Influence of gravel content and cement on conglomerate fracture

Abstract

Tight reservoirs are typically developed by horizontal wells and multi-stage hydraulic fracturing. The conglomerate reservoir is one type of tight reservoirs, which is different from homogeneous rock, such as tight sandstone. This is because that the existence of gravels makes conglomerate have strong heterogeneity. Thus, it is difficult to grasp the fracture mechanism and the law of fracture propagation of conglomerate, which limits the efficient development of the conglomerate reservoir. In this paper, the fracture characteristics and factors influencing the fracturing of Mahu conglomerate were studied by uniaxial compression, acoustic emission monitoring and X-ray computed tomography (CT) scanning experiments. The results show that the fracture characteristics of conglomerates are influenced by the gravel content and cement. The conglomerate in the study area is mainly divided into carbonate cemented conglomerate and clay cemented conglomerate. The fracture complexity of carbonate cemented conglomerate first increases and then decreases with increasing gravel content. However, for clay cemented conglomerates, the fracture complexity increases over the gravel content. The crack development stress is a significant parameter in the crack assessment of conglomerates. This study is useful to understand the influence of meso-fabric characteristics of conglomerates on their fracturing and crack evolution and guides the design of hydraulic fracturing.