| Abstract |
This paper presents and describes the technology, products, and techniques combined and used by an electrical-power production company and an oilfield service company to reduce by more than 50% the expense of cementing surface casings of geothermal wells in the Heber Field of southern California (Figure 1). Both Heber Field Company and Ormat Nevada Inc. are subsidiaries of Ormat Technologies, a vertically integrated company. Shallow alluvial fill and sandy formations underlying the field are prone to (1) break down under the hydrostatic pressure of the cement column, and (2) take the cement slurry into the formation instead of allowing it to fill the wellbore/casing annulus all the way to the surface. Cement-job designers used density-reduction additives, reactive flushes, and cement-set accelerators to overcome the tendency of the formation to take the slurry away from the casing. The drilling contractor also reduced the rate of penetration and drilling-fluid pumping rates to help avoid creating a wellbore of great volume that had to be filled with cement. Where the cost of a surface-cementing job in the field before ranged up to $190,000, it is now in the range of $119,750. |