Research On The Characteristics Of Reservoir In The Upper Paleozoic Of Heneshan-Jingbian Area,Ordos Basin

Hengshan-Jingbian area is located in the northern Ordos basin. The main natural gas reservoir is upper Paleozoic Shanxi formation and He8 section of Lower Shihezi Formation. Many problems exist in the research of reservoir in Hengshan-Jingbian area, such as ruleless multiple stage sand body, complex lithology, poor connectivity, the thickness of gas reservoir, the larger differences of gas-bearing grade. Using a variety of experimental analysis method and a large number of well logging data to research reservoir of Shanxi formation and He 8 section from the sedimentary facies, the characteristics of sand body distribution, petrology, pore structure, diagenesis and reservoir heterogeneity and so on. Finally, the controlling factors of reservoir quality are analyzed and comprehensive reservoir evaluation is studied.The sediments’ source rocks of Shanxi formation and He 8 section are mainly derived from the YinShan, DaQingShan and WuLaShan, which is based on the study of the paleocurrent direction, detrital composition, light mineral, heavy mineral and cathodoluminescence. The parent rocks are mainly derived from the ancient metamorphic series of the Archaean and Proterozoic. The supply clastic river from three directions, where are Qianwulajiahan, Jiabusha and Yijinhuoluo.The research area of Shanxi formation is located in the transition zone of meandering river delta plain subfacies and meandering river delta front subfacies. The main river development is small in scale, the sand bodies of distributary channel and subaqueous distributary channel interspersed in the floodplain microfacies and interdistributary bay microfacies. The research area of He 8 section is located in the transition zone of braided river delta plain subfacies and braided river delta front subfacies. The main river channel is in the shape of mesh. The sand body of distributary channel and subaqueous distributary channel is superimposed deposition, which is rapid lateral variation. The sand body tracking method can show the space form of different thickness sand body. The results show that the sand bodies of continuous deposition more thick, it extends farther. On the basis of the relationship between the combination of sand and mud, put forward the concept of advantaged sand body, and to determine the identification standard of the advantaged sand body, then to identify the advantaged sand body.Clastic grain structure of research area is similarity, and the rock types become an important factor affecting the physical property of reservoir. The different combination of rock types, which is controlled by sediments’ source rocks, lead to the four reserviors with different combination of pore types and physical properties. The Shan2 reservoir mainly developed dissolution pores and intercrystalline pores, the type of pore structure both have good and bad, the characteristic of reservoir is low porosity and high permeability. The reservoir of Shanl and lower He8 chiefly developed dissolution pores and intercrystalline pores. The different sandstone grain size lead to the type of pore structure and physical property of lower He8 reservior is beteer than Shanl reservior. The upper He8 reservior developed remaining intergranular pores, intercrystalline pores and dissolution pores, the type of pore structure is medium. A large number of pores developed in reservoir, and the pore porosity is the highest in the four reserviors, the permeability is second only to Shan2 reservior.Base on a variety of experimental anlysis to study diagenesis, diagenetic stage and diagenetic facies of research area. The result shows the diagenetic stage of research area is the middle diagenetic phase B. Lithic dissolution and feldspar alteration is very developed, which become the main types of diagenesis of formed reservoir pores. The microcrack is formed by fracturing communicate independent pores in tight sandstone, and it improve the liquidity of reservoir. Compaction, illite cementation, calcite cementation and siliceous cementation make reservoir becomes dense. Base on the study of diagenesis, physical property and pore structure, the diagenesis facies can be divided into 5 types, the 5 types of diagenetic facies covers the whole properties of combination of different rock types,and its can be used as an important parameter of reservoir division.Total research shows that source control the rock types of reservoir, rock types lead to the porosity development degree of reservoir. Sedimentation determines the distribution of sandstone grain size, the composition of sand and mud and the distribution law of sand body, at the same time, it effect the diagenesis. Diagenesis decreases the physical property of reservoir and magnifies the difference of reservoir properties. Sourse, sedimentary facies and diagenesis created the heterogeneity of reservoir, controlling the quality of reservoir.Base on the sedimentary facies, the advantaged sand body, diagenetic facies, physical properties and pore characteristics to evaluate and classify the reservoir. The result shows the reaserch area has developed three kinds of reservoirs. In conclusion the upper He8 reservoir is the best one, and the Shan2 reservoir is the worst one.