By Hugo Valdez and Tommie Rogers, ODS International Inc
In oil and gas recovery operations, tubular members are usually run or pulled using a workover rig or a snubbing unit. Workover rigs are basically small drilling rigs having a derrick and drawworks, and although they are less expensive to employ than full-sized rigs, their use can still be quite costly.
Snubbing units are smaller, easier to transport and less expensive to operate than workover rigs and are often employed when working a pressurized well that requires tubular members to be forced into the wellbore.
Figure 1: A power tong built specifically
for snubbing and well control applications.
A viable alternative that improves safety and efficiency during snubbing operations consists of a power tong set, with lead and back-up tongs that are mounted on the slip bowl of the traveling jack head of a snubbing unit and rotates with the slip bowl. Service lines for the tong set are not connected during string rotation.
In another version of this type of device, a fluid feed-through swivel is mounted on the tong set, secured to the necessary tong operating and control service fluid lines, such that the tong set can rotate with tong service lines between the tong set and the snubbing unit attached during rotation.
In an alternate form, the tong set is mounted on the jack head, independent of the rotary table, and the tong set does not rotate when the rotary table rotates.
Snubbing is an old technique dating back to the late 1920s in the United States that was primarily used in emergency situations, such as blowouts or uncontrolled wells.
Like coiled tubing techniques, snubbing allows a tubular to be run with a check valve on the end into a live well by means of specialized handling and sealing systems. However, instead of pipe coiled up on a reel, it uses tubing-type pipe lengths run in hole and made up to each other by conventional threaded connections. This means that larger-diameter pipe can be used than in the coiled tubing method.
The snubbing unit therefore offers better flow capacity, breaking load and rotation capacity and is able to put weight on the downhole tool. In contrast, tripping takes longer because the lengths of pipe have to be screwed together and the procedure for running the connections through the safety stack on the wellhead may be slow and represents a high risk for personnel if not done properly.
Figure 2: One model of the
snubbing tong is jack-mounted.
A snubbing unit consists basically of a pipe-handling system, a wellhead safety system, a hydraulic power unit and the downhole accessories incorporated into the snubbing string.
The pipe-handling system must be able to push the pipe into the well during the snubbing phase (also called light pipe phase), which occurs every time the pipe weight is lower than the wellbore pressure force against it.
Hydraulic units are commonly used with double acting jacks equipped with two system slips, one stationary and the other mobile (traveling slips).
The mobile system usually consists of only one set of single acting slips while the stationary system consists of two sets of opposing slips that keep the pipe in place, whatever the phase of the operation, and it is located below the low position of the traveling slips.
With the traveling slips closed and the stationary ones open, the pipe can be tripped over a length corresponding to the stroke of the jacks. Then, all that is required to bring the jack back to its original position is to close the stationary slips and open the traveling slips. After the traveling slips have been closed again and the stationary slips have been opened, the operation can continue.
The pipe is brought up from the pipe rack by a set of elevators, sheaves and a handling cable attached to the gin pole, and the connections are made by using a set of power tongs that remain hanging by cable at the height of the work area. The tong may also be attached to a tong arm fixed to the basket.
Operating in this manner requires specialized people, usually consisting of a foreman and three or four people per shift. The space in the snubbing basket is usually very limited and unstable, which magnifies the hazards associated with the manipulation of pipe, elevators and power tongs.
SNUBBING POWER TONG
ODS International and Rogers Oil Tools (ROT) have developed a patented power tong built specifically for snubbing and well control applications (Figure 1). It is the only tong designed to ride the jack incorporated with a swinging basket.
No tong pole and no pushing or pulling of the tong on and off the pipe is necessary, which eliminates nagging injuries (broken or mashed fingers, twisted or strained backs, shoulder damage) and significantly improves the efficiency of the operation.
ODS-ROT can provide different models, either slip or jack-mounted (Figure 2), providing the choice of eliminating personnel in the snubbing basket by utilizing the remote operation option.
The jack head tong carries the provision of having a three-section cage plate system that can be removed to allow the jack head tong to be open for full wellbore capabilities, matching the BOP’s bore. This is the fastest and safest way to trip pipe with a snubbing unit.
Snubbing is an old technique with relatively little innovation over the past several years. The hazards associated with this type of operations still must be considered when seeking to eliminate risks.
The snubbing power tong introduced in this article is a viable alternative, making operations safer by eliminating movement of the tong on and off the pipe. This eliminates nagging injuries and increases the operational efficiency, which ultimately impacts the overall costs of well servicing programs in benefit of operator and drilling contractors.
1. Perrin D.: Well Completion and Servicing, Technip, Paris, France (1995).
2. ODS-ROT Specification Manual, Internal Publication, Houston, TX (2009).