Experimental analysis of calcium carbonate scale formation and inhibition in waterflooding of carbonate reservoirs

Abstract

Deposition of inorganic salts such as calcium carbonate (CaCO3) can cause formation damage and production equipment failure during the development of a reservoir. In case of waterflooding, complex geochemical processes between the injection water, formation water and rock occur and the concentration of ions increases. Major contribution of scale control concentrates on understating the conditions scale formation and its inhibition.In this paper, we analyze experimentally the effect of oil composition and flow conditions on CaCO3 scale formation. We measured the induction period of CaCO3 crystallization in a stirred vessel with different Reynold numbers and the interfacial tension at the boundary between the aqueous scale inhibitor and oil at different percentages of organic components. In addition, we determined the performance of CaCO3 scale inhibition under different static and dynamic conditions in some Iranian carbonate core samples.The experimental results showed that if the interfacial tension was reduced by increasing the concentration of organic components to 1.5%, the CaCO3 precipitation decreases more than 30%. In addition, increasing the flow velocity (Reynolds number) had a great influence on the increase in the induction period of CaCO3 crystallization. However, the induction period was insignificantly changed at higher values.Using a recently developed scale inhibitor, we kept the CaCO3 formation at a constant concentration of 30mg/L. The efficiency of the inhibitor was insignificantly reduced if the temperature is increased up to 120°C. Core flooding experiments show that formation damage due to CaCO3 precipitation depends on the injection rate of the solution. In addition, the formation damage was mitigated to the 93% of initial permeability of the core samples. The results of this work improve our understanding from CaCO3 formation and can be used to predict and prevent it during waterflooding process in carbonate reservoirs.