Rate-Transient Analysis Based on the Power-Law Behavior for Permian Wells
- Wei-Chun Chu (Pioneer Natural Resources) | Nimish D. Pandya (Pioneer Natural Resources) | Ray W. Flumerfelt (Pioneer Natural Resources) | Chih Chen (Kappa Engineering)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- July 2019
- Document Type
- Journal Paper
- 2019.Society of Petroleum Engineers
- Chow pressure group, decline curve analysis, power-law behavior, rate-transient analysis, anomalous diffusion
- 20 in the last 30 days
- 109 since 2007
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In unconventional reservoirs, the application of many rate-transient-analysis (RTA) techniques relies heavily on the identification and analysis of the linear flow regime, which is characterized by a ½-slope on a log-log plot of Δp vs. t. Through our analysis of more than 400 wells with downhole pressure gauges in the Wolfcamp Shale of the Permian Basin, we observed power-law behavior, but with slopes much different from ½ over long periods of time. In many cases, the duration of the straight line with a slope different from ½ lasts for years, without ever converging to ½. In some cases, the slope changes over time but is rarely the characteristic ½-slope observed over long periods. Rate forecasts would be in error if we were to assume that the slope would converge to a ½-slope at a later time.
In this work, we present examples of Permian Wolfcamp horizontal wells each with a measured bottomhole pressure (BHP) to demonstrate the characteristic power-law behavior with slopes different from ½. Power-law behaviors are typical in heterogeneous systems and are identified using the Chow pressure group (CPG).
On the basis of the concept of power-law behavior, we developed a workflow to analyze single-phase rate-transient data with highquality measured BHP. Ultimately, the new workflow for RTA uses power-law characteristics to evaluate well performance and is a complementary tool to traditional methods such as the Arps decline-curve analysis (Arps 1945). In this paper, we outline a power-law analysis workflow scheme and demonstrate that the CPG is a convenient means for identifying the exponents of straight lines. In addition, we present case studies to demonstrate the application of this technique to predict the long-term well performance from choked-back wells, to evaluate long-term performance changes associated with offset fracture hits, and to estimate the hyperbolic-decline-curve b-factor.
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