Automatic density control and a high degree of data acquisition ensure that Seahawk cementing systems, such as this unit being installed in Texas, pump slurries as designed.

Deep water, deep wells, and extreme downhole environments challenge traditional cement systems and pumping equipment. New technologies extend conventional limits for safe, reliable well construction, allowing cost-effective exploration and development in oil and gas basins once considered too difficult to enter.

From engineered spacers and slurries to high-performance automated pumping systems, new cementing technologies are the backbone of today’s successful deepwater wells.

Ultra-deepwater frontiers

In an example of the demanding work expected of these state-of-the-art cement systems, an operator working in Indonesia recently developed a plan to drill several exploration wells in more than 7,000 ft (2,100 m) of water.

Currently, few rigs in the area are capable of drilling at this depth. Those that can are equipped with Seahawk cement pumping systems. More than 30 of these high-performance pumping systems are in use around the world, providing consistent density control and reliable operation even in the most challenging conditions.
Standard units include two 500-bhp six-cylinder diesel engines. Higher-horsepower diesel or electric power units are also available.

The standard automatic cement control system and optional advanced liquid additive system ensure that slurries are consistent with the engineering design. In operation, these systems work with a “brain box” control system, which links sensors and data acquisition devices throughout the equipment. Optional remote control systems remove personnel from the units, enabling operation and monitoring even over great distances.

Offshore Brazil, the pumping equipment has been working on four rigs, where their automated density control has proven reliable and critical to ensuring the quality of operations with high volumes of engineered, fit-for-purpose slurry.

The first unit in Brazil has been working since September 2007 and has pumped more than 13,600 bbl of slurry in 43 operations, with densities ranging from 11.5 to 15.8 ppg. The second unit was a fully automated, remote-control unit on a rig that pumped 3,000 bbl of slurries before moving on to the Gulf of Mexico. It is expected to return this year. Two more rigs recently began working offshore Brazil with Seahawk units aboard, and another six are expected this year.

Globally, next-generation units have been contracted for future vessels. For example, the Pride International drillship PS 1, expected to begin ultra-deepwater operations in late 2010, will host a new high-performance, 2,300-bhp Seahawk unit. This upgraded system will provide the additional horsepower, accuracy, and safety features required for next-generation, ultra-deepwater well construction operations.

Choices in Indonesia

For the current ultra-deepwater project in Indonesia, well construction engineers have faced a variety of options for the cementing operations. Although no
shallow water flow or shallow gas were detected while drilling the 28-in. hole section for the first well, the operator was concerned about the possibility.

Therefore, BJ Services engineers recommended the DeepLite cement system, a premium lightweight cement system specifically designed for riserless, deepwater applications with low potential for shallow water or gas flows. DeepLite slurries set quickly at low (less than 50°F/10°C) temperatures and gain much higher compressive strength than conventionally extended, accelerated slurries.

For the 22-in. casing in the first exploration well, engineers designed a 12.5-ppg lead and 15.8-ppg tail slurry with transition times less than 30 minutes and 844 and 3,273 psi compressive strength, respectively.

While pumping the 2,000 bbl slurry volume, the Seahawk cement unit operated continuously for more than seven hours without technical or mechanical problems. In addition, the cementer was able to rely on the automatic cement control system to accurately maintain the designed slurry density, even when the rig experienced difficulty delivering bulk cement to the unit.

Bulk cement delivery woes

Particularly on new rigs, bulk cement delivery has been seen as a problem — one that is easily overcome, but one that can add complications in early cementing operations.
A Seahawk unit on another new ultra-deepwater rig overcame similar bulk cement delivery issues while pumping 20-in. casing cement for two exploration wells in China.

The wells had moderate potential for shallow water flow. This situation often results in a recommendation for foamed cement, but in this case, the operator wanted to avoid using a foamed system.

Instead, engineers recommended LiteSet cement because of its high compressive strength and fast transition time. For both wells, 13.0-ppg lead and 15.8-ppg tail slurries were designed with compressive strengths of 1,000 and 3,450 psi (6,895 and 23,787 kPa) respectively for the first well, and 1,120 and 3,620 psi (7,722 and 24,959 kPa) for the second. (The operator was concerned about all the new equipment on the rig, so the thickening time was doubled to provide a safety margin in case of any equipment malfunctions. This change slowed the slurry’s transition time and affected the early compressive strength, which usually would be much higher for the LiteSet cement system.)

To simplify operations, a dry blending method was used to combine the lightweight additives with the dry cement at the bulk plant. Optimized handling techniques keep the blend from segregating by density during transit and on location.

While pumping for nearly six hours, the Seahawk unit was able to maintain a consistent slurry density, even when rig air volume was unable to move cement rapidly enough over the long distance it had to travel. (For later large operations, the rig added another compressor.)

Although it was not needed for this operation, the Seahawk system includes a monitoring module that compliments the standard densitometer for ultra-lightweight slurry designs. This module assesses the slurry’s liquid volume fraction, which allows accurate mixing even when slurry density is so low that conventional densitometers are unreliable.

The Seahawk unit’s high level of automation and monitoring provide unparalleled volumes of information for customers, engineers, mechanics, and technicians. In contrast to older cement systems that gauged only pumping pressure, rate, and slurry density, the new technology includes sensors for dozens of performance characteristics in the mixing system, powertrain, pumps, and other components.

In addition to enabling quick changes to pump rates or other job parameters to suit downhole conditions, these sensors allow automated safety shutdowns that help prevent injuries and costly equipment repairs.

Furthermore, modular design means the Seahawk unit’s six modules can be installed through openings as small as 5 ft wide by 7 ft high (1.5 by 2.1 m) and assembled in different shapes to fit the space available on a rig. Remote radiators and separate surge tank and liquid additive skids also are available.