Test results of another silica scale inhibitor for Malitbog geothermal brine, Tongonan, Leyte

Abstract

Silica scale inhibitor Geosperse CSX5110 was tested in Malitbog low-pressure (P = 0.6 MPag) and slightly oversaturated brine (SSI = 1.1-1.2) using a silica inhibition test set-up. Test runs in short durations using 5.0 ppm (13 days) and 0.5 ppm (5 days) dosing concentrations were conducted to evaluate the inhibitor's suitability to address the recurrent capacity decline of injection wells 5R1D and 5R4 due to silica deposition in wellbore formation. Both test runs showed the formation materials coated with distinct powdery silica deposits in contrast with the hard, cemented type and rough-edged silica deposition of the baseline (untreated) tests. The powdery deposits do not significantly attach to the inspection pipes inner walls. The presence of silica deposits loosely coating the formation materials with no significant change in the brine's total silica concentrations across the test set-up suggests the mechanism of molecular deposition may also be as important as silica deposition due to polymerization. The inhibitor acts as a dispersant to prevent the growth of silica particles bigger than the critical size necessary for the polymers to drop out in the brine solution and deposit in the inspection pipes and formation materials. Furthermore, the inhibitor may have interfered in the formation of hard deposits through cross-linking of silica particles. Additional tests are to be conducted to validate the preliminary results and evaluate whether the type of deposits may be acceptable to PNOC-EDC operations.