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IODP Expeditions 367 and 368

South China Sea Rifted Margin


Daily Science Report for 25 March 2017

Location: Hole U1500B (18°18.2707′N, 116°13.1951′E; proposed Site SCSII-8B)

Science Update: Cores 58R to 60R penetrated from 1388.5 to 1415.9 m and recovered 19.9 m (73%). These cores also cut slowly (4.3–5.4 h) but mostly smoothly and consistently. Since we had 52 rotating hours on the bit and we wanted to core and log deeper in Hole U1500B, we decided to retrieve the drill string to change the RCB bit. We circulated cuttings out of the hole, raised the bit up to 1242 m, and pumped 235 barrels of weighted (11.0 ppg) mud into the hole to stabilize it while we change the bit. We then pulled the drill string out of the hole (removing the top drive at 1066.0 m) and the bit cleared the seafloor at 2340 h. Cores recovered today contain sparsely to moderately plagioclase-rich phyric basalt that is fresh to moderately altered. The basalt also contains carbonate and iron oxide veins and a few thin intervals of sediment mixed with volcanic glass.


Daily Science Report for 24 March 2017

Location: Hole U1500B (18°18.2707′N, 116°13.1951′E; proposed Site SCSII-8B)

Science Update: Cores 51R to 57R penetrated from 1320.6 to 1388.5 m and recovered 32.4 m (48%). After Core 51R took 100 min to cut, the next five cores (52R–56R) penetrated quite quickly (all but one took only 5 to 25 min) and had relatively lower recovery. Core 57R cut slowly (3.6 h) but smoothly and consistently and recovered 8.34 m that is almost entirely basalt. We circulated 30 barrel mud sweeps after cutting each core. The lowermost sediments are dark greenish claystone with biogenic carbonate, overlying dark gray sandstone and finally a short interval of red claystone overlying basalt. The top of the basalt has a chilled margin and then consists of massive sparsely plagioclase-rich phyric and aphyric basalt that is fresh to moderately altered. The basalt also contains carbonate and iron oxide veins and one fracture filled with sediment (injection). Preliminary ages constrain the sediments recovered today to the Oligocene, although work is ongoing.


Daily Science Report for 23 March 2017

Location: Hole U1500B (18°18.2707′N, 116°13.1951′E; proposed Site SCSII-8B)

Science Update: Cores 46R to 50R penetrated from 1272.1 to 1320.6 m and recovered 30.2 m (62%). Although it took quite a long time to cut each of these cores (1.8 to 3.8 h), the penetration rate was very smooth and hole conditions were quite good. We circulated 30 barrel mud sweeps after cutting each core. Cores recovered transition downhole from dusky red claystone to greenish-gray silty claystone; ages also transition from middle/early Miocene to late Oligocene.


Daily Science Report for 22 March 2017

Location: Hole U1500B (18°18.2707′N, 116°13.1951′E; proposed Site SCSII-8B)

Science Update: Cores 35R to 45R penetrated from 1272.1 m and recovered 27.2 m (25%). The first seven of these cores took less than 20 min to cut and had extremely poor recovery (0 to 0.67 m). While cutting Core 42R, we encountered a substantial formation change at 1235 m and core recovery increased to 66% for Cores 42R to 45R. The time to cut Cores 43R to 45R also increased to 40–80 min. We circulated 30 barrel mud sweeps after cutting each core. The change in formation is also reflected in the lithology—dusky red claystone with greenish alteration zones as well as a few interbedded sandstone layers. Recovery and poor microfossil preservation continues to impact our ability to date the cores, but we are still close to the late/middle Miocene boundary.


Daily Science Report for 21 March 2017

Location: Hole U1500B (18°18.2707′N, 116°13.1951′E; proposed Site SCSII-8B)

Science Update: Cores 24R to 34R penetrated from 1058.7 to 1165.4 m and recovered 19.2 m (18%). The majority of cores took 15 min or less to cut and had extremely poor recovery (0 to 1.57 m, but mostly <0.44 m). The three cores that took 30 min or more to cut recovered 3.60 to 5.94 m. We circulated 30 barrel mud sweeps at 1068, 1078, 1087, 1097, 1107, 1116, 1127, 1136, 1146, 1156, and 1165 m. Cores recovered today are claystones, siltstones, and sandstones. Recovery and poor microfossil preservation severely impacts our ability to date these cores, but they are close to the late/middle Miocene boundary.


