Mobility Control In Dynamic Gravity Segregation Flow Systems

Abstract

RESERVOIR ENGINEERING Mobility control in dynamic gravity segregation flow systems BEN 1. NZEKWU BP Resources Canada Limited and DOUGLAS W. BENNION Hycal Energy Research Laboratories Limited ABSTRACT Experiments were carried out in a vertical sandpack to study the effect of gravity segregation on liquid displacement by a miscible liquid, a gas and a combination of the two. The advantages of using a foaming agent during simultaneous gas-liquid injection were also investigated. A gamma-ray attenuation technique was adapted to track the shapes of the moving displacement front and monitor in situ saturation profiles.The results show that high gas mobility and low density lead to early gas breakthrough and poor sweep efficiency. Even in miscible liquid-liquid displacements a density difference of 0.079 glcm3 leads to gravity override or underride by the displacing liquid. Dur-ing simultaneous gas-liquid injection the presence of gas increases the severity of the override/underride effect and reduces the displacement efficiency ofthe miscible liquid. In situ generation of foam is an effective method of controlling the mobility of the gas and improving the conformance of the displacement front. Introduction The purpose of this study was to investigate the characteristics of gravity segregating systems and the use of foaming agents to con-trol the mobility of air and water injected simultaneously into a liquid-saturated porous medium.One of the major factors responsible for poor conformance and low recovery efficiency of several displacement processes(l) is gravity segregation caused by a density difference between displac-ing and displaced fluids. For example gas-driven processes such as C02-flooding, alternating water-gas injection, steam injection and in situ combustion are affected by varying degrees of segregated flow behaviour.Several laboratory experiments and numerical studies of fluid flow in porous media have confirmed the importance of a density difference in the occurrence of segregation. Slower rates of segre-gation were observed in brine-liquid systems than in brine-air systems(2). With miscible liquids the length of the mixed zone was influenced by gravity segregation, and a greater reduction in dis-placement efficiency was observed when the mixed zone was narrow compared to the height of the experimental model (3). The presence of a broad transition zone tended to nullify the influence of a difference in density(4-5). Gravity segregation is generally

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“…A major challenge in carbon dioxide (CO2) enhanced oil recovery (EOR) is poor macroscopic CO2 sweep efficiency caused by the low viscosity and density of injected CO2 [1,2]. These adverse properties can result in viscous fingering and gravity override, greatly hindering oil recovery and sweep efficiency [3,4]. Reservoir heterogeneity can also cause injected CO2 to channel through high permeability zones (layers or fractures) resulting in early CO2 breakthrough, high CO2 recycling, and low incremental oil recoveries.…”

The Mechanism of Flow in Reservoir Regions Dominated by Gravity Segregation

“…Recently Rossen et al (1) and Jamshidnezhad et al (2) considered optimal injection strategies. Other authors have considered mobility control methods of minimizing gravity segregation (3,4) .…”