Performance Quantification of Enhanced Oil Recovery Methods in Fractured Reservoirs

Riyaz Kharrat,Mehdi Zallaghi,Holger Ott

doi:10.3390/en14164739

Riyaz Kharrat, Mehdi Zallaghi + Show 1 more

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https://doi.org/10.3390/en14164739

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Abstract

The enhanced oil recovery mechanisms in fractured reservoirs are complex and not fully understood. It is technically challenging to quantify the related driving forces and their interaction in the matrix and fractures medium. Gravity and capillary forces play a leading role in the recovery process of fractured reservoirs. This study aims to quantify the performance of EOR methods in fractured reservoirs using dimensionless numbers. A systematic approach consisting of the design of experiments, simulations, and proxy-based optimization was used in this work. The effect of driving forces on oil recovery for water injection and several EOR processes such as gas injection, foam injection, water-alternating gas (WAG) injection, and foam-assisted water-alternating gas (FAWAG) injection was analyzed using dimensionless numbers and a surface response model. The results show that equilibrium between gravitational and viscous forces in fracture and capillary and gravity forces in matrix blocks determines oil recovery performance during EOR in fractured reservoirs. When capillary forces are dominant in gas injection, fluid exchange between fracture and matrix is low; consequently, the oil recovery is low. In foam-assisted water-alternating gas injection, gravity and capillary forces are in equilibrium conditions as several mechanisms are involved. The capillary forces dominate the water cycle, while gravitational forces govern the gas cycle due to the foam enhancement properties, which results in the highest oil recovery factor. Based on the performed sensitivity analysis of matrix–fracture interaction on the performance of the EOR processes, the foam and FAWAG injection methods were found to be more sensitive to permeability contrast, density, and matrix block highs than WAG injection.

Highlights

More than half of the world’s total oil reserve is stored in carbonate reservoirs, and almost all are intensively fractured, characterized by low primary recovery
In the case of the stack of matrix blocks, capillary continuity and reinfiltration phenomena occur due to block-to-block interactions, which might lead to oil recovery reduction [5,6]
Based on the surface response modeling, water injection was of minor importance in oil-wet fractured reservoirs due to the low magnitude of driving forces to recover oil from matrix blocks

Summary

Introduction

More than half of the world’s total oil reserve is stored in carbonate reservoirs, and almost all are intensively fractured, characterized by low primary recovery. Several studies have examined the recovery mechanisms and driving forces in naturally fractured reservoirs [1,2,3,4]. Understanding the oil recovery mechanisms of these reservoirs depends on the magnitudes of the driving forces. Gravitational and capillary forces have the leading roles in capillary continuity and reinfiltration processes. In the case of the stack of matrix blocks, capillary continuity and reinfiltration phenomena occur due to block-to-block interactions, which might lead to oil recovery reduction [5,6]. In the reinfiltration process, drained oil from upper blocks can be reimbibing into lower blocks through the liquid bridges and film flow across contact points between vertical blocks. Capillary continuity in the vertical direction between matrix blocks can improve the oil recovery [5,6]

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