Shale oil potential and mobility in low- to medium-maturity lacustrine shales: A case study of the Yanchang Formation shale in southeast Ordos Basin, China

Oil mobility is essential for the evaluation of shale oil resources, yet there has been limited research conducted on the oil mobility of low- to medium-maturity lacustrine shale. This study integrates multiple methodologies such as organic geochemistry, mineralogy, oil-kerogen adsorption-swelling experiments, and in-situ conversion process (ICP) models to evaluate the mobility and potential for shale oil in the lacustrine shale of the Yanchang Formation in the Yaoqu 1 (YQ1) well situated in the southeastern region of the Ordos Basin. The Chang 7 shales are categorized as highly favorable source rocks, nonetheless, the oil contained within these layers predominantly exists in an adsorbed-swelling state, resulting in limited mobility as indicated by the oil saturation index, a modified oversaturation index, and production index. Therefore, the utilization of existing conventional techniques for shale oil exploitation is not viable for the Chang 7 shale characterized by low to medium maturity in the study area. Nevertheless, during the ICP, the quantity and mobility of oil within the Chang 7 shales exhibit a substantial increase as temperature rises. Moreover, once the Chang 7 type II shales reach a maturity level of around 0.91%R_o, they demonstrate noteworthy prospects for shale oil production. The findings of this study serve as a valuable reference for guiding the advancement of in-situ conversion process technology in the study area, while also offering substantial evidence for addressing the intricate challenge of crude oil mobility in low- to medium-maturity lacustrine shale reservoirs.