Novel Analytical Approach for Polymer Injectivity Tests in Los Perales Field, Argentina

Abstract

Abstract Polymer admission studies at the objective reservoir layers are one of the first critical experimental tests prior to field injection. Pressure build-up in the injector well is measured during a short period of time and its projections are used to select maximum polymer injection flow-rate and pumps. Complementary, polymer stability must be monitored during the injectivity test to reduce viscosity fluctuations, and a flowback test will finally validate the whole process asserting absence of polymer degradation at reservoir conditions. In Los Perales three wells were tested for HPAM polymer-flood. Near-wellbore pressure transient analysis is not accurately resolved by numerical simulators, so an analytical pressure build-up model considering polymer non-Newtonian rheology was developed to make projections adjusted to measured data. Polymer thermal variations and degradation mechanisms (mechanical and chemical) in surface facilities have been also studied (Katz Marquez, 2019). Then, a flowback test in one of the wells was performed to check for polymer degradation and validate the whole assay. During the injectivity test, measurements and further estimations, derived from the ad-hoc analytical model, showed that the objective polymer doses and injection flow-rate will be admitted by the reservoir. On the other hand, chemical degrading processes rise as challenging problems to deal with. Oxygen combined with hydrogen sulfide was found to be the main responsible for chemical degradation. One of the steps in the process of solving this issue was to develop an equation which allows us to predict viscosity behavior considering these effects. Hence, several ways to reduce degradation were implemented. Finally, the flowback test in one well validated the assay showing that combined degradation (mechanical and chemical) did not reduce active polymer concentration in more than 25%. In order to make degradation-free viscosity measurements, an ad-hoc 3D-printed anaerobic chamber for the viscometer was developed and successfully implemented. The present work serves as a guideline to perform injectivity test, estimate well pressure build-up, deal with chemical and mechanical degradation processes and validate the process through a flowback test a further data analysis.