Occurrence and mobility of shale oil in the Jiyang Depression, eastern China

Abstract

The occurrence of shale oil is important for its mobility and holds great significance in determining the available shale oil resources. Here, shale samples from three representative wells with different shale oil production levels in the Jiyang Depression, eastern China, were collected to evaluate the mobility of shale oil from its occurrence. The samples were subjected to Rock-Eval pyrolysis, X-ray diffraction, soluble organic matter, and N₂ adsorption measurements. The results indicate that the shales in the high production well have higher contents of clay or felsic minerals, more apolar oil components, and smaller pore sizes than those in the low production well. In particular, the shale oil occurrence exhibits two stages involving pore surface adsorption followed by pore void filling, which are separated by a total organic carbon (TOC) content of 0.6 wt% OC (equivalent to 7.7 mg/gRock, the lower threshold of shale oil content for mobility). The corresponding threshold of pore diameter is 10 nm. By integrating the shale oil occurrence with the oil properties at the producing intervals, the following indices are proposed to evaluate the shale oil mobility and high production level: shale oil content greater than 0.6 wt% OC or 7.7 mg/gRock, oil saturation index greater than 100 mg/gTOC, apolarity index greater than 1, and pore diameter greater than 10 nm. Our work provides an index regime to evaluate the mobility and high production probability of shale oil, which will benefit the exploration and development of shale oil resources.