A Comparative Study Of Tight Sandstone Reservoir

To look into tight sandstone reservoir, this thesis take Chang 8 oil formation in Banqiao-heshui area and the 2nd of Xujiahe Formation in Hechuan area as two study objects, which have similarly present-day buried depth and formation time, to comparative analysis petrology, physical property, porosity type and pore structure characters by using core, cast thin section, scanning electron microscope, physical property, and mercury injection data. This paper finds the similarities and differences of reservoir, Qualitative and quantitative analysis of the main reasons for the formation of tight reservoir through two aspects of sedimentary and diagenetic. The research reveals the formation of tight sandstone reservoir, the main results and understanding as follows:1. Rock types in Chang 8 oil formation in Banqiao-heshui area and the 2nd of Xujiahe Formation in Hechuan area are dominated bylithic arkose feldspathic litharenite, but the content of each component is different. The grain size and roundness and support type are same. They both belong to special low porosity and ultra low permeability reservoir, with highly correlated between them. Physical property in Chang 8 oil formation is better than that of the 2nd of Xujiahe Formation.2. The main reservoir space types are intergranular pore and feldspar dissolved pores in Chang 8 oil formation in Banqiao-heshui area and the 2nd of Xujiahe Formation in Hechuan area, respectively. The secondary pores are mainly distributed in the range of small porosity, and the large pores are the primary intergranular pores. The two area are mainly developed micro throat and fine throat, respectively and the connectivity in the 2nd of Xujiahe Formation is better than Chang 8 oil formation.3. Sedimentation is the basis of controlling reservoir physical properties. Rock composition and structure characteristic build the foundations for primary pore and secondary pore development, ling The macroscopic distribution of physical properties Controlled by sedimentary microfacies.4. Compaction, which is mainly affected by the maximum depth, is the main cause of reservoir densification, causing the close contact of particles, the rupture of rigid particles and the deformation of plastic particles, resulting in a large number of primary pore loss. The compaction degrees in the 2nd of Xujiahe Formation is higher than Chang 8 oil formation.5. Cementation promotes the formation of the reservoir, destroy the primary pores and secondary pores and changes pore structure. The cementation degrees in Chang 8 oil formation is higher than. the 2nd of Xujiahe Formation. Appropriate amount of rim chlorite also played an active role in the protection of reservoirs. Dissolution depends on the situation of study area. The dissolution degrees in the 2nd of Xujiahe Formation is higher than Chang 8 oil formation.Based on the comprehensive study of reservoir characteristics and deposition, diagenesis to the reservoir, we found deposition provides the material foundation for the development of the reservoir, but strong diagenesis is the the root cause of the reservoir being dense. Among them, the effect of compaction is the most obvious, and the cementation is the second, these two kinds of diagenesis affect the reservoir more than 70%, or even 90% of the primary pore loss. Dissolution can ameliorate the reservoir, but the strength varies from the formation temperature, the length of the dissolution time and the rock formation.