Just within the last decade, service providers began discussing the possibility of developing perforating systems for wells with bottomhole pressures up to 30,000 psi and

temperatures exceeding 450°F (232°C). Operators were avoiding projects with such extreme conditions because tools were so unreliable in those environments.

But, one major operator was willing to push the limits of the technical envelope in a Gulf of Mexico well. With measured depth more than 29,000 ft (8839 m), the well exhibited downhole temperatures up to 470°F (243°C) and had posed significant drilling, completing, and logging challenges.

“The operator was facing the same magnitude of challenges with its perforating strategy,” says Charlie McClean, an

application advisor for the Baker Hughes tubing-conveyed perforating product line. “In order to access the reservoir and make the well economically viable, the operator required a perforating system that would survive in an environment with extreme high pressure and temperature. However, technology that would enable any perforating system to withstand such extremes had not been refined within the industry at that time, due to the limited number of projects with such parameters.”

Understanding the well conditions and how the equipment would react before, during, and after detonation would be critical in the development of such a perforating system.

A perforating engineering consultant working with the operator says, “Any time the pressure and temperature envelopes are

pushed past known or comfortable limits for tubing-conveyed perforating [TCP] gun systems, it is imperative that the operator and service company understand all associated risks. This requires significantly more communications between the operator and the service company, from the development phase all the way through the perforating operations.”

Working closely together to gain a comprehensive vision for the entire project from completion to production, Baker Hughes and the operator developed, and Baker Hughes manufactured, the tubing-conveyed UltraConnect™ 35K high-pressure, high-temperature (HPHT) perforating system that would fire successfully at 35,000 psi.

Baker Hughes delivers the industry’s first tubing-conveyed ultrahigh-pressure/high-temperature perforating system, giving an operator in the Gulf of Mexico access to a previously inaccessible formation and proving a system capable of withstanding pressures in excess of 35,000 psi and temperatures as high as 470°F (243°C).

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“Not only did the perforation system perform flawlessly,” says the customer’s perforating expert, “but being able to deploy it on TCP rather than on wireline saved the operator several extra days of rig time.”

Designing out riskPerforating is a critical step in establishing connectivity between the reservoir zones and the wellbore in wells where the casing is cemented across the proposed production zone. Perforating guns contain explosive charges that create holes in the casing string to allow hydrocarbons to migrate into the wellbore. The guns typically consist of several main components, including:

� A detonating cord that connects to the back of each shaped charge

� Boosters (small explosive sleeves that are crimped to each end of the detonating cord) to initiate the detonating cord

� A hollow carrier into which the assembly fits

� A tandem sub connector that enables the gun system to be fully compatible with automatic-release systems and other devices that are functioned by way of gun gas.

“The Baker Hughes methodology for developing technologies requires extending existing solutions whenever possible,” explains Mark Sloan, a senior engineer in the Baker Hughes ballistic engineering technology group. “We started with our field-proven Model D and Model RD

pressure firing systems, which included DeepConnect™ rock-optimized charges designed for HPHT applications. Then, in accordance with the operator’s design verification processes, we tested multiple component configurations to improve performance at higher pressures and temperatures.”

To reduce the risks of operational downtime, the engineers selected a fully redundant firing system—two absolute pressure-activated firing heads that used rupture discs instead of shear pin firing heads, which are more commonly used in the global oil and gas industry. “The rupture discs provide a higher level of accuracy, which is critical in ultradeep HP wells to reduce the amount of pressure required for application,” Sloan says.

“The project’s high-temperature requirement made hexanitrostilbene the best choice for explosive,” adds Didhiti Talapatra, a Baker Hughes engineer and ballistics expert. “Exposures to high temperatures for more than the rated duration can cause the explosives to decompose, reducing the performance of the shaped charges and leading to a ‘stop fire’ along the explosive train.

“Also, depending on the rate of heating, deflagration—a subsonic combustion process that propagates through heat transfer—is possible. Deflagration can cause explosives to gas out and build enough pressure inside the gun body to rupture it.”

Testing and deploymentFull-system integrity testing—in which the operator was fully involved—was conducted at the Baker Hughes Center for Technology Innovation in Houston in purpose-built cells capable of safely containing testing pressures and temperatures.

A final test was performed to qualify the system for use, as per the customer’s specified well conditions, which consisted of the ultra-HPHT firing head system connected to two 1-ft gun bodies and a tandem sub, with detonation cord and booster-to-booster transfer. “This test was to validate the successful ballistic train activation of the firing heads, and the detonation cord booster-to-booster transfer at elevated temperatures and pressures,” Talapatra says. “All components used in the test were from the same batches that were previously qualified for use in the well.”

The ballistics team used the Baker Hughes PulsFrac™ software to model and calculate wellbore behavior, and to generate a detailed and comprehensive quality plan it shared with the operator.

With a quality plan in place, and all qualifying tests successful, the UltraConnect system was deployed in March 2014.

The perforating string included multiple perforating guns with a redundant firing system (modified to function at ultrahigh

pressures) and the new ultra-HPHT DeepConnect charges.

“After reaching perforating depth of 29,000 ft on the appraisal well, an absolute bottomhole pressure of 34,500 psi [which included the hydrostatic pressure] was applied and bled off to activate the time-delayed redundant firing system,” Talapatra says. “With a positive indication of gun detonation, circulation between tubing and annulus was confirmed and the assembly was pulled from the wellbore.”

“The comprehensive system integrity test program conducted by Baker Hughes [with specs, requirements, and design verification processes supplied by the customer], coupled with the redundant firing system, gave us a high degree of confidence in the gun system,” says Steve Zuklic, Baker Hughes TCP/well control tools product line manager.

“Baker Hughes stepped up to the plate and delivered this ultra-HPHT TCP system, which went off without a hitch,” concludes the operator’s perforating expert. “We were

very pleased with the spent guns retrieved from the well, which indicated high-order detonation, in what are some of the deepest well perforations in the world.”

An article on this new technology also appeared in the September 2014 edition of World Oil.

“ In order to access the reservoir and make the well economically viable, the operator required a perforating system that would survive in an environment with extreme high pressure and temperature.

Charlie McClean, application advisor for Baker Hughes

”

> Perforating guns shoot explosive charges like these through casing to create holes that allow hydrocarbons to migrate into the wellbore.

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