The influence of fracture surface morphology on propped fracture conductivity in tight sandstone reservoir

Abstract

The investigation on the influence of fracture morphology on conductivity mainly focuses on the research of non-propped fracture conductivity. Few studies, however, have addressed the relationship between fracture surface characteristics and propped fracture conductivity. In this paper, by defining the maximum volume capacity of the fracture surface (VMF), according to the size relationship between the filling volume of proppants and VMF, the distribution state of proppants in propped fractures are divided into four modes, which can reflect the distribution state of proppant particle at different positions of the same fracture or different proppant concentrations in the rough surface fractures. Taking rough-surface rock samples and smooth-surface rock samples from tight sandstone reservoirs as experimental materials, a series of propped fracture conductivity tests in four modes are designed, supplemented by a various of methods such as refined characterization of three-dimensional roughness parameters of fracture surface and evaluation of proppant breakage rate. The influence of fracture morphology on the conductivity of propped fractures is systematically studied. The results show that the influence of fracture morphology on the conductivity of propped fractures varies with the distribution modes, which is closely correlated with the filling state and volume proppant filled in fractures. The influence of fracture morphology on the fracture conductivity in different distribution modes is revealed. Especially under the condition of multi-layer proppants, a new damage mechanism of fracture conductivity caused by fracture surface morphology is proposed, which is defined the “Retention Effect” of proppant particles caused by fracture surface morphology. The damage degree of this effect is characterized by defining “Damage Index of Fracture Conductivity on Rough Surface” (RFCI), which can quantitatively and accurately describe the damage degree of propped fracture conductivity caused by fracture surface morphology. The research results of this paper are helpful to understand the effect of fracture surface morphology on the conductivity of propped fractures, and also help to establish a laboratory model of the conductivity of rough fractures.