Lateral targeting, well spacing, and completion design are three controllable variables of production for unconventional wells. Achieving the right balance between these variables results in wellbore configurations that minimize hydraulic fracture overlap, create enough fracture surface area to drain targeted reservoirs effectively, with minimal capital investment. Many operators have recently turned to eXtreme Limited Entry (XLE) Plug and Perf (P&P) as a method to increase the number of perforation clusters (i.e., fractures) while maintaining efficient proppant and fluid delivery. To achieve XLE, operators must vary perforation hole size, pump rate, and the number of holes to achieve higher perforation entry pressures. The planned result is high cluster efficiency, even in stages with a high number of clusters. By increasing clusters per stage and achieving high cluster efficiency, operators can effectively stimulate unconventional wells with fewer stages, thus reducing the amount of time and capital it takes to complete a well.
This paper presents a case study of the successful implementation of XLE with interdisciplinary evaluation and validation. The case study resulted in significant improvements and cost reductions in the completion designs. XLE was implemented on two batches in Williston Basin, ND. Both batches consist of Three Forks (TF) and Middle Bakken (MB) wells in a wine-rack pattern. The number of clusters per stage was varied from 6 to 15 to test variable cluster efficiency using XLE. Carbon fiber rod deployed fiber optics data (DAS and DTS), downhole camera surveillance, step-down tests, and radioactive (RA) proppant tracers were collected and integrated with the geological targeting data and daily fluid production rates for three of the wells (1 MB, 2 TF) to validate the efficiency of high cluster XLE stages.
Pump pressures and step-down tests confirm that the high perforation entry pressures required for XLE were achieved for all stages. RA tracer and DAS/DTS data indicate that 85–95% cluster efficiency is achieved using XLE, even in the higher cluster count stages. High cluster efficiency appears to be independent of the geologic target in both MB and TF wells. However, a slightly lower efficiency was achieved in stages that were completed within the TF interbedded unit. A minor heel-to-toe bias was observed in the DAS/DTS data. This was confirmed by the downhole camera data showing more perforation erosion in heel-ward perforations compared to toe-ward perforations.
The use of multidisciplinary data gathering and integration resulted in significant improvements to completion designs, confirming that XLE yielded high cluster efficiencies regardless of the geologic target, even with a large number of clusters (15 clusters per stage). By increasing clusters per stage, the operator is now able to complete wells with fewer stages, resulting in shorter operational time and reduced cost, while maintaining or increasing production. This paper presents a comprehensive evaluation of completion diagnostic measurements and the subsequent integration of these measurements with detailed geologic characterizations and "stage level" well performance evaluation. This multidisciplinary approach resulted in more reliable completion optimization decisions and a shorter cycle time from measurement to implementation.