The growing interest in closely spaced drilling units highlights the need to understand well performance under interference conditions in shale oil reservoirs, particularly in the Permian Basin. Over time, studies of the effect of well-completion optimization on production performance, along with studies on parent/child interference, have become more mature. The geomechanical effects of stress reduction from pressure depletion and its influence on child-well placement remain underexplored, however, and could play an important role in well planning.
This study examined this effect in the Midland Basin to demonstrate the geomechanical effects of production-induced pressure depletion on child wells at representative spacings, derived from basinwide well-spacing statistics. Additionally, the authors consider the relationship between depletion and production performance as a key factor in both early- and late-stage evaluations. They began with hydraulic-fracture-propagation simulations for two representative horizontal wells as parent wells in the Wolfcamp A (WCA) and Wolfcamp B (WCB) formations. This was followed by coupled flow and geomechanical simulations, yielding insights into changes in the principal stresses during production.
To examine whether well spacing and parent-well depletion play essential roles in the productivity of nearby new wells (child wells) over time, the authors used machine-learning methods, specifically extreme gradient boosting (XGBoost) and SHapley Additive exPlanations (SHAP), to identify critical factors across two representative time periods, using the field data and in-house geological model data.
With the knowledge of basinwide well-spacing patterns, the authors evaluated potential child-well placement strategies at various horizontal spacings and stacked placement scenarios at different times during the parent well’s production life (1 year and 5 years). Asymmetric growth behavior was quantified to indicate the effectiveness of infill-well stimulation.
The machine-learning analysis shows that, for wells completed from 2018 onward, productivity is primarily driven by well spacing and depletion, in addition to well-known productivity drivers (e.g., completion parameters and reservoir pressure). This highlights the importance of spacing and depletion effects in optimizing stimulation performance for recent tightly spaced drilling-unit development.
In addition, the coupled simulation results indicate that, for both WCA and WCB wells, fracture asymmetric growth is not obvious at 1 year of their parent wells’ production. WCA child wells show more obvious asymmetric growth characters at later time (5 years) of their parent wells’ production, suggesting earlier infill is preferred. Additionally, staggered well placement appears more beneficial for WCA child wells than for those in WCB.
This abstract is taken from paper SPE 223524 by Yiwen Gong and Timothy P. McMahon, Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin. The paper has been peer-reviewed and is available as Open Access in SPE Journal on OnePetro.
