Abstract

Shale oil reservoirs such as Bakken, Niobrara, and Eagle Ford have become the main target for oil and gas investors as conventional formations started to deplete and diminish in number. These reservoirs have a huge oil potential; however, the predicted primary oil recovery is still low as average of 7.5 %. Carbon dioxide (CO2) flooding has been a controversial approach to increase oil recovery in these poor-quality formations. This study investigated the effect of injector-producer spacing, in range of 925-1664 ft, on CO2 performance in these plays by using numerical simulation methods. CO2 utilization value under different injector-producer spaces has been calculated. Increments in oil production rate, cumulative oil, and oil recovery factor have been determined in 1, 5, 10 years of CO2-flooding start-point. In this study, unfractured horizontal injectors are modeled to avoid conformance problems in natural fractured unconventional formations. Furthermore, the physical behavior for CO2 flooding under different conditions has been discussed. Finally, simulation results were analyzed and compared with some of pilot tests which had been conducted in North Dakota and Southeast Saskatchewan. The results indicated that CO2 flooding performance would be more pronounced, by increasing oil production rate and oil recovery factor, as the injector-producer spacing minimized. However, CO2 utilization value is significant high when the injector-producer spacing is very short due to depleted volume closeness. Interestingly, CO2 utilization value for all spacing scenarios would gradually be reduced with flooding time. This reduction in the injected-gas utilization-value has been matched with the pilot test which performed in southeast Saskatchewan. In addition, CO2 efficiency indicator is generally in range of 4.85-44.5 Mscf/STB in these unconventional reservoirs which is relatively high as compared with conventional reservoirs. These results have been confirmed by a good match which has been obtained between simulation results and some of pilots' performance. This paper provides a thorough idea about how to optimize the injector-producer spacing for CO2 flooding in these complex plays. Also, this work explains that CO2 efficiency indicator is different in these unconventional formations as in conventional reservoirs.

Department(s)

Geosciences and Geological and Petroleum Engineering

Publication Status

Available Access

International Standard Book Number (ISBN)

978-151084198-7

Document Type

Article - Conference proceedings

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2024 Society of Petroleum Engineers, All rights reserved.

Publication Date

01 Jan 2017

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