Open Access

ARTICLE

Analysis of Hydraulic Fracture Network Morphology in Stimulated Coal Reservoirs with Pre-Existing Natural Fractures

Weiping Ouyang^1,2, Luoyi Huang^3,*, Jinghua Liu^3,*, Hongzhong Zhang^1,2

1 National Engineering Laboratory for Exploration and Development of Low-Permeability Oil and Gas Fields, CNPC Chuanqing Drilling Engineering Company Limited, Xi’an, 710018, China
2 Changqing Downhole Technology Company, CNPC Chuanqing Drilling Engineering Company Limited, Xi’an, 710018, China
3 School of Petroleum Engineering, Yangtze University, Wuhan, 430100, China

* Corresponding Authors: Luoyi Huang. Email: ; Jinghua Liu. Email:

(This article belongs to the Special Issue: Integrated Geology-Engineering Simulation and Optimizationfor Unconventional Oil and Gas Reservoirs)

Energy Engineering 2025, 122(4), 1491-1509. https://doi.org/10.32604/ee.2025.061171

Received 18 November 2024; Accepted 06 February 2025; Issue published 31 March 2025

Abstract

Hydraulic fracturing is a crucial technique for efficient development of coal reservoirs. Coal rocks typically contain a high density of natural fractures, which serve as conduits for fracturing fluid. Upon injection, the fluid infiltrates these natural fractures and leaks out, resulting in complex fracture morphology. The prediction of hydraulic fracture network propagation for coal reservoirs has important practical significance for evaluating hydraulic fracturing. This study proposes a novel inversion method for predicting fracture networks in coal reservoirs, explicitly considering the distribution of natural fractures. The method incorporates three distinct natural fracture opening modes and employs a fractal probability function to constrain fracture propagation morphology. Based on this method, the study compares hydraulic fracture network morphologies in coal reservoirs with and without the presence of natural fractures. The results show that while both reservoir types exhibit multi-branch fracture networks, reservoirs containing natural fractures demonstrate greater branching and a larger stimulated reservoir volume (SRV). Additionally, the study employs a fractal dimension calculation method to quantitatively describe the geometric distribution characteristics of fractures. The analysis reveals that the geometry and distribution of natural fractures, as well as reservoir geological parameters, significantly influence the fracture network morphology and fractal dimension. The contact angle between natural and hydraulic fractures affects propagation direction; specifically, when the contact angle is π/2, the fractal dimension of the hydraulic fracture network is maximized. Moreover, smaller lengths and spacings of natural fracture led to higher fractal dimensions, which can significantly increase the SRV. The proposed method offers an effective tool for evaluating the hydraulic fracturing of coal reservoirs.

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Keywords

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