Inorganic Scale Challenges and their Mitigation in an Onshore Abu Dhabi Field

Abstract

Abstract Inorganic scale precipitation has been observed in an increasing number of wells in an onshore Abu Dhabi field. Mitigation strategies have historically concentrated on laboratory analysis of scale samples and design of remedial acid treatments in combination with mechanical methods to clean out the wellbore. To evaluate success, well accessibility and production improvement checks are made before and after the job. This reactive strategy has had mixed results, and the emphasis is now shifting towards use of preventative techniques especially with the increase in Water Alternate Gas (WAG) and Artificial Lift (AL) operations, increased water injection and produced water re-injection. Detailed evaluation of the scale risk has been conducted via scale prediction modelling identifying that the major risk relates to calcium carbonate scale due to pressure reduction during production. In order to mitigate this risk, and to be able to minimise productivity losses and increasing costs associated with remediation treatments, the decision was made to evaluate the potential for scale prevention via downhole scale inhibitor application by squeeze treatments for naturally producing wells and by continuous injection for artificially lifted wells with Electrical Submersible Pump (ESP). Extensive 3rd party laboratory qualification of 8 different vendor recommended scale inhibitors for each application were carried out and the results will be presented in this paper. There were challenges faced during the testing of the scale inhibitors for squeeze application because the vendor supplied formulations had poor injectivity and led to formation damage during initial core flood tests. The 3rd party lab re formulated the vendor chemicals to minimise the potential for formation damage. Further core flood testing with the re formulated chemicals resulted in minimal formation damage while maintaining relatively long scale inhibitor squeeze return lifetimes. This work illustrates the importance of extensive chemical testing prior to field application to avoid any problems in the wells. The laboratory qualified scale inhibitor chemicals are planned to be trialed in wells which have been identified with a carbonate scale risk based on historical data or on results from prediction models under particular production conditions. The ultimate goal is to have in place a robust inorganic scale mitigation strategy as part of the field development plan to minimise well intervention and increase well availability.