Abstract

Flue gas displacement of oil is attracting attention as a feasible process forimproving oil recovery from light oil reservoirs. When obtained from surfacesources, the flue gas process has an added advantage of reducing carbon dioxide(CO2), a greenhouse gas, from being vented into the atmosphere.In-situ generation of flue gas is the product of spontaneous oil ignition whenair, a cost-effective and readily available gas, is injected into light oilreservoirs. The relatively high oil recovery potential of the flue gas processmakes it economically attractive. It may be necessary to enrich the injectedflue gas or air in order to maximize the recovery potential of the process. Theimprovement in oil recovery by enriched flue gas was studied as a function ofthe concentration of CO2 in the injected flue gas. The study wascarried out with a compositional simulator that was history-matched toexperimental data obtained in long core floods. At pressures ranging from 27.58MPa to 68.95 MPa, it was found that there was no appreciable improvement in oilrecovery below 25% CO2 concentration. Above 25% CO2concentration significant increase was observed in oil recovery. This increasehowever, peaked at 80% (for 68.95 MPa), 85% (for 62.05 MPa), and 90% (for 55.16MPa) CO2 and thereafter declined with increase in CO2concentration at the stated pressure conditions at 1.0 pore volume of gasinjected. This phenomenon was not observed for pressures below 55.16 MPa. Onthe other hand, oil recovery at gas breakthrough was practically constant forall the pressures tested until after 40% CO2 concentration; when aslight increase in recovery was observed.

Introduction

Primary recovery of light oil by the natural drive of the reservoir, ingeneral, can be up to 50% of the original oil in place1, especiallywith an efficient gravity drive. Secondary recovery process involving theinjection of immiscible fluid, water into the aquifer or gas into the gas cap, can recover 25% to 45% of the original oil in place. In addition to displacingoil from the pore space and driving it to the producing wells, the injectedfluid also maintains the pressure of the reservoir. Oil recovery practicesbeyond secondary are referred to as tertiary or enhanced oil recovery (EOR).EOR is practiced in addition to, or in lieu of primary and secondary processes.It is capable of recovering oil in excess of that possible by the secondaryrecovery process. About 3.7% of the current world oil production is from EOR.The largest EOR oil producer is the United States with 0.76 million barrels perday (12% of total oil production). Canada's EOR oil production of 0.4 millionbarrels per day (about 25% of total oil production) is next to that of the United States2. EOR methods can be broadly classified into thermaland non-thermal methods, with the thermal methods primarily intended for heavyoils. Non-thermal methods are normally used for light oils.3

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