Fracture Architecture Of Tensile Fault In Carbonates And Its Fluid-Rock Interaction

Fractures are very common in the field.Their internal structure characteristics and controls on migration and accumulation of oil and gas have drawn widespread attention.Through field trip,we found that tensile faults developed in carbonate rocks have significant differences.In order to find out what factors make those differences and understand the internal fluid activity and fluid-rock interaction in the carbonates,firstly,based on field observation and description of a large number of faults,we analyzed the fracture architecture and influence factors of those faults,and then,the fluid–rock interactions in fault zone were discussed in this paper,which were combined with test results and simulation experiment.More than 60 tensile faults exposed in carbonate rocks in Xintai and Yishui in Shandong province were investigated,and among those,26 normal faults were selected to research their internal structures in detail.Through plane and profile analysis on the macrostructures of fault zones,the dual internal structures of fault architecture,which consist of fault core and damage zone,are typical in the carbonate tensile fault zones,while fault architectures are not identical in various fault zones,and the differences are largely due to displacement,strata thickness,degree of consolidation of the rock and buried depth are the main factors.As the growth of the displacement and development of the fault core(three stage: not development,discontinuous development,continuous development),the ratio of fault core width to displacement will increase from 1:10 to 1:100,and the ratio of fault zone width to displacement will rise from 10:1 to 100:1.If strata thickness is less than the displacement,fractures would develop,in contrast,when strata thickness is more than the displacement,fracture will not develop.In the same fault zone,compared with the thicker strata,the fracture is much more intensive and the damage zone is wider in the thinner strata.Combined with literature review,we also analyzed samples from each structural unit using optical microscope to discuss the microscopic features and physical properties of different structural unit in fault zone,which provided theoretical foundation for sealing and connecting of fault zone.In this paper,the freezing point and uniform temperature of the fluid inclusions developed in calcite vines and analyst the cathodoluminescence of rock slices were tested,which helped us to divide the internal fluid activity times of the fault preliminarily and determine the nature and characteristics of the fluid.At the same time,combined with carbon and oxygen isotope characteristics,the fluid source and diagenetic environment were defined.Fluid-rock interaction develops very well in fault zone.In this research,we simulated the fluid-rock interactions in different temperatures and pressures,and we found that the dissolution and precipitation occurred at the same time in fault zone.With the increase of temperature and pressure,the dissolution changes gradually from solution pit to solution band and solution cone.With the increase of temperature and pressure,the deposition reduces first before increasing.The precipitation of mineral crystals are from half euhedral crystal to euhedral crystal.Dissolution and precipitation jointly controls fault sealing and connecting.Combined with previous studies,we discussed vertical migration and lateral sealing mechanism of fault and researched on the relationship between the different fracture and the migration and accumulation of oil and gas.