| Title | FOAM SLURRY FOR CEMENTING CASING IN GEOTHERMAL WELLS |
|---|---|
| Authors | V.C. Perez, S. Pye, A. Wilke |
| Year | 2015 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Geothermal, drilling, foamed cement, well integrity |
| Abstract | One of the more difficult aspects in geothermal well construction is ensuring a quality cement job to support the entire length of the casing. Good “anchoring” of the casing string is imperative to restrain the casing against thermal expansion and contraction upon cyclic exposure to hot geothermal fluids. The cement sheath also serves as a barrier against the ingress of potentially corrosive fluids. Unfortunately, the physical characteristics of a conventional cement slurry exerts a hydrostatic pressure and equivalent circulating density while pumping that are higher than the formation strength can withstand here in New Zealand. For long casing strings, it is common to experience total losses during the primary cement job that require several remedial or “backfill” cement jobs with risks of channeling or voids forming when cement is placed from above and no guarantee of a complete cement sheath around the pipe. Casing damage from post drilling well discharges have almost always been traced to either casing collapse or buckling as a result of a poor cement job. A collapsed production casing or pressure containment vessel of the wellbore may be catastrophic as it means the loss of the well. The loss of an already expensive well is compounded by further losses in production, hence, revenue. This paper sets out Mighty River Power’s (or MRP) development of cementing techniques to bring the primary cement slurry back to surface or, in the case of a liner cement job, to get the slurry to the top of the liner. |