| Title | Acidising Case Study -- Kawerau Injection Wells |
|---|---|
| Authors | Yoong Wei Lim, Malcolm Grant, Kevin Brown, Christine Siega and Farrell Siega |
| Year | 2011 |
| Conference | Stanford Geothermal Workshop |
| Keywords | Acidising, Silica, Kawerau, Injection, Scale Removal, Reservoir Engineering, Geochemistry, Well Intervention |
| Abstract | Brine at the Kawerau Geothermal Limited (KGL) plant was injected into three injection wells (KA43, KA44 and PK4A). Since plant commissioning, the capacity of the wells declined to the point where well intervention was necessary to avoid loss of generation. Investigative work was initiated with multi-rate injection tests which found that the injection index of the wells had declined significantly to approximately half of pre-utilisation levels. Further geochemistry analysis identified that the most likely source of injectivity decline was scaling due to colloidal silica forming in the formation. KA44 and PK4A were acidised using a standard 10% hydrochloric acid pre-flush followed by a 10%:5% HF:HCL mud acid solution. A 2” coil tubing unit with a 5 hole 45º nozzle bottom hole assembly was used giving a maximum pump rate of 3.5 - 4.0 barrels per minute. Feedzones were acidised one at a time starting with the deeper zones. Post well injection tests identified that the acidising had recovered the injectivity of the deeper feedzones but the shallower feedzones remain blocked with scale. The injectivity index at PK4A improved from 50 t/h.b to 84 t/h.b while KA44’s gross injectivity index increased from 25 t/h.b to 50 t/h.b. Camera runs carried out before and after acidising revealed excellent scale removal from the perforated liners. Pre and post acidising High Temperature Casing Corrosion (HTCC) logs also showed that the acid had not caused any measurable corrosion in the casings. |