Reservoir life is a common concern in developing older, mature fields. As technology has drastically reduced the amount of reserves stranded in the reservoir, extending reservoir life is still a major goal for most operating companies.

A number of technologies are being developed to achieve that objective. Among them is Perf-Drill’s Perforating Tunnel Tool.

The tool’s primary objective is to provide access through the casing in producing and/or injection wells. The tunneling technology enables wellbore access beyond nearwellbore damage to unaffected formation. Perf Drill has no o-rings or gaskets and can be run at any depth and at any temperature.

Single trip flexibility

The main components of the tool are an anchor and whipstock assembly, the tool body, a patented flexible drive shaft and bit, and the top external drive shaft.

The flexible drive shaft is internally spring-loaded to provide weight on bit (WOB) drilling control. Initial trajectory is achieved with 3,000 lb WOB to exit the casing with that weight maintained for the next 3.7 m (12 ft) of penetration.

The Perf-Drill build rate is nine degrees per foot. At 3.7 m of vertical drop WOB is reduced to 1,000 lb for the next foot of drilling. This allows the flexible drive shaft to point the bit at the trajectory presented at 4 m (13 ft) of penetration. The 3,000 lb WOB can be returned, and the Perf Drill tunnel can then be completed to 9 m (30 ft).

The tool is designed as a single-trip, through-casing, short-radius, lateral tunnel drilling tool. It is run in hole (RIH) as a single unit, the anchor set, and drilling initiated. The drilled production tunnel ID is 2.9 in. and can reach 9 m of lateral extension from the wellbore. A power swivel, top drive, or mud motor can be used as the rotational power source. The tool has drilled through 4 ½-in., 5 ½-in., 7-in., and 10 ½-in. P110 casing. In the 10 ½-in. project, the tool drilled through 7-in. casing set inside of the 10 ½-in casing for a total P110 steel thickness of 1.625 in, with the exit accomplished in 12 in. of vertical travel.

The casing exit design sets the guide path and trajectory of the Perf Drill Flexible Drive. The 16-in. long built-in “stubby” whipstock has a 10-degree exit face and is through-hardened to provide a slick guide for the bit. The patented design allows a 4.5-degree bend every 6 in. while maintaining rigidity and trajectory. As the leading edge of the bit encounters the casing wall and weight is applied to the drillstring, the bit pulls itself away from the whipstock while it drills the casing exit. The first flexible drive section, located only 6 in. behind the bit, allows the drive to bend and transfer the majority of applied weight to the leading edge of the bit. At least 75% of the weight applied to the bit transfers to the leading edge of the profile. This unique function of the flexible drive significantly extends whipstock life and overall tool efficiency.

The casing exit design sets the guide path and trajectory of the Perf Drill Flexible Drive. The 16-in. long built-in “stubby” whipstock has a 10-degree exit face and is through-hardened to provide a slick guide for the bit.

Injection rate improved

The tunnel tool was applied recently in two natural gas injection/production wells in an aquifer gas storage facility. Two months after the job was completed, the injection rates had improved by 50%. Well #1 improved from 2MMcf/d to 3.5MMcf/d, and well #2 improved from 3MMcf/d to 4.5MMcf/d.

The first well presented a unique problem – the need to drill through a 5 ½-in. OD liner and 7-in. OD casing to reach the formation. Using a specially designed bit, the company drilled through this double casing. In the first double casing exit, the tool completed the exit in about one hour. The operator decided to attempt the first complete tunnel as well with the special casing exit bit. When drilling slowed, after 5 m (17.5 ft) the operator pulled the entire tool and changed bits to drill the second exit.

Perf-Drill was RIH with the special dual-casing bit, set the anchor, and began drilling the double casing wall. After one hour, the tool exited the casing and drilled another foot to assure exit position. The tool was pulled out of the hole, leaving the whipstock assembly and bottomhole assembly (BHA) in place. The bit was changed, and Perf-Drill’s steel body bit with carbide inserts was then reentered in the initial hole and continued drilling to a 8.5 m (28 ft) TD, which was completed in one hour.

The second well (with two 8.5-m lateral exit tunnels) was completed without incident. Once the anchor was set, the tool was applied to exit the 5 ½-in. casing, drilling through it in 25 min. and continuing at 3,000 lb WOB for the next 4 m. At the 3.7-m penetration mark, the weight was reduced to 1,000 lb for the next foot of drilling. At 3.9 m (13 ft), when the tunnel traveled to horizontal, 3,000 lb was returned to the drive string, and the tool continued to a TD of 8.5 in one hour.

The operator decided to drill the second tunnel with the existing bit. The anchor was unset, and the tool was lowered 0.6 m (2 ft) and rotated 180 degrees to begin the second perforation tunnel. The casing exit required one hour. The 8.5-m tunnel took another two hours, a result in part of the carbide cutters having become dull while drilling the first perforation tunnel in the same well.

The second well had a normal 5 ½-in. casing string and was completed in one trip. This presented two Perf Drill perforation tunnels that each extended to 8.5 m from the wellbore. The first tunnel took 1.5 hours. The second tunnel required 3 hours. In one trip, the Perf-Drill tool was able to drill two 2.9-inch ID by 8.5 m deep perforation tunnels in 4.5 hours.

Looking ahead

This tunnel tool has operated from rigs as small as a single pole pulling unit to a snubbing unit, drilling through 23# 5 ½-in. pipe, cement, and 19.5 pound mud. One 9-m (30-ft) Perf-Drill tunnel presents the same formation exposure as 57 casing gun shots. The ability to penetrate past any near wellbore damage at any depth, any temperature, and any size pipe makes Perf-Drill an ideal tool for reentering old assets, drilling deep clean perforations, and helping to bring old producers back to higher production levels.

The Perf-Drill BHA consists of an anchor and whipstock assembly, the tool body, a patented flexible drive shaft and bit, and the top external drive shaft. (Images courtesy of Perf-Drill)