On the Mechanisms of Mobilization of Residual Oil Left After Waterflooding

Bidner, M.S.; Savioli, G.B.

doi:10.2523/81019-ms

Proceedings of SPE Latin American and Caribbean Petroleum Engineering Conference 2003

DOI: 10.2523/81019-ms

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On the Mechanisms of Mobilization of Residual Oil Left After Waterflooding

M.S. Bidner¹,

G.B. Savioli²

Abstract: TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractTo mobilize the oil trapped after secondary recovery by waterflooding, chemicals (surfactants, alcohols, alkalis, etc.) are injected into the reservoir. Chemical flooding has two main effects: 1) the interfacial tension between oil and water phases is decreased, and 2) these phases become partially miscible. A numerical model is proposed to analyze those effects on oil recovery.

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Cited by 2 publications

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The Impact of Gravity Segregation on Multiphase Non-Darcy Flow in Hydraulically Fractured Gas Wells

Dickins

McVay

Schubarth³

2008

SPE Annual Technical Conference and Exhibition

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Multiphase and non-Darcy flow effects in hydraulically fractured gas wells reduce effective fracture conductivity. Typical proppant pack laboratory experiments are oriented in such a way such that phase segregation is not possible, which results in mixed flow. Tidwell and Parker (1996), however, showed that in proppant packs, gravity segregation occurs for simultaneous gas and liquid injection at laboratory scale (1500 cm 2 ). Although the impact of gravity on flow in natural fractures has been described, previous work has not fully described the effect of gravity on multiphase non-Darcy flow in hydraulic fractures. In this work, reservoir simulation modeling was used to determine the extent and impact of gravity segregation in a hydraulic fracture at field scale. I found that by ignoring segregation, effective fracture conductivity can be underestimated by up to a factor of two.An analytical solution was developed for uniform flux of water and gas into the fracture.The solution for pressures and saturations in the fracture agrees well with reservoir simulation. Gravity segregation occurs in moderate-to-high conductivity fractures.iv Gravity segregation impacts effective fracture conductivity when gas and liquid are being produced at all water-gas ratios modeled above 2 Bbls per MMscf. More realistic, non-uniform-flux models were also run with the hydraulic fracture connected to a gas reservoir producing water. For constant-gas-rate production, differences in pressure drop between segregated cases and mixed flow cases range up to a factor of two. As the pressure gradient in the fracture increases above 1 to 2 psi/ft, the amount of segregation decreases. Segregation is also less for fracture half-length-to-height ratios less than or close to two. When there is less segregation, the difference in effective conductivity between the segregated and mixed flow cases is reduced. I also modeled the water injection and cleanup phases for a typical slickwater fracture treatment both with and without gravity effects and found that for cases with segregation, effective fracture conductivity is significantly higher than the conductivity when mixed flow occurs.Gravity segregation is commonly ignored in design and analysis of hydraulically fractured gas wells. This work shows that segregation is an important physical process and it affects effective fracture conductivity significantly. Hydraulic fracture treatments can be designed more effectively if effective fracture conductivity is known more accurately.v ACKNOWLEDGEMENTS

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The Impact of Gravity Segregation on Multiphase Non-Darcy Flow in Hydraulically Fractured Gas Wells

Dickins

McVay

Schubarth³

2008

SPE Annual Technical Conference and Exhibition

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Molecular Diffusion of CO2 From Carbonated Water (CW) Into the Oil – Experimental Observations

Pęksa

Wolf

Zitha

2013

SPE Asia Pacific Oil and Gas Conference and Exhibition

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Carbonated Water Flooding (CWF), an alternative enhanced oil recovery (EOR) method in which an oil reservoir is flooded with CO2-enriched water, can be considered as a promising solution for mobilization and recovery of residual oil in water wet rock. At the same time it is a possible mitigation option for an increasing CO2 concentration in the atmosphere and an opportunity for permanent and safe disposal of CO2 underground. One of the important aspects of the CWF process is molecular diffusion of CO2 from carbonated water into oil (DCWO). The process benefits from oil viscosity reduction, an increase in oil relative permeability and, as a result, enhancement of oil mobility. In contrast to many previous studies on the diffusion of carbon dioxide directly into oil by CO2 flooding, DCWO characterization is underexposed in laboratory work and literature. In order to understand the distribution of the total dissolved CO2 between the coexisting phases water and oil, we examine DCWO in experiments by visualization of oil swelling and recovery over time. To determine the phase behavior of the system, pore-scale diffusion experiments are conducted. In these experiments oil is initially placed in a dead-end pore and covered with water presumed to be from the first secondary recovery phase. Swelling of oil due to CO2 diffusion from a CO2 source, either a CW stream or a pure CO2 stream under P, T-conditions, have been recorded and visualized over time. As a result, pressure and oil-composition dependent, recovery of oil occurs. Based on the results we determined a dominant role of diffusion in the CW recovery process. Existence of ample contact time for water rupture was obtained. In the pore scale water barrier, its geometry (especially – the interfacial area) appears to be a limiting factor. At field scale, time in the range of hours does not play an important role in the overall recovery; however it is of importance for near well injection area. The results and visualizations of the conducted experiments will contribute to a better understanding of processes such as molecular diffusion in CWF, which will occur. In addition, DCWO results lead to process improvements for achieving recovery in both laboratory core floods and in the field, with an option for CO2 sequestration.

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On the Mechanisms of Mobilization of Residual Oil Left After Waterflooding

Cited by 2 publications

References 18 publications

The Impact of Gravity Segregation on Multiphase Non-Darcy Flow in Hydraulically Fractured Gas Wells

The Impact of Gravity Segregation on Multiphase Non-Darcy Flow in Hydraulically Fractured Gas Wells

Molecular Diffusion of CO2 From Carbonated Water (CW) Into the Oil – Experimental Observations

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