Fault System And Characteristic Of Oil-gas Accumulation In Fuyu Formation Of Wangfu Depression

Wangfu Depression is the secondary tectonic units in the Southeast Uplift of Songliao Basin,and its main target layer is Fuyu Formation.Serious of gas fleld have been found in structural high part in nineteen fifties.Such as Changchunling,Wuzhan,Sanzhan and Laozhou gas field,the proved gas reserves is about 100×108m3.Large scale oil reservoir have been found round the gas field in the early twenty-first century,its predicted reserves is about 3653×104t.The characteristics of petroleum exploration process is low resource ascertain rate.At present the proved oil reserves are all in the north slope of Wangfu Depression.There are only a little oil found in the southern slope.The main restrict factors of oil and gas exploration in Fuyu Formation of Wangfu Depression are two aspects.The first is that how much hydrocarbon potential of the source rocks in Wangfu Depression whether can provide enough oil and gas for hydrocarbon accumulation?The second is that the effect of faults or intensively faulted zone paly on the process of hydrocarbon migration and accumulation.In the light of the above problems,this study based on the data of seismic,well logging,logging oil test,and other test results,firstly evalution the hydrocarbon potential of sourece rocks,determine the range of around area for migration,then anatomical fault system characteristics,activity patterns and seal property.Discuss the relationship between combination of fault,sand and formation and migration and accumulation of hydrocarbon,clarify the mechanism of fault controlling on accumulation and laws of hydrocarbon enrichment.Fuyu formation is divided into 2 middle-term cyclic sequences,6 short-term cyclic sequences and 17 super-short-term cyclic sequences.MSC1 is divided into the base-level descend quickly and descend slowly,respective on F3-subsection and F2-subsection.MSC2 is elevated slowly and respective on F1-subsecion.Organic matter of source rocks is abundance organic,good type but low matrity in Wangfu Depression.Its generated hydrocarbon threshold is about 1000m,and the peak of generation hydrocarbon is about 1200m.Source rocks buried depther than 1200m are effectilve expulsion hydrocarbon.The area of them is about 370km2,and its volume is about 2.96×1010m3.The generation amounts of oil and gas of K1qn are 13.6×1011t and 4.4×108m3 in Wangfu Depression,the oil and gas resource are(0.68～2.72)×108t and(0.022～0.088)×1011m3 separately.The crude oil of Changchunling Anticline belt mainly comes from source rocks of K1qn1 in Wangfu Depression.The main fault trend in Fuyu Formation of Wangfu Depression is north-south direction,the fault density is high and combination type is diversity.The faults have three formation and development period,namely is extensional faults which are formed in faulted period from Huoshiling to Yingcheng,tensional faults which are formed in depression period at Qingshankou and compressional faults which are formed in reverse period from Nenjiang to neogene system.There are four types of intensively faulted zone in Fuyu Formation of Wangfu Depression,namely reverse-graben-reverse fault terrace,horst-graben-reverse fault terrace,reverse-graben-cisoid fault terrace and horst-graben-cisoid fault terrace.Intensively faulted zone have transverse sealing and lateral fluid conduction function in the process of oil migration.In the respect of hydrocarbon accumulation,while the strike of intensively faulted zone nearly parallels the dip direction of formation,the horsts and antithetics on both sides of it are favorable part to collect oil,while the strike of the intensively faulted zone nearly plumbs the dip direction of formation,the horst and antithetic on the side that is near the depression center are propitious to catch oil.the crossovers of intensively faulted zone are avail for oil accumulation.Though analysising the reservoir in Fuyu Formation of Wangfu Depression,the results show that the structure controls potential energy,the source rocks control oil reservoir region,intensively faulted zones control hydrocarbon migration,faults and sands control oil trap and pressure difference controls depth of oil layer.Namely,structure characteristic of Wangfu Depression controls the overall direction of oil and gas migration and the main distribution area.The effective expulsion area of source rocks controls the distribution of hydrocarbon.Intensively faulted zone have transverse sealing and lateral fluid conduction functions in the process of hydrocarbon migration and accumulation.The matching ways of fault trend,sand body distribution direction and tendency of stratum determine the formation of traps.The overpressure influence the downward depth of hydrocarbon migration and the depth limit of oil reservoir.According to the characteristics of hydrocarbon accumulation,the favorable zones have been selected and five exploration targets have predictied in the center and southern slope of the depression separately which is under lower degree of exploration.