October 1998 Vol. 219 No. 10  Production

Perry A. Fischer,  Engineering Editor

Expro innovates while Barrett lights up Wyoming

Two new subsea systems have been developed that reduce costs associated with deepwater completion and tree installations when traditional dual-bore systems are required. The systems have been commissioned for a current major North Sea development. A slickline perforating depth control system also has been developed. Expro Group, maker of the innovations, provided the following information.

Select-a-bore. The Completion Bore Selector System, run as part of the tubing landing string, provides wireline access to both the production and annulus bores of the tubing hanger. The tool is surface-controlled in parallel to a Tubing Hanger Running Tool (THRT) control system, and directs toolstrings to either bore, as required, via a hinged gate actuated by a sliding sleeve.

The tool will interface with either the THRT or Dual-Bore Subsea Completion Tree (DBSCT), a 1995 Expro invention. The potential for a string circulation path has been retained through use of a side-port in the annulus bore of the DBSCT, accessed via the BOP choke / kill lines.

The bore selector system, in a 6-3/8-in. ´ 2-in. configuration, has been successfully used in eight subsea completions, with no attributable downtime. These installations occurred in roughly 1,500 ft of water in a harsh environment, using a hydraulically actuated tubing hanger that required suspension plugs in both production and annulus bores.

Tree installation. Similar dual-bore riser requirements have existed for conventional tree installation operations, with monobore systems requiring a round-trip to surface to realign the riser for annulus bore access. Such an operation can be expensive in deep water. However, an application of the bore selector concept will deliver significant savings by interfacing with existing Lower Riser Package design.

The tool is positioned in the string immediately above the emergency disconnect and below the riser stress point. A Workover Control System provides hydraulically controlled selection functions. A position indicator, viewable with an eyeball ROV, has been incorporated to provide feedback. The tool recently completed two tree installations in 1,500 ft of water.

Slickline perforating. Preliminary field trials of a slickline perforating system have been successfully completed in the North Sea. Expro is now working with Unocal Thailand in the final stage of trials. The system offers a radio-safe method of initiating the explosive with a depth accuracy of ± 2 ft.

A new surface monitoring and software package makes such depth control possible. Variables that affect depth control, such as deviation, well and wireline characteristics, are monitored, and necessary depth corrections are made. The system can also be used in other services, such as production logging and packer setting.

The perforating tool mechanism consists of three main components:

1. Surface safety is ensured by individual mechanical-pressure and temperature switches that form short circuits over the detonator. Well pressure and temperature open the switches at a pre-determined depth, and close them upon retrieval.
2. The electronic trigger package controls output from a battery pack, which sends a pulse to the detonator only when all safety barriers are overcome and downhole parameters satisfy the pre-programmed firing sequence.
3. Industry-standard explosives are used in the trigger that make it compatible with most types / suppliers of tubing conveyed perforators, casing and strip guns. The detonator has a safety-shorting link that is removed only after safety surface switches have disabled the explosives.

Barrett blowout. The saga of Barrett Resources' Cave Gulch 1-29LAK well continues. In February 1998, while drilling ahead of casing at about 18,000 ft, the well took an incredible gas kick that blew drilling mud over two miles of Natrona County, Wyoming. It also separated the drillstem and forced pipe into the BOP, where it lodged. The well was eventually brought under partial control, and routed into a sales line at about 45 MMcfgd with ftp up to 10,800 psi.

The intent was to produce the well at a high rate, decrease reservoir pressure and re-enter the well to finish drilling and make a proper completion. Since going online Feb. 20, the well produced 7 Bcfg and ftp decreased to 8,800 psi. Barrett brought in a rig in early August with hopes of completing the hole. The plan worked well until Aug. 13 when the second blowout hit.

The well began venting from the BOP and cellar; apparently, the casing had failed. The rig was deemed too risky to move, and after several days of consulting with experts, the well was ignited for safety reasons. The derrick melted down in 43 minutes. With gas escaping from a 70-ft diameter around the wellbore, and flames reaching 30 ft high, the well is estimated to be burning more than 100 MMcfgd. The well is a total loss.

Barrett was drilling two offset wells nearby when the blowout occurred. Cave Gulch 3-29MAD was drilled to 21,965-ft total depth in the Mississippi Madison formation. After a delay to re-evaluate safety issues, the Madison was tested, but produced water. Operations will now move up hole to test the Tensleep formation. Another well, Cave Gulch 4-19LAK, located about 3,800 ft from the blowout, was drilling at 3,000 ft. This well will now attempt to intersect and kill the blowout well.

This has been an expensive field to develop, with these deep wells costing roughly $14 million each. Costs on the blowout well are more than $15 million, and are running about $200,000 per day, including lost revenue. Barrett, which owns a 70% stake, says it has sufficient insurance to cover most of the current loss, but not losses from production or depletion.

Production from Barrett's other 22 wells in the Cave Gulch area continues at about 55 MMcfgd. Total reserves in the area keep changing, but estimates keep inching upward, perhaps in the one-to-two TCF range.

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