Reservoir Characteristics And Control Factors Study Of The Chang-6 Formation In Zhengning-Yijun Area

Zhengning-Yijun area is located in the south of Ordos basin, it’s characterized by low degree of hydrocarbon exploration. Recently, this area of Yancharig formation is with prolific in oil & gas. Hower, due to the uneven distribution of drilling and less quantity, no one has studied on the sedimentary fades?diagenesis and reservoir characteristics systematically in this area. This paper goes on to research and discuss the characteristics of petrology, microscopic reservoir characteristics, diagenesis and reservoir physical properties. In this process, this paper analyses this points by means of methods under the guidance of sedimentology, reservoir sedimentology and oil geology. Mainly analyzes the reservoir characteristic and control factors.The paper suggests that the sandstone reservoir of Chang-6 formation was deposited on the background of gravity flow-delta-lake sediment environment according to sedimentary framework, structure, sedimentary rhythm, logging response characteristics and the sedimentary background of this area. The sandy clastic flow and the favorable fades belts for developing reservoir was turbidite. The main diagenesis in the studied area included the mechanical compaction, pressure solution, cementation, dissolution, metasomatism and rupture. On the basis of carbon and oxygen isotopic values in carbonate cement,laser Raman data?mudstone of vitrinite reflectance(group) and X-ray diffraction analysis of clay minerals, the diagenesis of the reservoir sandstone of Chang-6 is during the period of middle diagenesis A with five facies of diagenesis development, including solution pores+residual intergranular pore facies; illite, chlorite cementation residual intergranular pore facies; llite?chlorite cementation facies; carbonate cementation facies; shale compaction cementation facies. Abundant core description and observing, observation of thin-section of the cast, electron scan microscope and experimental analysis indicate that the Chang-6 reservoir sand-bodies mainly is fine-very fine grained lithic arkose and feldspathic litnic sandstone, and the main type of pore is feldspar dissolution porosity and residual intergranular porosity, It belongs to extremely low porosity with extremely low permeability reservoir. The pore texture of Chang-6 member is small sized porosity with minute throats?and the fracture of this area is very common.The paper holds that the reservoir is controlled by sedimentary microfacies, diagenesis and the diagenetic facies. In diagenesis, compaction and cementation leads to reservoir physical property variation, and dissolve effectively improved the reservoir properties; In diagenetic phase, dissolved pores+residual intergranular pore facies and illite, chlorite cementation residual intergranular pore facies controlled the distribution of the high quality reservoirs. The fractures of reservoir play a certain role to improve the reservoir property.