evolution path during the slip process induced by water injection fracturing were analyzed and determined;Based on the main influencing factors of fault activation process induced by water injection fracturing in coal measures,two types of water injection fracturing experiments and monitoring schemes for connected and unconnected cross section samples of high permeability reservoirs were designed,including the preparation of prefabricated cross section samples required for the experiment and the processing of sealing devices required for water injection fracturing sealing.Finally,a true triaxial stress loading A fluid solid acoustic emission coupling experimental platform for the three major systems of water injection fracturing and acoustic emission monitoring.The water injection fracturing induced fault activation experiment shows that the microseismic spatial distribution during fault activation during stress loading and the acoustic emission events generated during water injection fracturing tend to be near the fault location,and the acoustic emission event location during pressure maintaining water injection develops from the bottom end of the water injection hole to the section,consistent with the experimental results of the hydraulic fracturing conduction section;In terms of signal waveform,long period signals(LCS)mainly come from slow sliding of faults caused by water injection fracturing,while tremor like signals(TLS)are mainly related to slow sliding of faults caused by stress loading,while microseismic signals(SE),in addition to corresponding fracture events occurring within the rock mass,also include rapid sliding of faults.In addition,the industrial CT scan results of fracture samples after fracturing indicate that the fracture network generated during water injection fracturing expands and conducts the fracture in accordance with the pre controlled principal stress direction.The water injection induced fault activation experiment shows that the microseismic spatial distribution during fault activation is mainly concentrated at the center of the sample near the fault during stress loading and water injection stages,and a small amount of acoustic emission signals can be captured internally during pressure maintaining water injection,and most of them occur near the fault location;In terms of signal waveform,tremor like signals(TLS)mainly originate from the slow sliding of faults caused by stress loading.Long period signals(LCS)are mainly related to the expansion and sliding of the interrupted layer during water injection and the seepage diffusion of water injection along the fracture surface,while microseismic signals(SE)correspond to fracture events occurring around the fault layer.The engineering case verification shows that the spatial distribution and waveform characteristics of microseisms obtained from the two experiments can provide a reasonable explanation for the fault activation signals induced by on-site water injection fracturing.