Experimental study on the effects of steam temperature on the pore-fracture evolution of oil shale exposed to the convection heating

Wang, Lei; Yang, Dinglong; Kang, Zhiqin; Zhao, Jing; Meng, Qiaorong

doi:10.1016/j.jaap.2022.105533

Cited by 24 publications

(9 citation statements)

References 30 publications

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“…(4) According to Darcy’s law [ 19 , 20 ], the permeability of oil shale at different temperatures and pore pressures can be calculated using the following expression:

where k denotes the permeability of oil shale [m 2 ], Q represents the volume flow rate of nitrogen [m 3 /s], P 0 denotes atmospheric pressure, 0.1 MPa, L represents the sample length [m], μ denotes the dynamic viscosity of the gas [MPa s], P 1 represents the pressure at the inlet end of the sample [MPa], P 2 denotes the pressure at the outlet end of the sample [MPa], and A represents the cross-sectional area of the sample [m 2 ].…”

Section: Methodsmentioning

confidence: 99%

Study on Pyrolysis–Mechanics–Seepage Behavior of Oil Shale in a Closed System Subject to Real-Time Temperature Variations

Wang

Huang

2022

Materials

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In situ mining is a practical and feasible technology for extracting oil shale. However, the extracted oil shale is subject to formation stress. This study systematically investigates the pyrolysis–mechanics–seepage problems of oil shale exploitation, which are subject to thermomechanical coupling using a thermal simulation experimental device representing a closed system, high-temperature rock mechanics testing system, and high-temperature triaxial permeability testing device. The results reveal the following. (i) The yield of gaseous hydrocarbon in the closed system increases throughout the pyrolysis reaction. Due to secondary cracking, the production of light and heavy hydrocarbon components first increases, and then decreases during the pyrolysis reaction. The parallel first-order reaction kinetic model shows a good fit with the pyrolysis and hydrocarbon generation processes of oil shale. With increasing temperature, the hydrocarbon generation conversion rate gradually increases, and the uniaxial compressive strength of oil shale was found to initially decrease and then increase. The compressive strength was the lowest at 400 °C, and the conversion rate of hydrocarbon formation gradually increased. The transformation of kaolinite into metakaolinite at high temperatures is the primary reason for the increase in compressive strength of oil shale at 400–600 °C. (ii) When the temperature is between 20 and 400 °C, the magnitude of oil shale permeability under stress is small (~10−2 md). When the temperature exceeds 400 °C, the permeability of the oil shale is large, and it decreases approximately linearly with increasing pore pressure, which is attributed to the joint action of the gas slippage effect, adsorption effect, and effective stress. The results of this research provide a basis for high efficiency in situ exploitation of oil shale.

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“…(4) According to Darcy’s law [ 19 , 20 ], the permeability of oil shale at different temperatures and pore pressures can be calculated using the following expression:

Section: Methodsmentioning

confidence: 99%

Study on Pyrolysis–Mechanics–Seepage Behavior of Oil Shale in a Closed System Subject to Real-Time Temperature Variations

Wang

Huang

2022

Materials

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“…Previous studies have primarily focused on the transformation of organic matter during the ICP, particularly in relation to the assessment of recoverable oil and gas. − However, research on the evolution of petrophysical properties of shale reservoirs during the ICP remains insufficient. Earlier studies have focused on the petrophysical properties of oil shales during heat treatments. − Studies have shown that after undergoing high-temperature heat, micropore structures of oil shales display an intriguing trend. Specifically, the pore volume and the Brunauer–Emmett–Teller surface area (BET SSA) measured through low-temperature nitrogen adsorption–desorption (LTNA/D) display a pattern where they first decrease, then increase, and ultimately decrease .…”

Section: Introductionmentioning

confidence: 99%

Pore Structure Characterizations of Shale Oil Reservoirs with Heat Treatment: A Case Study from Dongying Sag, Bohai Bay Basin, China

