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AFE: rental equipment
Drilling equipment that is beyond the scope of the contractor-furnished items is almost always required to drill a well. These items must be rented at the expense of the contractor or operator, depending on the provisions of the contract. Regardless of which party is incurring the direct expense, rental equipment should be included in the authority for expenditure (AFE) for the well.
Some of these rental equipments may include:
These items can represent a substantial sum in deep, high-pressure wells.
Drilling contractors usually furnish BOPs, chokes, choke manifolds, and, in some cases, atmospheric degasser units. However, the equipment may not be satisfactory for a particular well. In addition, some land rigs currently operate with well-control equipment that is not state of the art, such as positive chokes, manual chokes, and manifold systems that do not have centrally located drillpipe- and casing-pressure gauges.
BOP rental is expensive. High-pressure stacks range from U.S. $1,500 to $3,000/day, exclusive of chokes or manifolds. The operator must define the worst pressure case that can feasibly be attained and select preventers accordingly. Cost estimates for a complete stack must consider the spherical, multiple ram sets, spools, studs, ring gaskets, and outlet valves.
Remotely controlled, hydraulic adjustable chokes are considered state-of-the-art and are available from several sources. Contractors seldom furnish this type of choke primarily because operators have always assumed this cost responsibility. These chokes usually cost U.S. $50 to $125/day with a 30-day minimum charge. Choke manifolds must be designed to withstand the maximum pressure ratings in addition to coinciding with current company philosophy.
Rotary tools and accessories
Rotary tools are items related to the drillstring or equipment that turns the string. The operator may be required to furnish (1) support equipment for the contractor’s drillpi, or (2) a completely different string, if the contractor’s drillpipe does not meet the requirements (i.e., tapered or work strings).
Some of the items that may require consideration include:
- Drill collars.
- Kelly drive bushing.
- Kelly cock valves (upper and lower).
- Inside BOP.
- Full-opening safety valves (FOSV).
- Safety clamps.
- Pipe rubbers.
The operator must evaluate the requirements for drillpipe sizes different from those offered by the contractor’s rig. A recent study of U.S. rigs showed that pipe sizes on the rig could be correlated with the IADC hydraulics code (Table 1). In addition, Table 1 includes guides for drill-collar and casing combinations.
For example, 4.5-in. drillpipe with 6.5-in. collars would not be recommended for drilling inside of 7.625-in. casing, because of the wear of the tool joints and collars on the casing. A smaller pipe- and collar-size combination would be recommended. If the 7.625-in. pipe were a drilling liner, a tapered string would be satisfactory, but an extra BOP might be required.
A work string consists of small-diameter drillpipe and collars. It is used generally during completions or workover operations. Because the pipe will be used inside production casing, the usual sizes are 2.375 to 3.5 in. Most operations require a rental string because few rigs drill with this size pipe.
A properly maintained mud system offers many benefits to the operator. To achieve the desired level of system efficiency, several specialized pieces of equipment may be required. Some of the equipment must be rented, even though the drilling rig may be well equipped with other drilling tools.
A complete suite of equipment required for the mud job usually depends on the mud type and weight. The following suite may be used for mud weights in the 8.33- to 12.0-lbm/gal range.
- Multiscreen shaker.
- Desilter (with pumps).
- Mud/gas separator.
- Degasser (vacuum).
- Pit/flow monitors.
- Drill-rate recorder.
- Gas detector.
Mud weights greater than 12.0 lbm/gal may require the use of additional equipment such as a centrifuge or mud cleaner. Oil muds need a cuttings cleaner to remove the oil from the cuttings prior to dumping.
Recently, great strides have been made in running casing. Specialized equipment and crews normally handle the task rather than using the rig crew and equipment. Because most rigs are not furnished with casing-running equipment, it must be rented.
Casing tools must be selected according to size and loading requirements. A commonly used method for evaluating the load requirement is to add a design factor of 1.5 to the in-air weight of the casing string. For example, a casing string that weighed 500,000 lbf in air would require 375-ton casing tools.
The suite of equipment to run casing depends on the operator’s preference. It can include:
- Protector rubbers.
- Power tongs.
- A power-tong hydraulic unit.
- Stabbing boards.
- Drift gauges.
- A thread-cleaning unit.
- Safety clamps.
In addition, it is usually desirable to rent several pieces of backup equipment in case of breakdowns, in most cases an inexpensive type of insurance. These items include:
- Backup tongs.
- A backup power unit.
- A backup elevator/slip combination unit.
Laydown and pickup machines were introduced to the industry in the late 1970s. These units increase the efficiency and safety of picking pipe up to the rig floor or laying it down on the pipe rack. Also, they usually minimize possible damage to pipe threads.