Following the inaugural 2005 SHALDRIL cruise, a debriefing meeting was held at Rice University in early June. At that meeting technical problems from the 2005 cruise were highlighted and an action plan formulated for the SHALDRIL 2006 cruise.
Although the rig had generally performed well with few mechanical problems during the inaugural cruise, a list of recommended improvements was compiled at the end of the 2005 cruise. This list was discussed at Seacore’s in-house debriefing, and it was decided Seacore would address all items prior to the 2006 SHALDRIL cruise.
The inhole tools were of greatest concern. Good penetration rates and core recovery were achieved in the softer clays of Maxwell Bay; however, subsequent boreholes in tills and harder sediments had met with little success. While weather conditions limited available site selection, it was agreed that the set of tools used had not met expectations and that an improved set of tools should be sourced for SHALDRIL 2006.
Modifications made for the 2006 SHALDRIL cruise are outlined below.
Rig Improvements
The most significant modification made to the rig was the installation of a new gimbal frame for the power swivel. One of the challenges of installing a drilling system on the Nathaniel B. Palmer was the limited deck space and the critical angle required to run drill pipe between the deck crane and the aft control cabin. This challenge was met by building an angled gimbal frame that directed the drill pipe into the narrow gap available.
Just prior to the 2005 mobilization a discrepancy between the plans and the resulting structure was discovered. This resulted in a hasty last-minute modification that corrected the angle, but resulted in a forward and aft error. The error had minimal effect while running wireline tools into the API string, but it may have contributed to the subsequent piggyback string failures.
A complete new gimbal frame was fabricated in the UK and installed during the 2006 mobilization. In addition to correcting the errors in the original frame, the new frame was also slightly shortened, effectively giving more height in the derrick. During the 2006 cruise this new gimbal frame has proven to be precise, and the larger diameter SHALDRIL wireline tools were run with no interference problems.
During the 2005 cruise the Nylatron-type material used to manufacture the rooster box wheels delaminated under extreme cold temperature. For the 2006 cruise a complete set of new wheels made of steel with rubber tires were fitted. Unfortunately, these wheels also failed and were replaced with the original wheels (kept as spares) after being machined concentric by the ship engineers. By changing wheels during rig moves minimal drilling time was lost, and the large stock of spares meant there was no risk of complete failure. This is an area of concern that will be addressed by Seacore's design department when the rig returns to the UK.
Other modifications to the rig were mostly associated with instrumentation and control, relating to the drill shack. There were also some safety features added to address possible hazards identified during the 2005 cruise, including a “dead” man cut out of the rig controls when the driller left the drill shack, better access to the derrick from the helo deck, and guarding of winches and wires.
Inhole Tool and Bit Development
All of the available options for inhole tooling that would be suitable for SHALDRIL 2006 were researched and assessed during summer 2005. The conclusions, recommendations, and budget were presented to the SHALDRIL committee at a meeting in Houston in August 2005. There were seven separate options outlined, but the preferred option was to work with Marshall Pardey and modify an existing set of DOSECC tools to suit SHALDRIL's requirements. It was decided at the meeting that while the modified system custom built for SHALDRIL was the way forward, there were some budget constraints that had to be addressed before a final decision could be made. Meanwhile, Seacore continued to work with Marshall Pardey on the final tool designs, and with American Diamond Tools for the bit designs. At the end of September Seacore placed an order for the production of one complete system for projects offshore New Zealand. The SHALDRIL committee was offered (and took) the opportunity to take advantage of discounted production costs associated with producing two systems at once, with Seacore buying the tools and leasing them to SHALDRIL for the 2006 cruise. Production was immediately started and the tools were fit-tested and inspected by the SHALDRIL committee in Salt Lake City in mid-December. (See Appendix 2-2 for a report on the inspection visit and description of the tools.)
Prior to the SHALDRIL 2006 cruise, Seacore completed two projects using the new inhole equipment. The inhole tools performed well, with recovery improving with increasing experience, but the initial production run of bits contained major flaws resulting in total failure. American Diamond Tools worked hard to rectify this fault, and subsequent bits have turned in high meterage. SHALDRIL II benefited greatly from this field-testing and experience. In addition to the initial order of two systems, Seacore has invested in a third complete set of tools with ongoing development of geotechnical tools to be run with the same bottom hole assembly.
Recognition should go to Marshall Pardey for the final design of the tools, to Bob Vredenburg, whose company built the tools, and to American Diamond Tools for the production of the diamond bits. The staffs of these companies showed great commitment, enthusiasm, and genuine interest for this project.