Fracture Conductivity of the Eagle Ford Shale

Abstract

Hydraulic fracturing is a well completions technique that induces a network of flow channels in a reservoir. These channels are characterized by fracture conductivity, a measure of how easily a liquid or gas flows through the fracture. Fracture conductivity is influenced by several variables including fracture surface roughness, fracture closure stress, proppant size, and proppant concentration. The proppant concentration within a fracture can significantly affect the magnitude of fracture conductivity, which enhances the productivity of a hydraulically fractured well. Therefore, understanding the relationship between proppant concentration and fracture conductivity is critical to the successful development of unconventional reservoirs such as the Eagle Ford Shale.

This work investigates the fracture conductivities of seven Eagle Ford Shale samples collected from an outcrop of facies B. Rough fractures were induced in the samples and laboratory experiments that closely followed the API RP-61 procedure were conducted on the samples to measure the unpropped and propped conductivities. Propped experiments were performed with 30/50 mesh white sand at two different areal concentrations within the fracture, 0.1 lb/ft^(2) and 0.2 lb/ft^(2). Assuming a cubical packing arrangement, the proppant pack is calculated to be a partial monolayer of 0.8 layers at 0.1 lb/ft^(2) and a pack of 1.6 layers at 0.2 lb/ft^(2).

The results show that when the fractures are propped with 0.1 lb/ft^(2) or 0.2 lb/ft^(2), fracture conductivity values are approximately two orders of magnitude greater than unpropped conductivity values. Therefore, even low areal concentrations of proppant in a fracture can significantly enhance conductivity in the Eagle Ford Shale. Comparing the results of the two propped experiment types, conductivity values at 0.1 lb/ft^(2) proppant concentration are on average 49% higher than conductivity values at 0.2 lb/ft^(2). This difference is attributed to the partial monolayer pack at 0.1 lb/ft^(2) and proppant pack of 1.6 layers at 0.2 lb/ft^(2). However as closure stress increases from 1,000 psi to 6,000 psi, fracture conductivity at 0.2 lb/ft^(2) decreases more slowly than conductivity at 0.1 lb/ft^(2). These results suggest that the conductivity of the denser proppant pack at 0.2 lb/ft^(2) is more resistant to the flow inhibiting effects caused by proppant embedment and proppant crushing.