| This paper selected the Upper Paleozoic shale as the main object in the Yushe-Wuxiang district of Qinshui Basin.Through a variety of means of experimental tests combined with relative geological theories and a research scheme composed of field investigations,indoor tests,theoretical researches and practical applications,the deposition distribution characteristics,geochemical characteristics,reservoir characteristics and the resource potential characteristics of shale in the study area were studied and analyzed.Results and conclusions were as follows:1.In the study area,the Upper Paleozoic formation was a series of deposional systems with platform facies,transitional facies,delta facies,and inland lake facies.The sedimentary strata from Benxi Formation to Shanxi Formation which included four shale sections was divided into three classic third-order sequences.The second section which developed best in the entire area had an average thickness of 49.03meters and an average shale content of 0.63.2.The organic matter type of the shale from the four sections was a primary type III.The organic carbon content of the shale in the first section was in the range of 0.32%to 11.4%,with an average of 1.84%.The vitrinite reflectance ranged from 1.46%to1.72%,with an average of 1.56%.The second shale section had an higher total organic carbon content of 3.77%and an average vitrinite reflectance of 1.66%.The total organic carbon content of the third shale section ranged from 1.26%to 3.21%,and the average vitrinite reflectance was 1.56%.The fourth shale section had an organic carbon content of 2.65%,and an average vitrinite reflectance of 1.56%.The thermal maturity of the shale from all the four sections came to the high maturation stage,which would be beneficial to generate massive amounts of methane.3.The lithofacies of the shale in study area had three main types,of which included black charcoal shale facie,silty shale facie,and mudstone-siltstone facie.The major mineral compositions were quartz and clay minerals,with an average content of 35.7%and 46.6%.The clay minerals mainly included I/S,kaolinite,and illite.The brittleness index of the shale was mainly over 40%,with a main range from40%to 60%,which could indicate a good potential of exploitation.The shale had formed a lot of organic pores,inorganic pores and microcracks.The pores had different development positions,intensity and shapes.Microcracks were found in the organic matter and clay minerals,with different shape,size and length.The stretching degree of pores in the shale was generally high,and the micropores and mesoporous were most common.The main pore size distribution were from 1 to 4 nanometers and from 30 to 60 nanometers.The average BET surface area was 11.11 m~2/g,and the average BJH pore volume was 0.021cm~3/g.Average pore size was 8.69 nanometers,in a range of 6.54 to 13.63 nanometers.4.On the basis of the situation of exploration in this filed and by means of volumetric method,we have predicted that the shale gas resources of these four sections was 1734.19×10~8m~3.After a comprehensive analysis,we have predicted four advantageous areas of each shale section.The advantageous area in the second shale section nearly covered the whole region,and the other three advantageous areas were located in the northern exploration area that was represented by Yangguangzhan-Shixia. |
PDF Full Text Request