Statistics and Case Studies of Drainage Frac Height and Zonal Contribution of Stacked Plays in the Midland and Uinta Basin

Abstract

Abstract In this study, we present statistics of the drainage behavior of 387 wells in the Midland and Uinta Basins, including drainage frac height (DFH), zonal contribution, and their variation throughout the life of the well. Case studies from both basins will also be presented to demonstrate how drainage information is utilized to achieve improved reservoir economics. A geochemistry-based method is used to quantitatively monitor drainage evolution and zonal contribution, and their variation through time. Produced oils are correlated to their contributing intervals represented by rock samples, allowing for a detailed quantitative analysis of the drainage behavior of the well. Statistical analysis is conducted on the production allocation results of 387 wells to evaluate their drainage behaviors. The study also leverages key reservoir properties derived from geochemistry using Reservoir Characterization Indices (RCI) to provide insights into drivers of the drainage behavior observed. In the Midland Basin, 90% of the P80 DFH (drainage frac height that covers 80% of production) falls between ~155’ to 400’, with a median of ~290’. In the Uinta Basin, it falls between ~80’ to 305’ with a median of ~210’. To evaluate the effectiveness of reservoir recovery, we also analyzed how much contribution is from outside the targeted interval, or "out-of-zone", vs. contribution from inside the targeted interval, or "in-zone" contribution. In the Midland Basin, the median "in-zone" contribution ranges from 65% to 100% for wells targeting Middle Spraberry through Wolfcamp. In the Uinta Basin, it ranges from 43% to 80% for wells targeting Castle Peak through Wasatch. Without considering the total reservoir thickness, the richness of geological zones in the Uinta Basin could be comparable to or even better than some of the zones in the Midland Basin based on the production contribution per 10 feet of thickness (PCPT). The Midland case presents that co-development wells show as much as 70% larger P80 DFH than parent wells. The staggered co-development approach outperforms stacked co-developed scenarios, having ~32% more contribution from superior reservoirs than other development scenarios. The Uinta Basin study compares cube-developed wells to individually developed wells. A significant observation is that ~40% of cube-developed wells exhibit a noticeable drainage change (>20’), in contrast to only ~30% of individually developed wells, suggesting cube-developed wells effectively create SRV across the stacked reservoirs without overcrowding wells. The study presents novel information about drainage behaviors and provides quantitative data for regional assessments and benchmarking in the Midland and Uinta Basin.