The objective of the study was to estimate which was the effective mobility of a polymer solution injected in an extra heavy oil reservoir, also try to stablish if there was a reduction on effective permeability as injection progressed, and finally estimate the mobility ratio between the reservoir fluid and the injected fluid.
Laboratory analyses were used to evaluate the behavior at surface conditions of the polymer solution before injection, and also the quality of the polymer solution prior injection. Tests were performed to estimate the effect of water reservoir salinity over the polymer solution viscosity, and the effect of Iron and Oxygen ion content present in the solvent used for preparation. After project start up, five fall off tests (pressure transient tests) at different stages of the injection process were performed in order to evaluate the mobility evolution over an extended period of time. The tests were executed every three months after the beginning of the injection of the polymer solution. Other diagnostics techniques were also studied, in order to gain insight of what other variables could affect the injection process, among them: Hall plot diagnostics, and fiber optic data.
The evolution mobility of the polymer solution at reservoir conditions was determined, and as injection progressed, the solution mobility decreased over time for the same concentration, according to results obtained from interpretation of well tests analysis, the mobility decreased from 342 mD/cP to 145 mD/cP. Given that the mobility of the oil was very low (between 0,8 mD/cP and 1 mD/cP), the mobility ratio evolution over time showed that a reduction in polymer effective permeability occurred as injection progressed, favoring the flooding process, also depending of the effective permeability, the mobility compared to water, was almost seven times lower. Laboratory analyses showed and important dependency between shear rate and polymer viscosity in the case of polymer solution prior injection, and also a possible risk of solution viscosity reduction due the high salinity of the reservoir water.
The injection data, fall off analysis, and Hall plot analysis, combined with the results of the laboratory analyses are of great importance for the topic of enhanced oil recovery process in the case of extra heavy oil reservoirs. The results obtained show also that it is necessary to evaluate the actual performance, besides of the core test and simulation results. Finally the knowledge accomplished in this work was used to obtain important information necessary to asset feasibility, in the case of a larger scale implementation of the process.