Daily Science Report for 20 March 2017

Location: Hole U1500B (18°18.2707′N, 116°13.1951′E; proposed Site SCSII-8B)

Science Update: Cores 12R to 23R penetrated from 942.3 to 1058.7 m and recovered 23.3 m (20%). Core recovery was highly variable with very low recovery (0 to 1.04 m) in very fast penetration (10 min or less) intervals. We circulated 30 barrel mud sweeps at 952, 961, 971, 981, 1000, 1010, 1020, 1030, 1039, and 1049 mbsf. Cores recovered today contain late Miocene claystone with silt as well as sandstone with claystone clasts.


Daily Science Report for 19 March 2017

Location: Hole U1500B (18°18.2707′N, 116°13.1951′E; proposed Site SCSII-8B)

Science Update: We finished lowering the RCB bit from 833.5 m, into the open hole below the end of the casing (842 m), and to the bottom of Hole U1500B at 846.0 m. We found only 1 m of fill, circulated 25 barrels of mud displacing the heavy mud out of the hole, and started RCB coring at 0115 h. Cores 2R to 11R penetrated from 846.0 to 942.3 m and recovered 40.5 m (42%). Core recovery was highly variable with very low recovery (0.05 to 1.31 m) in very fast penetration intervals. We circulated 30 barrel mud sweeps at 884, 903.3, 922.9, and 932.6 m. The uppermost 5.3 m of the first core below the casing (Core 2R) is composed primarily of heavy mud mixed with some cuttings. The rest of Cores 2R to 11R contain late Miocene dark gray claystone with a few sandstone interbeds, some containing claystone clasts.


Daily Science Report for 18 March 2017

Location: Hole U1500B (18°18.2707′N, 116°13.1951′E; proposed Site SCSII-8B)

Science Update: We recovered the drilling assembly that was used to drill the 842 m of 10.5 inch casing into Hole U1500B. When the underreamer arrived back on the rig floor (0730 h), all of its cutting structures were still attached, although one of them was clearly damaged and likely the cause of yesterdays torque event and subsequent reduction in penetration rate. We started assembling the RCB bottom-hole assembly at 0915 h and lowered it to the seafloor. We deployed the subsea camera system at 1615 h, started searching for the Hole U1500B reentry funnel at 1830 h, and reentered it at 1845 h. We recovered the camera system, lowered the bit down through the casing, and installed the top drive to prepare for RCB coring. At the end of the day, the bit was at 833.5 m, less than 10 m above the base of the casing.


Daily Science Report for 17 March 2017

Location: Hole U1500B (18°18.2707′N, 116°13.1951′E; proposed Site SCSII-8B)

Science Update: We continued with the installation of 842 m of 10.75 inch casing in Hole U1500B. We were drilling it into the seafloor with a drilling assembly composed of (1) a 9.875 inch tricone drilling bit, (2) an underreamer with arms set to 12.75 inches, and (3) a mud motor. We have been observing the top of the reentry system (reentry funnel and mud skirt) throughout the operation with the subsea camera. The only other information the drillers had to monitor the operation was the circulating pressures inside the drill string, fluctuations in overall drill string weight, and penetration rate.

