REMOVING WELLHEAD SLIPS
Removing the wellhead slips requires that the pipe string be lifted to take the string weight off the wellhead slips. The force required to move the pipe upward may be greater than the safe pull force of a workover rig and sometimes even greater than a drilling rig. A Casinjac can be used to safely apply the necessary pull force.
Factors contributing to the required lift force are:
- The pipe is stuck at a shallow depth
- The work-over or drilling rig is not rigged up over the hole.
- The wellhead slips are binding in the wellhead.
- The total weight of the pipe string
- The pull sub is not straight
- The pull sub is not welded on straight
SAFETY FACTORS
- Many of the present day workover rigs are 20 or more years old. Many have not been ex-rayed and/or completely inspected. The drilling lines have not changed and have been subjected to excessive ton miles. Operation of such rigs at or near their design capacity would not be safe.
- Mast support - Matting boards used to support the masts during rod and tubing work are often not adequate for casing pulling.
- The ground support is diminished when the hole around the wellhead is too large. Rain wets and softens the ground around and under the matting boards or cellar beams making it spongy and causing it to subside when a load is applied.
- If the pipe parts parts up the hole or above the ground the energy released puts the rig and personnel in danger. Pull subs should be inspected carefully before use, they should have a usable pipe collar on top, be the proper grade and weight and also be of sufficient length.
- Under heavy loads the drilling lines and the draw works chains
can break.
A Casinjac is mounted on the wellhead and is not subject to the limitations of matting boards, cellar beams, masts, drilling lines, draw works chains and soil conditions. Using a tool that is designed to handle heavy loads safely is not only more safe but more profitable.
WORKING THE CASING
In order to maximize the recovery of casing it is important to work the casing. Working the casing involves lifting and lowering the casing using a Casinjac and lifting and dropping the pipe using the work-over rig. This process conditions the hole and allows greater pipe movement up and down the hole. This process is continued until the casing no longer moves downward. The casing is then in a worked down condition. Sometimes it is necessary to move the casing up and down using the casinjac in order that the rig can pick up the casing upward enough to work the casing down effectively. Usually the forces used to work the pipe do not exceed 80% of the listed tensile strength of the casing and/or its joint strength whichever is less. The work-over rig is used to work the pipe down hole by picking it up and dropping it to effect a spudding action which allows the pipe to move down through areas in the hole which are impeding pipe movement. The casing can be marked using a crayon which can be used to monitor pipe movement. When the casing quits moving upward or downward a free-point procedure can be performed to determine the amount of free pipe.
FREE-POINTING
Free-pointing is a method of determining the free-point of a pipe string. The free-point being the down-hole location of a point above which the pipe can be parted and pulled without exceeding the safe pull force of the pipe. Experience has shown that the free-point determination is subject to the limitations of the equipment, procedure, and personnel used.
Basically what is required to determine the free-point is as follows:
- The ability to apply an adequate pull force and to measure it accurately.
- The ability to maintain this pull force at all times as the pipe moves up-hole.
- The ability to accurately measure the pipe stretch that results from a applied stretch force.
- The ability to measure the relative pipe movement at a given section of pipe down-hole when a stretch force is applied.
- The ability to apply enough pull force to cause it to move at the lowest possible depth while not exceeding the safe pull force of the pipe.
- The ability to work the pipe down after each free-point determination and before another free-point is attempted.
Current methods in use to free-point pipe strings are:
Using work-over rigs. The work-over rigs pull the string weight, set the brake and mark the pipe. The rig then pulls an additional amount of force (stretch force) and marks the pipe again. The distance between the marks represents pipe stretch caused by the stretch force.
The problems encountered when attempting to free-point with a work-over rig are as follows:
- The inherent inaccuracy of weight indicators and the infrequent calibration of same.
- The work-over rig is incapable of maintaining a constant pull force as the pipe moves up-hole. The inability to maintain a constant pull force as the pipe moves up-hole results in an inaccurate stretch determination.
- When the rig's pull force increases the rig "squats". its wire rope stretches, and the matting boards/cellar beam subsides. It is not possible to possible to determine the effect on the stretch measure ment these variables cause.
- Sometimes the work-over rig cannot pull the string weight, sometimes it cannot pull the string weight plus a reasonable stretch force. and often it cannot pull the string weight plus two consecutive stretch forces much less a third consecutive stretch force.
