Master of Science in Petroleum Engineering (MSPE)
Carbon capture and storage is one of the technologies that could help reduce CO2 concentration in the atmosphere while contributing to cutback of Greenhouse Gas emissions. Depleted oil and gas fields are favorable targets for CO2 storage because existing wells can be readily used as injection wells. However, a number of abandoned wells also serve as gateway to the reservoir which should be considered in the context of effective Carbon capture and storage. Wellbore cement is a very essential element in wellbore systems that serve as a barrier between different zones in the subsurface. The fractures inside wellbore cement sheath, one of the possible pathways for CO2 leakage to surface and/or fresh water aquifers, impair the effective sealing of the wellbore cement. Hence, the existence of microfractures poses a risk for Carbon capture and storage. The purpose of this experimental study is to gain understanding about the effect of acidic brine on the behavior of cement fracture and porosity. Two experiments were conducted, one under atmospheric and one under high pressure conditions, using CO2 saturated brine. Fracture widening was observed in CT images of the low pressure experiment and was verified with pressure drop calculations. The low pressure experiment resulted in the reduction of porosity whereas the high pressure experiment resulted in a slight increase in porosity. The porosity reduction was caused by calcite deposition which was confirmed by mineralogical analysis, ESEM images and effluent brine analysis. There were 2 mechanisms working simultaneously: leaching and precipitation (carbonation). It appeared that leaching took place first and drove the carbonation process. Leaching resulted in an increase in porosity whereas carbonation resulted in a reduction of porosity. In a possible leakage scenario, acidic brine exposure may result in a reduced fracture aperture due to carbonation coupled with confining stress around cement sheath.
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Yalcinkaya, Tevfik, "Experimental study on single cement fracture exposed to CO2 saturated brine under dynamic conditions" (2010). LSU Master's Theses. 1595.