Abstract
Economical development of unconventional resources continues demanding applications of new and innovative technologies. The Hydraulic Fracturing Test Site (HFTS-1) in the Midland Basin provides a unique dataset to further our understanding of fracture dynamics and its relationship with geomechanics. Cased hole DFIT data from three horizontal wells and open-hole micro-stress test data at four different depths from a pilot well were analyzed. Both horizontal minimum stress and reservoir pressure data obtained from these tests were used to calibrate the mechanical earth model derived from petrophysical interpretations. The calibrated mechanical earth model was used to build an unconventional fracture model (UFM) that captures both stress shadowing effects and interactions with natural fractures. Several challenges were encountered during the UFM modeling efforts. A discrete fracture network (DFN) model derived from image logs and core data was upscaled to reflect fracture complexity observed from microseismic data and adjusted to meet the UFM requirement. Stress anisotropy was another uncertainty and was estimated by comparing UFM simulation results with microseismic data. The calibrated fracture model was used to evaluate fracture treatments for over 400 stages in eleven child wells targeting two Wolfcamp formations.
Another objective of this study was to assess reservoir depletion from a geomechanics perspective. Geomechanical modeling was carried out to assess the effects of depletion around two parent wells using actual production history. Geomechanical modeling results indicated that no significant stress rotation occurred due to depletion around the two parent wells after 15 months of production. Microseismic depletion delineation patterns were observed during the restimulation of the two parent wells. At the very initial stage of restimulation, many microseismic events occurred quickly, indicating the reservoir stress reached a critical state.
This study demonstrated the values of fracture and geomechanical modeling and the importance of collaborations among multiple disciplines for unconventional development. This study presented an integrated earth-hydraulic fracture-geomechanical modeling workflow, and evaluated stimulation effectiveness and geomechanics impacts for unconventional development. Lessons learned from this study were shared in hope to provide values for future integrated modeling efforts and ultimately optimizing development strategy on well spacing and parent-child depletion effects.
