Miscible or Near-Miscible Gas Injection, Which is Better?

Thomas, F.B.; Holowach, Nancy; Zhou, Xuelong; Bennion, D.B.; Bennion, D.W.

doi:10.2118/27811-ms

Cited by 45 publications

(22 citation statements)

References 11 publications

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“…The results presented here illustrate a pore-scale mechanism, which could partly explain the previous reports (Shyeh-Yung 1991;Burger et al 1994;Thomas et al 1994;Soroush and Saidi 1999) that near-miscible gas injection could be a very effective oil recovery mechanism. The pore-scale experimental results presented here suggest that (to benefit from this mechanism) gas floods should be either near-miscible or multiple contact miscible (MCM) where two-phase flow is still possible behind the gas front.…”

Section: Discussionsupporting

confidence: 84%

“…2D simulation studies (Burger et al 1994; Thomas et al 1994) have demonstrated that injectant with less enrichment than that required for first-contact miscible with the oil often yields optimum oil recoveries owing to better sweep efficiencies in heterogeneous reservoir models. Field-scale simulations show that near-miscible solvents are attractive because of improved sweep over miscible solvents (Pande 1992).…”

Section: Introductionmentioning

confidence: 99%

“…Burger et al (1994) showed that economically optimum enrichment in high-viscosity-ratio secondary gas floods could be operated at pressures below the MMP. Thomas et al (1994) reported that gas-oil IFT can be reduced adequately under near-miscible conditions and that zero IFT is unnecessary for effective displacement processes in realistic porous media. Shyeh-Yung (1991) demonstrated that tertiary gas flood recoveries below MMP do not decrease as severely as predicted by slim-tube tests for CO 2 .…”

Section: Introductionmentioning

confidence: 99%

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Microscopic Mechanisms of Oil Recovery By Near-Miscible Gas Injection

et al. 2007

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As gas flooding becomes a more viable means of enhanced oil recovery, it is important to identify and understand the pore-scale flow mechanisms, both for the development of improved gas flooding applications and for the predicting phase mobilisation under secondary and tertiary gas flooding. The purpose of this study was to visually investigate the pore-level mechanisms of oil recovery by near-miscible secondary and tertiary gas floods. High-pressure glass micromodels and model fluids representing a near-miscible fluid system were used for the flow experiments. A new pore-scale recovery mechanism was identified which significantly contributed to oil recovery through enhanced flow and cross-flow between the bypassed pores and the injected gas. This mechanism is strongly related to a very low gas/oil interfacial tension (IFT), perfect wetting conditions and simultaneous flow of gas and oil in the same pore, all of which occur as the gas/oil critical point is approached. The results of this study helps us to better understand the pore-scale mechanisms of oil recovery in very low-IFT (near-miscible) systems. In particular we show that in near-miscible gas floods, behind the main gas front, the recovery of the oil continues by cross-flow from the bypassed pores into the main flow stream and as a result almost all of the oil, which has been contacted by the gas, could be recovered. Our observations in high-pressure micromodel experiments have demonstrated that this mechanism can only occur in near-miscible processes (as opposed to immiscible and completely miscible processes), which makes oil displacement by near-miscible gas floods a very effective process.

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Section: Discussionsupporting

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Microscopic Mechanisms of Oil Recovery By Near-Miscible Gas Injection

et al. 2007

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“…The 2D simulation studies (Burger et al 1994; Thomas et al 1994) have demonstrated that injectant with less enrichment than that required for first-contact miscible (FCM) with the oil often yields optimum oil recoveries owing to better sweep efficiencies in heterogeneous reservoir models. Field-scale simulations show that near-miscible solvents are attractive because of improved sweep over miscible solvents (Pande 1992).…”

mentioning

confidence: 99%

Visualisation of Residual Oil Recovery by Near-miscible Gas and SWAG Injection Using High-pressure Micromodels

2008

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We present results of high-pressure micromodel visualizations of pore-scale fluid distribution and displacement mechanisms during the recovery of residual oil by nearmiscible hydrocarbon gas and SWAG (simultaneous water and gas) injection under conditions of very low gas-oil IFT (interfacial tension), negligible gravity forces and water-wet porous medium. We demonstrate that a significant amount of residual oil left behind after waterflooding can be recovered by both near-miscible gas and SWAG injection. In particular, we show that in both processes, the recovery of the contacted residual oil continues behind the main gas front and ultimately all of the oil that can be contacted by the gas will be recovered. This oil is recovered by a microscopic mechanism, which is strongly linked to the low IFT between the oil and gas and to the perfect spreading of the oil over water, both of which occur as the critical point of the gas-oil system is approached. Ultimate oil recovery by near-miscible SWAG injection was as high as near-miscible gas injection with SWAG injection using much less gas compared to gas injection. Comparison of the results of SWAG experiments with two different gas fractional flow values (SWAG ratio) of 0.5 and 0.2 shows that fractional flow of the near-miscible gas injected simultaneously with water is not a crucial factor for ultimate oil recovery. This makes SWAG injection an attractive IOR (improved oil recovery) process especially for reservoirs, where continuous and high-rate gas injection is not possible (e.g. due to supply constraint).

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“…For instance, hydrocarbon gas injection simulation both as secondary and tertiary methods showed that enrichment at or below multi-contact miscibility can yield as well or even better results than injection with more enriched gases. Thomas, Holowach, Zhou, Bennion, and Bennion (1994) concluded from simulation studies that good recoveries can be achieved by low-IFT gas injection, and in the most cases, zero-IFT conditions, which expresses a miscible process is not necessary. Using a high-pressure glass micromodel, Sohrabi, Danesh, Tehrani and Jamiolahmady (2008) also confirmed that near-miscible gas injection gives good recoveries both as a secondary recovery technique and in waterflooded of reservoirs.…”

Section: Introductionmentioning

confidence: 99%

Analytical Model for Zones Distributions in Non-Horizontal Miscible WAG Injection

Namani¹,

Kleppe²,

Høier³

et al. 2012

EER

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The advantages of WAG (water-alternating-gas) injection compared to gas injection and waterflooding, from technical and economical points of view, are results of creating a mixed zone in which both water and gas are flowing simultaneously. Previously, an analytical model was developed in the literature to evaluate complete segregation distance and zone distributions for horizontal miscible WAG injection models. Even though this analytical model is derived using simplifying assumptions, it still gives good insight into the design of new projects when the lack of data does not allow a detailed full field reservoir simulation to be carried out. On the other hand, the advantages and disadvantages of applying WAG injection in dipped reservoirs, and up-dip or down-dip patterns are still in question while there isn't any analytical model available for analyzing process in this type of reservoir. This paper develops analytical equations for a non-horizontal model and investigates the effect of dip angle on segregation effects in miscible WAG injection process. Up-dip versus down-dip WAG injection is another subject which will be discussed in this paper.

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Miscible or Near-Miscible Gas Injection, Which is Better?

Cited by 45 publications

References 11 publications

Microscopic Mechanisms of Oil Recovery By Near-Miscible Gas Injection

Microscopic Mechanisms of Oil Recovery By Near-Miscible Gas Injection

Visualisation of Residual Oil Recovery by Near-miscible Gas and SWAG Injection Using High-pressure Micromodels

Analytical Model for Zones Distributions in Non-Horizontal Miscible WAG Injection

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