Effects of carbon dioxide injection on the displacement of methane and carbonate dissolution in sandstone cores
Maduakor, Ekene Obioma
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Previous coreflood experiments show that CO2 sequestration in carbonate rocks is a win-win technology. Injecting CO2 into a depleted gas reservoir for storage also produces hitherto unrecoverable gas. This in turn helps to defray the cost of CO2 sequestration. This thesis reports the results from experiments conducted on a Berea sandstone core. The experiments include displacement experiments and unconfined compressive strength tests. The displacement experiments were conducted at cell pressures of 1500 psig and temperature of 60oC using a 1 foot long and 1 inch diameter Berea sandstone core. Pure CO2 and treated flue gas (99.433 % mole CO2) were injected into the Berea sandstone core initially saturated with methane at a pressure of 1500 psig and 800 psig respectively. Results from these experiments show that the dispersion coefficient for both pure CO2 and treated flue gas are relatively small ranging from 0.18-0.225 cm2/min and 0.28-0.30 cm2/min respectively. The recovery factor of methane at break-through is relatively high ranging from 71%-80% of original gas in place for pure CO2 and 90% to 92% OGIP for treated flue gas, the difference resulting from different cell pressures used. Therefore it would appear that, in practice injection of treated flue gas is a cheaper option compared to pure CO2 injection. For the unconfined compressive strength tests, corefloods were first conducted at high flowrates ranging from 5 ml/min to 20 ml/ min, pressures of 1700-1900 Psig and a temperature of 65oC. These conditions simulate injecting CO2 originating from an electric power generation plant into a depleted gas reservoir and model the near well bore situation. Results from these experiments show a 1% increase in porosity and changes in injectivity due to permeability impairment. The cores are then subjected to an unconfined compressive strength test. Results from these tests do not show any form of weakening of the rock due to CO2 injection.