IODP Proceedings    Volume contents     Search
iodp logo


Summary of operations

Hole U1324A

A summary of operations in Hole U1324A is found in Table T1. A beacon was deployed at Site U1324 at 1040 h on 17 June 2005. Hole U1324A was spudded at 1610 h when the driller tagged the seafloor at 1066.0 meters below rig floor (mbrf) (precision depth recorder [PDR] = 1078.0 mbrf). After the bit was washed ahead to 5.0 mbsf, MWD drilling advanced without incident to 333.4 mbsf at a rate of penetration (ROP) of 30 m/h, where a wiper trip was made back to 60.8 mbsf. MWD drilling resumed to 477.7 mbsf, where another wiper trip was made back to 330.4 mbsf. Because of the potential for interbedded levee sands below 481 mbsf, we used heavy mud from this depth to the TD of 612 mbsf (20 m above the top of the Blue Unit). At ~2045 h on 18 June, MWD drilling advanced slowly at an ROP of 20 m/h, gradually increasing to 30 m/h while “pumping and dumping” 10.0 ppg mud. Drilling advanced to the depth objective of 612 mbsf by 0410 h the next morning. The hole was plugged with cement and heavy mud and abandoned. A free-fall funnel (FFF) was made up and deployed at 0808 h on 19 June with the bit at ~80 mbsf. The vibration-isolated television (VIT) camera was deployed and a visual inspection confirmed that there was no flow emanating from the top of the FFF and that the funnel was upright. The bit was pulled free of the seafloor at 0853 h. It was decided in view of the good hole conditions that wireline logging should be attempted in Hole U1324A. A logging/​cementing bottom-hole assembly (BHA) was made up with the 9⅞ inch polycrystalline diamond bit, bit, bit sub, controlled-length drill collar (CLDC), modified top sub, four CLDCs, tapered drill collar, six joints of 5½ inch drill pipe, and a crossover sub (length = 116.6 m). The second reentry of the expedition was made at 1828 h on 19 June, and the bit placed at the logging depth of 54.2 mbsf. A tool string consisting of the Hostile Environment Gamma Ray Sonde (HNGS), Dipole Sonic Imager (DSI), and General Purpose Inclinometer Tool (GPIT) was deployed. A more detailed description of wireline logging and LWD/MWD operations in Hole U1324A can be found in “Downhole measurements.”

Hole U1324B

A summary of operations in Hole U1324B is found in Table T2. The BHA was reconfigured to an APC/XCB array by replacing two of the CLDCs with a seal bore drill collar and nonmagnetic drill collar. This array was identical to the BHA used to core the Brazos-Trinity sites. After a VIT camera survey of the seafloor, the driller tagged the bottom at 1066.8 mbrf. Hole U1324B was spudded with the APC at 0250 h on 21 June 2005. The recovery of the first core established the seafloor depth at 1067.5 mbrf. Piston coring advanced without incident to 17.8 mbsf, where the corer did not achieve a complete stroke but did recover 9.91 m (recovery = 104%). APC coring continued to 357.9 mbsf by advancing by recovery. We observed that downhole pressure measurements from the previous day indicated pressures below hydrostatic, and the readings were consistent between both the T2P probe and the DVTPP. Comparing these abnormal readings with the deformation seen at the base of the APC cores, it was inferred that the suction applied to retrieve the piston cores may have deformed the material sufficiently to influence pressure readings in the formation. Hence, one XCB core was obtained prior to a deployment of the DVTPP and T2P probe. However, XCB coring did not improve pressure measurements; the subhydrostatic pressure readings continued to afflict most of the subsequent DVTPP measurements up to the eighth run in the hole. Just prior to the eighth measurement, a small interior leak in the DVTPP unit was discovered and repaired. This fixed the problem.

Piston coring continued to a TD of 394.5 mbsf by advancing by recovery. A total of 48 piston cores were shot in order to penetrate to this depth, and the average recovery was 101.3%. Nonmagnetic core barrels were used for all piston cores. The cores were oriented starting with Core 4H. The APC temperature (APCT) tool was deployed at Cores 6H, 9H, 12H, and 15H (see Tables T2, T16). Fluorescent microspheres were deployed in the core catchers of Cores 1H–11H, 13H, 15H, 17H, 19H, 21H–23H, 26H, 29H–32H, 35H, 38H–41H, 44H, 47H, and 50H (see Table T2). The Fugro cutting shoe that was sent out on the work boat was deployed on Cores 4H and 7H and odd-numbered piston cores up to and including Core 49H (see Table T2).

