The Control Mechanism Of Strike-slip Fault On Ordovician Carbonate Reservoir In The North Slope Of Tazhong Uplift

The Ordovician carbonate rocks in the northern slope of Tazhong uplift in the Tarim basin have experienced multi-period tectonic movement,multiple diageneses,and multi-period hydrocarbon charging.The unique petroleum geological background made the area have the characteristics of coexistence of karst and fault damage zone type reservoirs,complex reservoir-cap superposition relationship,and diverse hydrocarbon phases.The Strike-slip fault activities participated in the whole process of hydrocarbon accumulation.Therefore,the dissection of the Ordovician carbonate reservoirs in Tazhong uplift based on strike-slip faults is conducive to deepening the understanding of multi-type and multi-origin carbonate reservoirs in the Tarim Basin and also helps to solve the problems such as the unclear oil and gas enrichment factors in the study area.Using 3D seismic data,drilling data,logging data,oil,gas,and water geochemical data,and core samples,this research analyzes the impact of geometric and kinematic characteristics of strike-slip faults on the formation and evolution of fault damage zones,reservoirs,and caprocks,as well as oil and gas migration and preservation to further study the control mechanism of strike-slip faults on Ordovician carbonate reservoirs in the northern slope of Tazhong uplift.The active time of the strike-slip fault and the direction of the tectonic stress during the activity is determined.The types of strike damage zones in the north slope of the Tazhong uplift are identified,and the development rules of fractures in different damage zones are analyzed.It reveals how the evolution of strike-slip faults and the distribution of damage zones jointly affect the formation and evolution of reservoirs and caprocks with key diagenesis.The relationship between the distribution of geochemical parameters of oil,gas,and water and the distribution of strike-slip faults is expounded.The impact of strike-slip segmented characteristics on oil and gas preservation is also analyzed.The conclusions are as follows:The strike-slip fault in Tazhong uplift experienced three stages of tectonic activity from the end of Middle Ordovician to Late Ordovician(sinistral),Silurian-Devonian(sinistral),and Late Carboniferous-Permian(dextral).The faults with different arrangements and combination patterns form layered and segmented differential deformation and 4 types of strike-slip damage zones in strike-slip activities.The linking,bending,and tip damage zones have larger shape variables and stronger fault activity than the wall(linear)damage zones.The occurrence,density,and distribution of fractures in the damage zones are affected by the differential deformation of strike-slip faults.The strike of fractures is the same as that of adjacent faults,and the strike of dominant fractures in different damage zones is significantly different.The fracture density decreases with the increase of strike-slip fracture distance,and the fracture distribution range of the Yingshan Formation is larger than that of the Lianglitag Formation.The epigenetic and burial periods are key stages in the formation and evolution of reservoirs and caprocks.In the epigenetic stage,the strike-slip faults are mainly composed of wall(linear)damage zone,and the echelon strike-slip fault and vertical karst zonation structure controlled the formation and distribution of karst cavern-type and cavern-type reservoirs and caprocks in the slow flow zone.During the burial period,different types of strike-slip damage zones gradually formed,and the alternating occurrence of compressive and tensile stresses along the principal displacement zone controlled the development mode of fault damage zone reservoirs and diagenesis within the fault zone.The fluid is active in the intersection zone with the fault and the pull-apart damage zone,and diageneses such as dolomitization and dissolution takes place.The fractures formed in the early stage of compression and pullapart damage zones are easy to be cemented.Hydrocarbons enter the reservoir from the fault intersection zone and the pull-apart damage zone and migrate to the high position trap under the joint control of the occurrence of faults and strata.The change of the stress field in the late Caledonian,late Hercynian,and Himalayan periods makes the fault dredging capacity in the damage zone different,resulting in the difference of the crude oil maturity and gas charging around the fault zone,thus affecting the distribution of the current oil and gas phase.The different activity of strike-slip fault segments makes the main fault in the tension segment weak in sealing oil and gas,while the linear segment has a strong sealing ability.The research on the reservoir control mechanism of strike-slip faults in the northern slope of Tazhong Basin has been refined from the perspectives of segmentation,stratification,and staging of strike-slip faults.The establishment of reservoir-caprock evolution models based on the types and evolution of strike-slip fault damage zones and oil and gas migration models in different stress environments has deepened the understanding of the reservoir control mechanism of strike-slip faults.