Abstract
Marine–continental transitional strata were widely developed in the Ordos Basin in Upper Carboniferous - Lower Permian. The Taiyuan - Shanxi Formation possesses promising shale gas exploration layers. Shale samples from two drilling wells of Shanxi-Taiyuan Formation in Shilou and Xixian, Ordos Basin, were investigated to study their carbon–sulfur contents and distribution characteristics of organic components using carbon/sulfur analyzer and gas chromatography–mass spectroscopy. Using results of total organic carbon analyses, Rock-Eval pyrolysis, X-ray diffraction analysis, shale gas desorption experiments, and other relevant experimental data, the shale samples were comprehensively analyzed. The exploitability of the shale in the study area was evaluated. The Shanxi-Taiyuan Shale in the Shilou and Xixian areas was characterized by high total organic carbon contents of 7.1% and 2.1% and high Tmax values of 499 and 505 °C, respectively. The organic matter of the shale is types II2 and III. Moreover, biomarker parameters including n-alkanes, Paq, Pwax, average carbon chain length, and the ternary diagram of C27-C28-C29 steranes show the organic matter constituted terrestrial higher plants and aquatic low biological algae. Multiple n-alkane parameters show the organic matter input in the Shilou area is mainly derived from terrestrial higher plants. The Pr/Ph value and trace element indicators show the deposition environment is dominated by weak oxidation–reduction conditions. A shale gas desorption experiment shows the average desorbed gas contents of the shale samples in the Shilou and Xixian areas were 1.79 and 0.37 m3/t, respectively. The organic matter content determined the differences in shale gas properties between the two areas in Ordos Basin. The composition and content of inorganic minerals affect the reservoir physical properties. According to the analyses, the shale in the Shilou area has good shale gas reservoir characteristics in terms of desorbed gas content and the above-mentioned geochemical parameters. Furthermore, the Shanxi shale has good potential for shale gas industrial exploitation.
Highlights
Shale gas is generated and stored in dark mud shale, which acts as both source rock and reservoir rock (Dong et al, 2015; Hamblin, 2006; Law and Curtis, 2002)
The total organic carbon (TOC) reflects the abundance of organic matter in the sediment
The TOC values of the shale samples in Xixian were in the range of 1.2% to 2.6%, with an average of 2.1% (Sun et al, 2017)
Summary
Shale gas is generated and stored in dark mud shale, which acts as both source rock and reservoir rock (Dong et al, 2015; Hamblin, 2006; Law and Curtis, 2002). In order to further explain the main controlling factors of gas bearing differences, organic-rich shale core samples were collected from adjacent two places (Shilou and Xixian araes), Shanxi-Taiyuan marine–continental transitional strata, southeastern margin of Ordos Basin. Based on the comprehensive evaluation of Shanxi-Taiyuan Formation shale in Ordos Basin, the main controlling factors and exploration potential of marine–continental transitional shale gas in this area is proposed. Depositional environment led to dark gray–black shales frequently interbedded with sandy shales and coal seams, which rendered the Shanxi-Taiyuan Formation rich in oil, coal, natural gas, and other resources (Sun et al, 2017; Xiao et al, 2005). The chemical compositions and stable carbon isotopes of the gas samples were analyzed in MAT 271 mass spectrometer, and the concentration of gas was calculated according to the national standards (State Standard of China GB/T 6041–2002 and GB/T 10628–89). An analysis precision of Æ0.5% was obtained using the V-PDB standard
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
