Factors that impact scale inhibitor mechanisms

The formation of mineral scales such as barium sulphate and calcium carbonate remains an issue for the oil industry, after many years of oil exploration. In the last 10 years, the difficulty in dealing with scale deposition has been accentuated by the appearance of more complex conditions, involving complicated well completions for deepwater or long sub-sea tiebacks. If scale control measures fail in these situations then long distances between the scale deposits and the production platform are present. Intervention into such systems is either impossible or extremely expensive. To combat such problems, the front end engineering design stage (FEED) now attempts to bring together multidisciplinary teams to provide a full risk assessment of all areas in which production chemistry problems might arise. Hence, benefits come from each discipline team having as much knowledge as possible available to them. This thesis aims to fuel this knowledge by developing a fundamental understanding of how various factors, conditions or environmental, impact scale inhibitor mechanisms, so that the results can be incorporated into the FEED process. Key areas affecting scale inhibitor operation were investigated. From these studies, a number of important findings can be highlighted. The presence of calcium was found to improve scale inhibitor (SI) performance, especially phosphonate types, whilst magnesium ions had little effect on polymeric performances and detrimentally affected the phosphonates’ inhibition efficiency (IE). These trends were related to the SI affinity for the divalent ions – polymer PPCA binds to calcium but shows incompatibility at [Ca2+] > 1000ppm - observed as low IE, whilst the phosphonate DETPMP binds with either ion but prefers calcium. Two inhibition mechanisms - nucleation and crystal growth blocking - were identified for different types of SI species and were illustrated using static IE tests relating IE to [SI] left in solution. High IE corresponds to high [SI] and similarly low IE with low [SI]. These ...