Laboratory investigation of coal sample permeability under the coupled effect of temperature and stress

Abstract

The stress and temperature sensitivities of coal reservoirs are critical geological factors affecting coalbed methane (CBM) well exploitation; in particular it is important to reduce or eliminate their influence on coal reservoir permeability. To investigate coal permeability behavior at various effective stresses and temperatures, CH₄ permeability tests were conducted on raw coal samples under a varying effective stress of 2.0–8.0 MPa under five different temperatures (25°C–65°C) in the laboratory. The results show that the permeability of the coal samples exponentially decreases with increasing effective stress or temperature, which indicates obvious stress and temperature sensitivity. Through a dimensionless treatment of coal permeability, effective stress, and temperature, a new stress sensitivity index S and temperature index S_T are proposed to evaluate coal stress and temperature sensitivity evaluation parameters. These new parameters exhibit integrality and uniqueness, and, in combination with stress sensitivity coefficient α_k, temperature sensitivity coefficient α_T, and the permeability damage rate PDR, the sensitivities of coal permeability to stress and temperature are evaluated. The results indicate that coal sample stress sensitivity decreases with increasing effective stress, while it first decreases and then increases with increasing temperature. Additionally, coal sample temperature sensitivity shows a downward trend when temperature increases and fluctuates when effective stress increases. Finally, a coupled coal permeability model considering the impacts of effective stress and temperature is established, and the main factors affecting coal reservoir permeability and their control mechanism are explored. These results can provide some theoretical guidance for the further development of deep CBM.

Keywords

deep coal reservoir / permeability variation / stress sensitivity / temperature sensitivity

References

[1] Akbarzadeh H,, Chalaturnyk R J. ( 2014). Structural changes in coal at elevated temperature pertinent to underground coal gasification: a review. Int J Coal Geol, 131: 126– 146

[2] Bear J,, Corapcioglu M Y. ( 1981). A mathematical model for consolidation in thermoelastic aquifer due to hot water injection or pumping. Water Resour Res, 17( 3): 723– 736

[3] Biot M A. ( 1954). Theory of elasticity and consolidation for a porous anisotropic solid. J Appl Phys, 26( 2): 182– 185

[4] Chu T X,, Yu M G,, Jiang D Y. ( 2016). Experimental investigation on the permeability evolution of compacted broken coal. Transp Porous Media, 116( 2): 1– 22

[5] Durucan S,, Edwards J S. ( 1986). The effects of stress and fracturing on permeability of coal. Min Sci Technol, 3( 3): 205– 216

[6] Gao Z,, Li B B,, Li J H,, Wang B,, Ren C H,, Xu J,, Chen S. ( 2021). Coal permeability related to matrix-fracture interaction at different temperatures and stresses. J Petrol Sci Eng, 200: 108428

[7] Jones F O,, Owens W W. ( 1980). A laboratory study of low-permeability gas sands. J Pet Technol, 32( 9): 1631– 1640

[8] Karthikeyan , G. , Chand , J. , Chatterjee , R., ( 2020). Impact of geomechanics in coal bed methane development and production, barakar coals in central India. J Pet Sci Eng, 194( 1): 107515.

[9] Li Z Q, Xian X F, Long Q M ( 2009). Experiment study of coal permeability under different temperature and stress. J China Univ Min Technol, 38: 523− 527 (in Chinese)

[10] Liu Q S, Liu X W ( 2014). Research on critical problem for fracture network propagation and evolution with multifield coupling of fractured rock mass. Rock and Soil Mechanics 35(2): 305− 320 (in Chinese)

[11] Liu T,, Lin B Q,, Yang W. ( 2017). Impact of matrix–fracture interactions on coal permeability: model development and analysis. Fuel, 207: 522– 532

[12] McKee C R,, Bumb A C,, Koenig R A. ( 1998). Stress-dependent permeability and porosity of coal. Rocky Mt Assoc Geol, 143– 153

[13] Meng Y,, Li Z P,, Lai F P. ( 2021). Influence of effective stress on gas slippage effect of different rank coals. Fuel, 285: 119207

[14] Meng Y,, Wang J Y,, Li Z P,, Zhang J X. ( 2018). An improved productivity model in coal reservoir and its application during coalbed methane production. J Nat Gas Sci Eng, 49: 342– 351

[15] Meng Z P,, Li G Q. ( 2013). Experimental research on the permeability of high-rank coal under a varying stress and its influencing factors. Eng Geol, 162: 108– 117

