Transit to Hole 1026B
Following cementing of the 103/4 inch casing in Hole U1301B, we moved 0.55 nmi to Hole 1026B in DP mode while retrieving the drill string. We deployed a seafloor positioning beacon at 2356 h on 16 August.Hole 1026B
During Expedition 301, our plan was to retrieve the Hole 1026B CORK that was installed during Leg 168 and install a new CORK-II. After Leg 168, an ~1.0 m diameter minicone was placed in the top of the CORK (Fig. F19) by submersible to facilitate wireline reentry during nondrillship operations (ROV or submersible). We had to remove it so it would not interfere with engagement of the CORK-pulling tool. Because we did not know what problems we might encounter when trying to remove the minicone, we wanted to try this early in the cruise so that we would have time to devise a solution. This minicone could not be removed by submersible. We fabricated a special fork-shaped, jetted fishing tool (Fig. F20) to remove the minicone. We could maneuver the tool by rotating the drill string and pumping seawater through a port on the back side of the tool to move the bottom of the drill string.
We slid the fork-shaped fishing tool around the CORK, raised it, and broke the minicone off at the base of the conical portion. The minicone fell and landed on the ROV platform, and we used the fishing tool to nudge it off onto the seafloor immediately beside the reentry cone (where it still remains). We felt that the lower tubular portion piece of mini cone remaining on top of the CORK head would not interfere with our ability to latch the CORK pulling tool to retrieve the old CORK. The entire minicone removal process only required ~15 min and then we retrieved the drill string. We finished the fishing operation at 1200 h on 17 July when the fishing fork was back on the rig floor.Transit from Hole 1026B to Hole U1301A
While retrieving the fishing BHA, we moved back to Hole U1301A (0.55 nmi) in DP mode. For a description of operations in Hole U1301A, see "Site U1301."Transit from Hole U1301B to Hole 1026B
After completing the logging operations in Hole U1301B, we moved the ship back (~0.55 nmi) to Hole 1026B in DP mode.Hole 1026B
We started assembling the CORK retrieving tool at 2330 h on 2 August. We engaged the CORK and extracted it from the reentry cone at 0545 h on 3 August. The CORK extraction and pick up of the ROV platform assembly was visually observed with the camera system prior to raising the entire assembly back to the ship. Once the recovered hardware reached the ship, we spent 3 h disassembling the structure and laying out all the various components (Figs. F21, F22); this was completed at 1500 h on 3 August. This included the ROV platform, which was cut off in the moonpool area, and the CORK head with drill collars attached below it were disassembled on the rig floor. The drill collars consisted of one 30 ft 81/4 inch drill collar, one 20 ft drill collar pup joint, two 10 ft drill collar pup joints, and one 20 ft knobby joint.
At 1500 h on 3 August, we began to prepare for assembling the new CORK-II. A 41/2 inch casing packer was made up to a casing seal sub. We lowered to the moonpool where we attached three miniscreens just below the bottom of the packer. The lower end of the umbilical (leftover from ODP Leg 205) was attached to the top of the packer and we attached 14 joints (189.95 m) of 41/2 inch casing. The umbilical was banded to the casing using plastic tie wraps and stainless steel banding. Thirty-six rigid casing centralizers were attached to the casing to protect the umbilical during deployment. We attached the CORK-II running tool to the top of the CORK-II head (Fig. F23), secured the head to the top of the 41/2 inch casing string, and lowered it into the moonpool to make the final umbilical connections at the bottom of the head.
After making up a stand of 81/4 inch drill collars to the top of the CORK-II running tool, we connected the packer inflation hose from the running tool to the CORK-II head. Dual tethers were attached at 180° from the running tool to the quick disconnect on the top of the head; these are used to release the quick disconnect on the packer inflation line when the running tool is removed from the head after the CORK-II is fully installed.
We lowered the CORK-II assembly to the seafloor, deployed the camera/sonar system, and were prepared to reenter Hole 1026B to install the CORK-II at 0400 h on 4 August.
As we were preparing to reenter Hole 1026B with the fully assembled CORK-II, a ~1 m long(?), cylindrical, white foreign object was observed lying inside the reentry cone. We ultimately determined that the object was likely a BioColumn sampler lost (fell through a flow hole in the old-style ROV platform) during a submersible visit following ODP Leg 168 and prior to IODP Expedition 301. We had not seen this object during recovery of the original CORK because the view of the cone was blocked at all times by the ROV platform.
