Research Of Hydrocarbon Accumulation Conditions And Prediction Of Prospecting Target Of Yanchang Formation, Triassic, Shanbei-Yanchi Area

Ordos basin, which has become one of the petroleum foundation fields in China because of rich in petroleum resources, is a polycyclic cratonic basin with stable settlement and composite depression. Shanbei-YanchiArea locates in the north west of Ordos basin, and is a large field assembled, with low degree of prospecting. The sedimentary facies, source rock and reservoir-seal assembly of Yanchang Formation were studied by combination of drilling data, logging curves, seismic data and all kinds of analytical data in this dissertation. As a result, the reservoir forming mode was built up and the target areas were pointed out. The main achievements and ideas were summarized as following:1. The oil and gas of reservoir in Yanchi area came from interval7of Yanchang Formation. The analytical data demonstrated that the source rock in interval7was in medium-best level, and the organic matter was in low mature-matural stage.2. The transitional facies between lacustrine facies and delta were deposited in Yanchang Formation. Submerged distributary channel and tributary bay of delta front and branched channel and flood plain in delta plain were developed in Chang8and Chang9oil reservoirs. While, lacustrine mudstone focused in the strata of Chang7oil reservoir.3. The pore throat radiuses of Yanchi reservior varied, and were characterized by low-extra low porosity and extra-low permeability. And the type Ⅰ reservior in good physical property distributed in the submerged distributary channel and branched channel. The mudstone of study area showed multi-cycles and thin thickness, and its capillary pressure curves showed good sealing capacity.4. The analysis of reservoir forming conditions showed that the disequilibrium distribution of source rock in Chang7oil reservoir made the oil and gas accumulate in the south. Because the delta and fluvial facies were the reservoir of oil and gas, so their shape controlled the distribution of reservoir. Structural reservoir main formed in the west of study area, while the subtle reservoir focused in the central eastern. Also the feature of mudstone caused multi-layer oil and gas distributed in the vertical.5. The study area has a promising oil and gas resources prospect. The predict productivity is about14802×104t. Oriental reservior located in the south-central region, and suboptimal reservior distributed in the central west of study area.