Fault Sealing Mechanism Of Fault Block Reservoirs In Linnan Subsag Of Huimin Sag

Under the guidance of petroleum geology reservoiring theory and comprehensive application of seismic, logging, core and analysis materials, the type of fault sealing ability and mechanism have been studied. The influence of diagenesis, deep fluids, dynamic metamorphism on fault sealing ability is discussed. By systematic sampling near the cross-section of research area, the fault sealing ability in the studied area is evaluated using fault sealing coefficient and fuzzy mathematics method.The factors of influencing the fault sealing ability can be divided into three factors:broken distance, broken move stratigraphic, mudstone content and principal stress. According to the detailed analysis of the fault sample of cored nearby Linnan subsag respectively, the lithologic docking, mudstone daub, diagenesis, deep fluids as well as dynamic metamorphismis studied to learn about the mechanism of the fault sealing ability. The key are microscopic mechanism such as deep fluids as well as dynamic metamorphism which were studied less before.By casting body chip, scanning electron microscope, clay mineral, full rock mineral, carbonate content, isotope analysis and porosity, permeability and pressure mercury and other test of coring wells, the influence of diagenesis on fault sealing ability, and texted row-flooding pressure and porosity, permeability were analysed to explain the fault sealing ability under the high sandstone content circumstances. Fault is the channel of fluid migration and different temperature, pressure conditions form different diagenetic authigenic mineral assemblage so that the porosity, permeability are obvious different. Therefore, compared with normal sandstone, the authigenic mineral assemblage near the fault are markedly different and the property become worse because of carbonate cementation, clay mineral cementation, bituminous and iron such diagenesis cemented have destroy the reservoir. In addition, the corresponding layer in the footwall which is compared to the purpose in the upper plate are old layers, the degree of compaction in the two plates is different and the porosity and permeability is not identical.They also can influence the sealinga ability.The deep fluids of different terms could effect the diagenesis in the sedimentary basin especially near the fault. Deep fluids mainly contains CO2, CO, H2, K+, Na+, halogen and so on. Because the existence of K+, Mg2+, both clastic rocks and mudstone extensively choritization and illitization; Carbonatite develop dolomitisation and parankerite in the presence of CO2 fulid. All the chemical reaction happened in high temperatures. The CO2 fluid associate with deep fluids participate in the diagenetic process and the molten rock magma move along the fault, releasing CO2 into water and forming HCO3-, H+. So it increase the acidity and caused feldspar mineral to disslove and the fluid of HCO3-, Ca2+, Mg3+, Fe3+ combined and ankerite is formed. Deep fluids cause the fillings sensitive to temperature to redistribute, which greatly reduce the petrophysics and increased the fault sealing capacity.Dynamical metamorphism is occurred on both sides of the cross section under high stress generated by the fluctuation two plates during fault activity. Such as quartz, sericite and feldspar mineral grains are split and disconnected, formed the chessboard format structure, and the sandstone near section is mylonitization mylonitized and so on. In the early stage of fracture development, fault zone shows brittle deformation with tension fissure development and its property is good, at this time the fault has vertical translocation to the oil and gas. Along with the further strengthen of fault activities, it happens mylonitization near the fracture surface, and so the particle changes into the miliolite because of broken, grinding and crushing; while the porosity gradually decreases from the normal formation to near the mylonite; so in this situation the fault plays lateral sealing effective to oil and gas; Thenceforward, with the death of fault activity, cracks in the cemented rock pack are filled by carbonate, and make pore have the bad connectivity,and so the fault has the good sealing capacity in vertical and lateral direction.On the basis of comprehensive consideration of the influnce of mudstone content of the belt, regional stress, fluid pressure, the shape of cross section, the fault sealing coefficient and fuzzy evaluation method are used to evaluate the sealing ability. The higher of oil column, the better of the sealing ability.The relationship between oil column height, SGR, pore throat radius porosity, permeability and flooding discharge pressure are figured out according to the large quantities of measured data in the studied area. Shale content is positively correlated with displacement pressure and radius of pore throat, porosity are negatively correlated with discharge pressure.Whether faults having sealing ability lies in the configuration between the fault activity period and hydrocarbon migrating period. The starting of the hydrocarbon migration of Huimin sag was at the end of Ed and since Nm. If the fault is static after hydrocarbon migration, faults are enclosed in the vertical,so oil and gas will migrate in the parallel direction;On the contary, vertical hydrocarbon are often open, then oil gas will move from the deep to the shallow along the fault, forming a series of oil formations in the vertical in shallow appropriate trap.