To hydraulically fracture a well requires large investments in equipment, horsepower, materials and manpower. An engineer can be overwhelmed with the selection of completion fluids, perforation strategy and treatment size, as well as coordination of frac crews. In the end, however, the primary characteristic of the treatment that provides any economic benefit is a conductive fracture that economically increases well production.
Although the primary goal of a hydraulic fracture is to create a highly conductive flowpath, it is often the most poorly understood parameter in the treatment, with pressure transient and rate transient testing frequently indicating disappointingly short fractures of limited conductivity. In order to design an optimized fracture treatment, it is imperative that numerous factors be understood, including proppant embedment, formation spalling, temperature degradation, conductivity loss over time, non-Darcy flow, multiphase flow, non-uniform proppant distribution, cyclic stress, gel damage, fines migration, and other effects.
This paper introduces many of these factors and describes their individual impacts on fluid flow within propped hydraulic fractures. It will also demonstrate the cumulative effect of many of these factors upon fracture conductivity and calculate the corresponding impact on well performance. A fracture treatment optimized to accommodate these damage factors will be shown to differ dramatically from treatments in which these phenomena were ignored.
The authors present field data demonstrating that these effects are not only real, but can substantially impact well productivity. A field study in which the operator intentionally designed fractures to better accommodate these effects will be shown to significantly improve conductivity and fracture half length, as well as production and profitability. Readers of this paper will be armed with a more realistic view of fracture conductivity and fluid flow within propped fractures which, when incorporated into fracture designs, will yield more optimal fracture stimulations, improved production rates, and superior economic returns.