Evaluation of the Results of the Tongonan-1 CO2 Gas Injection Project, Leyte, Philippines

Abstract

The Tongonan-1 CO2 Gas Injection Project aims to reduce gas emissions from the geothermal power station by injecting the gases to the reservoir through mixing with the separated Tongonan brine prior to injection. Silica deposition in the brine line could also be inhibited due to lowering of the brine pH after gas mixing.

The brine has a pH of 6.1 to 6.2 and an SSI of 1.10. Injection of 0.36 to 0.60 TPH of non-condensable gases resulted in a brine pH lowering to 5.2-5.6, with a notable increase in dissolved gases of 20 ppm CO2 and 5.5 ppm H2S. Inspection of the test spools showed that deposition of amorphous silica, calcite and anhydrite in the gas - treated brine line was insignificant. Ultrasonic thickness gauging in the injection set-up showed that thinning was insignificant indicating that corrosion was minimal.

Although the tests showed the feasibility of injecting gases to the reservoir, coupled with modifying the brine pH to minimize silica polymerization, conditions during the test were not ideal due to operational constraints. For one, the amount of gas injected was low (0.60 TPH), or only 16% of the amount of waste gases (3.78 TPH) available from one of three turbine units. Also, the brine requirement (598 TPH) to dissolve the injected gases was high, making it difficult to operate the system. These concerns will limit the feasibility of CO2 injection in industrial applications, especially in fields with a limited amount of brine.