| Title | Reverse Circulation of Foamed Cement in Geothermal Wells |
|---|---|
| Authors | Spielman, Paul; Hernandez, Rafael; Nguyen, Hao |
| Year | 2006 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Drilling; Cement, reverse circulation, foamed cement, lost circulation |
| Abstract | Drilling in geothermally active locations can pose significant challenges for conventional cement systems and circulation methods. To overcome these challenges in two geothermal wells in Hawaii, two departures from the conventional were applied: (1) a lightweight cement slurry created by adding nitrogen to the slurry, causing it to foam, and (2) placement of the slurry down the annulus, using a process called “reverse circulation.” This paper presents two case histories that show how these technologies and techniques were successfully used in casing cementation in two geothermal wells. Only one well is described in detail since the operations were similar in principle. Foamed cement technology was implemented because the stresses caused by temperature changes that happen to a cement sheath in a geothermal well may crack a conventional cement sheath due to heat-induced changes in casing diameter. Foam cement sheaths are more ductile and can tolerate expansion and shrinking without losing their sealing capabilities. Additionally, a geothermal well often experiences lost-circulation problems that require the reduction of circulation pressures while circulating cement in place. To help minimize these circulation pressures, cement was pumped in reverse, i.e. the cement was pumped down the annulus and back up the pipe, rather than pumped down the pipe and forced back up the annulus. Reverse circulation significantly reduced placement pressures and allowed placement of the cement with no apparent losses. |