Appropriate well spacing decision is critical for unconventional asset development. Operators generally use three methods to identify optimum well spacing: trial and error, pilots, and modeling. The field trials and pilots often involve significant capital investment and require significant time before conclusive results can be observed. On the other hand, modeling is cost effective and time efficient but has large uncertainties in the results, which must be carefully calibrated with the field measurements to narrow down the uncertainty range. In this paper, these three methods are systematically integrated to study well interference and identify optimum well spacing for Wolfcamp development at Delaware basin.
First, multiple well spacing pilots are drilled and produced with various diagnostic signals collected, such as Microseismic, Bottom Hole Pressure (BHP), fluid sampling, etc. Then the general production trend analysis is performed for these pilot results combined with other available public data from the Delaware basin. After that, a well spacing trial with good quality of data is selected as the modeling target. A full-scale 3D multi-well reservoir model with geomechanical effects was built for history match of the oil, gas, water productions, and pressure. The modeling results are carefully calibrated with the field data at different time and length scales. The potential production interference of different well spacing is captured as Estimated Ultimate Recovery (EUR) reduction compared to the base case. At the same time, stochastic studies with hundreds of simulation runs are performed on a simple reservoir model to investigate the impacts of production of interference for different well spacing and subsurface parameters.
The results show that the production interference among horizontal wells have large uncertainty due to the heterogeneous subsurface parameters and the hydraulic fracturing process. The EUR reduction correlations obtained from this workflow then integrate with economic criteria (i.e. capital efficiency, Net Present Value (NPV), and cash flow) to determine the optimum well spacing.
