The Fault-cap Co-control Hydrocarbon Accumulation Models Of Hailaer Basin-take Beier Depression For Example

Joint controlling of fault and caprock is to research the oil and gas migration andaccumulation pattern from the perspective of the oil and gas preservation conditions. In orderto identify characteristics and control factors of hydrocarbon accumulation in Beier Sag,based on the geological data, seismic data, drilling data, well logging and analysis test dataetc., this article systematically combed the tectonic evolution process of Hailer basin,analyzed the effect of tectonic evolution on hydrocarbon accumulation, divided the petroleumsystems, evaluated the caprock sealing ability, summarized accumulation models ofpetroleum systems controlled by different caprocks systematically combined fracture typeand reservoir-controlling function. The results showed that the Hailaer basin has experiencedresidual basin, initial rift basin, strong rift basin, fault-depression transform period anddepression period five evolutionary stages. Passive rift period formed excellent hydrocarbonsource rocks and oil gas accumulation belt with warped reverse fault footwall. Active riftperiod formed hydrocarbon source rocks and multiple types of oil and gas accumulation zone.Fault-depression transform period resulted in maturity of source rock and formed primarypetroleum accumulation because of basin rapid subsidence. In the late fault-depressiontransform period，basin inversion formed inversion tectonic belt which controlled the oil andgas accumulation of secondary reservoir. So two petroleum systems–the lower petroleumsystem and the upper petroleum system were formed. Hydrocarbon source rock of middleMember K1n1, reservoir rock of middle and lower Member K1n1and cap rock of upperMember K1n1consisted of lower petroleum system. Hydrocarbon source rock of upperMember K1n1, reservoir rock of upper Member K1n1and Member K1n2and cap rock ofMember K1d1consisted of upper petroleum system. In addition, part of oil and gasdiscovered in Damoguaihe Formation is the result of later adjustments and belongs tosecondary reservoir of upper petroleum system. Cap rock of lower petroleum system islocated in upper cycle of Member K1n1and upper petroleum system is located in lower cycleof Member K1d1. High displacement pressure which is up to7Mpa, existing overpressure,and in late diagenetic A sub-stage indicates strong sealing ability of various sets of caprock.Degree of damage that fracture destroyed effective thickness of caprock sealing is mainly atmedium in upper cycle of Member K1n1and is mainly at medium and small in lower cycle ofMember K1d1. Through comprehensive evaluation, the cap rock acreage of good sealingability is larger, which was primary distributed in Bei53well and Bei29well of Bessie subsags, and caprock sealing level of most other areas is medium. The sealing ability ofMember K1n1caprock is at good and medium, and poor sealing capacity caprock is almostnon-existent. According to the fracture active stages and the characteristics of fault fracturingformation, faults were divided into four types, early stretching fault, medium-termtranstensional fault, early stretching and medium-term transtensional fault, early stretchingand medium-term transtensional and late reversal fault. Early stretching fracture mainlyplayed a blocking role on lower petroleum system. Early stretching and medium-termtranstensional fault primary played a dual function which was conducting function ofpetroleum hydrocarbon migration and accumulation through the cover layer and blockingfunction of oil and gas migration and accumulation on upper and lower petroleum system.Early stretching and medium-term transtensional and late reversal fault mainly playedadjustment role on petroleum accumulated at antephase, and indicated the secondaryreservoir formation and distribution of Member K1d1. Lower petroleum system in Beier Sagis primary petroleum accumulation controlled mainly by caprock of Member K1n1andsealing ability of early stretching and medium-term transtensional faults, so it’s hydrocarbonaccumulation model is controlled by caprock and blocking faults. On one hand, upperpetroleum system is primary petroleum accumulation controlled mainly by caprock ofMember K1d1and sealing ability and conducting capacity of early stretching andmedium-term transtensional faults. On the other hand, upper petroleum system is secondaryhydrocarbon reservoirs formed by adjustment function of early stretching and medium-termtranstensional and late reversal faults. Therefore, upper petroleum system is hydrocarbonaccumulation model controlled by adjustment faults passing through caprock.