The Hydrocarbon Accumulation Rules And Favorable Area Prediction Of Chang6, Yanchang Formation, Yanggelao,Ordos Basin

The Yanggelao exploration area in Zhidan is a new exploration block of western oil production plant of Yanchang Oil Field in Triassic Yanchang Formation.The degree of early exploration in this area is low so the geological understanding of this area is weak. Through the study of the blocks around like Loufangpin and Yanwumao, we have found good oil and gas shows in Chang6in Zhidan and achieved good effects in practical exploration and development. It is necessary to study the oil and gas enrichment patterns and main controlling factors of reservoir of this area in order to improve the success rate of exploration in Yanggelao and provide a reasonable basis for the next exploration development and deployment in this area. Based on core data, logging, logging data, laboratory analysis, production test data, combined with the results of previous studies, the paper carried out researches on sedimentary facies, reservoir characteristics, structural characteristics, distribution characteristics of source rocks in Yanggenao block. According to the results, the paper analyzed reservoir types in the study area, law of oil and gas accumulation, and finally determined the distribution of the favorable exploration and development area in this region.Stratigraphic division and correlation is the basis for geological research work.The accuracy of stratigraphic division and correlation plays a decisive role in late research of sedimentary facies, structures, type of reservoir and the master factors of accumulation. The regional marker beds of Zhangjiatan shale in Chang7and the member of Xibozi in Chang4+5, along with the reverse cycle characteristics in Chang6are used to clamp the vertical position of Chang6oil formation. Then according to the thin resistive layer, K2and the upper of Chang6, developed in this area, as well as the changes of sedimentary cycles, Chang6is divided into sub oil groups; finally, stratigraphic wells is linked to make the whole district close, and at the same time the stratification results are checked according to the top structure maps.On the basis of stratigraphic classification and correlation, combined with the researches of predecessors on sedimentary facies and reservoirs of Zhidan area in Ordos, mainly based on the date of drilling, well logging and laboratory analysis, this paper has studied on sedimentary facies, micro-structure and reservoir characteristics in Yanggelao. The paper points out that Chang6oil group is fan delta frontal subfacies, and the main producing formations are Chang61and Chang62. Chang61mainly develops delta frontal underwater distributary channel and branch bay microfacies,while Chang62mainly develops delta frontal underwater distributary channel, mouth bar, sheet sand, branch bay and prodelta-littoral mud microfacies; the reservoir lithology of Chang6is mainly arkose and debris arkose with lower porosity and extra-low permeability. The district is located in the north wing of a nose structure outside the work area as a whole. A small nose structural shows in zheng242-4171well area, which migrates during the period of sub-oil group; Based on the laboratory date analysis of Well Yanchang38, Well Yanchang40, Well Yanchang41and Well4009outside the study area, the paper determined that the lower limit of the porosity in Chang6is8%, and thus that of permeability is0.1MD, using empirical approach method.A discussion on the conditions of the oil source, the reservoir, caprock and reservoir-trap is carried on according to previous researches on characteristics of source rocks in the Ordos Basin. The paper analyses the main controlling factors of hydrocarbon accumulation in Yanggelao area and summarizes the major reservoir type developed in this area. It concludes that the Chang6reservoir formation is mainly affected by types of source rocks, sedimentary microfacies and local tectonic uplift. The main types are sandstone up dip pinchout reservoirs and tectonic lithologic reservoir. On this basis, the paper further clarifies the relationship between the conditions of source rocks, sedimentary microfacies and structural characteristics and hydrocarbon accumulation, summed up the law of oil and gas enrichment and proposed the hydrocarbon accumulation mode. It points out that the oil and gas migrate both vertical and lateral in this area, generally migrating as a way of "climbing".The paper conducted a favorable prediction of major oil layers in Chang6oil group and a comprehensive evaluation of Chang6mainly based on sedimentary microfacies, thickness of sandstone reservoir, structural development, dates of testing and production and explanation of oil and water layers, referring to source rock characteristics, storage conditions and distribution of existing drilling. The results of the evaluation show:the Ⅰ class favorable exploration and development zones are the northeast of the study area along the4121-2,4120-2,4120,4171well area and the northwest section4119,zheng242,4122,4006-4, zheng19wells area; the Ⅱ class lies in southwest4164well area and its west side.