Static and Dynamic Testing of Silicate Scale Inhibitors

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Abstract Alkaline surfactant polymer (ASP) floods in sandstone reservoirs are associated with silicate scaling of production wells. Silicate scaling has been a significant problem in ASP-flooded fields in China (e.g., Daqing field) and Canada. This paper describes the results of both static and dynamic testing that reproduced the field conditions in a typical oil production well in a field under ASP flood. The tests were used to screen chemical inhibitors for the prevention of magnesium silicate scaling. Carbonate and silicate were allowed to scale concurrently in both tests. The static test was used to screen inhibitors, and the best performers were tested dynamically. The static and dynamic tests correlated well in terms of individual inhibitor results. In the static test, silicate slowly forms from the beginning of the test and calcium carbonate forms about two hours into the test. In the dynamic test, calcium carbonate forms very slowly while silicate scale forms more quickly and dominates. It is interesting to note that none of the chemicals tested acted as a threshold inhibitor and prevented scaling at low doses. Rather, the inhibitors tended to delay scaling. Significant delay of scaling required doses of 50 to 100 ppm (as active). This effect was observed both in static tests and dynamic tests. Although none of the products tested acted as threshold inhibitors, the best inhibitors could still be effective in the oilfield if silicate scaling can be delayed long enough so that fluids are moved out of the well before significantly depositing on surfaces downhole.