A Study On The Dominated Factors Of P₂x₈in Gaoqiao Region

Due to distribution of sand body of UPPer Paleozoic and very variety of reservoir physical characteristics and serious heterogeneity in Gaoqiao region in south of Ordos Basin,the article eyes on the problems existing in this area,under the guidance of Stratigraphy, sedimentology and reservoir geology theories, On the basis of previous research, with the data of lithology, physical characteristic, electrical characteristic and test information in the area of Members8of Xiashihezi Formation (P2Xs)of Permian, I have made a further study on tectonic features and sedimentary facies characteristics, reservoir properties, pore structure characteristics, diagenesis and heterogeneity in this region. On this basis, deeply analysis of the reservoir main controlling factors.This study based on the reservoir characteristics, from the comprehensive angles of deposition and diagenesis, we analyze the dominated factors of favorable reservoir.At last we get some conelusions as follows:(1)The P2X8reservoir in the region of study belongs to braided river delta deposition, the North of region main develop braided river delta plain subfacies, Central and South main develop braided river delta front subfacies.This subfacies mainly is the delta front,it develop the underwater distributary channel, channel migration are frequent in the horizontal, multiphase superposition in the vertical, sectors-connecting nature of sand bodys is well.(2)The main sedimentation type of the P2X8reservoir in the region of study is coarse grain sedimentary, The maturity of the rock texture is better,its main rock types are quartz sandstone and lithic-quartz sandstone; Its interstitial material is basically made up of Illite(Hydromica),kiesel,Kaolinite and Ferrocalcite; the dissolved pore is the main poretype, followed by Intergranular pore and intercrystal pore,and develop a small amount of micro-cracks;the main pore structure is the pinhole-thin throat type; reservoir porosity is5.0to12.0%, the average is8.37%;permeability is0.1to0.5mD, the average is0.704mD, reservoir quality is expressed as "low-porosity and low-permeability"(3)The reservoir heterogeneity is serious, areal heterogeneity suffer the effects of the differences in reservoir properties and sedimentary facies, The sand body of main channel is better than the sand body of river edge, vertical (in layer and inter layer)heterogeneity controlled by the superposition of the sand body,as well as the characteristics of distribution of development of the muddy intercalation and compartment.(4)This reservoir experienced varying degrees of compaction, cementation, denudation, metasomatism, and fracturing in process of diagenetic.(5)Studies have shown that:The P2X8reservoir in the region of study are mainly affected by differences in source rock composition,the factors of the depositional environment and hydrodynamic conditions, as well as diagenesis. In diagenesis, compaction is the main reason what make a significant loss of the reservoir primary pores, cementation will led to porosity decrease, dissolution is a major factor what can effectively improve reservoir properties.This research results have value for P2X8reservoir evaluation and optimization of the favorable areas,as well as the exploration and exploitation of reservoir in Gaoqiao region.