Permeability Model for Nigerian Oil Sand as Candidate CO2 Storage Reservoir

Abstract

This research examines the challenges associated with storing captured CO₂ in the Niger-Delta reservoirs by examining the effect of the stored gas on the reservoir rock sample.  Mitigation against increasing CO₂ in the atmosphere is uppermost in environmental research due to its negative effects and therefore there is need to explore all possible reservoirs, apart from abandoned crude oil reservoirs, for CO₂ storage. In this research, a model was developed to study permeability variation during CO₂ injection to oil sand as a candidate CO₂ storage reservoir. Four existing permeability models of Tixier, Timur, Coates-Dumanoir and Aigbedion were employed together with a proposed model. The proposed model was a combination of irreducible water saturation equation from Timur model and the Coates-Dumanoir permeability equation. The proposed model took cognizance of changing porosity phases, since the injected CO₂ is reactive and affects the properties of the reservoir rock. The model equation obtained is the model gave permeability value ranging from 16.94 to 2.74 mD for Imeri oil sand. In comparison, the Timur model gave permeability values from 1.45 to 0.002 mD; Tixier value ranges from 42.85 to 0.01 mD; Coates-Dumanoir value of 287.72 to 7.49 mD while value given by Aigbedion rangs from 9.01 to 2.6 mD. In the course of the research it was discovered that Imeri oil sand formation, though has very high porosity which could be a pointer to early stage leakage, is highly reactive with the injected CO₂. This reactivity is a good condition for permanent storage of the injected gas and is therefore recommended, with reservation, as a potential CO₂ storage reservoir.  The proposed model will also give the expected CO₂ gas mobility with increasing period of injection.

Key words: CO₂ storage; Oil sand; Porosity variation; Permeability; Permeability model