The CPT, once sitting on the ocean floor, uses the weight of the unit, as well as suction anchors, to force a cone-shaped probe into the seabed to depths of up to 150 feet. By pressurizing the inside of the probe and modifying the load cell design inside the cone, the CPT is insensitive to external hydrostatic pressure, which can reach 5,000psi at a working depth of up to 13,000 feet. The design is the achievement of Ronald Boggess, a marine services operations manager for Gregg. It essentially takes the pressure factor out of the equation at these depths and allows for much more accurate readings of density, shear strength, and tip resistance in soil whose consistency has been described as oatmeal. The innovations in both the cone and the Seabed CPT provide tremendous advantages for the user. Productivity increases by providing two to three times the footage in a period with less impact on the exploration site.
One of the many hurdles Boggess had to overcome was finding a way to maintain the correct amount of tension on the cable that provides the feedback from the probe and relays data to the control station on deck. He went to Ogura to find a solution, and he selected the OPC-80N Electromagnetic Mag-Particle Clutch, which is designed to deliver high performance under constant slip conditions. While some modifications were necessary, the OPC-80N is providing consistent and repeatable torque in places few humans have ever seen.
The Ogura magnetic particle clutch is designed for any number of applications requiring fast response time and stable torque. These units can also be set for continuous slip, which makes them ideal for tension applications like Gregg's. Since voltage to torque is a linear function, the output torque of these clutches can be easily controlled by varying the input current. Conversely, torque is virtually independent of slip speed, with only minimal changes with large increases or decreases in speed.
In addition to the OPC's operational characteristics, the OPC was chosen for its dependability and long life. With almost unimaginable costs associated with undersea exploration, it is critical for this component to be as reliable as possible. The OPC by design has no wear surfaces, as is typical of a friction clutch. Torque is transferred by magnetizing the particles inside the clutch cavity, which bind together and transfer torque from input to output. The strength of the binding particles is controlled by the current/voltage to the coil, so the more current/voltage, the greater the torque. Torque to current/voltage is almost linear, which allows for precise control on the cable tension. These clutches also incorporate large oversize bearings for increased robustness and side load capacity. Large shaft seals retain the powder and prevent any contamination from the external environment. These features combined lead to extremely long operating life.
After Hurricane Katrina in 2005, new regulations came into effect requiring additional and earlier research to be done before the construction of anchored floating oil platforms. The Gregg Seabed CPT System provides the specific information that is critical in determining the safest and most productive site selection. Though Gregg has made a great contribution to the oil industry, there are additional opportunities for growth in both the scientific industry and the ocean mining industry.
Mike Vasko is regional sales manager for Ogura Industrial Corp.