The geochemical characteristics and gas potential of the Longtan formation in the eastern Sichuan Basin, China

Abstract

The Longtan Formation in the Sichuan Basin contains abundant organic-rich mudstones and coals, however, few studies have been conducted about their gas potential. A comprehensive study has been conducted on the Longtan sediments in order to determine their critical properties and gas potential. The Longtan samples, especially the coals, contain abundant organic matter, whereas S1 and S2 values are generally very low due to high thermal maturity. The organic component is dominated by the vitrinites, which comprises more than 95% of dispersed organic matter. The high vitrinite reflectance values (∼1.88–2.14% Ro) indicate a post thermal maturity of these sediments, which is consistent with the reliable Tmax values. The predominant mineral components are clay minerals and quartzs, and the brittle nature of the studied samples can be confirmed by the high contents of the brittle minerals and high brittleness indexes. The porosity positively correlates with total organic carbon (TOC), and abundant organic-matter, intraparticle, interparticle pores and fractures have been detected in these studied samples. The Longtan Formation in the study area was mainly deposited in an oxic environment. According to the 1D basin modelling, the Longtan sediments reached the maximum Ro after they have been buried to the maximum depth at late Cretaceous, and they began to generate gas at middle Jurassic. Attention shall be paid on the co-exploration and co-exploitation of shale gas and coalbed methane of the Longtan Formation of eastern Sichuan Basin in the future.