Experimental study on conductivity and stress sensitivity of fully supported fractured shale cores

Abstract

Proppants are often used in hydraulic fracturing to prevent fracture closure. However, there are few studies on the mechanism of proppant placement on the conductivity of fully supported fractures and the stress sensitivity of the conductivity under cyclic loading by using shale split cores. In this study, the Brazilian splitting method was used to simulate the reservoir fractures after hydraulic fracturing in the cylindrical shale cores of Shengli Oilfield. Then, different types of proppants with different particle sizes and fluids with different viscosity were selected to test the stress sensitivity and conductivity of fully supported fractures under cyclic loading. The results reveal that the selection of proppants with a large particle size and the adoption of the sand paving method with a high particle concentration will increase the conductivity of fractures. In the experimental test range, the fracture conductivity of 40–60 mesh quartz sand was one order of magnitude higher than that of 60–100 mesh quartz sand. The fracture conductivity of the two magnitude orders was higher than that of 100–200 mesh quartz sand. The conductivity of the large-sized proppant placed at the front end of fractures was 6.21 times higher than that of hybrid placement. Under cyclic loading, irreversible damage to the conductivity of fully supported fractures is mainly caused by the concave embedding, fracture, sliding of proppants, and the adsorption retention of fracturing fluids. Under the influence of multiple factors, the fracture conductivity has a linear relationship with the change of confining pressure. This study can provide a reference for improving the conductivity of fully supported fractures and the variation of conductivity under cyclic loading.