- Using electric wire-line tools to free-point. This method is used to free-point stuck drill pipe and to free-point casing in work-over operations and is used less often during plugging and abandonment work. Usually a drilling rig or a work-over rig is used to move the pipe string, The free-point tool measures pipe movement over narrow range (about 6 feet or so). The free-point tool is positioned in the hole where it assumed that the pipe is 100% free, the rig applies a specified pull force and the tool indicator is adjusted to read 100%. The tool is then lowered to a lower depth, the pull force is applied, and another reading is taken to indicate pipe movement and compared to the initial reading. The tool is lowered to different intervals and readings taken until no pipe movement is indicated,
Assuming the wire-line operator is competent, the instruments etc: are of good design and good condition the following has been observed when free-pointing using wire-line tools and methods.
- A pull force is chosed that is within the capabilities of the work-over rig or drilling rig and often well below the safe pull force of the pipe string being free-pointed. Obviously this precludes an observation that would show that the pipe string would possibly show that the pipe would move at a lower depth if the pull force was sufficient.
- The pipe string is not worked down prior to the application of the specified pull force and the attendant free-point measurement. This often results in a free-point indication that indicates the top of an down-hole area of tightness rather than the maximum free-point depth.
- If the wire-line procedure applied a safe pull force that would assure the movement of all free pipe and if the procedure worked the pipe down after each free-point observation, it appears that this method world provide good information.
- When the pull force is applied by a work-over or drilling rig the repeat ability and accuracy is suspect due to reasons previously cited.
Free-pointing with a Wellhead Casinjac
A Wellhead Casinjac can be equipped with instrumentation to accurately measure and apply necessary forces and to accurately measure the pipe stretch resultant from these forces.
- The safe pull force can be applied resulting in the movement of the maximum amount of pipe at the safe pull force.
- The pull can be held constant as the pipe moves up-hole, allowing for observing an accurate stretch measurement resulting from a given pull force.
- Consecutive stretch forces can be applied and their respective stretch
amounts observed.
These observations lead to the following reasonable conclusions:
- If the free-points observed are nearly the same the pipe is stuck at one point.
- If the free-points are greater as more stretch force is applied the pipe is partially stuck up-hole and the free-point lowers as the pipe is pulled through tight spots.
- If the free-point depths diminish as the stretch force increases then the hole is probably deviated and the pipe becomes wall stuck as it tries to align itself.
- Using a calibrated digital pressure indicator and an encoding linear transducer lift forces and pipe movement can be measured as accurately as any method currently available.
- If the pipe sting is a combination string, it is necessary to know the amount and weight per foot of each segment and where it occurs in the string.
- Repeating a specific pull force and working the pipe down after each free-point procedure can be easily down using a work-over rig and a casinjac.
PARTING THE PIPE
The pipe string is parted in one of the following ways:
- It is parted be backing off
- It is cut mechanically
- It is cut using an explosive shaped charge in the body of the pipe
- It is parted by a shaped charge splitting the collar
- It is parted by using dynamite or nitro explosives located in the collar
A casinjac can provide a precise and constant pull force. Manufacturers of explosive devices used to part pipe recommend that the pipe be in tension by amount at least by 1.3 times the weight of the being shot off.
Sometimes it requires that the pull force required to finish parting the pipe will approach the safe pull force of the pipe. When parting the pipe using mechanical cutters the casinjac can hold the pipe using a rotating bearing to prevent subsidence. Casinjacs with a rotating bowl have been used to unscrew casing patches.
RUNNING PIPE
A casinjac can be used to run pipe.Casinjacs have been used to run pipe when a work-over rig or a drilling rig could not safely handle the string weight.
Pictures
PROFITS
The use of casinjacs often results in increased income from more pipe recovery, safety, and cost savings.
Sometimes operators fail to include Casinjac use in their job planning:
they try to use a work-over rig or drilling rig to get the pipe off the well head slips, when they are unsuccessful they call for a casinjac. This results in rig time costs while waiting on casinjacs.
Sometimes operators use a work-over rig to free-point and when they try to part the pipe they can't pull it and have to come up the hole and shoot the pipe again. This results in less pipe recovery and the costs of shooting the pipe twice.
The use of Casinjacs to obtain a more accurate free-point, to finish parting the pipe if necessary when the explosive does not completely do its job.