At ~0759 h with the bit at ~779 m, we saw the mud skirt and reentry funnel rotate very quickly indicating that torque had built up in the drill string. At the same time, we also observed that the penetration rate slowed down substantially. We suspected that one or more of the underreamer arms had lost its cutting structure (roller cone). Our options at this point were limited to (1) continue to drill it in to the full depth or (2) pull it back to the ship, shorten the casing string, and try to drill that in. We had only ~80 m more of penetration until the casing was fully installed. Based on the coring information from Hole U1500A, much of this interval was loosely-consolidated fast-penetration formation, with only a couple of short intervals of firm formation, so we continued to drill it in. Although penetration rates slowed quite a bit, we were able to continue advancing the entire system into the seafloor. This fact led us to suspect that if the underreamer cutters had come off, they likely had been pushed off into the borehole wall behind the casing. At 1740 h, a reduction in drill string weight indicated that the mud skirt had landed on the seafloor. We dropped the go-devil to activate the hydraulic release tool (HRT), and at ~1833 h the drilling assembly released from the casing. We raised the bit and underreamer back up to 841.4 m—inside the casing—and filled the casing annulus with 100 barrels of mud to inhibit sand from being sucked back up into the casing as we pull the drilling assembly out of the hole (as previously happened at Hole U1499B). We then pulled the drill string out of the hole. After the bit cleared the seafloor (2220 h), we conducted a short survey of the reentry system, which is barely visible in the cutting mound. Tomorrow, we plan to reenter Hole U1500B and start RCB coring from ~846 m.


Daily Science Report for 16 March 2017

Location: Hole U1500B (18°18.2707′N, 116°13.1951′E; proposed Site SCSII-8B)

Science Update: At 0030 h, we started drilling the 842 m of 10.5 inch casing into the seafloor at Hole U1500B. The rest of the day was spent advancing the bit to 588.3 m. Along the way, we circulated 30 barrels of mud at 335.6, 374.6, 394.0, 423.1, 452.2, 481.4, 510.6, 539.6, and 568.8 m. Scientists continued to finalize their Site U1499 reports while considering ways to integrate the data. They also processed and analyzed the Hole U1500A data.


Daily Science Report for 15 March 2017

Location: Hole U1500B (18°18.2707′N, 116°13.1951′E; proposed Site SCSII-8B)

Science Update: We finished assembling the 841.3 m of 10.5 inch casing and latched it into the mud skirt sitting on the moonpool doors at 0400 h. After assembling and testing the pilot bit, underreamer (set to 12.75 inches), and mud motor, this drilling assembly was lowered through the casing. The casing running tool (hydraulic release tool [HRT]) was attached to the top of the drilling assembly and then secured to the mud skirt/casing. The entire system was lowered through the moonpool at 1130 h. Most of the rest of the day was spent lowering it to the seafloor. We deployed the subsea camera system at 2015 h, installed the top drive at 2315 h, and by midnight we were preparing to start drilling it into the seafloor.


Daily Science Report for 14 March 2017

Location:
Hole U1500A (18°18.2762′N, 116°13.1916′E; proposed Site SCSII-8B)
Hole U1500B (18°18.2709′N, 116°13.1949′E, water depth 3801.7 m; proposed Site SCSII-8B)

Science Update: We continued recovering the drill string; the bit arrived back on the rig floor at 0640 h. We disassembled the bit, cleared the rig floor, and conducted required routine rig servicing (drill line slip and cut). From 0900 to 2400 h, we prepared the casing running tool (Hydraulic Release Tool) and assembled the first 49 joints (666.35 m) of 10.75 inch casing. We plan to drill a total of 842 m of casing into the seafloor at Hole U1500B with a 9.875 inch tricone bit, an underreamer set to 12.75 inch, and a mud motor.


Daily Science Report for 13 March 2017

Location: Hole U1500A (18°18.2762′N, 116°13.1916′E; proposed Site SCSII-8B)

Science Update: Cores 29R to 36R penetrated from 770.0 to 854.6 m and recovered 27.6 m (36%). The majority of the core recovered was in Cores 30R, 33R, 35R, and 36R (25.29 m). For the other cores, penetration rates were very fast and recovery very low (2%–9%, inferred to be less consolidated silts/sands). We circulated 30 barrel mud sweeps at 796, 806, 815, 825, 835.2, 844.9, and 854.6 m. We pulled the bit out of the hole and it cleared the seafloor at 2330 h. Based on the Hole U1500A information (cores, drilling, and borehole conditions), we decided that to achieve our deep coring and logging objectives at this site, we will drill 850 m of casing into the seafloor at our next hole. This will place the base of the casing in the relatively fine-grained stable formation we recovered in the last two cores and isolate the multiple intervals of unstable formation above (inferred sands/silts). Cores recovered today are late Miocene sandstones and claystones.


