Reservoir Structural Strategies on the Integrity of Gas Mobility Ratio

O. Abunumah, P. Ogunlude, E. Gobina
Centre for Process Integration and Membrane Technology, School of Engineering, The Robert Gordon University, Aberdeen,
United Kingdom

Keywords: structural parameters, structure rhythm, characterisation, gas flow, porous media, porosity

Summary:

Fluid mobility is an essential engineering quantity for characterizing reservoir fluid recovery. In Enhanced Oil Recovery (EOR), mobility ratio is a mathematical term to describe the mobility of the displacing fluid relative to that of the displaced fluid, usually oil or gas. The ratio provides useful information on the type of displacing fluid to be selected and the operating strategy required to maintain the integrity of the ratio. Displacing fluid include gas, polymer, and water. The operating structural effect on polymer is well developed in the literature, however, this type of study is lacking for gases. In this study, four commonly injected EOR gases, CH4, N2, Air, and CO2 have been simultaneously investigated to determine the effect of operating structural strategies on the mobility ratio integrity. An experimental method involving 5 analogous structural strategies have been conducted. 192 experimental runs were carried out, using injection pressure and core temperature operating conditions ranging from 0.20-3.00 Bar and 293-673K, respectively. A comparative analysis used the respective gas mobility as an evaluation criterion for studying mobility ratio integrity. The results reveal that the mobility ratio is significantly affected by the structural strategy of the EOR process. The External Diameter, Reservoir Quality, Radial Thickness and Porosity has a linear effect on the mobility ratio integrity. Tortuosity, Compression Factor, Aspect Ratio, Pore Density, Pressure Gradient, Pore Size, and Specific Surface Area showed power and high-order polynomial relationships. In all the cases, CH4 mobility experienced the highest impact from structural strategy. The mobility integrity for the four gases had the highest impact when exposed to Reservoir Quality structural strategy. The findings from this study can be directly applied in selecting suitable injection gas and screening reservoirs for gas EOR processes. Where there is reservoir variability, engineers can appreciate the effect on the respective EOR gas mobilities and manage hydrocarbon recovery more effectively.