EXAMPLES
Example 1:
A drilling rig was rigged up over an existing well. The plan was to pull 7,000 ft. of 7" casing, re-enter the well, and drill a deviated hole kicking off about the 7,000 ft. depth. The big rig could not get the pipe off the well-head slips. They called for Casinjacs. After lifting the string off the slips and stacking out the pipe a free- point was determined with the Casinjac using the pipe stretch method. A wire-line truck had been called out initially to free-point the pipe after the rig got the pipe off so then a free point was determined using the wire-line free-point tools. The wire-line free-point was 2300' and the casinjac free-point was 2400'. The cost of the Casinjac service was $1,100.00 the cost of the wire-line service was $2,500.00. Conclusion: A work-rig could have been used with a Casinjac to get the pipe of the slips and free-point the cost of the wire-line truck could have been saved, and the cost off moving in a rigging up the drilling rig could have been saved ( $150,000 plus)
Example 2:
A casinjac was used to lift a pipe string (9 5/8" x 53.5# pipe) to remove the well head slips. The pipe was stuck so shallow that the string could not be stretched far enough to remove the wellhead slips. The Casinjac free-pointed the pipe to maximize the recovery below the surface pipe.
Example 3:
After removing the wellhead slips and stacking out. The work-over rig attempted to work the pipe down. At this point the rig was unable to lift the pipe far enough to drop it to work the pipe down. A Casinjac was used to work the pipe up and down to free it up so the rig could work it down effectively. After alternately working the pipe up and down with the Casinjac and the workover rig 7,000' of 5 1/2" x 17# N-80 pipe was recovered.
Example 4:
Plugging operation - Free-pointing
A wire-line was used to free-point a string of 7 5/8" casing: the wire-line operator suggested that the pipe was "dead stuck" at 5,000'. A Casinjac was used to free-point the same string. This free-point indicated that the pipe was free at 7,000 ft. The consultant called the operator and the consultant was instructed to shoot the pipe at 7,000 ft. 7,000 ft. was recovered.
Example 5:
Plugging operation - Free-pointing
During this operation two strings of pipe were recovered. 11,500 ft. plus of 5 1/2" casing and 7,000' plus of 9 5/8"x53.5#. The company man didn't want to remove the wellhead slips without using a annular blowout preventor that would allow passage of the wellhead slips. A Casinjac was rigged up on the blow-out preventor and the casing was stretched to allow removal of the slips above the preventor. Try doing this with a workover rig. A wireline was used to free-point the pipe as was the casinjac. The wireline free-point was 6,000 ft. The casinjac free-point was 8,000'. The casinjac operator related to the company man that the pipe could be worked down further which would mean recovery below 8,000'. The company man called his supervisor and was instructed to cut the pipe at 7,000' 7,000' was recovered. The conclusions concerning this operation are obvious.
Example 6
Plugging operation - Free-pointing and working the pipe On a Friday afternoon a string of pipe (5 1/2" x 17# N-80) was free-pointed using a casinjac. The free-point indicated was 1,900'. The work-over rig was shut down for the weekend. The casinjac was used to work the pipe the remainder of the day Friday and all day Saturday and Sunday. This activity required only the casinjac operator and a helper. On Monday morning the pipe free-pointed at 6,000 ft...6,000 ft. was recovered. The net gain was $16,400.00. (4,100 x 4.00).
Example 7:
Plugging operation - Free-pointing
This operation involved recovering 5 1/2"x17# N-80 casing. All that remained on this location was a cased hole. The top of cement was 10,000 ft. The work-over rig operator had determined using his slick-line that he would be able to get to only 5,000' with his explosive cutter due to mud conditions. A Casinjac was used to get the well off the wellhead slips. The pipe was worked down with the workover rig. A free- point was determined by first lifting the string weight. (17# x 10,000 ft. = 170,000 lbs.) then applying a stretch force of 40,000# to indicate 7,000' free. The operator suggested that the the pipe be worked down further to see is more pipe could be recovered. Casinjac operator suggested that first additional 40,000 lbs of stretch force be applied. (210,000# to 250,000#) this was done and this second consecutive 40,000 stretch force indicated 9,400 ft. free. The operator rented a string of tubing, cleaned out the hole, and 9,400' pf pipe was recovered.