Daily Science Report for 12 March 2017

Location: Hole U1500A (18°18.2762′N, 116°13.1916′E; proposed Site SCSII-8B)

Science Update: Overall core recovery today (Cores 16R to 28R) penetrated from 660.6 to 777.0 m and recovered 39.4 m (34%). Penetration rates within the upper part of this interval (17R to 23R, 660.6–728.5 m) were very quick (5–10 min), and we only recovered 6.67 m (10%). A formation change occurred at 728.5 m—Cores 24R–27R (728.5 to 767.3 m) took 30–50 min to cut and included substantially improved recovery (32.1 m; 83%) of clays/claystones. We thought this would be a good formation for the base of our planned Hole U1500B casing, until the last core of the day (28R) once again returned to a fast-penetrating, low-recovery interval inferred to be sands. We pumped 30 barrel mud sweeps at 680, 699, 719, 728.5, 747.9, and 767.3 m. Cores contain late Miocene claystones, siltstones, and foraminfer sandstones; some of the silt/sandstones contain claystone clasts and contorted sedimentary structures.


Daily Science Report for 11 March 2017

Location: Hole U1500A (18°18.2762′N, 116°13.1916′E; proposed Site SCSII-8B)

Science Update: Today we RCB cored from 426.7 to 494.6 m (7R to 13R), drilled without coring from 494.6 to 641.2 m, and then resumed coring from 641.2 to 660.6 m (15R to 16R). All cores penetrated the formation very quickly, with all but two only taking 5 min. Recovery was extremely poor (0 to 14 cm), except for Cores 9R (2.86 m) and 13R (1.06 m). Overall today’s RCB cores penetrated 87.3 m and recovered 4.2 m (5%). We pumped frequent mud sweeps (30 barrels at 436, 446, 455, 475, 494, 505, 564.3, 583.7, 612.8, 632.2, and 650.9 m). Cores are late Miocene silty claystone with some short intervals of foraminifer-rich sandstone.


Daily Science Report for 10 March 2017

Location: Hole U1500A (18°18.2762′N, 116°13.1916′E; proposed Site SCSII-8B)

Science Update: After the drawworks clutch diaphragm had been replaced (0930 h), we resumed drilling without coring from 340.5 to 378.2 m. While drilling down, we pumped 30 barrel mud sweeps at 350.2 and 378.2 m. We recovered the center bit and started RCB coring at 1245 h. Cores U1500A-2R to 6R penetrated to 426.7 m and recovered 22.4 m (46%). Thirty barrel mud sweeps were circulated at 397.6 and 417.0 m. Cores recovered late Miocene clays with a few rare silt interbeds.


Daily Science Report for 9 March 2017

Location:
In transit
Hole U1500A (18°18.2762′N, 116°13.1916′E; proposed Site SCSII-8B)

Science Update: We continued lowering the RCB bit to the seafloor while in transit. At 0415 h, we arrived at Site U1500 (proposed Site SCSII-8B) and started lowering the subsea camera system to observe the bit tag the seafloor to establish the water depth (3801.7 m). After recovering the camera system, we started drilling without coring in Hole U1500A at 0935 h. At 1930 h, the bit had reached 340.5 m when the drawworks clutch diaphragm that had been replaced earlier in the expedition failed. The rest of the day was spent disassembling the clutch and starting the repair. We plan to use the new spares that were delivered to the ship by boat on 27 February.


Daily Science Report for 8 March 2017

Location:
Hole U1499B (18°24.5705′N, 115°51.5990′E; proposed Site SCS-14A)
In transit to Site U1500 (proposed Site SCSII-8B)

Science Update: We assembled the FMS-sonic and natural gamma ray tools and started lowering the tool string at 0130 h. The tool string was able to reach 1010 m and we were able to make two passes of the open hole up to the base of the casing at 651 m. Initial results indicate that we collected excellent data in intervals with good borehole diameter. The tool string arrived back on the rig floor at 0925 h and all of the logging equipment was off the rig floor at 1030 h. We pulled the end of the drill string out of Hole U1499B at 1120 h, recovered the seafloor beacon, and started the transit to Site U1500 (proposed Site SCSII-08B) in dynamic positioning mode. While in transit, we continued to recover the drill string (arrived back on the rig floor at 1830 h) as well as assemble a new RCB bit and begin lowering it to the seafloor. At the end of the day, the bit was 2056 m below the rig floor.


