Shale Gas Reservoir Characteristics And Evaluation Of The Upper Ordovician And Lower Silurian In The Southern Sichuan

The black shale of the Upper Ordovician and Lower Silurian in the Southern Sichuan, with high maturity and total organic matter content, is a significant target for shale gas exploration. In this thesis, several methods of field sections,geochemical analysis, core observation, Ar-ion-beam-SEM, logging data,high-pressure mercury intrusion, gas expansion methods were used to investigate the petrology, geochemistry, reservoir geology of black shale in Weiyuan, Changning,Zhaotong of Southern Sichuan, put forward a lithofacies classification for shale based on rock mineral composition and total organic matter content(TOC), analysised the control factors of the reservoir development, established the evalution standard of reservoir and evaluated the black shale in our study area.Combine inorganic constituents and organic constituents, put forward a classification for black shale. The TOC play a significant role in shale reservoir, so TOC was introduced into our classification in this study and the black shale was divided into high TOC shale, middle TOC shale and low TOC shale based on TOC.Based on shale mineral composition, the inorganic constituents took terrigenous silt,intrabasinal quartz, clay mineral and carbonate mineral as parameters, divided black shale into silty shale, siliceous shale, calcareous shale, argillaceous shale and mixed shale. The shale was divided into totally twenty-four lithofacies and eighteen lithofacies were identified in our study area.Qualitative and quantitative methods were used to study the the reservoir space and pore structure of black shale. Through making a comparison of the physical property and gas-bearing property in different lithofacies, try to find the favorable lithofacies for shale gas reservoir. Compared with conventional reservoirs, shale has an extremely low porosity and low permeability. Nanorepores are the main reservoir space, include organic matter pores, inter-particle pores, intraparticle pores.Mercury injection show macropore volume account for about 17.9% of total pore volume in average, N2 adsorption indicates mesopores are major composition of the shale poresand organic matter pore is the main source of shale pores. Shale reservoir capacity and measured gas content was positively correlated with the TOC content. The composition of shale gas is different in different lithofacies, the siliceous shale and siliceous mixed shale have a high percentage of free gas and the calcareous shale have hardly any free gas.Compared with Well JY1, the quality of shale reservoir was mainly controlled by organic matter, lithofacies, reservoir thickness and formation pressure, Changning area is the most favorable target area.