Implication Of Future Carbon Dioxide Injection On Selected Niger-Delta Reservoir Rocks And Fluids.

Abstract

Mitigation against increasing carbon dioxide, CO2, in the atmosphere is uppermost in environmental research due to its negative effects and the most effective approach is in the area of underground carbon storage. In this research, a model was developed to study the possible alteration of porosity and permeability during CO2 injection to Kwale sandstone reservoir, Kwale shales, Imeri oil sand and Ota Kaolinitic clay. The proposed model combined the Timur model irreducible water saturation equation and the Coates-Dumanoir permeability equation, to describe CO2 injection influence on the Kwale reservoir permeability. The proposed model gave permeability values ranging from 0.06 milliDarcy to 92.46 milliDarcy for the Kwale sandstones and shale; 2.01 to 10.2 milliDarcy for Imeri oil sand and 1.8 to 10.2 milliDarcy for Ota Kaolinitic clay samples. In comparison, the Timur model gave permeability values from 0.0 to 634 milliDarcy; Tixier values range from 0.0 to 10053 milliDarcy; Coates-Dumanoir gave values of 6.68 - 8550 milliDarcy while Aigbedion gave values ranging from -3.7 to 5.94 milliDarcy. The published Kwale sands permeability ranges from 0.8 to 87 milliDarcy. During this research it was discovered that the injection of CO2 into Kwale sandstones resulted in an increase in the porosity of the sandstone, which is an indication of possible reaction between the injected CO2 and the formation. This made the Kwale sandstone formation a potential CO2 storage reservoir. It was concluded that the black Kwale shale lacked storage integrity as the stored gas may migrate to nearby reservoirs. The grey shale is recommended for CO2 storage as there was observed increase in porosity which is an indication of possible reaction with the CO2 to form new minerals which will make the gas to remain underground. Imeri oil sand formation is too porous and is recommended, with reservation, as a potential CO2 storage reservoir. The Ota Kaolinitic clay with its moderate initial porosity and reducing porosity with CO2 injection is a potential storage reservoir for CO2. It was observed that there is no single equation to describe the permeability variation with time for the samples considered but the permeability is a second degree polynomial in time and porosity immediately after injection but has an exponential relationship with the time/porosity after some days of injection. Moreover, research was conducted on the possible leakage of the stored CO2 to a nearby formation being drilled or produced.