Abstract
Seawater injection is widely used to maintain the offshore oil reservoir pressure and improve oil recovery. However, injecting seawater into reservoirs can cause many issues such as reservoir souring and scaling, which are tightly related to the seawater breakthrough percentage. Accurately calculating the seawater breakthrough percentage is important for estimating the severity of those problems and further developing corresponding strategies to solve those issues. The validation of using natural ion boron as tracer to calculate seawater breakthrough percentage was investigated. Boron can interact with clays, which can influence the accuracy in seawater breakthrough calculation using boron. Therefore, the interaction between boron and different clays at various conditions were studied, and Freundlich adsorption equation was used to describe the boron adsorption isotherms. Then boron adsorption isotherms were coupled into the reservoir simulator to investigate the boron transportation in porous media, and the results in turn were further analyzed to calculate the accurate seawater breakthrough percentage. Results indicated that boron adsorption by different clays varied. pH value of solution can significantly influence the amount of boron adsorbed. As a result, the boron concentration profile was delayed in coreflood test. The results of reservoir model fit perfectly with that of coreflood test, indicating the validation of boron reaction model. Based on the reservoir simulator results, boron concentration profile in produced water was successfully used to calculate seawater breakthrough percentage by considering the clay content distribution. However, the seawater breakthrough point cannot be calculated by boron as boron concentration is still at the formation level due to boron desorption.
