Development and field use of the Blue Whale Inflatable Service Packer for deepwater drilling applications solves big problems offshore.

Inflatable service tools have been widely used in oil and gas drilling and production operations for nearly 70 years. Like traditional mechanical service tools, they are frequently used as retrievable testing, treating, or squeeze packers; retrievable or permanent bridge plugs; or permanent cement retainers. The fundamental difference between traditional packing element-type service tools and inflatable service tools is in the much greater expansion capability of the inflatable packing element, the enabling technology of all inflatable tools. Typical expansion of a mechanical packing-element tool is roughly 3/8-in. per side.

Inflatable elements may expand in excess of 11-in. or more per side. This expansion ratio allows a single tool to seal a wide range of casing and openhole sizes. Inflatable tools have the ability to deploy through wellbore restrictions (planned or unplanned) and create an effective seal in the larger ID below. Inflatable elements can also seal effectively in irregular-profiles such as open hole. The wide sealing range of inflatables reduces inventory requirements and makes them ideal for use in non-standard casing.
Baker Oil Tools recently introduced the Blue Whale Inflatable Service Packer (ISP), the industry's first heavy-duty, drillpipe-conveyed, inflatable service tool developed specifically for critical, deepwater applications. It allows operators to perform a variety of well intervention operations in setting IDs from
6¾-in. through 36-in., in temperatures up to 300°F (150°C) and differential pressures up
to 5,500 psi.

Blue Whale ISP typically serves in applications such as:

• A service packer to perform a test in large-diameter casing when the operator cannot get a good shoe test. The tool isolates the shoe from the liner hanger to determine which is leaking. A second ISP can then be used to squeeze the liner top, if required.
• A retrievable bridge plug acting as a secondary barrier below a subsea wellhead restriction in an offshore, pre-drilled well.
• A permanent cement retainer in an openhole plug-back and kickoff. Using the packer with its cement retainer kit and inexpensive tailpipe, a cement balance plug is first spotted in the open hole. The bottomhole assembly (BHA) is picked up and the ISP is set. The run-in string is then released from the permanent cement retainer, and a cement plug is placed on top. The hard cement is tagged and an openhole sidetrack drilled.

Blue Whale ISP was developed in order to provide a fit-for-purpose, inflatable solution for heavy-duty, deepwater applications. The development of the tool was in response to two jobs in the deepwater US Gulf Coast area that had problems with the deployment of an older generation inflatable packer system.

Review and analysis of these problem jobs identified the following deficiencies of standard inflatable tools for use in heavy duty, deepwater operations:

• Tubing connections were not compatible with heavyweight drillpipe applications.
• Element anchoring forces in high expansion may not be sufficient for extreme piston forces (more than 900,000 lb).
• Tensile limits were significantly lower than drillpipe limits.
• Inflation and deflation passages were not suitable for heavily weighted mud systems.
• Incompatibilities exist with drilling fluid and element (shop) pre-fill fluid.
• Tools were incompatible with automatic pipe-handling systems.
A number of design improvements were incorporated into Blue Whale ISP to address these concerns:
• Tubing connections were eliminated and minimum 3½-in. internal flush (IF) top and bottom connections were included on the tool.
• The main packing element was lengthened from 66-in. to 103¼-in. to increase the anchoring force.
• Material specifications were changed to increase tensile strength to 300,000 lb and torsional strength to 5,000 ft-lb.
• Inflation and deflation flow areas were increased by more than 100% to improve inflation and deflation mechanics of the element.
• Element-fill compatibility with potential well fluids was greatly improved.

Case history No. 1 - Beryl field, United Kingdom sector, North Sea

The operator had to abandon a slot to allow for a new well but did not want to risk spearing the top of the 20-in. casing and pulling it to surface following a casing cut. Casing integrity problems could cause the casing to part and either damage the jacket or require a costly fishing operation. A plan was designed with two ISPs positioned in the ID of the 20-in. casing above the cut to allow the casing to be retrieved to surface using a dual/false rotary-type system. Testing by the operator proved the anchoring capabilities of the ISP under load conditions. A 137/8-in. ISP was set in the 18.73-in. ID of 20-in. 133 lb/ft casing. Testing showed that even with a minimum element-inflation pressure of only 200 psi, the ISP remained anchored under a tensile load of 190,000 lbs.

