Oil mobility in the Lianggaoshan shale strata: insights from integrated analyses of reservoir properties, fluid quality, and producibility

The Jurassic Lianggaoshan Formation in the Fuxing area has recently emerged as an important unconventional oil and gas play in China. However, it remains unclear whether the crude oil originates from shale or interbedded siltstone. This study integrates multiple methodologies, such as mineralogy, reservoir characterization, and organic geochemistry, to evaluate oil mobility within Lianggaoshan shale strata in terms of reservoir properties, fluid quality, and producibility (e.g., oil–reservoir correlation). Results indicate that the lithofacies can be classified into organic-rich argillaceous shale, organic-poor argillaceous shale, and siltstone based on total organic carbon (TOC) content and mineral composition. The permeability, mobile water saturation, and newly defined pseudo-mobile porosity all illustrate positive correlations with the classic total porosity, suggesting that the higher the porosity of a rock sample, the larger the volume of mobile fluids. This is particularly the case for organic-rich argillaceous shale, which possesses the highest average total porosity of 7.31 % and contains the most mobile petroleum fluids, with saturated hydrocarbons accounting for an average of 71.36 %, thereby demonstrating greater mobile pore volume and superior fluid quality compared with other lithofacies. Light hydrocarbons provide a novel contribution to oil − reservoir correlation. The analysis reveals a closer chemical affinity between produced oil and hydrocarbons retained in organic-rich argillaceous shale, confirming the shale as the actual producing reservoir. In a nutshell, the Jurassic Lianggaoshan Formation in the Fuxing area is a typical hybrid shale reservoir with self-sourced and producible oil fluids, in which the organic-rich argillaceous shale is the most favorable lithofacies for exploitation.