Daily Science Report for 7 March 2017

Location: Hole U1499B (18°24.5705′N, 115°51.5990′E; proposed Site SCS-14A)

Science Update: To prepare for wireline logging of Hole U1499B, we released the bit in the bottom of the hole at 0000 h, raised the end of the pipe from 1052.7 up to 877.3 m, and shifted the mechanical bit release sleeve back into the circulating position. We then raised the end of the pipe up to 780 m and pumped 235 barrels of heavy mud into the hole to help maintain good hole conditions so we could log. At 1030 h, we had raised the end of pipe back up inside the casing to 85.1 m and started to prepare the rig floor for logging. We assembled the first logging tool string (with resistivity, sonic, density, and natural gamma tools) and started lowering them at 1345 h. The tool string was able to reach 1050 m and we successfully logged up to the base of the casing at 651 m. This tool string arrived back at the rig floor at 2215 h and the rest of the day was spent taking it apart. Based on the first logging run results, we decided to conduct a second logging run with the FMS-sonic and natural gamma ray tools.


Daily Science Report for 6 March 2017

Location: Hole U1499B (18°24.5705′N, 115°51.5990′E; proposed Site SCS-14A)

Science Update: After recovering Core U1499B-44R (1062.4–1072.1 m, 0.45 m recovered, 5%), we dropped the next core barrel and started cutting Core 45R. While cutting this core, there were periods of erratic torque, high pump pressures, and some short times when the drill string could not be rotated. The driller raised and lowered the drill string and was able to keep coring. Just after we put the core line into the drill string to retrieve Core 45R, the pipe became stuck. For ~45 min we worked the drill string, until it was freed at 0615 h; then we removed the core line from the drill string. We raised the bit back up to 994 m and worked to clean out the hole. Eventually at 1045 h, conditions had improved enough that we retrieved Core 45R at 1150 h (1072.1–1081.8 m; 0.09 m recovered; 0.9%). We spent the next 9 h attempting to wash, ream, drill, and circulate our way back to bottom. However, we never were able to get below ~1050 m (~30 m above the bottom of the hole) without the drill string getting stuck. We decided at 2045 h that further attempts to get back to the bottom of the hole and RCB core deeper were not reasonable, so we started to prepare the hole for wireline logging. We circulated 50 barrels of mud to clean cuttings out of the hole, retrieved the core (wash) barrel that was in place during the hole remediation efforts, and lowered the rotary shifting tool (RST) on the coring line to release the bit in the hole. Cores 44R and 45R recovered lithic-rich sandstone and sandy siltstone. No microfossils are observed, so we are not able to assign an age.


Daily Science Report for 5 March 2017

Location: Hole U1499B (18°24.5705′N, 115°51.5990′E; proposed Site SCS-14A)

Science Update: After changing the bit and getting back to the bottom of the hole at 1013.9 m, we dropped the RCB core barrel at 0115 h and resumed coring. Cores 39R–43R penetrated from 1013.9 to 1062.4 m and recovered 4.1 m (4%). We pumped 30 barrels of mud after each of these cores. The cores contain gravels composed of a variety of lithic-rich sandstones. No microfossils are observed, so we are not able to assign an age.


