Investigation of pore structure alteration and permeability enhancement of shale matrix by supercritical water treatment after hydraulic fracturing

Abstract

Shale gas reservoirs are unconventional tight gas reservoirs, in which horizontal wells and hydraulic fracturing are required to achieve commercial development. The fracture networks created by hydraulic fracturing can increase the drainage area extensively to enhance shale gas recovery. However, large volumes of fracturing fluid that is difficult to flow back to the surface and remained in the shale formation, will inevitably lead to damages of the shale formations and limit the effectiveness of stimulation. Supercritical water (SCW) treatment after hydraulic fracturing is a new method to enhance shale gas recovery by using appropriate heat treatment methods to the specific formation to convert the retained fracturing fluid into a supercritical state (at temperatures in excess of 373.946°C and pressures in excess of 22.064 MPa). An experiment was conducted to simulate the reaction between shale and SCW, and the capacity of SCW treatment to enhance the permeability of the shale was evaluated by measuring the response of the shale porosity and permeability on SCW treatment. The experimental results show that the shale porosity and permeability increase by 213.43% and 2198.37%, respectively. The pore structure alteration and permeability enhancement of the shale matrix were determined by analyzing the changes in pore structure and mineral composition after SCW treatment. The mechanisms that affect pore structure and mineral composition include oxidative catalysis decomposition of organic matters and reducing minerals, acid-catalyzed decomposition of carbonate minerals and feldspar minerals, hydrothermal catalysis induced fracture extension and cementation weakening induced fracture extension. SCW treatment converts harm into a benefit by reducing the intrusion of harmful substances into the shale formation, which will broaden the scope and scale of shale formation stimulation.

Keywords

Shale gas / Formation damage control / Formation heat treatment / Supercritical water

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (No. 41902154; No. 51674209; No. 51604236), the Sichuan Youth Science and Technology Innovation Research Team Project (No. 2021JDTDO017), the Sichuan Province Science and Technology Innovation Miaozi Engineering Cultivation Project (No. 2021100), the China Scholarship Council (No. 202109225004), and the Open Fund of State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development (No. 33550000-21-ZC0613-0335).

References

[1] Y. Ren, X. Guo, C. Xie, H. Wu, Experimental study on gas slippage of marine shale in southern China, Petroleum 2 (2) (2016) 171-176.

[2] C. Zou, S. Pan, Z. Jing, J. Gao, Z. Yang, S. Wu, et al., Shale oil and gas revolution and its impact, Acta Pet. Sin. 41 (1) (2020) 1-12.

[3] D. Dong, Y. Wang, X. Li, C. Zou, Q. Guan, C. Zhang, et al., Breakthrough and prospect of shale gas exploration and development in China, Nat. Gas. Ind. 36 (1) (2016) 19-32.

[4] H. Xie, F. Gao, Y. Ju, L. Xie, Y. Yang, J. Wang, Novel idea of the theory and application of 3D volume fracturing forstimulation of shale gas reservoirs, Sci. Bull. 61 (1) (2016) 36-46.

[5] Q. Li, H. Xing, J. Liu, X. Liu, A review on hydraulic fracturing of unconventional reservoir, Petroleum 1 (1) (2015) 8-15.

[6] C. Xu, Y. Kang, Z. You, M. Chen, Review on formation damage mechanisms and processes in shale gas reservoir: known and to be known, J. Nat. Gas Sci. Eng. 36 (2016) 1208-1219.

[7] J. Guo, C. He, Microscopic mechanism of the damage caused by gelout process of fracturing fluids, Acta Pet. Sin. 33 (6) (2012) 1018-1022.

[8] L. You, B. Xie, J. Yang, Y. Kang, H. Han, L. Wang, et al., Mechanism of fracture damage induced by fracturing fluid flowback in shale gas reservoirs, Nat. Gas. Ind. 38 (12) (2018) 61-69.

[9] Z. Hu, Y. Mu, Z. Gu, X. Duan, Y. Li, Law of imbibition effect on shale gas occurrence state, Nat. Gas. Ind. 40 (5) (2020) 66-71.

[10] X. Liu, W. Zeng, L. Liang, J. Xiong, Experimental study on hydration damage mechanism of shale from the Longmaxi Formation in southern Sichuan Basin, China, Petroleum 2 (1) (2016) 54-60.

[11] B. Lin, J. Guo, X. Liu, J. Xiang, H. Zhong, Prediction of flowback ratio and production in Sichuan shale gas reservoirs and their relationships with stimulated reservoir volume, J. Petrol. Sci. Eng. 184 (2020), 106529.

[12] L. You, X. Li, Y. Kang, M. Chen, Z. Hao, An experimental study on cyclical thermal stimulation to enhance permeability of water-bearing organic-rich shale, J. SW Pet. Univ. 43 (1) (2021) 120-132.

[13] M. Chen, Y. Kang, L. You, Advantages in formation heat treatment to enhance permeability in tight reservoir, Nat. Gas Geosci. 24 (6) (2013) 1226-1231.

[14] C. Zou, Q. Zhao, D. Dong, Z. Yang, Z. Qiu, F. Liang, et al., Geological characteristics, main challenges and future prospect of shale gas, Nat. Gas Geosci. 28 (12) (2017) 1781-1796.

[15] T.D. Fowler, H.J. Vinegar, Oil Shale ICP -Colorado Field Pilots, SPE Western Regional Meeting, 2009.

[16] W.A. Symington, D.L. Olgaard, G.A. Otten, T.C. Phillips, M.M. Thomas, J.D. Yeakel, ExxonMobil's Electrofrac Process for in Situ Oil Shale Conversion, 26th Oil Shale Symposium, Colorado School of Mines, 2006, pp. 16-18.

