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AFE: cementing
Cement is used in completing wells to provide zonal isolation. Completing an authority for expenditures (AFE) as part of well planning requires estimation of the materials and services required for cementing the well.
Overview
Cost development for cementing charges requires an evaluation of:
- Cement type and volume.
- Spacer-fluid requirements.
- Special additives.
- Pumping charges.
These various charges usually apply for:
- Each primary cement job.
- Stage slurries.
- Squeeze slurries.
- Plugs.
- Surface-casing top-outs.
Factors affecting cost
Cost will vary for land and offshore jobs.
Pumping charges
Onshore and offshore pumping charges for one cementing company are shown in Fig. 1. The charges increase with depth and for the offshore case. Also, pumping charges for casing and drillpipe will vary.
Fig. 1—Depth vs. pumping charge.
In addition to the primary cementing pump, most operators use a standby pump unit in case of mechanical failure on the primary unit. The ill effects of cementing-up the casing or drillpipe as a result of equipment failure overshadow the standby pumping unit charges. Rates for land-based standby pump trucks are approximately U.S. $100 to $150/hour.
Cement spacers
A cement spacer is used to separate the cement from the drilling mud in an effort to reduce cement contamination. The chemical cost for a barrel of spacer fluid is approximately U.S. $50 to $100 depending on the amount of retarder. Barite charges or other weight materials must be added. In addition, diesel charges in the spacer must be considered when the drilling fluid has a continuous oil phase.
Cement additives
The major cost for large cement jobs, such as surface casing, is the chemical and additives charges. Typical costs are listed next.
- Cement U.S. $7.00/sack
- Barite U.S. $15.00/sack
- Gel U.S. $15.00/sack
- Mixing charges U.S. $0.95/ft3
A reasonable rule-of-thumb for computing the cost of special additives, such as water-loss agents and thinners, is 75%; of the charges for cement, gel, and barite.
Quick-set, top-out cement is often used on surface casing. It provides short-term strength that allows surface-equipment rigging to proceed while waiting on the other cement to cure. The slurry usually consists of 50 to 100 sacks of cement at approximately U.S. $10/sack.
References
Noteworthy papers in OnePetro
Harms, Weldon M.and Sutton, David L. 1983. Ultralow-Density Cementing Operations. 9597-PA. http://dx.doi.org/10.2118/9597-PA.
PAVLICH, J.P. and WAHL, W.W. 1962. Field Results of Cementing Operations Using Slurries Containing a Fluid-Loss Additive for Cement. 133-PA. http://dx.doi.org/10.2118/133-PA.
External links
See also
Authority for expenditures (AFE)