Shale gas accumulation potential of the Upper Cretaceous Qingshankou Formation in the southeast Songliao Basin, NE China

The purpose of this paper is to provide both quantitative and qualitative visual analyses of the nanometer-scale pore systems of immature and early shales, as well as to discuss the biogenic shale gas accumulation potential of the Upper Cretaceous section of the Songliao Basin. To achieve these goals, mineralogical compositions were determined using transmitted and reflected light petrography, X-ray diffractometry and scanning electron microscopy (SEM), while the nanostructure morphology and pore size distributions (PSDs) were quantified using field emission scanning electron microscopy (FE-SEM) and low-pressure nitrogen gas adsorption (LP-N2GA). The results of these analyses indicate that nanometer-scale pores are well developed in the immature and low-maturity shale, and that these shales contain many types of reservoir pores. The mudstone layer of the Qingshankou Formation (K2qn) contains a high permeability characteristic and good rock fracturing conditions, while it is also thick (>9 m in thickness) and rich in fine organic matter. Overall, analysis of the entire formation using source rock and reservoir evaluations indicate that the first member of the Qingshankou Formation (K2qn1) has a greater shale gas accumulation potential than the second and third members of the Qingshankou Formation (K2qn2-3).