Systematic sampling

Alan Foley

June 3, 2014

PROD on a rare sunny day west of Shetlands. Photo from Benthic. 

Benthic's Alan Foley, discusses the company's seabed drilling and sampling system, the Portable Remotely Operated Drill (PROD).

Since 2001, Benthic has operated a seabed drilling and sampling system to assure the integrity of the seabed for a variety of applications including mooring, piling and pipeline route survey. This seabed system or PROD, an acronym for Portable Remotely Operated Drill, has grown from its roots as a geological hard-ground coring system into a full-range geotechnical site investigation tool able to operate in water depths of 3000m.

Typical projects handled by the system have been in deep- water areas of Norway, Angola and East Africa, where the seabed applications shine compared with vessel-mounted rigs. Other deployments have included in the Caspian, Timor Sea, Solomon Islands, Korea, all coasts of Australia and Patagonia. While not completely insulated from the effects of bad weather, seabed operations can continue in poor weather, with control and power being fed to the PROD seabed unit via an armored umbilical, when vessel-based drills run for shelter.

Operating in water depths down to 3000m, PROD can be deployed from DP anchor handlers, or PSVs. The system offers many commercial and technical advantages, especially in deepwater, where the fixed location on the seabed provides precise control over the drilling parameters without the effects of vessel motions, and allows multiple tools to be deployed in the same borehole, without the need to travel back to the surface for each tool change.

Starting with a standard suite of soil borings, comprising of coring and cone penetrometer data, the offerings of the seabed system have expanded to include ball penetrometer, seismic probe, pore pressure standpipes and in-situ hydrocarbon sensors. These tools have proven useful in establishing parameters for geohazard analysis and, in conjunction with geophysical data, provide a basis for pre-lay site clearance and baseline measurement of critical geotechnical parameters.

With increasing emphasis on well safety since 2010, Benthic has expanded the pore pressure measurement capabilities of the cone penetrometer (CPT) system to integrate the results of laboratory testing of core samples. The resulting reports can provide critical analyses of near-seabed conditions for mitigating risk in jackup rig siting, well tophole design, slope stability, seismic hazard analysis in seismic zones and the measurement pressure in shallow formations for shallow water flow potential. These conditions all present risks, not only to pipelines and structures, but also to exploration wells through the setting of conductor penetration parameters. In deepwater settings these analyses can save days of lost NPT with a rig on location and negate the need for moving seabed locations.

Increasingly as deepwater wells move into areas with stiff seabeds and unknown drilling conditions the capabilities of PROD’s in-situ measurement techniques come to the fore. The seismic probe has the capability to provide direct measurement of transmission seismic velocity values, including Vp and previously unavailable Vs values. This has resulted in meaningful measurement of Poisson’s Ratio and other rock properties within the range of the PROD probes. As analysis techniques are refined the measurement of velocities, pore and fracture pressures below the maximum penetration level of the drillstring will remove uncertainty in difficult drilling conditions. In the future Vertical Seismic Profiling will extend the depth of analysis and surface wave techniques have the potential to expand the lateral coverage using the seabed seismic probe.

Lights, camera, action in a port at night.

In Arctic areas comes a challenge of permafrost and gas hydrates therefore measurement of temperatures with cone penetrometers is a key. As the reach of these remote sensing systems allows more integration of geotechnical results with geophysical, data the reach of geophysical data to enable engineering-quality assessment is increasing. This removes the need for drilling open hole to ever increasing depths and allowing riser or dual gradient mud systems more accurate pressure control. In preparation, Benthic is already building a new generation of launch and recovery systems to cope with increasing depths and weather conditions, and will build the next generation PROD4 with an extended the water depth capability of 3500m. These systems will work in conjunction with AUV and other seabed acquired data to allow earlier and more comprehensive site assessments.

Benthic is investing heavily in the next generation of engineers “We have a graduate training program in Benthic taking on six graduates across several disciplines,” commented CEO Stephen Pywell. In 2014 Benthic will take on a further six, both geo-sciences professionals and engineering professionals.

Following the production of the new units the original PROD1 will relocate to Houston as part of a new development and training centre, with courses running internally and externally to introduce seabed drilling to the GoM and industry-wide.

Recently extensive activity in deepwater mineral mining in the Pacific since 2009 has pointed to a wider scope for seabed sampling. Benthic sees a growing opportunity in other environments, where the PROD equipment can offer some distinct advantages over more conventional equipment in some of the most challenging environments around the world.

With an emphasis on working in challenging environments and using a readily adaptable system on a range of vessels seabed systems can fit schedules and budgets where permanently deployed rigs are absent.