In the Salton Sea Field of Imperial County, California, the operating company successfully applied foamed calcium aluminate phosphate (CaP) cement to achieve long-term zonal isolation in a geothermal well that presented a corrosive carbon dioxide (CO_2) environment. Weak formations along the wellbore of the shallow well required tight management of drilling-mud weight and cement density to help avoid circulation loss during drilling and cementing. This paper (1) describes the case history of Del Ranch Well 14, (2) describes the cement, (3) discusses the job design, and (4) compares/contrasts the performance of conventional cements to that of CaP cement.rnCO_2 is a common element in downhole fluids, whether naturally occurring in ground waters or the result of CO_2 injection processes. When CO_2 comes into contact with the Portland cement traditionally used to cement well casings, it produces a deterioration phenomenon, called carbonation, in the cement. Over time, the loss of cement caused by carbonation can (1) cause serious damage to downhole tubulars and (2) destroy zonal isolation integrity, resulting in costly remedial services or even abandonment of a well.rnCaP is specially formulated cement that is both CO_2 and acid resistant. It comprises four basic components: calcium aluminate cement, sodium polyphosphate, Class F fly ash, and water. CaP has been laboratory tested and proven at temperatures as low as 140°F and as high as 700°F. Under test conditions that cause Class G and H cements and latex-containing Portland cements to lose up to 50% of their weight, CaP cement's properties are only slightly affected and might actually improve.rnSome sections of the cement sheath were cemented with foamed slurry to provide added protection against formation breakdown.
展开▼
