Title: Invaded water flowback capability of high volatile bituminous coal after nitrogen displacing: from a perspective of fracture and seepage pore structural complexities

Authors: Xin Li; Xuehai Fu; Jijun Tian; Xueliang Liu; Yanyan Ge; Meng Wang; Shun Liang; Wenfeng Wang

Addresses: School of Geology and Mining Engineering, Xinjiang University, Room 601, Building No. 1, No. 1230, Yan'an Road, Urumqi, Xinjiang Uygur Autonomous Region, 830047, China ' Key Laboratory of Coalbed Methane Resource and Reservoir Formation Process, China University of Mining and Technology, Ministry of Education, Room 337, South Jiefang Road, Xuzhou, Jiangsu Province, 221000, China ' School of Geology and Mining Engineering, Xinjiang University, Room 601, Building No. 1, No. 1230, Yan'an Road, Urumqi, Xinjiang Uygur Autonomous Region, 830047, China ' Xinjiang Energy Co. Ltd., Room 2519, Xinjiang Energy Building, No. 477, Xuanwuhu Road, Urumqi, Xinjiang Uygur Autonomous Region, 830047, China ' School of Geology and Mining Engineering, Xinjiang University, Room 317, Building No. 3, No. 1230 of Yan'an Road, Urumqi, Xinjiang Uygur Autonomous Region, 830047, China ' School of Geology and Mining Engineering, Xinjiang University, Room 207, Building No. 3, No. 1230, Yan'an Road, Urumqi, Xinjiang Uygur Autonomous Region, 830047, China ' School of Mines, China University of Mining and Technology, Room 615, No. 1, Daxue Road, Xuzhou, Jiangsu Province, 221000, China ' School of Geology and Mining Engineering, Xinjiang University, Room 203, Building No. 3, No. 1230, Yan'an Road, Urumqi, Xinjiang Uygur Autonomous Region, 830047, China

Abstract: Water-based fracturing is applied for stimulating coal reservoir. However, invasion of water can result in low flowback efficiency and low coalbed methane (CBM) yield. Nitrogen injection is an effective method to enhance CBM production. In this study, nitrogen displacing water experiments using water saturated high volatile bituminous coal were conducted, during which magnetic resonance imaging (MRI) tests were applied to determine flowback capability. To research the relationship between flowback capability and complexities of fracture and seepage pore, characterising methods including micro-CT and mercury intrusion porosimetry (MIP) were used. The results show that flowback capabilities of complex structural seepage pores and fractures were low. Water is easily flooded into simple structural seepage pores and fractures, and water flowback capabilities of these simple spaces are relative higher, compared with those of the complex ones. Water phase trapping during nitrogen displacing water happens due to water imbibition and Jamin effect occurring in complex structural seepage pores and fractures. [Received: April 27, 2019; Accepted: August 7, 2020]

Keywords: coalbed methane; CBM; retained water; permeability; magnetic resonance imaging; MRI; pore structure; flowback; nitrogen injection; high volatile bituminous coal.

DOI: 10.1504/IJOGCT.2021.117453

International Journal of Oil, Gas and Coal Technology, 2021 Vol.28 No.2, pp.210 - 234

Accepted: 07 Aug 2020
Published online: 22 Jul 2021 *

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