Studies in a number of mature fields in Oman have shown that alkaline surfactant polymer (ASP) flooding can potentially yield significant incremental recoveries with respect to water flooding. The technique however, is still immature especially in PDO as reflected in the number of key risks that have been identified; (i) poor injectivity of the ASP slug, (ii) effectiveness of reservoir sweep, (iii) formation of scale in the wells and facilities and (iv) persistent emulsions in the produced fluids. Analysis of these risks has highlighted the need for piloting before full field implementation.
Two stages of piloting have been considered, Single Well Chemical Tracer (SWCT) test and Continuous Injection Pilot (CIP). This paper covers the SWCT trials with focus on design and implementation challenges and finally discusses performance and results.
A total of five wells were selected for the trial in three different fields across Oman to capture different reservoir settings. The ASP SWCT tests aim to confirm the suitability of the ASP process, the potential recovery factor increase and mitigate some key risks, mainly injectivity and sweep. The trials are designed to evaluate the remaining oil saturation before and after injection of ASP cocktails to determine incremental oil recovery.
Various challenges were faced in planning the project. Completion challenges due to age of existing wells / casing, well shape, type of artificial lift, need to produce / inject water and ASP cocktail from same wells. Water source / tie-in for preliminary flooding also varied in each field. Handling of produced fluids during tests required special attention to avoid destabilizing the production station. Treatment sequence, equipment layout and logistic requirements were different for each field. Procedures were developed for each field incorporating chemical preparation and mixing. Overall, Project Management and good interface were critical to successful implementation of the tests, the first in PDO.