A Comprehensive Review of RTA/DCA Methods in Unconventional Reservoirs

Rate Transient Analysis (RTA) and Decline Curve Analysis (DCA) have been utilized as critical tools in calculation of oil production for unconventional reservoirs. Due to the ultra-low permeability of these wells, time scales of flow regimes are different than those of conventional reservoirs, where transient regimes last longer, and the decline behaviors change, factors that make forecasts more challenging. There are several RTA/DCA methods for originally developed conventional and unconventional reservoirs including recent techniques. However, petroleum engineers require a single comprehensive reference where RTA/DCA methods are covered with detailed explanations, as well as an outline of their assumptions, limitations, strengths, and appropriate applications. This study tackles the lack of such a resource, delivering a comparative work that includes theory, practice, and examples. A comprehensive literature review has been carried out to investigate the RTA/DCA methods for unconventional reservoirs in detail, explore the newest techniques and the different methods repurposed from existing conventional approaches with a longer history of use, robustness, and applicability. We also provide a detailed account of the limitations and the advantages of different methods when applied to different types of fields. We achieve this by developing real field applications in different parts of the world and discussing the challenges and opportunities of each RTA/DCA method for a particular type of well. RTA/DCA methods have shown to be a practical tool for both conventional and unconventional reservoirs, and can be applied across many types of oil and gas wells throughout the world. This work shows the parameters best suited for a successful application of these recovery methods in unconventional sites. Moreover, the evidence collected here will serve as a resource for engineers looking for a summary of the most important criteria to be followed in order to apply oil recovery methods in new wells. We expect that future oil production in unconventional reservoirs can be boosted by the results provided in this work. The novelty of this study centers on the lessons drawn from the real-world applications of RTA/DCA methods like Duong's, or stretched exponential decline, to recover oil from unconventional reservoirs. We expect these lessons to define the proper utilization of distinct methods for different reservoirs in future studies and the field.