Operational Challenges and Monitoring of a Polymer Pilot, Matzen Field, Austria

Abstract

Summary Four main areas of uncertainty can be described in polymer-injection projects: Are we able to deliver the polymer solutions at the required quality to the wellhead? Are we able to inject polymers at the required quantity and quality? Are we producing sufficient incremental oil? Are we able to separate and treat oil and water cost-effectively after polymer breakthrough? The monitoring program that was developed for the polymer-injection pilot aims to reduce the uncertainty and quickly identify operational difficulties, as described in the following: Polymer quality at the wellhead: The polymer concentration and viscosity of the “source” solution and injected polymer solution were measured at various locations in the surface facilities. A quality check of the delivered polymer (including a filter ratio test of the dissolved polymer) was performed, the biological activity monitored, iron content measured, and polymer solution investigated for “fish eyes.” The monitoring program enabled us to identify challenges related to shearing the polymers after changing the operating envelope, to identify problems related to biological activity, and to ensure data quality for interpretation of the pilot. Injectivity and degradation: Monitoring involved wellhead- and bottomhole-pressure measurements, repeated falloff tests, and visual observation of the polymer solutions in the well. The results showed the mobility reduction of the polymer solutions and an indication of induced fractures. Combining the various measurements led to identification of an operational issue—the injectivity decreased more than expected from polymer rheology and prepilot water-quality assessment. The reason was the combination of fines and small oil droplets existing in the injection water with polymer- and biological-generated mass that plugged the pores during injection. Incremental oil: Accurate measurement of the produced-water cut, especially for those wells producing at water cuts greater than 90%, is key for reporting accurate incremental oil. In addition, water salinity at the producing wells was measured, and a repeated tracer program was instituted. The results have been used to assess the reservoir architecture and incremental oil related to polymer injection. The challenges in the interpretation of the pilot conformance could be resolved by use of these data. Polymer, oil, water treatment: The surface facilities are monitored constantly for separation efficiency and plugging owing to back-produced polymers. Operating challenges are seen in all treatment steps for full-field polymer-injection implementation because of both oil/water separation and handling of the polymers in water-treatment facilities.