After meeting to discuss our options, we decided to retrieve the camera/sonar system and attach a grapple-fishing tool to the camera frame. We ran back down to the seafloor and attempted to fish the object out of the reentry cone. Unfortunately, when the grapple touched the object, it slid down the reentry cone and slipped into the throat of the cone. We recovered the camera/sonar system again, removed the grapple-fishing tool, and ran back to bottom to observe the reentry cone, thinking that the object might have fallen inside the casing and continued all the way to the bottom of the hole. Unfortunately, we could see that an object remained inside the throat of the reentry cone, likely resting on top of the casing hanger assemblies. We lowered the end of the CORK-II's 41/2 inch casing into throat of reentry cone in an attempt to dislodge it so that it might fall freely to bottom of the hole. Instead, the casing worked past the object, so we pulled the casing back up and observed the object catching on the casing stabilizers, lifting it out of throat, but then falling off into the reentry funnel and sliding back into the throat of the reentry cone. This process repeated itself each time a casing centralizer was lifted out of the cone throat. We decided that we needed to try to another fishing tool, so we pulled the casing clear of the reentry cone at 1155 h on 4 August and recovered the camera/sonar system. We removed the grapple fishing tool and attached a modified wireline spear (added two sets of three 6 inch long hex head bolts welded at a 45° upward angle) to the camera/sonar system frame using a wire rope sling. This time we successfully engaged the object, pulled it from the reentry cone, and, while moving the ship 20 m away from the reentry cone, we observed the object being dragged through the seafloor mud. When we retrieved the camera/sonar system with the fishing tool, the object was missing; it had apparently dislodged during retrieval and fallen to the seafloor.
Once again we deployed the camera/sonar system, and we reentered Hole 1026B with the CORK-II assembly at 1850 h on 4 August. During reentry, we once again observed what appeared to be a white tubular object lodged inside the throat of the reentry cone. We continued to lower casing to 2849 mbrf; however, it was apparent by the drag that something was still inside the reentry cone assembly. When we pulled the casing back up through the reentry cone, we observed an object jammed onto one of the casing centralizers. We pulled the casing clear of the reentry cone at 1945 h on 4 August and offset the ship 35 m away from the hole to ensure that if the object fell off it would not go back into the hole. We inspected the object and verified that it was not the same one that had been removed in the earlier fishing operation, but it may have been a part of that assembly that had broken off. The new fish had what appeared to be a stainless steel T-handle. To remove the object, we worked the camera/sonar system up and down over it until it finally fell off. While offsetting the ship back to Hole 1026B, we observed the first fished object lying on the seafloor 20 m from hole; it appears that this object fell straight down.
Ultimately, we reentered Hole 1026B at 1945 h on 4 August and the casing, packer, and umbilical assembly was lowered to 2849 mbrf without meeting any resistance. The top drive was picked up and the casing was further lowered to 2859 mbrf just short of landing the CORK-II head in the reentry cone.
The instrument string deployed inside the 41/2 inch casing of the CORK-II consisted of a sinker bar, three OsmoSamplers, a lower seal (gravity) plug, Spectra rope, sinker bar, Spectra rope, and a top seal (gravity) plug. This was made up and deployed in the same manner as it was for the Hole U1301A CORK-II. Once the instrument string was installed, the CORK-II head was landed without difficulty. We inflated the single 41/2 inch casing packer (without using a go-devil) and began preparing to deploy the ROV/submersible platform.
Final assembly of the ROV platform was completed and the platform was deployed as before using the logging wireline and the mechanical deployment tool (Lula) (Fig. F15). When the mechanical deployment tool carrying the reentry cone touches down on the CORK-II head, the mechanical release is activated, releasing the platform, which free falls around the CORK-II down onto the top of the reentry cone.
The platform was successfully released without any of the difficulties we experienced when deploying the platform in Hole U1301A; repairs and modification to Lula prior to Site 1026 operation and modified deployment procedures were successful. We recovered Lula at 1015 h on 5 August. We then deployed the camera/sonar system to inspect the platform and CORK-II and to observe the release of the CORK-II running tool. When the camera reached the seafloor, we observed that the platform had not landed properly. However, one side of the platform hung up on the plate at the base of upper set of gussets on the CORK-II head during the free fall. After reviewing the engineering drawings of the CORK-II head and platform, it became clear that in some orientations it is possible for the platform to hang up on the CORK-II head. This can easily be prevented by installing three additional vertical gussets to the top of the CORK-II head. We modified the remaining CORK-II head assemblies.
We disconnected the running tool from the CORK-II head at 1125 h on 5 August. Strictly by chance, the camera/sonar system was aligned perfectly with the J-slot on the CORK-II running tool, and we were able to observe the un-jaying process. Once the running tool was released, we used the running tool to nudge the high side of the platform and it dropped into place on top of reentry cone at 1130 h. It should be noted that this was the first deployment of the considerably lighter (expanded metal) ROV platform design. This design flaw had existed in earlier CORK-II installation designs, but the greater weight of the earlier platforms probably was enough to overcome any momentary hangups. The installation of the new Hole 1026B CORK-II was successfully completed at 1130 h on 5 August. The final installation is shown in Figure F24.Transit from Hole 1026B to Hole U1301B
While retrieving the CORK-II running tool, we moved the ship 0.55 nmi back to Hole U1301B to attempt remedial cementing of the backed-off 103/4 inch casing string. For a description of operations in Hole U1301B, see "Site U1301."
Next Section | Table of Contents