Internal Structure Of Strike-slip Fault Zones And Petroleum Accumulation In Low-non Porosity Rocks

Strike-slip fault zones play crucial roles in oil/gas accumulation in low-non porosity rocks. In this thesis, referring to numerous domestic and foreign research works, terminology related to strike-slip fault zones has been clarified and the main factors that influence microscopic deformation in fault zone in low-non porosity rocks has been well studied. Based on field investigation and measurement conducting in Niugou fault zone and Zhuanshanhu fault, Siping City, Jilin Province, we presented typical characteristics of strike-slip fault zone in low-non porosity rocks, and its formation and evolution processes were systematic studies. Subsequently, setting Xujiaweizi Fault Depression as target region, we further studied effects inner structures in strike-slip fault zone have to oil/gas accumulation.Under different conditions which vary in lithology, temperature, confining pressure, effective pressure and burial depth, the deformation mechanisms in fault zones mainly include cataclasis, catagenesis and cataclastic flow, and result from their combined effects brittle deformation occurs in strike-slip fault zone in low-non porosity rocks, forming the typical “dual structure” namely fault core and damage zone in fault zone.Generally, when the burial depth is less than 3km or being elevated to position with depth less than 3km after diagenesis, there are amounts of fractures developing in fault core and both fault core and damage zone can migrate oil/gas with lithology juxtaposition. When burial depth more than 3km, penetrability of cohesive cataclasite in fault core is 1-2 orders of magnitude higher than those in wall rocks and correspondingly permeability in damage zone is 1-6 orders of magnitude higher than those in wall rock; when confining pressure increase from 100 MPa to 200 MPa, penetrability in inhesive cataclasite, cohesive cataclasite, damage zone and wall rocks decrease. However, penetrability in damage zone still at its highest while permeability in fault core at its lowest, with fault core acting as entrapment.In this work, control function of inner structures in Xuzhong and Xudong strike-slip faults on oil/gas accumulation in Xujiaweizi volcanic work area were well studied. Gas accumulation distribution centrals on strike-slip fault zone, displaying a normal distribution. Analysis on control function of inner structures on gas entrapment can provide theoretic fundamental for studies fault zone sealing in low-non porosity rocks.