Hydrocarbon Migration Pathway System Of Panyu Low Uplift In The Pearl River Mouth Basin

The Pearl River Mouth Basin (PRMB) is one of the most prolific oil provinces in China.Since 2001, CNOOC (China National Offshore Oil Corporation) China Ltd. Shenzhen has hadgratifying achievements in the natural gas exploration of Panyu Low Uplift and north slope ofBaiyun Depression in PRMB, revealing the PY-LH natural gas field plays and finding a series ofnatural gas-bearing structures, such as LHI9-3,LH19-1,PY30-1,PY29-1,PY34-1,LH19-5,PY35-1,and et al. Consequently understanding about the hydrocarbon accumulation of this areahas come further. However, the mechanisms of hydrocarbon accumulation are not yet clear,especially the hydrocarbon aspect. Hydrocarbon migration is the main controlling factor ofhydrocarbon reservoir formation and distribution, and is a weak link on study of the hydrocarbonaccumulation regulation in this area. Therefore, it is necessary to further study of hydrocarbonmigration pathway system in this area.Hydrocarbon migration pathway system and hydrocarbon migration-accumulation analysisof Panyu Low Uplift in the Pearl River Mouth Basin are the core to our study in the dissertation.On the basis of predecessors' exploration and development research results, combined with arealgeology,seismics,geochemistry and well drilling data analysis, study the palaeo-physiognomyreconstruction and deposit system evolvement,the skeleton sand body distribution,fault system,time-space configuration of migration pathway system,hydrocarbon migration route, et al, set upthe pattern of hydrocarbon migration and the history of hydrocarbon migration-accumulation.Above all, dynamic courses of the hydrocarbon migration and mechanisms of hydrocarbonaccumulation can be obtained.Three main high-quality source rock formations are in Baiyun Depression, respectivelyEocene WenChang Formation, Eocene-Oligocene EnPing Formation and Oligocene ZhuJiangFormation. With great hydrocarbon potential and good reservoir-seal, petroleum geology iscondition excellent. During the geological time, hydrocarbon fluid is very active in Panyu LowUplift. Faults, sand carriers and Eocene-Oligocene unconformity are three types of migrationpathway, faults and sand carriers is the main type in this area. The type of pathway system thatoil-gas migrate by fault-sand conductor along structure ridge in the form of three-dimensionalnetted ladder is the most distinct characteristic in this area. Oil-gas transported to mid-shallowlayer reservoir at stratum along different pathway, with the different distance and finallyaccumulates in some effective traps.The skeleton sand body is the main migration pathway for oil-gas's long distance lateraltransport. According to sand body distribution and transportation capability, three oil-gasmigration stratums can be conformed: the lower sand stratum(under MFS18.5),the middle sandstratum (SB16.5～SB13.8) and the upper sand stratum (above SB13.8). The lower sand stratumdistributing all over the study area is the main lateral migration pathway. Oil-gas migrated fromBaiyun Depression to Panyu Low Uplift through the fault-sand migration pathway system. Themiddle sand stratum composed of delta sand is near the SB13.8,SB15.5 and SB16.5 sequence inPanyu Low Uplift. The upper sand stratum composed of deltafront-delta-shore siltstone mainly isin Panyu Low Uplift. Additionally, high-quality mudstone separating layers are between the threeoil-gas migration sand stratums. The oil-gas has the characteristics that stratified flow.Faults play a very important role in the hydrocarbon migration-accumulation of this area,and are the dominant pathways for hydrocarbon vertical migration, especially the active faults.The early-fault in northern slope of Baiyun Depression connected the source rock and the sandbody under MFS18.5, transported the petroleum to the reservoir under MFS18.5 from the sourcerock in Baiyun depression. The antithetic faults which actived after 13.8Ma in Panyu Low Upliftplayed an important role in carrying the hydrocarbon to mid-shallow layer reservoir.Based on the palaeo-geomorphologic analysis, it is suggest that there is a structure ridge inthe southeast of Panyu Low Uplift along PY2911-PY3012-LH1951-LH1941-PY1611, whichcontroled oil-gas accumulation in the area. Combined with the analysis of the geochemical dataand oil-gas pool distribution, the route and direction of oil-gas migration is actually along thePY2911→PY3012→LH1951→LH1941→PY1611 structure ridge from south to north..