John Shaughnessy, Darrell Lantz
Smith Tri-Tech Fishing Tools
Lewco Integrated Technical Solutions
This piranah mill is designed to eliminate the possibility of coring while milling up the cemented pipe (Fig. 1).
The recovery of drill pipe that has been cemented in deep, high-pressure, high-temperature well environments requires well thought out risk-management procedures. 1
- This cone-buster mill is designed to mill up bit cones and loose junk (Fig. 2). [13,589 bytes]
- Bladed mills are used to mill up cement, junk, and packers (Fig. 3). [13,620 bytes]
- This concave mill shows wear features incurred after milling off a tool joint (Fig. 4). [14,416 bytes]
- Boot baskets catch junk during the milling operation. Once the pumps are kicked out, material falls back into the boot (Fig. 5).
- A packer-type shoe (burn shoe) was used to washover cemented-in pipe positioned within the casing string (Fig. 6).
- This photo show 100% wear on the packer-type shoe after washing over the cemented-in drill pipe (Fig. 7).
- During the fishing operation, a two-stage mill was used to mill off the remainder at the tool joint (Fig. 8).
- This one-piece, double-bowl overshot is dressed with a Series 150 grapple on the bottom of the tool and a series 70 grapple on the top (Fig. 9).
During these situations, engineers must evaluate all alternatives, such as fishing or sidetracking possibilities, in regards to costs, time, and production considerations.
Each step in the procedure must weigh the advantages of reasonable pipe recovery procedures vs. the risk of losing previous progress.
BackgroundAmoco recently spent about $8 million to drill, evaluate, and case a Cretaceous Tuscaloosa reservoir objective in the Parlange No. 7 well. Unfortunately, a mechanical failure contributed to 780 ft of drill pipe being cemented in the hole, requiring 6 weeks of fishing to recover 27 joints of cemented drill pipe.
Typically, reservoir objectives in this area, located in the Judge Digby field, Pointe Coupee Parish, La., are drilled with a 6-in. hole to about 21,500 ft. To reach this depth, a 16,000-ft string of intermediate casing is set, followed by running 4,000 ft of drilling/production liner. The final hole section is usually about 2,000 ft long.
Cement proceduresThe conditions for completing a successful cement job are challenging in the Tuscaloosa because of the high reservoir temperatures (375° F.) and extreme well bore lengths. Thus, displacement times are long, requiring the cement blend to be more retarded (or inhibited) than most slurries.
Because the small hole size limits the volume that can be pumped, obtaining efficient mud removal within the annular space behind the productive casing usually requires constant moving of the pipe during the cement process. The depth and reservoir pressures, however, limit this ability.
The resulting cement job must balance the small volumes and long displacement times associated with the deep depth. The annular hole volume calculation for a 41/2-in. liner set in a 6-in. hole, using 0.0153 bbl/ft, is about 30 bbl.
The casing liner is run to total depth on drill pipe. Then, cement is pumped through the drill pipe and casing liner to the annular space behind the casing at the objective reservoir. Once the cement is in place, the drill pipe is released and pulled to the surface.
In general, the more cement that can be pumped, the more likely a noncontaminated cement will be in place behind the casing liner. A critical section that requires a good cement bond is located in the annular space between the last casing set and the liner that is being run.
The greater the excess cement volume circulated above the liner, located next to the drill pipe, the more likely good cement will be bonded in that annulus. The small clearances in this example well, however, limit that volume.
An excess of cement volume that yields only a few hundred feet of cement in the previous liner (without drill pipe) may not be enough to avoid contamination in the liner lap. An excess of 20 bbl is 550 ft in the previous liner, without drill pipe, but is more than 800 ft opposite the 41/2-in. liner running string.
The excess volume is about 40% of the total pumped. Under high temperatures, the cement's designed pumping time can become meaningless when displacement is interrupted. Thus, there is no room for errors when it comes to cement operations in the Tuscaloosa.
The cement operation, as generally described above, went well on the Parlange No. 7. Unfortunately, as the setting tool was being pulled from the liner top, mechanical problems related to the rental equipment prohibited pulling additional pipe for about 1 hr.
Thus, the cement set up before it was possible to pull the drill pipe, resulting in a cemented string.
OptionsAt this point, there were two options to regain access to the reservoir:
- Clean out the well by washing over the 31/2-in. drill pipe.
- Sidetrack above the fish.
For the operation on the Parlange No. 7 well, the drill pipe had 43/4-in. OD tool joints positioned inside the 75/8-in. casing (61/4-in. ID). If the fishing operation involved milling off each stuck tool joint, a clearance of only 13/8-in. would remain. If all the tool joints were milled off, however, the pipe would be recovered one joint at a time, involving a round trip of about 18 hr for each joint.
In comparison, the sidetracking option would require cutting a window in the 47.1 lb, 75/8-in. liner followed by the redrilling of about 2,600 ft of hole. Since this section of hole took 39 days to drill before the drillstring was cemented in, this option was avoided because it would take much longer.
In addition, sidetracking operations would depend on the durability of the high-temperature mud motors. In this case, the drilling assembly would encounter a large differential pressure because higher mud weights would be required to drill the liner section as compared to that of the objective sands.
This reservoir pressure regression complicates well planning in the Tuscaloosa play. Because the regression begins at about 20,000 ft, the differential pressure becomes very significant, usually requiring the higher pressure formation, in this case located at a shallower depth, to be cased off before proceeding.
