| Title | Field Application of Calcite Antiscalant in New Zealand: Screening Process, Performance Evaluation and Management of Operational Issues |
|---|---|
| Authors | Farrell SIEGA, Alan FERGUSON, Ian RICHARDSON and George ALLAN |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | calcite scaling, antiscalant, management |
| Abstract | Calcite scaling is a major problem encountered in several geothermal fields in New Zealand. Production from a geothermal well can decline by as much as 50% in one year depending on the fluid oversaturation with respect to calcite and the rate of scale deposition. Mechanical clean-out and acidising are two commonly used options to recover loss in productivity due to calcite deposition inside the wellbore. These options however are not considered cost-effective as these require periodic application, in addition to the high cost of doing the job and business interruption with wells needing to be taken off-line. Scaling inside the wellbore can be proactively managed with the use of antiscalant chemical, if the potential for calcite scaling can be accurately determined based on fluid chemistry and downhole investigation. The antiscalant is normally dosed below the flashpoint using a capillary tubing, and this has been proven to be effective in controlling calcite blockage formation inside the wellbore. The screening process for a suitable antiscalant chemical requires careful consideration of the chemistry of the fluid produced and the downhole temperature-pressure condition of the geothermal reservoir. Moreover, evaluating the performance of the selected antiscalant will require conducting a series of field trials that monitor the fluid chemistry and well massflow, including addressing any operational problems in downhole delivery system or detrimental side effects on geothermal power plant operation. This paper will discuss the screening process for antiscalant chemicals available in the market including the required laboratory testing before deciding on a short-term field trial. This paper will also discuss the long-term monitoring activities necessary to evaluate the overall performance of the antiscalant, the management of the antiscalant delivery system and any observed effect on power plant operation. |