Daily Science Report for 4 March 2017

Location: Hole U1499B (18°24.5705′N, 115°51.5990′E; proposed Site SCS-14A)

Science Update: We finished recovering the drill string at 0215 h, attached a new RCB bit (C-7), lowered it to the seafloor, and then deployed the subsea camera system at 0915 h. We paused rig floor operations from 0915 to 1045 h to conduct required routine rig servicing (drill line slip and cut) before we resumed lowering the drill bit to the seafloor. At 1345 h, the bit and camera were in position and we were immediately able to see the reentry funnel clearly in the center of the cuttings pile caldera. It took us 22 min to position the bit over the funnel and reenter Hole U1499B at 1407 h. We retrieved the camera and lowered the bit down through the 651 m of casing and into the open hole to 848.1 m. We installed the top drive and circulated/rotated until 987 m—only ~27 m from the bottom of the hole—before the bit encountered any resistance. This was easily penetrated and we only encountered 1 m of fill on the bottom of the hole. At the end of the day, we were retrieving the core barrel that was in place while getting back to the bottom of the hole. As soon as that is done, we can resume RCB coring from 1013.9 m.


Daily Science Report for 3 March 2017

Location: Hole U1499B (18°24.5705′N, 115°51.5990′E; proposed Site SCS-14A)

Science Update: RCB Cores U1499B-37R and 38R penetrated from 994.5 to 1013.9 m and recovered 2.25 m (12%). We circulated 30 barrels of mud at 994.5 m and then circulated the cuttings out of the hole with 70 barrels of mud after Core 38R. We decided to stop coring to change the RCB bit as we wanted to core deeper and the bit had accumulated 40.6 rotating hours. Before pulling the bit up into the casing and out of the hole, we first raised the bit up to 780 m, circulated the hole with 35 barrels of mud, and then filled the uncased (open) part of the hole with 235 barrels of heavy mud (11.0 ppg; barite). This is intended to help stabilize the hole while we are changing the bit and reduce the amount of fill we have to drill out to get back to the bottom of the hole and resume RCB coring. This may also give us some indication of hole conditions we might encounter for planned downhole logging after coring is finished. We lowered the subsea camera system to observe the reentry funnel as we pulled the bit out of the hole. While we were still in the hole, we could see the drill pipe clearly in the center of the crater created by the cuttings mound. Although the reentry funnel’s concentric black and white stripes were not visible, we shouldn’t have any problems finding and reentering the hole tomorrow. The bit was pulled out of the hole at 1655 h and we spent the rest of the day recovering the drill string (except for a 0.5 h repair of the pipe racker). At midnight the bit was at 435.7 m below the rig floor. Cores 37R and 38R are medium to coarse-grained sandstone and occasional sedimentary, and slightly metamorphosed, breccia. Age dating in these lowermost cores remains unclear as they are mostly barren, but it appears that we in the late Oligocene.


Daily Science Report for 2 March 2017

Location: Hole U1499B (18°24.5705′N, 115°51.5990′E; proposed Site SCS-14A)

Science Update: RCB Cores U1499B-32R to 36R penetrated 48.5 m from 946.0–994.5 m and recovered 6.05 m (12%). It took 2–3 h to cut each core. The drill string became stuck momentarily while cutting Core 33R. We circulated 30 barrels of mud after cutting Cores 32R and 35R–37R. Cores 31R to 36R are medium to coarse-grained sandstone and occasional sedimentary, and slightly metamorphosed, breccia. Age dating in these lowermost cores is not yet clear as they are mostly barren, but it appears that we are in the late Oligocene.


Daily Science Report for 1 March 2017

Location: Hole U1499B (18°24.5705′N, 115°51.5990′E; proposed Site SCS-14A)

Science Update: RCB Cores U1499B-27R to 31R penetrated 48.5 m from 897.5 to 946.0 m and recovered 23.96 m (49%). Core 30R took only 45 min to cut, as opposed to the cores above (27R, 205 min; 28R, 130 min; and 29R, 120 min). When raising the bit off bottom, the drill string became stuck momentarily, so we circulated 30 barrels of mud and hole conditions improved. The penetration rate for Core 31R went back up (130 min), but the drill string became temporarily stuck again; this time we circulated 90 barrels of mud and coring was able to continue. Cores 26R to 29R contain dark brownish claystone with greenish-gray claystone, siltstone, and calcareous-rich claystone interbeds. Core 30R contains a transition from brownish to greenish claystone with clasts (manganese nodules), to sandstone with pebbles, to matrix-supported breccia, to sandstone. Our micropaleontologic analyses are ongoing but we suspect we may be near the early Miocene/Oligocene boundary.