Burn shoeWeighing these options in relation to time and cost savings, the team chose to fish out the drill pipe. There are a variety of fishing tools available for fishing operations (Figs. 1-5); however, the team chose to utilize a burn-shoe/washover technique.
First, a 61/4-in. OD burn shoe was run on 53/4-in. wash pipe (Figs. 6 and 7). The burn shoes were dressed with a tungsten carbide cutting surface (cut-rite) on the ID to minimize potential casing damage.
The cement located around the fish was of good quality, and there was no apparent channeling. Many of the recovered drill pipe joints had a smooth sheath of cement, making the joint appear similar to a 43/4-in. drill collar.
Hydraulic erosion, instead of wear on the shoe, became the major factor for limiting the burn shoe's penetration rate. As more of the fish was covered, the wash pipe's flow restriction, involved with swallowing the cemented drill pipe, resulted in a condition of poor hole cleaning.
On occasion, the shoe had to be pulled to allow the ID build-up to fall down and be swept out as the hole was rereamed. The maximum number of drill pipe joints washed over in one run was five joints, resulting in 30% wear on the burn shoe.
Unconventional approachThe increase in circulating pressure and the decrease in annular flow, as caused by the formation of the hard cement sheath around the drill pipe, could have been addressed by increasing the ID of the cut-rite in the shoe.
This would have been the conventional, "get the most cut up to lessen the problem" approach. Team members, however, took an unconventional, two-step approach to address the risk of annular pack-off while maintaining an economic penetration rate.
First, they decided to decrease the cut-rite ID used to cut away the cement and obtain more circulation clearance. Then, they increased the shoe's OD for purposes of stabilization. This decision was based on the hardness and quality of the cement sheath left on the drill pipe from the first washover.
The decrease in ID actually increased annular flow and penetration rates while decreasing the circulating pressure and shoe wear. Therefore, the hole was more efficiently cleaned, resulting in an improved wash-over process.
Typically, the washover and burn shoe procedures consisted of running the assembly until it tagged the fish or cement cap remaining above the fish from the previous run. While washing over and drilling through the cement, penetration rates of about 4-5 ft/hr were maintained at a rotary speed of 45-75 rpm, with 2,000-8,000 lb bit weight and 1,500-3,000 psi of pump pressure. The operational parameters for milling the tool joints were similar, but progress declined to 1-2 ft/hr.
Because the burn shoes shaved off the tool joint ODs during the milling operation, there was no way to both wash over and grab the fish once the wash pipe bottomed out as the tool joints and pipe stem became flush.
Therefore, after the wash pipe was pulled, a two-stage mill was used to mill off the remainder of the tool joint (Fig. 8). Dual grapples were then used to latch onto the 31/2-in. tube (Fig. 9). The shaved tool joints held together well enough to allow backing off the washed-over pipe on five occasions.
As follows, 23 trips were required to recover the fish, totaling 27 joints of drill pipe:
- Ten trips were made with wash pipe.
- Nine trips were made with overshots.
- Two trips were made with mills.
- One trip made with a screw-in sub.
- The final trip was made with a spear.
Therefore, the design of the wash over shoe became critical for the success of the operation. The shoe could not damage the casing because it was needed for long-term well production. In addition, if the shoe damaged the drill-pipe fish, it would significantly increase removal time.
Ongoing evaluationFollowing each trip, the team evaluated the ongoing costs and time associated with the fishing procedures, centering on the continued effectiveness of free pipe recovery and wash-over operations.
There was always less risk in attempting the recovery of free pipe as compared to continuing the washover process. A fishing operation, however, requires continuous progress that makes or exceeds the economic limit for moving forward with this activity.
The possibility of mechanically wedging the wash pipe over the drill pipe, possibly resulting in an unrecoverable mess, always existed. For each of the 23 trips, the viability of a sidetrack was risk weighed against continuing the fishing operations.
At the end of a trip, it was known at what depth a sidetrack could begin. If the fishing string became stuck, the sidetrack point would have to be moved up the hole.
The fishing results can be summarized as follows:
- Total cost of the fishing operation-$1.5 million.
- Sidetrack option (estimated)-$3.5 million and 60 days. This includes less chance for a good cement job and significantly more risk.
- The primary job on the 41/2-in. liner was good.
- The production liner was not damaged by the burn shoes or wash pipe.
- The job will provide a base line for future fishing operations.
- Shaughnessy, J.M., Lantz, D., Pullen, S., Daugherty, R., and Lashley, T., "Patient Fishing Saves Deep Well," The Brief, November 1998, p. 10.
John Shaughnessy is a drilling engineer for BP-Amoco working on the Tuscaloosa drilling team. He has 21 years of experience working on a variety of drilling projects. He holds a BS in chemical engineering from the University of Pittsburgh.
Darrell Lantz is a drilling foreman for BP-Amoco in the Tuscaloosa drilling team. He has 19 years' oil field experience offshore on the the shelf and deepwater as well as land. Lantz holds a BS in petroleum engineering from Mississippi State University.
Tommy Lashley is operations manager for Smith Tri-Tech Fishing Services. He has 32 years' oil field experience, both domestic and international. Lashley has been running fishing tools for 23 years.
Scott Pullen is a consulting engineer with Lewco Integrated Technical Services. He has worked in the oil and gas industry for more than 20 years. He has a petroleum engineering degree from Texas Tech University.
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