Micro-Pore Reservoir Spaces and Gas-Bearing Characteristics of the Shale Reservoirs of the Coal Measure Strata in the Qinshui Basin

摘要

To study the exploration potential of the Carboniferous-Permian transitional shale reservoirs in the Qinshui Basin, the Y5 well was selected as the research object, and experiments including organic geochemical tests, microscopic observations, scanning electron microscopy, X-ray diffractionanalysis, high-pressure mercury intrusion, methane isothermal adsorption, and low-temperature nitrogen adsorption were carried out to analyse the physical properties of the shale reservoirs of interest. The results show that (1) The organic matter type of the samples is type III, the totalorganic carbon contents range from 0.27% to 20.52% (avg. 3.15%), the RO values are between 2.45% and 3.36% (avg. 2.86%), and the Tmax values range from 311.00 °C to 575.20 °C (avg. 493.31 °C). These results indicate that the organic matter inthe study area is abundant and has experienced a high degree of thermal evolution. (2) The brittleness index is low (avg. 43.81%), and the shale pores in the study area are well developed. The pores contain organic matter-hosted pores, intraparticle pores, interparticle pores, and micro-cracks.(3) The methane isotherm adsorption average contents of the two samples are 0.2968 m3/t and 1.0824 m3/t, and the average contents of the on-site desorbed gas content and measured total gas content are 0.55889 m3/t and 0.8624 m3/t, respectively. (4)The kaolinite and illite contents have a significant negative effect on the specific surface area of the macro-pores and the specific pore volume of the meso-pores. The illite content is conducive to the development of the pore diameter and specific surface area of the meso-pores, and thequartz content has a positive correlation with the specific pore volume of the macro-pores. (5) The measured total gas content has a significant positive correlation with the total organic carbon and a weak positive correlation with the contents of quartz and illite, and the desorbed gas contentshows the same correlations. This study demonstrates the physical properties, microscopic pore characteristics, and gas-bearing characteristics of shale reservoirs and their influencing factors in detail.