Summary
Lightweight, low-compressive-strength cement slurries save Appalachian basin
operators thousands of U.S. dollars per well when compared with two-stage
cement jobs using a packer-collar tool. The average amount of annular fill-up
that is required in the typical southern West Virginia Devonian shale well is
3,000 ft. Because the shale is naturally fractured and has a low fracture
gradient of 0.3–0.4 psi/ft, many operators opt to cement the air-drilled,
unconventional gas wells with a 12-ppg lightweight silicate cement.
Over the past 5 years, more than 800 wells have been cemented with
water-extended cement slurry, pumped at 12 ppg. Interestingly, the
cement’s compressive strength in 72 hours measures only 500–700 psi, not nearly
enough to be “seen” with the cement-bond logging tools most commonly employed.
In fact, at least one operator waits a full 7 days before running a
variable-density log because that is about the time needed for the cement to
develop enough compressive strength and acoustical impedance to be seen.
While solving one problem related to cutting authorized-for-expenditures
well costs, the lightweight cement caused another problem: lost production days
because of waiting on cement (WOC). Using knowledge of available Portland
cements and a proprietary compressive-strength enhancing agent, a new cement
blend was developed that could get higher strengths and better acoustical
impedance. This paper will document how one large northeast operator
successfully solved the problem of cycle-time reduction while maintaining the
cement density at 12 ppg. Key aspects related to the solution, including
laboratory testing of the cement and cement additives and examples of
post-solution cement-bond logs, will be shown. Economics related to lost days
of production over a 100-well drilling program will also be discussed.
© 2005. Society of Petroleum Engineers
View full textPDF
(
1 KB
)
History
- Original manuscript received:
3 March 2004
- Revised manuscript received:
24 February 2005
- Manuscript approved:
15 July 2005
- Version of record:
15 September 2005
View Cart
