Experimental study of interference and competition mechanism of multi-cluster fractures in hydrate-bearing sediments

Abstract

During the stimulation of hydrate-bearing sediment reservoirs, multi-cluster hydraulic fracturing has demonstrated superior stimulation effects and enhanced gas production rates compared to single-cluster hydraulic fracturing by establishing artificial fracture networks. However, due to limitations in experimental equipment, research on the mechanisms of interference and competition among multi-cluster fractures in hydrate-bearing sediments has predominantly relied on numerical simulations, with experimental studies being nearly non-existent. To address this gap, this paper presents the independent development of a multi-cluster fracturing experimental system specifically designed for hydrate-bearing sediments, and conducts a series of multi-cluster hydraulic fracturing experiments. The study investigates the influences of hydrate saturation, initial stress state, injection rate, and clay mineral type on the competition and interference mechanisms among multi-cluster fractures. The results indicate that a slight increase in hydrate saturation creates a favorable environment for fracture development, reduces fluid loss in upper fractures, and significantly enhances the energy available for the development of the second cluster, thereby improving fracture quality. However, further increases in hydrate saturation result in the preferential allocation of fluid for the development of the first cluster, forming a dominant pathway and complicating the initiation of the second cluster. Under low injection rate conditions, both clusters initiate, albeit with average fracture quality. An increase in the injection rate intensifies competition among fractures, leading to improved quality of upper fractures that tend to propagate along the path of least resistance, thereby placing the second cluster at a disadvantage in the competition.