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.

Occurrence Space and State of Petroleum in Lacustrine Shale: Insights from Two-Step Pyrolysis and the N2 Adsorption Experiment

“…The physical state of shale oil mainly includes free and adsorbed oil. ,,, Free oil exists in both inorganic and organic pores, ,, while adsorbed oil is mainly found on the surface of inorganic minerals and OM. ,, Although the adsorption capacity of different minerals varies, they have a very low adsorption capacity compared to OM . The mobility of shale oil is significantly reduced because of the strong affinity between adsorbed oil and the pore surface. ,, Theoretically, free oil is the actual amount of available shale oil, and the free oil in this research designates the movable oil. In previous studies, soluble OM content and pyrolysis S 1 in shale were effective characterization parameters of the oil content. ,,,, However, the adsorbed/free oil was removed simultaneously in the extraction process because the soluble OM could not distinguish the physical state of the oil. , Therefore, this study does not consider the soluble OM content but directly uses rock pyrolysis parameters to evaluate the shale oil content.…”

“…The threshold of petroleum mobility is the key to unconventional resource exploration. Compared to adsorbed oil, free oil contributes more to the overall shale oil production. , Some researchers have long struggled with determining the lowest limit of the pore diameter of movable oil. Through physical simulation experiments, Zou et al proposed that oil in pores with pore sizes above 20 nm can flow freely.…”

Application of mathematical statistics to shale gas-bearing property evaluation and main controlling factor analysis

“…Organic-rich shale is both a source rock and unconventional reservoir 1 . As an unconventional natural gas reservoir, shale can not only store free gas but can also adsorb gas 2 , 3 .…”

Insight into Geochemical Significance of NO Compounds in Lacustrine Shale Source Rocks by FT-ICR MS

“…The shale rocks of the third member of the Shahejie Formation in Well Pushen 18-1 obtained a daily oil production of 420 t oil flow, indicating that the Dongpu Depression is of great potential for shale oil [15]. Previous studies have also reported that shale oil is rich in the Dongpu Depression [16,17]. Some research on the hydrocarbon compounds that were generated from the mud shale in the Dongpu Depression has been carried out [18,19].…”