Integrated Investigation of CO₂-EOR Mechanisms in Huff-N-Puff Operations Based on History Matching Results


Improved Oil Recovery (IOR) techniques in Unconventional Liquids Rich Reservoirs (ULR) are still a new concept because there is no commercial project for any IOR technique so far. Carbon dioxide (CO₂) based EOR technique has been effectively applied to improve oil recovery in the tight formations of conventional reservoirs. Extending this approach to unconventional formations has been extensively investigated over the last decade because CO₂ has unique properties which make it the first option of EOR methods to be tried. However, the applications and mechanisms for CO₂-EOR in unconventional reservoirs would not necessarily be the same as in conventional reservoirs due to the complex and poor-quality properties of these plays. Since the first CO₂-EOR huff-n-puff project was conducted in conventional reservoirs in Trinidad and Tobago in 1984, more than 130 additional projects have been put in operation around the world, mainly located in USA, Turkey, and Trinidad and Tobago. In this study, we combined Decline Curve Analysis (DCA) for the production data of these projects with numerical simulation methods to produce one typical graph accounts for the main mechanisms controlling CO₂-EOR performance in conventional reservoirs. On the other hand, we have couple of CO₂-EOR huff-n-puff pilot tests conducted in Bakken formation between ₂008 and ₂016. Two engineering-reversed approaches have been integrated to produce a unique type curve for the performance of CO₂-EOR huff-n-puff process in shale oil reservoirs. Firstly, a numerical simulation study was conducted to upscale the reported experimental-studies outcomes to the field conditions. As a result, different forward diagnostic plots have been generated from different combinations for CO₂ physical mechanisms with different shale-reservoirs conditions. Secondly, different backward diagnostic plots have been produced from the history match with CO₂ performances in fields' pilots performed in some portions of Bakken formation located in North Dakota and Montana. Finally, fitting the backward with the forward diagnostic plots was used to produce another unique type curve to represent CO₂-EOR performance in shale oil reservoirs. This study found that the delayed response in the incremental oil production resulted from CO₂ injection in shale reservoirs is mainly function of CO₂ molecular diffusion mechanism. On the other hand, the CO₂ diffusion mechanism has approximately no effect on CO₂-EOR performance in conventional reservoirs which have a quick response to CO₂ injection. This finding is very well consistent with the experimental reports regarding the role of diffusion in conventional cores versus shale cores. In addition, this study found that kinetics of oil recovery process in productive areas and CO₂-diffusivity level are the keys to perform successful CO₂-EOR project in shale formations. This paper provides a thorough idea about how CO₂-EOR performance is different in the field scale of conventional reservoirs versus shale formations.

Meeting Name

SPE Improved Oil Recovery Conference 2018 (2018: Apr. 14-18, Tulsa, OK)


Geosciences and Geological and Petroleum Engineering

Keywords and Phrases

Carbon dioxide; Curve fitting; Diffusion; Numerical methods; Numerical models; Oil fields; Oil shale; Petroleum reservoir engineering; Petroleum reservoirs; Shale; Shale oil, Decline curve analysis; Diffusion mechanisms; Improve oil recovery; Improved oil recovery; Numerical simulation method; Numerical simulation studies; Oil recovery process; Unconventional reservoirs, Enhanced recovery

Document Type

Article - Conference proceedings

Document Version


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© 2018 Society of Petroleum Engineers (SPE), All rights reserved.

Publication Date

01 Apr 2018

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