Oil content and mobility in a shale reservoir in Songliao Basin, Northeast China: Insights from combined solvent extraction and NMR methods

Abstract

The volatility of light hydrocarbons means that the conventional dichloromethane (DCM) extraction method may underestimate shale oil content, thereby limiting its usefulness in studies of oil content and mobility within shale pores. Here, a method involving a combination of DCM extraction and low-field (LF)–NMR. spectroscopy was developed for a study of a typical shale oil reservoir in Songliao Basin, Northeast China, measuring its total, adsorbed, mobile, and free oil contents and oil, gas, and water saturation. Factors affecting mobility were also considered. Total oil contents were in the range of 7.2–13.4 mg g−1 rock; adsorbed oil contents determined by DCM extraction accounted for 18%–67% of the total; and total oil saturation was in the range of 23%–40%. Mobile oil saturation ranged from 10% to 32% (17% in average), with free oil saturation averaging 9%. A total-oil correlation coefficient as a function of asphalt A extraction was first time developed. Increasing porosity made no contribution to favorable “sweet spots” for shale oil production. Mobile oil was stored in both meso and macro pores, rather than only in larger pores. Shale intervals with high contents of total organic carbon tended to store oil in an adsorbed state. These findings may improve resource estimation and shale oil sweet spot exploitation.