[17] Y. Kang, M. Chen, Z. Chen, L. You, Z. Hao, Investigation of formation heat treatment to enhance the multiscale gas transport ability of shale, J. Nat. Gas Sci. Eng. 35 (2016) 265-275.

[18] Q. Guan, P. Ning, J. Gu, Sub/supercritical Water Technology and Principle, Metallurgical Industry Press, Beijing, 2014.

[19] C.M. Huelsman, P.E. Savage, Intermediates and kinetics for phenol gasification in supercritical water, Phys. Chem. Chem. Phys. : What PC 14 (8) (2012) 2900-2910.

[20] H. Jin, Y. Wu, L. Guo, X. Su, Molecular dynamic investigation on hydrogen production by polycyclic aromatic hydrocarbon gasification in supercritical water, Int. J. Hydrogen Energy 41 (6) (2016) 3837-3843.

[21] A.G. Kalinichev, S.V. Churakov, Size and topology of molecular clusters in supercritical water: a molecular dynamics simulation, Chem. Phys. Lett. 302 (5) (1999) 411-417.

[22] A.G. Kalinichev, S.V. Churakov, Thermodynamics and structure of molecular clusters in supercritical water, Fluid Phase Equil. 183-184 (2001) 271-278.

[23] P.E. Savage, Organic chemical reactions in supercritical water, Chem. Rev. 99 (2) (1999) 603-622.

[24] P.A. Marrone, G.T. Hong, Corrosion control methods in supercritical water oxidation and gasification processes, J. Supercrit. Fluids 51 (2) (2009) 83-103.

[25] L. Qian, S. Wang, D. Xu, Y. Guo, X. Tang, L. Wang, Treatment of municipal sewage sludge in supercritical water: a review, Water Res. 89 (2016) 118-131.

[26] L. Guo, L. Zhao, Y. Lu, H. Jin, Coal supercritical water gasification hydrogen generation polygeneration technology, J. Eng. Thermophys. 38 (3) (2017) 678-679.

[27] Q. Zhao, L. Guo, Y. Wang, Z. Huang, L. Chen, H. Jin, Thermophysical characteristics of enhanced extra-heavy oil recovery by supercritical water flooding, J. Eng. Thermophys. 41 (3) (2020) 635-642.

[28] Z. Chen, Supercritical Water Oxidation Treatment of Oil-Based Drill Cuttings from Shale Gas Field, Doctoral Thesis, University of Chinese Academy of Sciences, 2018.

[29] M. Chen, P. Li, Y. Kang, X. Zhou, L. You, X. Zhang, et al., Effect of aqueous phase trapping in shale matrix on methane sorption and diffusion capacity, Fuel 289 (2021), 119967.

[30] Y. Kang, P. Li, M. Chen, S. Fang, C. Dai, H. Liu, et al., Enhancing porosity and permeability of shale matrix through supercritical water treatment, J. Nat. Gas Sci. Eng. 101 (2022), 104530.

[31] M. Chen, P. Li, Y. Kang, X. Gao, D. Yang, M. Yan,Application of heat treatment to prevent fracturing fluid-induced formation damage and enhance matrix permeability in shale gas reservoirs, in: SPE/IATMI Asia Pac. Oil Gas Conf. Exhib., 2021.

[32] J. Zhang, The Kinetics of Organic Wastewaters Oxidation and the Mechanism of Nitrogen Transfer in Supercritical Water, Shandong University, 2012.

[33] T. Xu, The Study on the Hydrogen Donation Capacity of Supercritical Water, Beijing University of Chemical Technology, 2012. Master Thesis.

[34] L. Li, P. Chen, E.F. Gloyna, Generalized kinetic model for wet oxidation of organic compounds, AIChE J. 37 (11) (1991) 1687-1697.

[35] R.K. Helling, J.W. Tester, Oxidation of simple compounds and mixtures in supercritical water: carbon monoxide, ammonia and ethanol, Environ. Sci. Technol. 22 (11) (1988) 1319-1324.

[36] A. Stirling, T. Rozgonyi, M. Krack, M. Bernasconi, Pyrite in contact with supercritical water: the desolation of steam, Phys. Chem. Chem. Phys. 17 (26) (2015) 17375-17379.

[37] H.H. Ma, S.Z. Wang, L. Zhou, Kinetics Behavior and Sulfur Transformations of Iron Sulfide during Supercritical Water Oxiation, Advanced Materials Research, Trans Tech Publ, 2012, pp. 1939-1942.

[38] G. Zhao, Y. Liu, T. Chai, H. Wang, J. Tian, Experiment for separating the effluent water with different acidic and alkaline mixtures in continuous supercritical water oxidation system, J. Saf. Environ. 16 (4) (2016) 297-301.

[39] J. Yu, Catalytic Gasification of Lignite and Intermediates with Heterogeneous Catalysts in Supercritical Water, Kunming University of Science and Technology, Kunming, 2017, p. 152.

[40] L. You, X. Li, Y. Kang, M. Chen, J. Liu, Advantages of thermal stimulation to induce shale cracking after hydraulic fracturing overorganic-rich shale reservoirs, Nat. Gas Geosci. 31 (3) (2020) 325-334.

[41] T. Yang, Seepage Characteristic in Rock FailureddTheory, Model and Applications, Science Press, Beijing, 2004.

[42] J. Chen, D. Georgi, H. Liu, B. Lai, Fracturing Tight Rocks by Elevated Pore-Water Pressure using Microwaving and its Applications, SPWLA 56th Annual Logging Symposium, 2015.

[43] W. Zhou, Evolution of inorganic pore structure and lts controlling factors in Longmaxi formation shale, Doctoral thesis, China Univ. Geosci., 2019, pp. 70-72.