The job was subsequently run with two ISPs in a straddle arrangement (effectively making one redundant). The elements in each tool were inflated with just over one barrel of seawater, at a depth of 542 ft (165 m) for the lower tool and 522 ft (159 m) for the upper tool. The casing was lifted out of the subsea wellhead with a break-over weight of more than 200,000 lb and retrieved to surface. The ISPs had been in position for 6 days, which included 2 days of downtime waiting on weather.

Case history No. 2 - Shearwater development, United Kingdom sector, North Sea

After the 20-in. casing parted while running in, the casing connection was re-engaged after landing in the wellhead, allowing operations to continue. However, there were concerns about the quality of the cement job on this casing string. An ISP was required to perform a pressure test on the 20-in. shoe. The tool system also had to be configured to allow it to perform a cement squeeze should the shoe leak, and also be run as a bridge plug in the same run, if required.

The versatility of the Blue Whale ISP allowed these requirements to be met. The 137/8-in. ISP was run to its initial setting depth of 2,931 ft (894 m) on 5-in. drillpipe. After releasing and landing the setting ball, no positive indications of tool function were observed from surface. Inspection showed that wellbore debris had lodged between the ball and ball seat, preventing inflation of the element. The backup system was deployed with the ball on seat during run-in. The tool was set at a revised setting depth of 510 ft (155 m). With 20-in., 133 lb/ft casing, an inflation volume of 43 gal. was used. The wellbore fluid and inflation fluid were both 10.38 ppg water-based mud with a final inflation pressure of 2,000 psi. The ISP was successfully set and pressure-testing completed. Results indicated no circulation of fluids to the shoe section.
Case history No. 3 - Thunder Horse development, US Gulf Coast

A hurricane threat forced the operator to quickly mobilize a bridge plug system to temporarily suspend the well. As a result of complications in the drilling program, an obstruction just below the mudline prevented the use of a conventional hurricane plug system, which requires tailpipe weight to energize the pack-off. Because of its ability to provide wellbore isolation without tailpipe weight, a 77/8-in. Blue Whale ISP was deployed. With this tool, it was possible to seal in the non-standard 11¾-in. 113 lb/ft casing and maintain this isolation without hang-off weight below.

A number of other challenges had to be met in a short time. The element pre-fill fluid (fresh water) was potentially incompatible with the wellbore fluid (16 ppg synthetic oil-based mud). Mixing these types of fluids could cause formation of an emulsion or sagging of the solids in the mud system when trapped in the element during setting. Either could lead to deflation complications when the tool was released.
The pre-fill fluid problem was solved by another concern. Due to the depth, temperature and pressure, there was a concern that when deflating with fresh water, hydrates could form. For this reason, the element pre-fill fluid used was a 10 ppg sodium chloride (NaCl) solution. However, because of sagging and emulsion concerns, NaCl and synthetic, oil-based mud could not be mixed in the element. For this reason, a "fluid reservoir" system was designed and then tested at freezing conditions. This system allowed carrying in a known volume of inflation fluid at the bottom of the drillpipe, and still allowed for automatic filling of the drillpipe during run-in of the oil-based mud from the well.

The NaCl was separated from the mud system by a wiper dart. When inflation was required, the fill port from the drillpipe to annulus was closed by a drop ball. Pressure from surface was applied to pressurize the drillpipe fluid and move the dart downwards, which pushed the NaCl fluid into the element. Once the required inflation pressure was reached, applied surface pressure was bled off and a mechanical disconnect operated. With the bridge plug now set, surface pumping was continued to displace excess sodium chloride. The separation dart landed in a seat and applied surface pressure reopened the drill pipe to the annulus by shearing a pressure-operated circulating valve, eliminating the need to pull a wet string.

The system was run into the well to a setting depth of 6,292 ft (1,918 m) and set using the fluid separation system to an inflation pressure of 2,500 psi. The plug was pressure tested to 3,645 psi prior to the casing and riser being circulated out to seawater, resulting in a drawdown above the plug of some 2,400 psi. The system was left in the hole until its retrieval 38 days later.

Conclusions

A key contributor to the tool's high success rate is close planning and coordination between operator and service provider. These types of tools require more detailed pre-job planning, engineering, and implementation than traditional packing-element service tools. A software package developed by Baker Oil Tools specifically for Blue Whale ISP facilitates planning and control of the process, from structured pre-job information gathering, through system implementation tools such as element performance envelopes, to a database recording system. This results in accurate job reporting and post-installation history recording.

Blue Whale ISP is a significant advance in the technology of inflatable tools. When used in heavy duty, deepwater drilling operations, it offers unsurpassed versatility in setting range and tool applications.

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