Open Access

ARTICLE

Capillary-Controlled External Liquid Invasion and Trapping in Shale Gas Reservoirs: Experimental and Numerical Insights into Permeability and Productivity Impairment

Xusen Huang¹, Wei Lv², Long Liu¹, Hongchuan Xing¹, Tian Zeng¹, Zhiyuan Yao¹, Liuyang Fan¹, Mingyang Li¹, Siyu Chen³, Houshun Jiang^2,*
1 Chuanwei Operations Department, PetroChina Southwest Oil & Gas field Company, Chengdu, China
2 State Key Laboratory of Low Carbon Catalysis and Carbon Dioxide Utilization, Yangtze University, Wuhan, China
3 Southwest Branch, China Petroleum Engineering & Construction Corporation, Chengdu, China
* Corresponding Author: Houshun Jiang. Email:
(This article belongs to the Special Issue: Enhanced Oil and Gas Recovery in Unconventional ReservoirsⅡ)

Energy Engineering https://doi.org/10.32604/ee.2026.083307

Received 01 April 2026; Accepted 08 June 2026; Published online 28 July 2026

Abstract

External liquid invasion associated with fracturing stimulation and flowback operations fundamentally alters multiphase flow behavior in shale gas reservoirs, yet the coupled invasion–retention mechanisms and their impacts on gas transport remain insufficiently understood. In this work, an integrated experimental–numerical framework was employed to investigate permeability impairment, liquid retention mechanisms, and productivity response induced by external liquid invasion. Gas permeability experiments conducted on Longmaxi Formation shale cores under varying liquid saturation and wettability conditions demonstrated that external liquid invasion progressively reduced gas permeability with increasing liquid saturation, showing an approximately one-order-of-magnitude decline under fully liquid-saturated conditions and more severe permeability impairment under strongly water-wet conditions. Numerical simulations showed that invading liquid preferentially accumulated and remained trapped within the near-fracture matrix, where capillary forces and viscous resistance jointly suppressed liquid mobilization during flowback. This persistent liquid retention degraded gas-phase permeability and led to pronounced reductions in gas well productivity. Compared with the invasion-free case, external liquid invasion reduced the peak gas production rate by 29.0% and cumulative gas production by 16.98%. The intensity of liquid retention exhibited a clear stage-dependent evolution during reservoir development. In the early development stage characterized by low liquid saturation, capillary-driven invasion and retention of externally injected liquid resulted in substantial liquid accumulation and severe productivity impairment. In contrast, the retention intensity of invading liquid was significantly weakened during the mid-to-late development stages with higher liquid saturation. Reservoir wettability exerted a dominant control on invasion-induced retention, with stronger hydrophilicity enhancing capillary trapping and liquid film stability, thereby amplifying flow resistance and productivity loss. These findings provide a mechanistic understanding of external liquid invasion damage in shale gas reservoirs and offer quantitative insights into its evolving impact on multiphase flow and gas well productivity.

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Keywords

External liquid invasion; shale gas; multiphase flow; permeability damage; capillary trapping

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