Fines Migration in Shale Fractures During Reactive Transport

Abstract:

Shales are ultrafine-grained rocks with a broad variety of mineralogy and reactivity, exhibiting structural and chemical features over a wide range of length scales. To commercially produce hydrocarbon resources from these materials, a high-pressure particle-laden low-pH stimulation fluid is injected that opens and connects flow conduits through the rock. Among the physicochemical interactions between the shale rock and these reactive fluids, fine-grained, chemically recalcitrant particles are commonly produced due to multiple factors, including but not limited to matrix dissolution, clay dispersion, fracture surface spalling, and proppant failure. This particulate movement is highly dependent on the shale surface minerals and the fluids interacting with them. The generated fines can subsequently occlude fluid flow pathways by surface deposition and size exclusion, leading to diminished fracture conductivity.

Here we generate a synthetic fracture, by conducting a Brazilian test, in an Eagle Ford shale core plug and subject it to reactive transport using an acidic brine. The pressure drop across the core plug is continuously logged and a high-resolution micro-CT scan is conducted before and after the reactive flood. This two-tiered approach tracks the resulting change in fracture conductivity and topography. The effluent fluid is continuously collected, and time series analysis of the fluid chemistry is performed. We use these data to determine the extent to which fines migration plays an important role in the evolution of shale fracture surface with time during exposure to low-pH fluid used in hydraulic fracturing operations.