Shallow Hydrocarbon Accumulation Periods Of Wenliu Structure In Dongpu Depression

Based on the study of petroleum geology, burial history, thermal evolution history andreservoir geochemical characteristic of Wenliu area in Dongpu depression, it is identifiedthat Dongying formation reservoir is charged earlier with oil from lower S3 member.Geochemical analysis on the free, absorbed and inclusion hydrocarbon in pore of oil-bearingsandstone reveals two type of fluid property with different geochemical index and chargetime. All these achievements are applied in rebuilding hydrocarbon accumulation period andhistory of Dongying formation of Wenliu area and indicating the exploration prospect. Themain conclusion are drawn as following: (1)Dongying formation consists of alternating beds of varicolored and reddish brownfluvial sandstone and mudstone, which lack hydrocarbon generation potential. Oil source isthe lower Shahejie formation, which form the pattern of "lower_generating andupper_reservoiring". (2)Following the deposition of Dongying formation , intense tectonic movement inWenliu area result in the second and third class faults rejuvenate in Eastern and WesternWenliu area and Liangzhuang area,which form small scale secondary or matching faults.North China tectonic movement episode â…¡c ause structure inversion and trap formation,which is favorable for traps adjacent to major fault to entrap hydrocarbon migrated fromunderlying source. (3) Dongying formation sandstone experience early phase of incipient diagenesis. Amongauthigenic clay mineral, there are less illite and more illite /smectite interbed, which limitK-Ar isotope dating. (4) Burial and thermal evolution history of source rock suggest: during theintermediary and later stage of Dongying format deposition, source rock of S3 member reachgenerating and expelling peak, simultaneous with Dongying formation trap formation. Stratafrom Miocene to Quaternary fail to compensate the denudation at the end of Oligocene.Generation of S3 member source rock in central uplift and frank of sag is confined.Himalayan movement contributes less to the reservoir of Dongying formation. (5) The saturated hydrocarbon chromatographic and biomarker characteristic of thefree, absorbed and inclusion hydrocarbon of Dongying formation in Wenliu area have greatsimilarity, featuring brief charge time. The captive oil in inclusion is less mature than free oiland weakly affected by biodegradation, which belong to immature oil entrapped during earlystage of trap formation.(6) The hydrocarbon accumulation period and history of Dongying formation isidentified quantitively first time. There are two phase of reservoir formation of Dongyingformation in Wenliu area based on integrated geology , reservoir geochemistry andinclusion study. The first phase see the main reservoir formation during 21.0-24.0Ma,equivalent to the interval between intermediary stage of Dongying formation deposition andthe end of denudation. The second phase occurs after 1.75Ma when the sag continues to bury,generate and accumulate in the vicinity, contributing less to the reservoir of Dongyingformation.(7)According to petroleum system analysis, reservoir formation pattern of Dongyingformation is rebuilded: early and intermediary charge follows latter breach and adjustment.The favorable exploration prospect is the trap controlled by latter active faults in WesternWenliu and Liangzhuang faulted zone.