POOL-FORMING RULES OF OIL AND GAS IN THE THIRD MEMBER OF THE FUNING FORMATION, THE NORTH JIANGSU BASIN

The oil and gas assemblage in the third member of the Funing Formation(Ef³),the North Jiangsu Basin is a main target stratum of progressive increasing in proven oil reserves and output recently.The good-quality brackish-water-facies source rocks formed in the middle-lower part of the Fu-2 Member (Ef²) of the basin is the principal source rocks of Ef₃ oil pools.The favorable reservoirs lie in the upper parts of upper and lower Ef³ sandstone,and thick layers of lake-facies mudstone with poor hydrocarbon-generating ability lie between the reservoirs and the middle-lower part of Ef³ source rocks.Therefore,the association of source rocks,reservoirs and caprocks becomes worse,and need to be linked up by faults so as to form good oil pools.Oil pools of Ef³ appear in definite locations.They are mainly formed nearby inherited nose uprift belts and contemporaneous faults or large late-stage faults.Favorable structural types and organic matching of sedimentary systems,tectonic frameworks and trap bodies are necessary elements to form the oil and gas pools of Ef³.The pool-forming model of oil and gas in Ef³ showed that the main objects of oil and gas exploration should be focused on inherited uplift belts and contemporaneous faults or large late-stage faults in the districts with unfavorable source rock-reservoir-caprock matching.