A new fishing service tackles the junk problem in wellbores, helping to avoid sidetracks and workovers.

A new through-tubing system helps clear difficult junk- and sand-blocked wellbores that until now have required workover or bypass drilling. By permitting drilling and completion to continue, this system avoids delays and high-cost rig time; in Venezuela, Alaska and the North Sea, initial fishing job successes have saved millions of dollars.
Weatherford's Thru-Tubing Fishing Group offers this service with a new tool called the Cyclone Bailer, designed for horizontal and deviated wellbores.
Boosting available vacuum
The initial testing, under the direction of Dick Giroux and Mike Luke, senior engineers at Weatherford, resulted in design of a new Venturi-type nozzle and configuration. This new nozzle increased the vacuum to attract sand and large debris downhole. Where available, Venturi nozzle tools delivered about a 3-in. mercury vacuum. The new bailer tool provided up to 27 in.
In one of the first tests, a prototype 21/16-in. tool using a 21/16-in. nozzle vacuumed up more than 2 tons of sand from a 95/8-in. casing in less than 10 minutes with a 1-bbl/min flow rate, retaining it in a 51/2-in. wash pipe.
In its release design, the bailer combines vacuum-generating cyclone nozzles, a high-performance screen, washpipe or bailer sections and a flapper valve to retain solid junk. Other components such as a sand screen and burnover shoe are added as needed, and tools are available in several ratings, sizes and configurations.
Initial Lake Maracaibo successes
One of the first through-tubing fishing jobs took place on Lake Maracaibo in April 2001, following several failed attempts by two through-tubing fishing companies to recover remaining perforating gun debris that prevented passage through the area. The tubing size was 31/2 in., 9.3 lb/ft with a minimum restriction of 23/4 in.
The crew decided to run in the hole with a 2.125-in. OD motor head assembly consisting of a coiled tubing connector, dual-flapper backpressure valve, hydraulic heavy-duty disconnect, a dual-actuated circulation sub, a 21/8-in. OD coiled tubing drilling motor, a bailer, 25 ft of 25/16-in. OD wash pipe and a 25/8-in. OD by 1.0-in. ID carbide-dressed burning shoe with flapper cartridges inside. The work string was 11/2-in. OD coiled tubing with a wall thickness of 0.125 in., 80 K material. Bottomhole temperature registered at 240°F (115°C), bottomhole pressure at 2,700 psi and wellhead pressure at 0.
Workers tested the bottomhole assembly (BHA) prior to running in the well. They used a circulation of 0.3 bbl/min while running in and made a tag at 5,679 ft (1,732 m). At 5,500 ft (1,678 m), they picked up the tubing, increased the pump rate to 1.06 bbl/min, 4,150 psi, then established circulation. By moving the work string and tools up and down, crews lowered the BHA to 5,679 ft (1,732 m) and advanced to 5,807 ft (1,771 m). After 20 minutes at this depth, they pulled out of the hole; the washpipe was full to 23 ft (7 m) with gun debris and carbonate. Crews then made a second run with the same BHA; the circulation rate registered at 0.3 bbl/min, and a tag was noted at 5,807 ft (1,771 m). They picked up the tubing and tool string to 5,790 ft (1,766 m) and increased the pump rate to 1 bbl/min at 4,200 psi. They lowered the work string and tools to 5,807 ft (1,771 m) and worked down to 5,810 ft (1,772 m). After moving the tubing and tools up and down several times during a 10-minute time span, they pulled out of the hole; the washpipe contained 10 ft (3 m) of gun debris and carbonate.
Total footage advancement was 131 ft (40 m) with 33 ft (10 m) of gun debris weighing 64 lb. The job eliminated the need for a costly workover.
The second success with the tool occurred when a major operator drilled a well on Lake Maracaibo budgeted for 28 days drilling and completion. Numerous problems pushed the time to 68 days to run a 31/2-in. slim hole to the zone of interest. The operator then moved the drilling rig off of the well and moved a jackup into place for perforating.
The zone to be perforated was at about 16,650 ft (5,078 m). The electric line was unable to reach the required depth, so slick line was rigged up to clean the well. Only some aluminum and rubber debris could be recovered from the well; the holdup depth (HUD) had not been increased. Workers decided to run a 2.25-in. OD skirted magnet. This was the largest outer diameter possible due to a 2.313-in. profile nipple in the completion above the 31/2-in. liner. When they retrieved the slick line, the mandrel of the magnet had pulled out of the skirt and magnet, leaving a two-part fish. The skirt of the magnet was 304 stainless steel with a 2.25-in. OD, a 2.1875-in. ID and a 1.02-in. hole in the center to accommodate the mandrel. Inside this part of the fish was a 2.25-in. magnet made of 4140 material with a 5/8-in. tapered thread that the mandrel screwed into.
