Evolution of multi-cluster fracturing in high-density layered shale considering the effect of injection scheme

Abstract

Shale oil reservoir is generally characterized by well-developed bedding planes, and multi-cluster fracturing is the most effective technique to achieve stable shale oil production. In this paper, a multi-cluster fracturing model for a horizontal well in shale with high-density bedding planes is established. The fracture morphology, fracture geometry, fracturing area and multiple fracture propagation mechanism are analyzed under simultaneous fracturing, sequential fracturing, and alternative fracturing. Results show that in the case of small cluster spacing and three clusters, the growth of the middle fracture is inhibited and develops along the bedding planes under both simultaneous fracturing and alternative fracturing. For sequential fracturing, the increase in the interval time between each fracturing advances the post fracturing fracture deflecting to the pre-existing fractures through the bedding planes. The reactivation of the bedding planes can promote the extension of the fracturing area. Increasing the injection rate and the number of clusters promotes the activation of bedding planes. However, it is preferable to reduce the number of clusters to obtain more main fractures. Compared with modified alternating fracturing and cyclic alternating fracturing, alternating shut-in fracturing creates more main fractures towards the direction of the maximum in-situ stress. The fracturing efficiency for high-density layered shale is ranked as simultaneous fracturing > alternative fracturing > sequential fracturing.