Key factors controlling shale oil enrichment in saline lacustrine rift basin: implications from two shale oil wells in Dongpu Depression, Bohai Bay Basin

Abstract

Comparative analyses of petroleum generation potential, reservoir volume, frackability, and oil mobility were conducted on 102 shale cores from the Dongpu Depression. Results show the shale has high organic matter contents composed of oil-prone type I and type II kerogens within the oil window. Various types of pores and fractures exist in the shale, with a porosity of up to 14.9%. The shale has high brittle mineral contents, extensive fractures, and high potential for oil mobility due to high seepage capacity and overpressure. Although the petroleum generation potential of the shale at Well PS18-8 is relatively greater than that at Well PS18-1, oil content of the latter is greater due to the greater TOC. The porosity and fracture density observed in Well PS18-1 are greater and more conducive to shale oil enrichment. Although the shales in Wells PS18-1 and PS18-8 have similar brittle mineral contents, the former is more favorable for anthropogenic fracturing due to a higher preexisting fracture density. Besides, the shale at Well PS18-1 has a higher seepage capacity and overpressure and therefore a higher oil mobility. The fracture density and overpressure play key roles in shale oil enrichment.