Siliceous scaling deposition from geothermal brine is recognized as detrimental to the smooth operation of steam generation and injection facilities; the control of such deposition is costy and less well understood. Scales normally encountered in geothermal wells are often different from the conventional cases. Silica (amorphous and colloidal) and poor crystallized metal silicates are the most common scale types in geothermal applications.
There are a number of ways to control this type of scaling, including both engineering (e.g. maintain pressure and temperature) and chemical means (e.g. controlled precipitation and inhibition). This paper will focus on preventative techniques by the use of chemical inhibitors.
Currently there are no standard or generally accepted laboratory test methods to study these types of fouling problems. However, using a low-pressure test method and testing apparatus, we are able to rank the scaling inhibition performance of several generic chemicals. Furthermore, the chemical was successfully packaged into formulations that are suitable to a specific geothermal well condition where large amount of iron are present, complicated with the codeposition of barium sulphate scale. The mechanisms of silica/metal silicate scale formation and inhibition, including the verification test using a HPHT apparatus for this geothermal application, are discussed in this paper.