Multi-round diverting fracturing technology for deep-seated thin coal seams and its application: A case study of the G3-1 well group in the Yichuan block, Ordos Basin

Authors

• LI Shuguang, PetroChina Coalbed Methane Company Limited, Beijing 100028, China; China United Coalbed Methane National Engineering Research Center Co., Ltd., Beijing 100095, ChinaFollow
• NIE Zhihong, PetroChina Coalbed Methane Company Limited, Beijing 100028, ChinaFollow
• JI Liang, PetroChina Coalbed Methane Company Limited, Beijing 100028, China
• ZHOU Changhui, PetroChina Coalbed Methane Company Limited, Beijing 100028, China
• BAI Kunsen, China United Coalbed Methane National Engineering Research Center Co., Ltd., Beijing 100095, China
• HUANG Li, China United Coalbed Methane National Engineering Research Center Co., Ltd., Beijing 100095, China
• ZHEN Huaibin, PetroChina Coalbed Methane Company Limited, Beijing 100028, China; China United Coalbed Methane National Engineering Research Center Co., Ltd., Beijing 100095, China
• XING Xuejie, PetroChina Coalbed Methane Company Limited, Beijing 100028, China
• ZHAO Haifeng, College of Petroleum Engineering, China University of Petroleum (Beijing), Beijing 102249, China

Abstract

Objective Deep coal seams in the Yichuan block of the Ordos Basin are characterized by small thicknesses, vertical multi-layer superimposition, and strong vertical and horizontal heterogeneities. When used to develop these coal seams, multi-stage horizontal well fracturing faces challenges such as uneven fracture propagation across various stages in the horizontal direction and a low production degree of multiple coal seams in the vertical direction, complicating commercial exploitation. To address these issues, this study proposes a multi-round diverting fracturing technology based on a vertical cluster well group. In this technology, vertical layered fracturing using vertical cluster wells is employed to achieve the commingled exploitation of multiple layers; intra-layer multi-round fracturing facilitates fracture network diversion to form uniform and dense fracture networks, while the well factory pattern of the well group contributes to expanded fracture network coverage, reduced costs, and enhanced efficiency. Methods This study investigated the G3-1 well group in the Yichuan block. Using fluid-solid coupling and the iteration of fracture propagation dynamics, multiple parameters, including pore pressure, induced stress, and fracture geometry, were updated in each fracturing round, with the stress field evolution, fracture diversion, and inter-well fracture network propagation patterns during multi-round fracturing being analyzed. Based on this, multiple parameters were optimized, encompassing well and row spacings, fracturing fluid combination, proppant ratio, fracturing sequence, and pump-off time between two adjacent fracturing rounds. Consequently, a reservoir stimulation scheme was developed. This scheme, with the synergistic fracturing of a vertical cluster well group as the core, facilitates uniform inter-well fracture propagation horizontally and enhances the joint production of multiple coal seams vertically. Results Field application results indicate that after multi-round synergistic fracturing using a diamond-shaped well pattern with a well spacing of 400 m and a row spacing of 200 m, the fracture length and stimulated reservoir volume (SRV) of the No. 8 coal seam increased from 320 m in the first round to 480 m and from 15.0 × 10⁴ m³ to 36.6 × 10⁴ m³, respectively. In contrast, the No. 5 coal seam exhibited an average fracture length of 412 m and an average SRV of 13.9 × 10⁴ m³ in various fracturing rounds. The SRV utilization rate of the G3-1 well group increased from 65% to 89%. Compared to wells subjected to conventional single-round fracturing in adjacent areas, the cumulative gas production of the well group increased by 42%. Conclusions The dynamic stress induced by multi-round fracturing can alter the subsequent fracture propagation direction. This promotes the interconnection of fractures created in different fracturing rounds across varying coal seams and wells, thereby enhancing both the coverage of inter-well fracture networks and effective SRV. For deep-seated thin coal seams and strongly heterogeneous blocks, it is advisable to comprehensively determine well pattern deployment, fracturing sequence, and the interval between two fracturing rounds based on the dynamic evolution of in situ stress. Furthermore, subsequent fracturing parameters should be adjusted in time as per the fracture propagation results of previous rounds. These efforts will help transform local reservoir stimulation via a single well into overall synergistic stimulation using a well group. The results of this study will provide a reference for the development of blocks with multiple thin coal seams.

Keywords

deep-seated thin coal seam, vertical-clustered well group, synergistic fracturing, multi-round fracturing, fracturing parameter optimization

DOI

10.12363/issn.1001-1986.26.04.0220

Recommended Citation

LI Shuguang, NIE Zhihong, JI Liang, et al. (2026) "Multi-round diverting fracturing technology for deep-seated thin coal seams and its application: A case study of the G3-1 well group in the Yichuan block, Ordos Basin," Coal Geology & Exploration: Vol. 54: Iss. 9, Article 17.
DOI: 10.12363/issn.1001-1986.26.04.0220
Available at: https://cge.researchcommons.org/journal/vol54/iss9/17

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