Continental shale oil in China has large resource potential and is mainly of low-moderate maturity. The reservoir is initially filled with un-expelled heavy oil and unconverted organic matter, making it difficult to obtain economic production through horizontal drilling and hydraulic fracturing. In-situ conversion technology is considered feasible for clean production of shale oil. When the formation is heated, various chemical kinetic reactions of organic matter and retained hydrocarbon occur. Consequently, fluid composition and rock pore space will change dramatically, making the thermal-reactive flow coupling process more complex. In this paper, the composition of kerogen, cracking of hydrocarbon, heat loss to overburden and underburden, fluid and formation parameters evolution are incorporated, and a multiphase multicomponent coupled thermal-reactive flow 3D numerical model and numerical solution method is developed. The proposed model is verified through simulation cases, and the impact of parameters including heating temperature, heating pattern, and initial kerogen concentration on cumulative production is analyzed. Besides, the feasibility of in-situ conversion process in shale oil reservoir is quantitively evaluated from economic aspect. The proposed model can be used to analyze the in-situ conversion process and provide theoretical support for the effective development of low-moderate maturity shale oil reservoir.

1. Introduction

Continental shale oil is widely distributed in China and considered to be one of the most promising replacement resources. Shale oil resource in China is mainly of low-moderate maturity. A conservative estimate suggests that the recoverable resource of low-moderate maturity shale oil is 700–900×108 t (Zhi et al., 2019). Such shale oil with low thermal maturity is quite different from shale formation of high maturity in both storage type and exploitation technology (Zhao et al., 2018). Low-moderate maturity shale formation mainly contains retained hydrocarbon and mass of unconverted solid organic matter (Zhao et al., 2020). Due to poor mobility of un-expelled hydrocarbon, horizontal drilling and fracturing technology are insufficient to obtain economic production. Thus, an alternative technology is urgently needed for the clean and effective development of low-moderate maturity shale oil reservoir.

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