Most current hydraulic fracturing operations are performed in unconventional reservoirs (i.e., tight gas and oil reservoirs and organic-rich shale plays) that have sub-microdarcy permeability and require stimulation to achieve commercial flow. Hydraulic fracturing helps unlock these reservoirs by creating a fracture network to access the resources. This paper evaluates the mechanism by which a nonuniform partial monolayer of small-sized proppants with particle sizes much less than 100 mesh can significantly enhance the conductivity of the complex microfracture (MF) network.
To evaluate smaller proppant particles, a new test design was used to measure fracture conductivity of unpropped MFs and MFs propped with extremely small quantities of ultra-fine particulates (UFPs) on outcrop samples from Marcellus, Eagle Ford, and Barnett Shale formations, including an actual Delaware Wolfcamp core. Geomechanical testing on formation samples determined their mechanical properties, UFP distribution along the created fracture faces before and after UFP treatment was studied using computed tomography (CT) scans, and X-ray diffraction quantitatively assessed reservoir rock mineralogy to identify potential rock-fluid interactions that could affect longterm conductivity.
This study evaluates the impact of effective stress on the created MF permeability, helping understand the influence of UFPs on long-term MF conductivity. Additionally, the effective conductivity is influenced by the UFP concentration, core mineralogy, and sample anisotropy of the outcrop cores used for this study.
Field applications of UFP materials have proven to be successful with increasing well productivity and sustaining higher productivity over a significantly longer period of time. This experimental study demonstrates the impact of small quantities of extremely small proppant materials on the effective conductivity of MFs created during hydraulic fracturing operations. The improved conductivity observed during these tests clearly demonstrates that these materials can increase the effective permeability of the formation surrounding primary hydraulic fractures.
This paper provides summarized test results and computer simulation to establish well productivity effects. The experimental results are compared to actual well productions to validate the study.