The 2.25-in. OD with a 2.313-in. restriction above negated the possible use of an overshot. Crews made several trips using slick line with various types and sizes of spears without recovering the fish. Their last attempt was with a lead impression block; upon retrieval, the crew discovered debris above the magnet's skirt.
The operator then tried coiled tubing with the bailer to remove the debris so that further fishing operations could continue. The BHA consisted of: 11/2-in. coiled tubing, a 23/16-in. motorhead assembly, a 21/8-in. coiled tubing drilling motor, a 21/16-in. Cyclone Bailer, a 21/16-in. screen, 92 ft of 21/16-in. wash pipe and 21/4-in. double-flapper check valves with rotary shoe.
Workers ran coiled tubing to the top of the fish while circulating at 0.25 bbl/min until tagging the fish at 16,613 ft (5,067 m). They increased the pump rate to 0.75 bbl/min, applied 2,000 lb of weight, and the fish started moving down the hole. The fish continued down the hole until reaching a depth of 16,708 ft (5,096 m).
Original depth of this well was 16,710 ft (5,097 m); crews pulled out of the hole as the fish was well below perforating depth. The recovery at surface was one joint of the wash pipe full of an extremely viscous oil-based drilling fluid, water and debris-type emulsion. The second joint was primarily water, and the bottom joint had about 10 ft (3 m) of sludge, later determined to be barite. Coiled tubing was rigged out of the way, and a memory gamma ray/casing collar locator log was run on slick line showing a HUD of 16,707 ft (5,096 m). Electric line then was rigged up and the well perforated.
Cost to drill the well was estimated at US $14 million. If crews could not remove the fish or at least move it to below the desired depth of the perforations, it would have required moving a rig back over the hole and, at the minimum, pulling the completion. In the worst case, a sidetrack would have been necessary.
Later on Lake Maracaibo, a Petroleos de Venezuela SA (PDVSA) well would be the third of the bailer rescues. The objective of this through-tubing fishing job also was to clean perforating gun debris, this time resulting from perforating 3.5-in., 9.3-lb tubing.
The first attempt to clean up the debris involved running 1.5-in. OD coiled tubing as the work string, a 1.69-in. OD motorhead assembly and a 2.25-in. OD three-bladed junk mill. Circulation fluid was 8.3-lb/gal freshwater and 3% potassium chloride with 350 cf/m nitrogen. The BHA tagged at 5,864 ft (1,789 m). Workers picked up the tubing 10 ft (3 m) and increased the circulation rate to 0.6 bbl/min, 2,400 psi; the BHA advanced to 5,866 ft (1,789 m), but was unable to move farther. PDVSA pumped 10 bbl of 20% hydrochloric acid and pulled the BHA out of the hole. The next BHA consisted of a 2.125-in. OD motorhead assembly, 2.125-in. bailer, 2.125-in. OD coil tubing drilling motor, 25 ft (8 m) of washpipe and 2.625-in. OD carbide-dressed burning shoe with flapper assembly inside.
PDVSA ran this assembly in the hole without pumping, tagging at 5,866 ft (1,789 m). It picked up work string and tools to 5,816 ft (1,774 m) and established circulation at 1 bbl/min, 4,100 psi. It lowered the tubing to 5,866 ft (1,789 m), then moved the work string up and down on the debris; the work string and tools reached 5,869 ft (1,790 m). After 10 minutes of circulation, workers pulled the BHA out of the hole and recovered 13.5 lb of gun debris. On their second attempt, they ran the BHA in the hole again, tagging at 5,869 ft (1,790 m). With circulation flow at 1.1 bbl/min and 4,100 psi, crews worked the BHA up and down for 10 minutes, pulled out of the hole and recovered another 5 lb of gun debris. A third run with the same BHA tagged at 5,869 ft (1,790 m) and worked to 5,888 ft (1,796 m) in 10 minutes, recovering 23 lb of gun debris. A fourth run tagged the debris at 5,888 ft (1,796 m) and worked to 5,893 ft (1,797 m) with a 1.1-bbl/min circulation rate, 4,150 psi. Fluid used was 8.3 lb/gal with 450 cf/m at 0.5 bbl/min. The tool string then began pulling excess weight for 10 ft (3 m), so crews pulled it out of the hole for inspection. The BHA was in good condition and working fine. Total recovery of debris: 29 ft (9 m) weighing 49 lb.

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