Summary
Drilling activities in diverse areas can pose significant challenges for
conventional cement systems and circulation methods. To overcome these
challenges, a unique cementing system and a circulation method have been tested
in the field with great success. This paper details how these technologies and
techniques were successfully used in the cementation process of one casing
string in a relatively shallow geothermal well in central California and a
relatively deep string in central Wyoming.
Globally, many wells experience lost-circulation problems that require the
reduction of circulation pressures to allow proper placement of cement to
provide annular coverage. To help minimize these circulation pressures, cement
was directly pumped into the annulus, significantly reducing placement
pressures and allowing placement of the cement with no apparent losses—a
process referred to as the reverse-circulation placement technique (RCPT). In
the deep and shallow applications discussed, the placement technique and the
individual slurry designs address temperature issues.
Introduction
Drilling and completion of geothermal and deep, hot wells pose a number of
challenges, including very high temperatures (250°F or greater)—at great depths
and at relatively shallow depths. The high temperatures pose challenges while
the well is being drilled and completed and after construction has been
completed.1–3 In a geothermal well, carbon dioxide (CO2) may be encountered in
some of the formations, which can be a serious corrosive threat to both the
cement and the casing in the well.
The most common problem faced when drilling wells in geothermal fields is
lost circulation. Because of the typically fractured nature of formations in a
geothermal field, lost circulation can cause serious problems during drilling
and while casing is cemented across lost-circulation zones. Lost circulation
that occurs during a cement job can lead to incomplete sealing of the annulus,
which may require remedial cementing in an attempt to fill the annulus.4–6
Traditionally, when lost circulation is a problem, operators rely on
conventional lost-circulation treatments before cementing. Additionally,
various lightweight-cement systems are used to help minimize the pressure while
cement is circulated into an annulus, which can help minimize the potential for
lost circulation and associated problems.7,8
In central Wyoming, a 15,932-ft string of 10¾-in. pipe was successfully
cemented by use of the RCPT. The positive results have led to additional
applications of the technology in other parts of the U.S.A.
A central California geothermal well was cemented by use of the technology
as well. The RCPT was used to cement a 13⅜-in. casing string at a total depth
of 3,720 ft.9,10
© 2005. Society of Petroleum Engineers
View full textPDF
(
1,665 KB
)
History
- Original manuscript received:
21 January 2004
- Revised manuscript received:
1 March 2005
- Manuscript approved:
2 April 2005
- Version of record:
15 June 2005
View Cart
