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doi:10.2204/iodp.proc.342.103.2014

MDHDS deployment

The MDHDS is part of a three-component system (Figs. F11, F12) designed to deliver a downhole tool, decouple the tool from the drill string, and recover the tool. The uppermost component is the Multifunction Telemetry Module (MFTM), which allows real-time communication with the ERS and other tools. The ERS delivers and retrieves the MDHDS and the attached downhole tool to the BHA and passes data from a communications tether to the MFTM. The MDHDS, once seated in the BHA, is the platform from which the penetrometer (or some tool to be designed in the future) is deployed (Fig. F12).

Components

Multifunction Telemetry Module

The MFTM (Fig. F11) is a downhole sonde that allows real-time communication with downhole tools through the Schlumberger armored seven-conductor cable. The MFTM was developed by the Lamont-Doherty Earth Observatory Borehole Research Group and is used both to activate latching of the ERS and to capture data streams from probes attached to the inner core barrel of the MDHDS assembly through a communications tether.

The telemetry system has four components (Fig. F13):

1. The telemetry surface control panel (TSCP);

2. A standard Schlumberger Vector 7-46P seven-conductor armored cable for use in logging operations;

3. A Schlumberger logging equipment cablehead (LEH-QT) that makes the physical and electrical connections from the wireline logging cable to the downhole tool string; and

4. The MFTM, which captures the data stream from the probe and broadcasts it to the surface panel.

The MFTM is designed to work with multiple tool platforms; a series of switches mounted in the communication board allows the user to make adjustments depending on the platform used (Fig. F14). In this particular application, the T2P communicates through a 2 mm coaxial cable to the ERS. Communication is passed through the ERS to the MFTM through a standard Schlumberger 31-pin connector. This allows real-time monitoring of the formation pressures and temperatures penetrated by the probe. These data can be viewed in real time through simple plots. Data are simultaneously acquired by the TSCP data acquisition software and stored while also being transferred to a second data analysis system for more complicated real-time data manipulation.

Electronic RS

The ERS (Fig. F11 and violet shading in Fig. F12) was developed by Stress Engineering Services for use with the SCIMPI CORK system and the MDHDS. The ERS deploys and retrieves the MDHDS (or any downhole tool) within the drill pipe on the electric wireline.

The ERS is an adaptation of the standard 3 inch RS running tool designed to run on the Schlumberger logging line. Its purpose is to enable running a downhole tool (with an up-looking RS overshot) on the logging line through the drill string for downhole emplacement. A 24 VDC motor in the ERS is commanded from the surface to rotate until the RS pulling neck on the downhole instrument, probe, or tool string is released. This capability is to be used in place of a jarring action to shear off an RS connection or using Kinley cutters. The ERS can also capture a tool with an appropriate up-looking pulling neck. To engage an RS pulling neck profile on deck (or downhole), the ERS has a snap-lock feature for which motorized action is required to unlock and return the tool to a locked position.

The ERS is composed of the electronics section, wired through a sinker bar, to a motor section that contains the latching mechanism at the bottom of the ERS (bottom of Fig. F13 and Fig. F15). The ERS electronics housing is unable to pass through the MDHDS landing shoulder. Therefore, an elongated sinker bar allows the ERS to reach as far as 4.92 m into the MDHDS outer barrel subassembly to retrieve the MDHDS after it has been deployed (Fig. F16). The ERS is latched at the surface and lowered into the borehole. An electric motor within the ERS is commanded from the surface to rotate until the RS pulling neck on the downhole instrument is released (Fig. F17). This motor can both unlock the ERS from the downhole tool and return the ERS to a locked position so that it can be used to retrieve the downhole tool. A prototype of the ERS was used during IODP Expedition 327 to successfully deploy the Hole U1301B CORK system (Expedition 327 Scientists, 2011).