Coring resumed with the XCB and deepened the hole to 608.2 mbsf. The XCB-cored portion of the hole was 223.8 m (average recovery = 80.8%). The total cored interval was 608.2 m (average recovery = 93.7%). In compliance with the operational protocol, heavy mud (10.5 ppg) was continuously pumped starting at 481 mbsf until the bottom of the hole. Fluorescent microspheres were deployed in 10 XCB cores: 53X, 56X, 59X, 62X, 64X, 66X, 68X, 70X, 72X, and 74X (see Table T2).

When drill pipe connections were made to recover or deploy tools or core barrels, the heavy mud would “U-tube,” creating a large air gap in the pipe. The impact of the core barrel at the top of the mud level in the pipe tended to shatter the core liner as a result of the sudden deceleration. To avoid this, the core barrels were lowered on the coring line and then intentionally jarred and released by the core winch operator after the barrel landed. The sinker bars were then removed from the drill string to prevent oil saver leakage from spraying mud over the rig floor and derrick. Once the core was cut, the sinker bars were stabbed and the core barrel recovered. This resulted in two coring line roundtrips for each core.

The DVTPP was deployed 10 times in this hole (229.1, 362.4, 387.9, 464.3, 493.1, 522.0, 541.2, 560.4, 589.2, and 608.3 mbsf) (see Table T16). The pressure data prior to DVTPP Deployment 8 were not usable. The T2P probe was deployed 10 times (~30 min each; 51.3, 89.3, 117.8, 136.3, 368.0, 394.5, and 593.2 mbsf). Because of deployment and electronic problems, none of the data obtained from the T2P in this hole were usable. It was observed that an additional benefit of filling the hole with heavy mud made DVTPP and T2P deployments easier because the tools and BHA became easier to extract from the bottom of the hole after sustained periods without rotation during the deployment process.

Because it was not possible to measure the equivalent circulating density (ECD) of the mud, as was effectively done in Hole U1324A, the conservative measure of pumping 10.5 ppg mud was adopted. The mud engineer calculated that we expended 3880 bbl of 10.5 ppg mud while drilling this hole. In accordance with the operating protocol, the hole was plugged with 44 bbl of 11.0 ppg neat cement, forming a plug of ~145 m. The cement was followed by 40 bbl of 10.5 ppg mud and then chased with 50 bbl of seawater. The hole was observed using the VIT camera with the bit at ~80 mbsf and no flow was detected. The bit was pulled free of the hole at 0025 h on 26 June. As the vessel was moved off location, a subsea release dart was pumped down to swab the inside of the pipe. This was followed by extensive seawater flushing of the drill string.

Hole U1324C

A summary of operations in Hole U1324C is found in Table T3. The vessel was repositioned 20 m west of Hole U1324A in dynamic positioning (DP) mode. After a VIT camera survey of the seafloor indicated no obstructions, Hole U1324C was spudded when the driller tagged the seafloor at 1066.5 mbrf. The hole was then drilled ahead to 50.0 mbsf, where the T2P probe was deployed with good results. Following the retrieval of the probe, a single APC core was obtained for physical property analyses. Following this procedure, three more T2P deployments were made at 100, 150.0, and 200.0 mbsf, each measurement followed by a single APC core. The hole was then drilled to 250.0 mbsf, where a DVTPP measurement was made, followed by a single piston core. Once again the hole was drilled from 250.0 to 300.0 mbsf, where the fourth T2P deployment was made, followed by a single APC core. The hole was then drilled to 405.0 and 505.0 mbsf, followed each time by a single piston core. The last piston cored advanced to a TD of 511.8 mbsf. When the driller advanced beyond 481.0 mbsf, heavy mud (10.5 ppg) was continuously pumped in accordance with the operating protocol for this site. A total of eight piston cores were obtained, the last seven were advanced by recovery. The cored interval was 55.1 m (average recovery = 100.9%). The cores were not oriented and were all obtained with the nonmagnetic core barrel. The Fugro cutting shoe was deployed on even-numbered core barrels. Before the drill string was withdrawn from Hole U1324C, the hole was observed with the VIT camera and no flow was evident. Because penetration in the hole was terminated above the sand layers, it was not necessary to plug this hole with cement. The bit was pulled free of the seafloor at 0135 h on 28 June and positioned 204 m above the seafloor. The vessel was then offset in DP mode to Site U1322. The beacon was recovered before departing location at 0240 h.