Anisotropy in Thermal Recovery of Oil Shale—Part 1: Thermal Conductivity, Wave Velocity and Crack Propagation

Guoying Wang,Jing Zhao,Zhiqin Kang,Dong Yang

doi:10.3390/en11010077

Abstract

In this paper, the evolution of thermal conductivity, wave velocity and microscopic crack propagation both parallel and perpendicular to the bedding plane in anisotropic rock oil shale were studied at temperatures ranging from room temperature to 600 °C. The results show that the thermal conductivity of the perpendicular to bedding direction (KPER) (PER: perpendicular to beeding direction), wave velocity of perpendicular to bedding diretion (VPER), thermal conduction coefficient of parallel to beeding direction (KPAR) and wave velocity of parallel to beeding direction (VPAR) (PAR: parallel to bedding direction) decreased with the increase in temperature, but the rates are different. KPER and VPER linearly decreased with increasing temperature from room temperature to 350 °C, with an obvious decrease at 400 °C corresponding to a large number of cracks generated along the bedding direction. KPER, VPER, KPAR and VPAR generally maintained fixed values from 500 °C to 600 °C. 400 °C has been identified as the threshold temperature for anisotropic evolution of oil shale thermal physics. In addition, the relationship between the thermal conductivity and wave velocity based on the anisotropy of oil shale was fitted using linear regression. The research in this paper can provide reference for the efficient thermal recovery of oil shale, thermal recovery of heavy oil reservoirs and the thermodynamic engineering in other sedimentary rocks.

Highlights

Oil shale is a fine-grained sedimentary rock that typically has a high ash content along with combustible organic matter
We mainly study the influence of temperature on the anisotropy of thermal conductivity and wave velocity of oil shale
To study the effect of temperature on the evolution of anisotropy of thermal and physical characteristics of oil shale from room temperature to 600 ◦ C, the thermal diffusion, thermal conductivity, P-wave velocity and crack propagation both perpendicular and parallel to the bedding plane were studied in this paper

Summary

Introduction

Oil shale is a fine-grained sedimentary rock that typically has a high ash content along with combustible organic matter. Called kerogen, can be decomposed into oil shale oil and pyrolysis oil gas [1] at specific temperatures. Oil shale resources are abundant across the world and are often thought to be an important supplementary energy source. China’s oil shale reserves rank second in the world, equivalent to 476 tons of shale oil [2]. Exploitation of oil shale can be aboveground (ex situ) or underground (in situ). Because of the problems of high cost and high pollution, ex-situ retorting pyrolysis of oil shale has been gradually eliminated in recent years, and the method of in-situ direct pyrolysis of oil shale has been gradually replacing ex-situ pyrolysis

Results

Discussion

Conclusion