Motion Decoupled Hydraulic Delivery System

The MDHDS is composed of an inner barrel subassembly (IBS) (Fig. F18 and green in Fig. F12) and an outer barrel subassembly (OBS) (Fig. F19 and brown in Fig. F12). The penetrometer is attached to the IBS. On the rig floor, before the MDHDS is deployed, the IBS is latched to the OBS (Fig. F20). The latching system (MDHDS latch) is near the bottom of the MDHDS (Fig. F19). When using a narrow-diameter penetrometer like the T2P, the bottom of the MDHDS can be outfitted with a flapper guide tube. This tube protects the penetrometer as it passes through the flapper at the drill bit and acts as a guide to ensure vertical deployment (surrounding T2P, bottom of Fig. F12). For larger diameter penetrometers like the Sediment Temperature-Pressure (SET-P) tool, the flapper guide tube is not used.

The MDHDS latch is cocked with an external lever (Fig. F21). This compresses a 316 stainless steel spring within the MDHDS latch and shifts an internal sleeve to lock the latch piston in place. The latch spring rate is 88 lb/inch. When the spring is locked in the latched position, it is compressed 2.5 inches.

The internal sleeve is then fixed in place with shear pins. The shear screws are off-the-shelf ¼ inch brass set screws. These screws typically shear at 1330 pound-force (lb_f) ± 10%. With two shear screws installed, the total force to shear the screws is ~2660 lb_f. With the IBS latched in place, the center of the shear screw head is effectively blanked off. Thus, a piston area is created by the O-ring seals on the outside of the shear screw head sealing inside the shear screw housing. This area is equal to 7.220 in². Therefore, the drill string pressure required to shear the screws and shift the inner latch subassembly is 2660 lb_f/7.220 in² = 368 psi.

The latched MDHDS is conveyed by the ERS on the wireline to sit on the landing shoulder of the standard BHA. The MDHDS latch is activated by raising the drill string pressure (Fig. F22A) to shear the two shear screws. When the screws shear, the drill string pressure forces the piston further down until the spring reaches its solid height of 2.34 inches (Fig. F22B). Thus, the spring force is 2.91 inches × 88.0 lb_f/inch = 256 lb_f in its fully compressed position.

The latch piston pressure area is 1.997 in². Thus, the drill string pressure necessary to balance the spring force is 256 lb_f/1.997 in² = 128 psi. This is well below the pressure required to shear the shear screws (368 psi). When the drill string pressure is released, 256 lb_f of spring force is released. However, the O-ring static friction must be overcome before the piston can move. The latch piston O-ring static friction was measured and found to be ~200 lb_f. This means that there is an “overforce” of ~56 lb_f to start the piston moving once the drill string pressure is released. Given the latch piston area of 1.997 in² and the overforce of 56 lb_f, the pressure within the drill string must be <56 lb_f/1.997 in² = 28 psi in order for the latch spring to expand. The rig floor is ~11.5 m above sea level, and the standpipe drain point in the derrick is 10 m above the rig floor. Thus, the hydrostatic head inside the undrained drill string is (11.5 m + 10 m) × 1.46 lb_f/in²/m = 31.4 lb_f/in². Therefore, the standpipe pressure must be bled down to –3.4 psi for the spring to begin moving the piston upward (–3.4 psi + 31.4 psi = 28 psi) into the unlatched position. This means the water level needs to be dropped ~2.2 m below the standpipe drain point. Once the piston begins to move, the dynamic friction is much less and the piston will move rapidly upward until it shoulders.

Relieving the drill string pressure allows the spring to expand (Fig. F22C), which allows the shear screw housing and dog housing to move downward, unlocking the latch piston, which then remains held in place by the drill string pressure. The IBS is then freed from the OBS (Fig. F22D). At this point, the IBS may fall by its own weight.

The penetrometer is next pumped into the formation by raising the drill string pressure once more to ~6.9 MPa (1000 psi). The driving force on the penetrometer is roughly the drill string pressure multiplied by the inner diameter (ID) of the area of the flapper tube. The flapper tube has a 3 inch ID and the area equals 7.069 in². The seal is leaky, so this is an approximate calculation. The piston area that creates the SET-P driving force is created by the tight fit between the IBS and the MDHDS latch. The procedures call for doubling the drill string pressure as used for the T2P, 13.8 to 17.23 MPa (2000 psi to 2500 psi), to drive the SET-P into the formation.

