Mechanism model for shale gas transport considering diffusion, adsorption/desorption and Darcy flow

Abstract

To improve the understanding of the transport mechanism in shale gas reservoirs and build a theoretical basic for further researches on productivity evaluation and efficient exploitation, various gas transport mechanisms within a shale gas reservoir exploited by a horizontal well were thoroughly investigated, which took diffusion, adsorption/desorption and Darcy flow into account. The characteristics of diffusion in nano-scale pores in matrix and desorption on the matrix surface were both considered in the improved differential equations for seepage flow. By integrating the Langmuir isotherm desorption items into the new total dimensionless compression coefficient in matrix, the transport function and seepage flow could be formalized, simplified and consistent with the conventional form of diffusion equation. Furthermore, by utilizing the Laplace change and Sethfest inversion changes, the calculated results were obtained and further discussions indicated that transfer mechanisms were influenced by diffusion, adsorption/desorption. The research shows that when the matrix permeability is closed to magnitude of 10⁻⁹ D, the matrix flow only occurs near the surfacial matrix; as to the actual production, the central matrix blocks are barely involved in the production; the closer to the surface of matrix, the lower the pressure is and the more obvious the diffusion effect is; the behavior of adsorption/desorption can increase the matrix flow rate significantly and slow down the pressure of horizontal well obviously.

Keywords

shale gas / diffusion / adsorption/desorption / transport mechanism / horizontal well

References

[1] BumbA C, MckeeC R. Gas-well testing in the pressure of desorption for coalbed methane and Devonian shale [J]. SPE Formation Evaluation, 1988179-185

[2] FathiE, Yucel AkkutluI. Nonlinear sorption kinetics and surface diffusion effects on gas transport in low-permeability formations [C]. SPE124478. 2009 SPE Annual Technical Conference and Exhibition, 20094-7

[3] LuffelD L, HopkinsC W, SchettlerP D. Matrix permeability measurement of gas productive shales [C]. SPE 26633. 68th Annual Technical Conference and Exhibition of the Society of Petroleum Engineers, 19933-6

[4] GaoC, JohnL W. Modeling multilayer gas reservoirs including sorption effects [C]. Paper SPE29173-MS. SPE Eastern Regional Conference & Exhibition, 19948-10

[5] AyalaH L F, ErtekinT, DewuminM. Compositional modeling of retrograde gas-condensate reservoirs in multi-mechanistic flow domains [J]. SPEJ, 2006, 11(4): 480-487

[6] AyalaH L F, ErtekinT, DewumiM. Numerical analysis of multi-mechanistic flow effects in naturally fractured gas-condensate systems [J]. J Pet Sci Eng, 200713-29

[7] RichardF S, BinQin. Examination of the importance of self diffusion in the transportation of gas in shale gas reservoirs [J]. Petrophysics, 2008, 49(3): 301-305

[8] JavadpourF, FisherD, UnsworthM. Nanoscale gas flow in shale gas sediments [J]. JCPT, 2007, 46(10): 16-21

[9] JavadpourF. Nanopores and apparent permeability of gas flow in mudrocks (shales and siltstone) [J]. Canadian Petroleum Technology, 2009, 16(8): 16-21

[10] BeygiM E, RashidiF. Analytical solutions to gas flow problems in low permeability porous media [J]. J Springer Science+Business Media, 2010421-436

[11] FreemanC M, MoridisG J, BlasingameT A. A Numerical study of microscale flow behavior in tight gas and shale gas reservoir systems [J]. Transport in Porous Media, 2011, 90(1): 253-268

[12] FreemanC M. A numerical study of microscale flow behavior in tight gas and shale gas reservoir systems [C]. SPE141125. SPE International Student Paper Contest at the SPE Annual Technical Conference and Exhibition. Florence, Italy, 201019-22

[13] OzkanE, RaghavanR, ApaydinO G. Modeling of fluid transfer from shale matrix to fracture network [C]. SPE 134830. SPE Annual Technical Conference and Exhibition, 201019-22

[14] GaoS-s, YuX-h, LiuH-Xun. Impact of slippage effect on shale gas well productivity [J]. Natural Gas Industry, 2011, 31(4): 55-58

[15] Sakhaee-PourA, BryantS. Gas permeability of shale [J]. SPE Reservoir Evaluation & Engineering, 2012, 15(4): 401-409

[16] ErtekinT, KingG R, SchwererF C. Dynamic gas slippage: A unique dual-mechanism approach to the flow of gas in tight formations [J]. SPE Formation Evaluation, 198643-52

[17] ScheideggcA E. Physics of flow through porous media [M]. WANG Hong-xun Tr, 1982BeijingPetroleum Industry Press

[18] LiX-p, ZhangL-h, WuF, LiY, LiuQ-guo. A new method for well test analysis of horizontal gas well [J]. Acta Petrolia Sinica, 2008, 29(6): 903-906

[19] OzkanEPerformance of horizontal wells [D], 1988Oklahoma, USATulsa University