The Effects of Fracture Orientation and Elastic Property Anisotropy on Hydraulic Fracture Conductivity in the Marcellus Shale
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AbstractProduction of hydrocarbons from low-permeability shale reservoirs has become economically feasible thanks to advances in horizontal drilling and hydraulic fracturing. Together, these two techniques help to create a fracture network, which act as fluid conduits from the reservoir to the wellbore. The efficacy of a fracturing treatment can be determined through fracture conductivity analysis. Fracture conductivity is defined as the product of fracture permeability and fracture width, and describes both how much and how easily fluid can flow through fractures. It is therefore directly related to well performance.The goal of this work is to explore fracture conductivity of Marcellus shale samples fractured in both horizontal and vertical orientations. The Marcellus shale, located primarily in Pennsylvania, Ohio, West Virginia, New York, and Maryland, is the largest gas-bearing shale formation in North America, and its development has significant implications on regional economies, the energy infrastructure of northeast United States, and the availability of petrochemical plant feedstock.In this work, a series of experiments was conducted to determine the propped fracture conductivity of 23 different outcropsamples from Elimsport and Allenwood, Pennyslvania. Before conductivity measurements were taken, the pedigree of samples was verified through XRD analysis, elastic rock properties were measured and compared against literature values, and fracture surface contours were mapped and measured. Fracture conductivity of both horizontally and vertically-fracture samples was determined by measuring the pressure drop of nitrogen gas through a modified API conductivity cell.Results show that fracture conductivity varies as a function of fracture orientation only when anisotropy of the rock's mechanical properties is pronounced. It is hypothesized that the anisotropy of Young's Modulus and Poisson's Ratio play a significant role in fracture mechanics, and therefore in the width of hydraulically-induced fractures. Ultimately, the experiments conducted as part of this work show that fracture conductivity trends are strongly tied to both proppant concentration and the rock mechanical properties.
