Mechanical Degradation of Polymers During Injection, Reservoir Propagation and Production - Field Test Results 8 TH Reservoir, Austria

Abstract

AbstractThe polymer pilot test performed in the 8 TH sandstone reservoir in Austria shows incremental oil production. Soon after increasing oil cuts were detected, polymer was back-produced from the wells which were showing the oil production response. The polymer concentration increased to about 100 ppm in the back-produced water.Size Exclusion Chromatography was used to determine the molecular weight distribution of the back-produced high molecular weight polymers (HPAM). The results showed that careful sampling is required to avoid degradation of polymers during the sampling procedure. Analyzing pressurized samples revealed that some degradation of polymers from the original average molecular weight of 20 MDa to 8 MDa occurred.To investigate where in the surface facility-injection-reservoir-production system degradation took place, specific field tests and laboratory experiments were performed.Chemical and biological degradation was excluded as reservoir conditions are benign (50 °C, 20,000 ppm) and nitrogen blanketing and biocides are used.At the surface facilities, no degradation was detected. Swabbing and laboratory experiments showed that severe mechanical degradation occurs in injection wells if injection is performed under matrix injection conditions owing to high flow velocities in the near-wellbore. However, induces fractures are substantially decreasing mechanical degradation. To avoid severe degradation of HPAM, the flow velocities in the near-wellbore and related mechanical degradation have to be evaluated and the injection designed accordingly.In the reservoir, polymers are not degraded as the flow velocities are low.Sucker Rod Pumps as used in the production wells in the polymer pilot area do not lead to polymer degradation. This means surface polymer samples can be taken to investigate the degradation in the injection well.Surface sampling has to be performed pressurized to avoid high shear rates and oxygen in the samples.