Logging Plan | Table of Contents
The Site WP-2 drilling program consists of drilling two holes (A and B) to characterize the site before installing a reentry cone, casing string, and drilling a third hole (C) in which to install the ION instrument string. Time estimates to accomplish these objectives are estimated to be around 26 days. Drilling Holes A and B will consume ~11 of the 26 days allocated for the ION work. Installation and setting up the reentry cone and casing for Hole C is estimated at 10 days. The remaining five days on site are devoted to the installation of the instrument and battery package (Figs. 6, 7).
Piston coring (advanced hydraulic piston corer [APC]) to refusal (~180 mbsf) will be used in the first hole to ensure the most complete recovery and characterization of the upper sedimentary section. Below that, single extended core barrel (XCB) and rotary core barrel (RCB) coring will be used to drill the remaining sedimentary rock above basaltic basement (~420 mbsf), and an additional 10 m into basement, if possible. Hole B will be washed/drilled down with the RCB to ~380 mbsf. Coring will commence and continue ~100 mbsf into the basaltic basement. A full suite of wireline logging will then be initiated (see "Logging Plan" section).
A reentry cone will then be assembled and lowered to the seafloor with ~60 m of 16-in casing. It will be washed to depth and the reentry cone released on the seafloor. The drill string will then be recovered and a drilling bottom-hole assembly (BHA) made up with a 14-3/4-in tricone bit will be reassembled. Hole C will then be reentered and the hole deepened to ~460 mbsf. The drill string will again be recovered before making up ~445 m of 10-3/4-in casing. The casing string will be lowered to just above the seafloor before approaching the reentry cone. The 10-3/4-in casing will be run to depth and then cemented in place. The drill string will again be recovered before making up the final BHA to drill a 9 7/8-in hole. Because the instrument string should be located in a relatively homogeneous and unfractured zone, the hole is planned to be 100 m in basalt basement. Actual penetration will be decided in the field. This decision will be based on information provided by the cores and wireline logs from Hole B, drilling data provided by the drillers, and the amount of allowable time remaining in the program to complete the leg objectives.
After the hole is drilled to depth and the drill string recovered, the instrument package will be made up in a carrier and then crossed over to 4-1/2-in casing. The instrument package for Leg 191 consists of two seismometers (Fig. 6). Centralizers will be equally spaced on the casing string to keep it centralized within the borehole (Fig. 7). Once lowered into place, the instruments will be cemented in place through the drill string and support tubing. Afterward, the drill string will be disconnected from the 4-1/2-in casing, leaving it at a predetermined height above the reentry cone (Fig. 7). A battery package will then be lowered into the throat of the reentry cone (Fig. 7) before releasing the drill string and recovering it back onto the ship.
Engineering Tests at Shatsky Rise
The first objective of the actual drilling plan for the HRRS (Figs. 8, 9) is to familiarize the drillers with how the fluid hammer operates and with the weight on bit requirements for these types of bits. Also, since the fluid hammer operates with very high pressure and flow requirements, it will allow the pumps and other ancillary pieces of equipment to be checked out to ensure that adequate drilling parameters will be maintained during the course of the HRRS work. This will be accomplished by first deploying the fluid hammer with an underreamer bit and without casing. The ring bits must be run with casing and will only be picked up if the hammer can be adequately operated with the flow and pressure generated by the mud pump system.
A number of shallow holes will be made while instructing the drilling crew in the proper drilling technique required for this fluid hammer. The drill string will be round tripped; this bit will most likely be changed to the other type of underreamer bit so that information can be gained as to how it drills compared to the first underreamer bit. A similar number of shallow holes will also be drilled with this bit to establish operating characteristics. After the BHA is recovered, a decision will then be made as to which type or version of bit will be run with the first casing string.
Based on the drilling results of the first two underreamer bits and the sea states, a short length of 13-3/8-in casing (~20 m) will be picked up and mated up to the lower section of HRRS casing running tool. Once assembled, the running tool and casing will be lowered from the rig floor to be supported on the moonpool doors while the hammer and BHA are assembled. When the BHA and upper section of the running tool are assembled, they will be lowered and mated up with the lower section of the running tool.
Once assembled and with space-outs confirmed, the whole casing/BHA will be lowered to the seafloor on drill pipe. The vibration-isolated television (VIT) camera will be deployed to help locate an appropriate location in which to spud. The bit will be placed on the seafloor while the VIT camera is recovered. The casing will then be drilled to depth. Next, the VIT camera will again be deployed to confirm that the casing is in the proper position before installing the free-fall funnel (FFF). When positioning is confirmed, the VIT camera will be recovered and the FFF assembled around the drill string. The FFF will be released and the VIT camera once again deployed to verify proper position of the FFF before releasing the running tool. Upon verification, a dart will be pumped down the drill string to shift a sleeve so that the BHA and pilot bit can be withdrawn from the installed casing. Before recovering the VIT camera, it will be used to survey the site and installed casing.
If all operations have gone as planned, the scenario will be repeated two more times but with progressively longer strings of casing as the comfort level increases and the success of the operation is achieved. The additional lengths of casing might include 35 and 50 m. However, these lengths will be solely dependent upon the success of the previous installation.
Depending upon the amount of time remaining in the HRRS program schedule, a smaller Model 185 fluid hammer will be tested inside one of the installed 13-3/8-in casing strings. The ideal scenario would be to deploy the Model 185 fluid hammer to deepen the 14-3/4-in hole beneath the casing with a 9-7/8-in bit. The 185 fluid hammer has been suggested as the next smaller size fluid hammer that may be used in the HRRS system to install a nested casing string.
The gas hydrate autoclave sampling and monitoring system known as the HYACE System, modified at the Technische Universität Berlin with support from the European Commission and from ODP, is also scheduled to be tested during Leg 191, pending SSP approval and the success of land tests. Testing of the HYACE tools (i.e., the autoclave downhole rotary corer and the autoclave percussion corer) has been allotted a maximum of 72 hours at the end of the HRRS tests. Once all the HRRS operations are completed, the ship will be repositioned, and the APC/XCB BHA will be deployed so that the HYACE tools can be deployed. The hole will remain in the sediment section of the formation and will not penetrate more than 300 m.
Logging Plan | Table of Contents