[16] Meng Z P, Liu S M ( 2018). Geology and Engineering of Coalbed Methane Development in Coal Mine Area. Beijing: Science Press

[17] Meng Z P, Zhang J X, Liu H, Liu S S, Zhou X D ( 2014). Productivity model of CBM wells considering the stress sensitivity and its application analysis. J China Coal Soc, 39( 04): 593− 599 (in Chinese)

[18] Meng Z P,, Zhang J C,, Wang R. ( 2011). In-situ stress, pore pressure and stress-dependent permeability in the Southern Qinshui Basin. Int J Rock Mech Min Sci, 48( 1): 122– 131

[19] Niu S W,, Zhao Y S,, Hu Y Q. ( 2014). Experimental investigation of the temperature and pore pressure effect on permeability of lignite under the in-situ condition. Transp Porous Media, 101( 1): 137– 148

[20] Norishad J. ( 1989). Coupled thermal–hydraulic–mechanical phenomena in saturated fractured porous rocks: numerical approach. J Geophys Res, 89( B12): 10365– 10373

[21] Oda M. ( 1985). Permeability tensor for discontinuous rock masses. Geotechnique, 5( 4): 483– 495

[22] Ohnishi Y,, Ohtsu H,, Nakamura I. ( 1982). Coupled stress-flow finite element analysis of rock slope near pressure tunnel. In: International Committee for Numerical Methods in Geomechanics. Vol. 2: 579–585. Canadian Geotechnical Society, Edmonton: Alberta

[23] Pan Z J,, Connell L D. ( 2012). Modelling permeability for coal reservoirs: a review of analytical models and testing data. Int J Coal Geol, 92: 1– 44

[24] Perera M. ( 2017). Influences of CO₂ injection into deep coal seams: a review. Energy Fuels, 31( 10): 10324– 10334

[25] Sakurovs R,, Day S,, Weir S,, Duffy G. ( 2008). Temperature dependence of sorption of gases by coals and charcoals. Int J Coal Geol, 73( 3–4): 250– 258

[26] Shang X J,, Wang J G,, Zhang Z Z,, Gao F. ( 2019). Three-parameter permeability model for the cracking process of fractured rocks under temperature change and external loading. Int J Rock Mech Min Sci, 123: 104106

[27] Shi J Q,, Durucan S. ( 2005). A model for changes in coalbed permeability during primary and enhanced methane recovery. SPE Reservoir Eval Eng, 8( 4): 291– 299

[28] Shi J Q, Durucan S, Shimada S ( 2014). How gas adsorption and swelling affects permeability of coal: a new modelling approach for analysing laboratory test data. Int J Coal Geol, 128−129: 134− 142

[29] Somerton W H,, Soylemezoglu M,, Dudley R C. ( 1975). Effect of stress on permeability of coal. Int J Rock Mech Min Sci Geomech Abstr, 12( 5–6): 129– 145

[30] Sparks D P, Mclendon T H, Saulsberry J L, Lambert S W ( 1995). The effects of stress on coalbed reservoir performance, Black Warrior Basin, USA. In: Proc. 1995 SPE Annual Technical Conference and Exhibition, Paper SPE 30743, Dallas, Texas

[31] Teng T,, Wang J G,, Gao F,, Ju Y,, Jiang C B. ( 2016). A thermally sensitive permeability model for coal-gas interactions including thermal fracturing and volatilization. J Nat Gas Sci Eng, 32: 319– 333

[32] Terzaghi K ( 1943). Theoretical Soil Mechanics. New York: Wiley

[33] Wang J M,, Zhao Y S,, Mao R B. ( 2019). Impact of temperature and pressure on the characteristics of two-phase flow in coal. Fuel, 253: 1325– 1332

[34] Yin G Z,, Jiang C B,, Wang J G,, Xu J. ( 2013). Combined effect of stress, pore pressure and temperature on methane permeability in anthracite coal: an experimental study. Transp Porous Media, 100( 1): 1– 16

[35] Zhang J,, Standifird W B,, Roegiers J C,, Zhang Y. ( 2007). Stress-dependent fluid flow and permeability in fractured media: from Lab experiments to engineering applications. Rock Mech Rock Eng, 40( 1): 3– 21

[36] Zhang J,, Lang J,, Standifird W.. ( 2009). Stress, porosity, and failure-dependent compressional and shear velocity ratio and its application to wellbore stability. J Pet Sci Eng, 69( 3–4): 193– 202

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