Wolfcamp formation is the largest continuous oil and gas discovery at Permian basin as a result of the new horizontal drilling and hydraulic fracturing technology. One of the critical decisions in developing this huge resource is to optimize well spacing of the horizontal wells. Due to the heterogeneous distribution of rock properties, fluid types, uncertainties in fracture geometry, multiphase flow, operating conditions, and economic/commercial criteria, it is very challenging to get a reliable solution for optimum well spacing. Although there are more than 4,000 wells had been drilled at Wolfcamp formation in the Midland basin and Delaware basin, it is still not clear to the industry what is the optimum well spacing of long-term field development.
The well interference factor is often used as one of the key inputs for well spacing optimization. In this paper, we focus on the lateral well spacing of a single formation layer. First, the concept of WPS (Wells Per Section) is explained and the business impact of well spacing is illustrated. Then the well interferences are classified into different categories based on the temporal and spatial features. The Frac Hits and pressure interference are examined in details with field trail data and been linked with well spacing decisions.
It is found that Frac Hits can be used a good indicator of the maximum well spacing between horizontal wells. The near-term pressure interference does not necessarily mean long-term production interference. Long-term EUR reduction for different well spacing is a good choice for well spacing optimization. Different DCA parameters should be used for different well spacing during the DCA analysis process. We also found that the statistical nature of the well spacing problem requires a statistical solution to capture a range of uncertainties. Integrated statistical models are very useful to get long-term production profiles and decline trends.
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