Technical Scheme and Application Prospects of Oil Shale In Situ Conversion: A Review of Current Status

Abstract

Petroleum was the most-consumed energy source in the world during the past century. With the continuous global consumption of conventional oil, shale oil is known as a new growth point in oil production capacity. However, medium–low mature shale oil needs to be exploited after in situ conversion due to the higher viscosity of oil and the lower permeability of shale. This paper summarizes previous studies on the process of kerogen cracking to generate oil and gas, and the development of micropore structures and fractures in organic-rich shale formations during in situ conversion. The results show that the temperature of kerogen cracking to generate oil and gas is generally 300–450 °C during the oil shale in situ conversion process (ICP). In addition, a large number of microscale pores and fractures are formed in oil shale formation, which forms a connecting channel and improves the permeability of the oil shale formation. In addition, the principles and the latest technical scheme of ICP, namely, conduction heating, convection heating, reaction-heat heating, and radiation heating, are introduced in detail. Meanwhile, this paper discusses the influence of the heating mode, formation conditions, the distribution pattern of wells, and catalysts on the energy consumption of ICP technology in the process of oil shale in situ conversion. Lastly, a fine description of the hydrocarbon generation process of the target formation, the development of new and efficient catalysts, and the support of carbon capture and storage in depleted organic-rich shale formations after in situ conversion are important for improving the future engineering efficiency of ICP.

Evaluation of Recoverable Hydrocarbon Reserves and Area Selection Methods for In Situ Conversion of Shale

“…The most developed continental shale in China is mainly distributed in northern areas, such as the Ordos, Songliao, Bohai Bay, and Junggar Basins, which cover an area of approximately 400,000 square kilometers, with 200,000 square kilometers of it comprising layers containing ultra-rich organic matter (TOC > 4 wt.%) and having Ro values less than 1.0% [5][6][7][8]. China has focused geological studies on shale oil since 2010, especially on key technological breakthroughs and exploration dimensions [9][10][11][12]. Moreover, in 2023, there were over 2500 horizontal wells, and the shale oil yield reached 342 × 10 4 t. However, global shale oil exploration and development practices have revealed that the existing horizontal well and hydraulic fracturing techniques are not able to achieve the cost-effective development of immature to low-moderate-maturity shale hydrocarbon reserves [13][14][15][16][17].…”

“…In addition, the in situ electrical heating conversion technology proposed by Shell in the 1960s is the most prominent technique to date. They believe that in situ electrical heating conversion technology is the preferable method based on a number of field trials that were successfully conducted [8][9][10]. Moreover, in comparison to other existing technologies for this purpose, this technology has been confirmed to be the most feasible option for hydrocarbon extraction from immature to low-moderate-maturity shales.…”