Numerical Study of Fishbone Multi-Lateral Well Fracturing in the Deep Coalbed Methane Reservoir

ABSTRACT: Multi-stage hydraulic fracturing of horizontal wells is an important reservoir stimulation method for efficient CBM development, and multi-lateral wells have certain advantages in improving the productivity of a single well. However, there are few studies on fracturing of fishbone multi-lateral wells. Petrel-Kinetix is used for numerical simulation to explore the influence of three factors on fracturing of fishbone multi-lateral wells: the Angle between the branch well and the main hole, the Angle between the main hole and the in-situ stress, and the number of clusters. The results show that the SRA changes with the angle between branch wells and the main wellbore, and there would be an optimal angle, and there exists a minimum SRA between 0 and 90 degrees and the maximum SRA was achieved when the main wellbore was along the maximum horizontal principal stress. The SRA increases with the number of perforation clusters. But after 7 clusters, the SRA decreased with increasing number of clusters. This study may be helpful to the application of fishbone multi-lateral well fracturing and the optimization design of well type and fracturing parameters. 1. INTRODUCTION As a high-quality unconventional energy source, the demand for CBM (coalbed methane) is on the rise (Wen et al., 2019). China's CBM reservoirs are characterized by low permeability and low pressure, and the permeability and other physical properties of deep CBM reservoirs are even worse. Hydraulic fracturing is an important means of reservoir modification to increase production, which can significantly increase the production capacity of a single well (Yu et al., 2019). The fracturing process of coalbed methane is still mainly based on conventional multi-stage fracturing of horizontal wells. A large number of fracturing process technology studies and fracturing numerical simulation studies have supported the efficient development of CBM. Zhang Juntao et al. proposed a fracturing technology suitable for deep-seated CBM in the Yanchang block, including the fracturing fluid optimization technology mated with the formation as well as the CBM fracturing process technology consisting of large-displacement fracturing technology, low-sand-ratio fracturing technology, pulse-added-sand technology, and composite-support technology (Zhang et al.,2015). Fang et al. took the NY1 well of Longtan Formation coal seam in southeast area as an example, and completed the fracturing of the well by optimizing the fracturing process, based on the system of drag-reducing water fracturing fluid, and in accordance with the technological ideas of large-displacement, low-sand-ratio, segmented plugging, and composite sand-adding with different grain sizes. The operation pressure was smooth in the process of fracturing of the NY1 well without sand plugging phenomenon, and a high production rate was achieved (Fang et al., 2022). Li et al. used gray correlation method to carry out sensitivity analysis on the capacity of coalbed methane wells after acid pressure in Daning-Jixian block, and the results showed that the influence of acid pressure construction factors on the capacity was higher than that of geological factors and drainage factors. And they proposed to use low density and low particle size proppant to improve the proppant transportation distance and proppant fracture length (Li et al., 2022). Pu et al. analyzed the applicability of temporary plugging and fracturing technology and the development law of hydraulic fractures under the condition of high stress level by numerical simulation, and the results showed that the presence of coal is favorable to the growth of hydraulic fractures, especially under the condition of low stress difference and low stress level. The effectiveness of temporary plugging and fracturing technology in deep coal seams is weaker than that in shallow coal seams (Pu et al.,2023). Zhao et al. analyzed the influence of cluster spacing of hydraulic fracturing on the gas production effect of horizontal wells through numerical simulation software, and the simulation results showed that the cluster spacing of 60∼80 m for multi-stage fracturing in horizontal wells of No.6 coal seam in Shizuishan mining area was more appropriate (Zhao et al., 2024).