Reservoir Characteristics And Controlling Factor Of Chang 3 Group In Zhenbei-Yanwu Area

Zhenbei-Yanwu area is located in the southwest of the Ordos Basin. In tectonic it Is connected with Tianhuan depression to the West and belongs to the edge of Shanbei slope.There is a good indication of oil and gas in the sandstone of Chang3 group in oil exploration of Jurassic.To support the exploration and development of Chang 3 group,we focus on reservoir characteristics and control factors of Chang 3 group Yanchang Formation of Triassic in Zhenbei-Yanwu area.With a variety of test and analysis methods such as core observation,scanning electron microscopy, thin section observation,ect,we reached a throughly understanding of the reservoir characteristics and the controlling factors of Chang 3 group.(1) Chang 3 reservoir mainly contains medium-coarse lithic feldspathic sandstones, feldspathic lithic sandstones and Lithic Sandstone with low componential and textural maturities.(2)The reservoir space is mainly pore, the pore types are mainly intergranular pores, remaining intergranular pores and intragranular dissolved pores while primary intergranular pores are rarely seen.(3)Physical property test show that it has fine pore and micro throat with an average porosity being 13.3%~15.0% and the average permeability being 0.88~5.57 mD.It`s a typical low porosity and low permeability reservoir.(4)The main diagenesis in Chang3 reservoir include mechanical compression, pressure solution, cementation, dissolution and metasomatism, and tight reservoir is mainly effected by strong compaction and pressure solution. According to the environment and sequence of diagenetic revealed by diagentic minerals, reservoir facies can be divided into three types: Kaolinite-chlorite cementation-feldspar dissolution facies, middle quartz overgrowth –intergranular corrosion hole facies and weak cementation-residual intergranular pore facies.(5)Based on sedimentary facies, sedimentation sand bodies of reservoir and its plane distribution, pore types of reservoir, pore structure and physical property parameter, the reservoir of Chang 3 group can be divided into four categories: type I, type II?type III and type IV. Evaluation is made based on reservoir classification and the evaluation results show that the Chang 3 group Reservoir is mainly of type II and type I,followed by type III.Reservoirs are mainly in East and West wings of Tianhuan depression, it has a droplet-like distribution along the nose structure zone; affected by reservoir properties of sand bodies, reservoir in the east is relatively large, while in the west the reservoir is small. Both reservoir has a good prospect of construction and exploration.