Exploration potential of Zhaoxian shale gas of Carboniferous Benxi Formation in Ordos Basin

Abstract

In recent years, the domestic study on shale gas has been affected greatly by significant research achievements of overseas marine-facies shale gas exploration and development. In order to study exploration potential of Zhaoxian shale gas of Carboniferous Benxi Formation in Ordos Basin, the petrology, organic geochemistry and gas-bearing capacity of Zhaoxian shale samples from Benxi Formation were investigated. Based on these parameters, the exploration potential of these shales were estimated by applying mathematical statistics and analysing logging response characteristics. Results showed that the Zhaoxian shale was located in the lower part of the Benxi Formation, it was formed in a marine sedimentary environment with a thickness of 15-30m, logging was characterized by higher gamma anomalies and high compensation neutrons. The brittle minerals were mainly quartz, carbonate rock and pyrite, with an average of 36.9%, and a maximum of 50.9%. The total organic carbon (TOC) content was greater than 1% in general and the average value was 2.8%. Organic matter type of the shale samples was mainly type II2 and a few samples were of type II1 organic matter. Vitrinite reflectance values (1.82% on average) showed that shale samples were at mature-high mature stage, which enables good pyrolysis gas generation. The desorbed gas content ranged between 0.34∼2.01 m3/t with an average of 0.99 m3/t. All the evidences indicate that Zhaoxian shale from Carboniferous Benxi formation was of great potential for shale gas exploration.