Study On The Pool-forming Mechanism In The Second Strata Of Suhongtu Formation, Chagan Sag

On the basis of analyzing and summarizing the previous results,using the data ofgeology,geochemistry and geophysics,directed by the hydrocarbon accumulationtheory,this paper gives a comprehensive research on the hydrocarbon accumulationconditions,geochemical characteristics of source rock and oil and oil-sourcecorrelation,passage system and migration,hydrocarbon generation and expulsionhistory,accumulation models and main controlling factors in the second strata ofSuhongtu formation,Chagan sag,has obtained the following results and recognitions:The results show that K1s1,K1b2,K1b1are effective source rocks in Chagansag,hydrocarbon source rocks have high abundance of organic matter and belong togood hydrocarbon source rocks,and the tape of organic matter belongs to transitiontype,and the organic matte of the hydrocarbon source rocks has a high degree ofthermal evolution; Based on analyzing geochemical characteristics of source rock andoil and oil-source correlation,proposed hydrocarbon source rocks occurred in thereducing-weak reducing environment,the crude oil of K1s2was mainly from thesource rock of K1s1and K1b2; Based on analyzing passage system and migration,proposed the hydrocarbon accumulation mainly occurred vertical migration andlateral migration,including the fault is the mainly passageway of vertical migration,the connected sand body and the unconformity are the mainly passageway of lateralmigration; Based on the recovery of burial history and geothermal hintory in Chagansag, proposed the Suhongtu formation depositional stage and the Yingen formationsedimentary period is the most important of hydrocarbon generation and expulsionperiod in Chagan sag, the source rocks of the second strata of Bayingebi formationwhich has the largest amount of hydrocarbon generation and expulsion,is mostimportant for hydrocarbon accumulation,combined with the analysis of fluid inclusion,the hydrocarbon accumulation of the second strata of Suhongtu formationhad two injections of oil,the first of injection has been occurred from the Suhongtuformation depositional stage to the Yingen formation sedimentary period,and thisinjection is the most important for hydrocarbon accumulation of the second strata ofSuhongtu formation,the second of injection has been occurred in Wulansuhaizuformation depositional stage which was supplied oil by the source rocks of the firststrata of Suhongtu formation;At last,the pool-forming model of lower generation andupper storage is established, proposed the main controlling factors of oil pool-formingin the second strata of Suhongtu formation,Chagan sag are the effective source rocks,the effective pathways,tectonic background and the preservation on conditions.