Prospecting Advantageous Regions Of Chang-8Member,Yanding Area,Ordos Basin,China

In recent years,Yanding area had became the main exploration in Changqing oilfield. Oil and gas exploration has yielded fruitful results in Yanchang formation.There has been found many industrial oil flow well.It also shows a good exploration prospect. Chang-8reservoir is a new exploration layer.The oil group of small layer divided not fine, reservoir characteristics and controlling factors of hydrocarbon accumulation studied inadequate restricted the later oil and gas exploration and development seriously.In view of this situation, this paper based on sedimentology and petroleum geology theory, used drilling core data, thin section identification and scanning electron microscope as test analysis tools, combianted the deposition, sandstone distribution, reservoir evaluation and trap analysis deepedly,than get the following conclusion:Based on the study of core admission data,comprehensive logging data and physical property data for Chang-8member, useing the K1as the top boundary, according to the sedimentary characteristics,the Chang-8member is finely divided into two sand groups or four small layers, namely chang-81,chang-82and chang-81,chang-8i,chang-82,chang-82. By dividing and contrasting stratigraphic all over the study area,the sand body thickness of chang-8member changed not much all over the atudy area.Combining with sedimentary system background, according to heavy mineral assemblage distributions and coal line distributions,there’re two source system of the research area where’re from the North and the North West. By useing the vertical continuity analysis of small layer sand body to get the sand body distribution characteristics. Chang-8member of Yanding area located in the delta plain which is anastomosed stream deposition.Distributary channel is the favorable facies for sandbody development.The main rock type of chang-8member in the study area are feldspathic litharenite and lithic arkose sandstone which are mainly fine sand block.There’re several kinds of cements,including8main types which are kaolinite, illite, chlorite, calcite, chlorite film, interstitial iron calcite, zeolite and silica mass.The pore types are lithic dissolved pore, feldspar dissolved pores, intergranular pore and intergranular dissolved pore.Dissolved pore developments in some layers of zeolite. Cracks are visible.The porosity of chang-8member is low porosity as5-10%, followed by the porosity of10-15%which is a typical low porosity and low permeability reservoir. Chang-81member is the worst and chang-822member is the best. The dissolved pore and intergranular pore reservoir is best, followed by intergranular pore and dissolved pore, intergranular pore. The reservoir property in study area is mainly controlled by sedimentary factors and intergranular pore growth. Carbonate cementation is a kind of destructive cementation though chlorite, kaolinite cementation are kinds of constructive cementation.According to the structural characteristics analysis of Yanding area,there’re3types of oil reservoir development in the study area.The structural reservoir is mainly developed in the west Tianhuan syncline axis, from west edge thrust fault block formation.The lithologic reservoir is mainly developed in the east Tianhuan syncline axis, the distributary channel to the high position of pinch formation.The fault block reservoir is mainly developed in the the west margin fault zone which are free bottom water reservoir.By recessing the top surface structural map and sandstone distribution map,25different types of traps found in the study area. According to the size of traps,the number of drilling traps,the show of oil and gas for traps and oil testing results of traps to evaluate traps, getting15realistic traps and4evaluation traps.The oil property of chang-8in the study area is similar.The stratum pressure is low. the stratum water is dominated by CaCl2type. The initial stage of water flooding effect is obvious but the later water flooding effect is not significant. The Chang-8member vertical distribution is multilayer but the reservoir changes greatly in lateral connectivity, mainly forming lithologic oil pool with mudstone lateral sealing and physical changes of reservoir plugging. Main controlling factors are hydrocarbon range and hydrocarbon generating intensity of source rock controlling the range of reservoir region, sedimentary system distribution controlling the oil pool distribution zone,reservoir property development controlling high reservoir location discovery. In addition, migration pathway, cover layer and so on are all factors can not be ignored to study for oil pool form.Based on the tectonic characteristics of obvious, select the nose structure or structural high part of reservoir development. The most favorable development zone, not with the current development of coincidence, have good permeability or nose structure with high industrial oil flow or structural high part of the favorable area. Through the laminated chart of the favorable area for production established of chang-8member’s four small layers, there can get the most favorable area distributing in the Tianhuan syncline wings Hongjingzi Hongliugou area, followed by Youfangzhuang, Jipan and Xiaojianzi area where are distributed in8regions, with the cumulative area of185.58km.