Properties and shale gas potential of continental shales in the Jurassic Mohe Foreland Basin, northern China

Abstract

Reservoir properties and shale gas potential of the Upper Jurassic continental shales from the Mohe Foreland Basin were investigated based on organic geochemical analysis, X‐ray diffraction, scanning electron microscopy, low pressure nitrogen adsorption, high pressure mercury injection, and porosity and permeability analyses. The results indicate that the shallow lacustrine shales of the Emuerhe Formation are characterized by high total organic carbon content (0.43–22.83 wt.%), low hydrocarbon generative potential (less than 5.0 mg HC/g rock), type II kerogen, and a moderate thermal maturity stage (Ro of 1.05–1.46%). The inorganic pores dominate the pore system, and pores associated with clay minerals largely contribute to the surface area. The inorganic pore‐dominated lacustrine shale reservoir is characterized by dense, low porosity, and poor connectivity. The shales of the Emuerhe Formation show strong heterogeneity in mineralogy and are relatively enriched in clay minerals (33–66 wt.%). Due to the lack of biogenic silica, the effect of brittle minerals on hydraulic stimulation is ambiguous in the shallow lacustrine shales. The widely distributed, extensionally unfilled fractures can not only enhance hydrocarbon storage and migration capacity, but also play an important role in the generation of artificial reservoir fracturing. The pore network of lacustrine shales contributed by inorganic pores and unfilled micro‐fractures could also generate a relatively high porosity and permeability. The high‐mature thick shales in the northwest area of the Xingan Town would be the favourable zone for the shale gas exploration and exploitation in the Mohe Foreland Basin.