Effect of Fracturing Fluid/Shale Rock Interaction on the Rock Physical and Mechanical Properties, the Proppant Embedment Depth and the Fracture Conductivity

An experimental study was conducted to investigate the effect of fracturing fluid/shale rock interaction on the rock physical and mechanical properties, the proppant embedment depth, and the fracture conductivity. The rich organic shale samples obtained from the Longmaxi (LMX) and Wufeng (WF) shale gas reservoirs, both located in Southern Sichuan Basin in China, were used for the experiments. The degree of proppant embedment upon rock/fluid interaction and resultant conductivity loss was directly measured in both types of rocks. Results show that the degree of alteration of the rock mechanical properties upon rock/fluid interaction depends on the mineral composition and the cementation of the shale matrix. The rock matrix cemented by clay minerals (e.g., LMX shale) was softer and more susceptible to alteration upon the rock/fluid interaction than that of the rock matrix cemented mostly by calcareous materials (e.g., WF shale). The conductivity tests carried out under 60 MPa closure stress have shown that the proppant embedment caused 47.55% reduction in the fracture conductivity of LMX shale samples with 34% clay content. While the fracture conductivity reduction due to proppant embedment was 25.94% in WF shale samples with 7% clay content. Based on the experimental results, it was concluded that upon rock/fluid interaction more significant reduction is expected in the rock physical and mechanical properties of the shale rocks with richer clay contents resulting greater proppant embedment depth and the higher fracture conductivity loss.