Zhang

et al. 2023

ACS Omega

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Heat treatment plays a significant role in determining the petrophysical properties of shale reservoirs; however, the existing studies on the evolution of pore structures are still insufficient. This study conducts a series of tests, including Rock–Eval, low-temperature nitrogen adsorption–desorption, nuclear magnetic resonance (NMR) T 2, and T 1–T 2 tests on samples from Shahejie Formation, Dongying Sag, Bohai Bay Basin. The tests aim to determine the changes in the shale pore structures under increasing heat treatments (ranging from 110 to 500 °C) and identify the factors that control pore structures. The results show that the gradual decomposition of organic matter leads to an eventual decrease in the total organic carbon (TOC) content. The decrease in TOC is more prominent when the temperature exceeds 300 °C. For shales with lower TOC contents (<2%), the Brunauer–Emmett–Teller specific surface area (BET SSA) first decreases, then increases, but eventually decreases again. However, the average pore diameter demonstrates an opposite trend when the temperature increases. In contrast, for organic-rich shales (TOC > 2%), the BET SSA increases at temperatures above 200 °C. The similarity between the D 1 values implies that the complexity and heterogeneity of shale pore surface only undergo minor changes during heat treatment. Porosity shows an increasing trend, and the higher the contents of clay minerals and organic matter in shales are, the greater the change in porosity is. The NMR T 2 spectra suggest that micropores (<0.1 μm) in shales first decrease and then increase, whereas the contents of meso- (0.1–1 μm) and macropores (>1 μm) increase, corresponding to the increase in free shale oil. Moreover, shale pore structures are primarily controlled by clay minerals and organic matter contents during heat treatments, with higher contents resulting in better pore structures. Overall, this study contributes to detailing the shale pore structure characteristics during the in situ conversion process (ICP).

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“…The essence of immature shale development and utilization is to heat solid organic matter to pyrolysis temperatures and degrade it into oil and gas resources . The pyrolysis of kerogen causes a large number of pores and cracks in the solid skeleton of immature shale. , The formation of new pores and fractures provides a channel for the heating of immature shale and also for the flow of oil and gas generated by pyrolysis. − Therefore, the accurate characterization of pore structure and the accurate understanding of thermal evolution mechanisms in the process of in situ production of immature shale is of great significance to analyze the seepage and production processes of pyrolysis-derived oil and gas and to guide the in situ development technology of immature shale. − …”

Section: Introductionmentioning

confidence: 99%

High-Temperature-Induced Pore System Evolution of Immature Shale with Different Total Organic Carbon Contents

et al. 2023

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The pyrolysis process of source rock, especially organic-rich immature shale, is required for oil and gas extraction, during which the evolution of the pore structure system in the immature shale determines the heat conduction and fluid flow under the heating treatment. Although some sound achievements have been made regarding the pyrolysis of immature shale, the effect of the total organic carbon (TOC) content on the pore structure evolution of immature shale remains unclear. With respect to this issue, in this work, a series of N 2 adsorption/desorption and nuclear magnetic resonance (NMR) experiments were conducted, and fractal dimension theory was also introduced to analyze the pore structure evolution of immature shale subjected to heating treatment in a quantitative manner. The results indicate that the adsorption branch of the nitrogen adsorption–desorption isotherm can be divided into three stages. The pore structure of different TOC immature shales does not change significantly, and they are all slit-shaped. In addition, immature shale with a higher organic content has a higher hydrocarbon expulsion strength and a higher pore volume growth rate, which indicate that the pyrolysis of organic matter greatly affects the pore structure of immature shale during heating. This phenomenon shows that the pyrolysis of organic matter greatly influences the pore structure of immature shale during the heating process. The pores of immature shale in the study area have significant fractal characteristics, the fractal dimension is between 2.397 and 2.636, the pore space of the sample is extremely small, the pore structure is extremely complex, and the heterogeneity is strong.

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Experimental study on the effects of steam temperature on the pore-fracture evolution of oil shale exposed to the convection heating

Cited by 24 publications

References 30 publications

Study on Pyrolysis–Mechanics–Seepage Behavior of Oil Shale in a Closed System Subject to Real-Time Temperature Variations

Study on Pyrolysis–Mechanics–Seepage Behavior of Oil Shale in a Closed System Subject to Real-Time Temperature Variations

Pore Structure Characterizations of Shale Oil Reservoirs with Heat Treatment: A Case Study from Dongying Sag, Bohai Bay Basin, China

High-Temperature-Induced Pore System Evolution of Immature Shale with Different Total Organic Carbon Contents

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