Abstract
Cyclic water huff and puff (CWHP) has proven to be an attractive alternative to improve oil production performance after depletion-drive recovery in fractured-vuggy carbonate reservoirs. However, due to the impact of strong heterogeneity, multiple types of fractured-vuggy medium, poor connectivity, complex flow behaviors and oil-water relationship, CWHP is merely suitable for specific types of natural fractured-vuggy medium, usually causing a great difference in actual oil-yielding effect. It remains a great challenge for accurate evaluation of CWHP adaptability and quantitative prediction of production performance in fractured-vuggy carbonate reservoir, which severely restricts the application of CWHP. For this study, we firstly enable the newly developed fuzzy grey relational analysis to quantify the adaptability of CWHP. With production history of several targeted producers, the accuracy of the proposed method is validated. Based on the traditional percolation theory and waterflood mechanisms in various types of fractured-vuggy medium, a quantitative prediction model for cyclic water cut fwp and increased recovery factor ΔR is presented. The CWHP production performance is discussed by using the Levenberg-Marquardt algorithm for history matching. With a better understanding of the fwp ~ ΔR curve characteristics in different types of fractured-vuggy medium, proper strategies or measures for potential-tapping remaining oil are provided. This methodology can also offer a good basis for engineers and geologists to develop other similar reservoirs with high efficiency.
Highlights
Cyclic water huff and puff (CWHP) has proven to be an attractive alternative to improve oil production performance after depletion-drive recovery in fractured-vuggy carbonate reservoirs
Previous studies showed that the fractured-vuggy carbonate reservoirs are largely dependent on primary depletion and natural water flooding for exploration, and the oil recovery factor is quite low with only 6.0%~8.0%10
To tackle the drawbacks of rapid production decline and low recovery rate caused by weak natural energy and sharp water cut rise, many researchers made great attempts to investigate the feasibility of cyclic water huff and puff (CWHP)[15,16], N2 stimulation[17], N2 flooding[12,18,19] and N2-based foam[20] to enhance oil recovery for fractured-vuggy carbonate reservoirs, as they believed that there should be a certain EOR method suitable for this type of reservoir
Summary
Cyclic water huff and puff (CWHP) has proven to be an attractive alternative to improve oil production performance after depletion-drive recovery in fractured-vuggy carbonate reservoirs. Due to the impact of strong heterogeneity, multiple types of fractured-vuggy medium, poor connectivity, complex flow behaviors and oil-water relationship, CWHP is merely suitable for specific types of natural fractured-vuggy medium, usually causing a great difference in actual oil-yielding effect. It remains a great challenge for accurate evaluation of CWHP adaptability and quantitative prediction of production performance in fractured-vuggy carbonate reservoir, which severely restricts the application of CWHP. How to resolve the adaptability evaluation of the CWHP and understand the actual production performance in various types of fractured-vuggy bodies in order to search suitable potential-tapping strategies or measures remain a great challenge to all of us[24,25]. Few studies used this method to study the adaptability of CWHP in fractured-vuggy carbonate reservoirs
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