| Liangjia and Wanchang structural belts are located respectively in the southernand middle part of Chaluhe faulted depression of Yitong basin，and they are theimportant tectonic units in Yitong basin. Petroleum exploration results indicate greatpotential of oil and gas resources in Chaluhe faulted depression，and Wanchangformation which in the shallow layer is an important hydrocarbon formation. Basedon the previous research, and according to the core, drilling, well-logging and seismicdata, this paper detailedly studies hydrocarbon reservoir forming characteristics ofWanchang formation in Liangjia-Wanchang structural belt from the aspects ofsedimentary characteristics, petroleum geological conditions, reservoir formingdominated factors.Wangchang formation in Chaluhe faulted depression has been divided into threelithological sections, furthermore, this paper detailedly divided Wanchang formationinto sand groups in order to indicate stratigraphic development and research reservoirbetter. So, we chose the steady mudstone in region as formation marker, and dividedWangchang formation into sand groups for single well according to sedimentarycycle.Then, traced out and closed up horizons on the whole seismic sections bywell-seismic synthetic. Finally, divided Wangchang formation into9sand groups inall study area. Stratigraphic correlation displays that each sand group is welldeveloped and extensive. The change of sand groups’ thickness are not great in Liangjiastructure belt, but thickening toward lake basin center in Wanchang structure belt. Thedetailed stratigraphic division and correlation lay a foundation for the study offavorable reservoir and enrichment strata for oil and gas accumulation.Sand sedimentary of Liangjia and Wangchang structural belt are controlled bythe No.2fault and the basin-controlled fault in southeastern margin respectively. In Liangjia structural belt, because the No.2fault developed large dip angle and locatednear provenances, middle fan and outer fan of nearshore subaqueous fan are thedomainant sedimentary facies of Wanchang formation, and can be further divided intobraided channel, peripheral turbidite micro-facies and interchannel micro facies;Shallow and semi-deep to deep lake subfacies mudstone are also developed. InWangchang structural belt, as the affection of listric normal faults in southeasternmargin, fan delta front subfacies is the domain sedimentary facies of Wanchangformation, and can be further divided into underwater distributary channel, mouth bar,sand sheets and interchannel micro-facies; In addition, shallow lake subfaciesmudstone is widely developed.By study the lateral and longitudinal distribution of sedimentary faces, in thesedimentary period of Wanchang formation, C30well area and X121well area are thelong-term stable provenance directions in Liangjia structural belt, and mainlydeposited braided channel sandstones; C101well area near the basin-controlled faultto the Chaluhe area is the long-term stable provenance direction in Wanchangstructural belt, and mainly deposited underwater distributary channel sandstones,which were respectively transported toward Bonihe-Taiping and Xin’anbaodepressions. With the water uplifting and declining, the inner Wanchang formationdeveloped different cycles in the whole study area.According to the comprehensive study on the scale and the organic geochemicalcharacteristics of deep source rock in Liangjia-Wangchang structural belt, it isindicated that source rocks in the first and third members of Shuangyang formationand the second member of Sheling formation are the best ones in the study area,which hold great thickness and high content of organic carbon, and of which organicmatter mainly belongs to type Ⅱ2. In contrast, the source rocks in the first member ofSheling formation, the first and third members of Yongji formation are relativelygood.Reservoir of Wanchang formation mainly developed braided channel, underwaterdistributary channel and mouth bar sandstones. Using the method of whole areaseismic inversion under the controlling of acoustic logging, we can study sand bodyof reservoir. Based on the inversion results, sand body of Wanchang formation ischaracterized by widely distribution and great thickness. In Liangjia structural belt,the thickness of sandstone in C30-C12well area and X120-X121well area is great, and the first and second members of Wanchang formation have thick sand bodies. InWanchang structural belt, the thickness of sandstone in C101well area, C27well area,C20well area and C4-C38well area is great; Sand body thickness of the first memberof Wanchang formation is the greatest, but has a decreasing trend from the second tothe third member. On the Physical Properties, Wanchang formation mainly developedmedium porosity and medium permeability sandstone, high porosity and permeabilitysandstone are also developed; The first and third members of Wanchang formationhave good reservoir conditions, but not for the second member due to the badpermeability.According to study the stratigraphic and structure features in the research region,source rocks in the first and third members of Shuangyang formation and the secondmember of Sheling formation provided oil and gas for the upper reservoir. No.2faultand the southeastern margin basin-controlled fault and their derivative faultscontribute to the vertical and lateral migration of oil and gas. Braided channel,underwater distributary channel and mouth bar sandstones are good reservoirs. Thickmudstones in Wanchang and Qijia formations are good cap rocks. Regional tectonicinversion happened in the late sedmentary period of Qijia formation contribute to thetrap forming. In general, this region has great hydrocarbon accumulation conditions.Three times of the hydrocarbon filling in Chaluhe fault depression providedsufficient oil and gas source for the reservoir of Wanchang formation inLiangjia-Wanchang structural belt. Considered the strong tectonic movements in thelate Neogene which damaged the upper reservoir of Wanchang formation, it makesthe first and second members of Wanchang formation good reservoirs for petroleumaccumulation. Reservoir types in Wanchang formation are mainly of fault-blockreservoir, faulted anticline reservoir and sandstone lens reservoir. |
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