Discrete Fracture Networks (DFN's) incorporated into hydraulic fracture modeling and reservoir simulation are typically constructed and calibrated to all available high-quality natural fracture data from image logs and core, which generally results in an extremely limited calibration data set. To extrapolate these data over large areas, more broadly sampled data sets, such as discontinuity-related 3-D seismic attributes are often used. Broad spatial trending methodologies can potentially misrepresent natural fracture systems through over-reliance on seismic attributes that are commonly influenced by noise. The Hydraulic Fracture Test Site (HFTS) provides a rare insight of the subsurface natural fracture network and controlling factors on fracture distribution from a mechanical and lithological standpoint. The physical occurrence of hydraulic fractures and their interaction and relationship to preexisting natural fractures can be predicted using analytical models. Such model outputs can be applied to provide higher confidence when developing DFN's.
The Hydraulic Fracture Test Site (HFTS) is located in Reagan County, TX (Figure 1). Understanding subsurface controls and operational impacts on natural and hydraulic fracture development is a primary objective of the HFTS and the focus of this paper. It should be noted that the analytical workflow described here utilizes measured rock parameters versus fluid and other engineering parameters which vary during the completion job.
The HFTS operation involved drilling and completing 11 horizontal wells, recompleting 2 existing horizontal wells, and drilling a slant well to collect a low-angle core at 82 degrees inclination, drilled at a closest approach of 89' from an Upper Wolfcamp (UWC) well and 135' from a Middle Wolfcamp (MWC) well (Figure 2). Along with the slant core, an extensive well data set was collected, including open-hole logs, microseismic, cross-well seismic, pressure data, oil, water and proppant tracers, geochemical data (oil fingerprinting), and fiber coil production logs (Figure 3). The slant core fracture analysis consists of an integrated data set which makes up the fundamental calibration data for the analytical model discussed in this paper.
