Theoretical and experimental study on the long-term conductivity of heterogeneous artificial fractures in tight reservoirs

Abstract

Volume fracturing technology is used to achieve economic recovery of crude oil in tight reservoirs. Then, the fluid flows into the wellbore through artificial fractures in the fractured zone, and the reservoir permeability is improved. Therefore, the study of the conductivity of artificial fractures is the key link for the fracturing development of tight reservoirs. Presently, experimental and theoretical studies on conductivity are based on a homogeneous model, which cannot reflect the nonuniform distribution of proppants in actual artificial fractures. Experiments on the long-term nonuniform sand spreading of artificial fractures in tight reservoirs are carried out in this paper with different influencing factors. Then, the influences of the matrix of proppant performance, proppant concentration, reservoir lithology, reservoir permeability and closure stress on the long-term conductivity of artificial fractures are clarified. The calculation model of the long-term conductivity of heterogeneous artificial fractures considering the reservoir characteristics, fracturing technology and reservoir characteristics is established based on the conductivity loss mechanism. Finally, the conductivity model is applied to the 7th tight reservoir block in the Ordos Basin, and the productivity prediction results are compared. The results show that the average loss of the conductivity of the heterogeneous artificial fractures is 26.6% relative to the initial state, and the loss of the conductivity is mainly at the initial stage of closure, accounting for approximately 90% at the condition of 60MPa confining pressure. The calculation accuracy of the theoretical nonuniform conductivity model is 92.2%, which can describe the continuous depression of the artificial fracture conductivity after introduction into the tight reservoir numerical simulation.