During this test, we installed a tension device inside the IBS to house a communications tether. The tether allowed real-time communication from the penetrometer to the rig floor. This tension device, consisting of a rigid and elastic cable and a series of pulleys, held the communications tether in tension at all times, taking up slack as the drill string heaved downward and letting it out as it heaved upward (Fig. F23). The tether is connected to the top of the T2P and the bottom of the ERS with Teledyne-Impulse IE4M connectors (Fig. F24).

Deployment

On the rig floor, the MDHDS is assembled, the latch set, and the penetrometer attached. The MDHDS and the penetrometer are then hoisted into position using the MDHDS lifting clamp, attached just below the fishing neck (Fig. F25). The penetrometer and the MDHDS are lowered inside the drill string until the MDHDS rests on the lifting clamp at the top of the drill pipe (Fig. F26). The wireline with the attached MFTM and ERS is lowered to ~1 m above the fishing neck. If a tether is used, the tether is pulled up from where it rests within the fishing neck, and the IE4M connector at the up end of the tether is mated with the IE4F outlet at the base of the ERS (Fig. F27). The IE4 locking nut is then installed. The wireline is then slowly lowered until the ERS latches onto the fishing neck at the top of the IBS. A communications test is run to ensure data from the T2P is properly transmitted through the Schlumberger wireline to the data acquisition computer. Once communication is confirmed, the entire assembly is lifted 1 m, the MDHDS lifting clamp is removed, and the tool string is lowered into the drill string. If a tether is not used, then the ERS is lowered until it latches to the fishing neck. Wireline tension is monitored during lowering.

Prior to deployment, the BHA should be positioned 1.5 m above the bottom of the hole (Fig. F28A). The static wireline load is recorded just before the MDHDS is landed in the BHA, and MDHDS is then landed in the BHA. The MFTM actuates the ERS to unlatch the MDHDS, and the ERS is raised 3 m (Fig. F28B). When the ERS is picked up, the load should be substantially less than the load present just before the MDHDS was rested on the BHA landing shoulder. If the load does not drop off, then the ERS did not successfully unlatch and the process is repeated. In this configuration, wireline tension should drop ~500 lb_f after a successful unlatching. If unlatching is successful, then deployment may begin. With the MDHDS latched and landed in the BHA, all the drill string fluid is forced through the center of the OBS through a contact seal between the MDHDS landing shoulder and the wall of the BHA. Next, the drill string is slowly pressurized to ~6.9 MPa (1000 psi), a pressure in excess of the 368 psi necessary to shear the brass shear screws. The pressure should be held for 3–5 min to fully transmit the pressure to the shear screws. Pressure is then bled off. This allows the MDHDS latch spring to expand, allowing the latch piston to shift into place with the relief groove directly over the dogs. At this point, the penetrometer may pass through the BHA under its own weight, though it may not.

Approximately 5 min after pressure is bled off, the drill string pressure is raised once again to ~6.9 MPa (1000 psi) and the probe is pumped out (Fig. F28C). The probe is driven a maximum of 2.9 m into the formation. After 2.9 m, the piston head seal passes through the flapper guide tube, circulation is re-established, and there is no more driving pressure on the penetrometer. The BHA is then picked up 2 m (Fig. F28D), allowing for ±3.0 m of vertical motion. At this point in the deployment, the OBS is fixed relative to the BHA, and the IBS is fixed relative to the bottom of the hole. There are no seals in contact between the inner and outer barrel, thus no seal friction exists that could induce heave motion into the probe. Circulation is terminated. The penetrometer is now deployed, and the tool is left in place to record pressure and temperature dissipation.

The probe is extracted by using the MFTM to actuate the ERS into a closed position, lowering the MFTM-ERS assembly until latching with the RS fishing neck that is attached to the MDHDS inner barrel (Fig. F28E). In an ideal deployment, in which the ERS was raised 3 m, the BHA was raised 2 m, and the tool was driven 2.9 m into the formation, the ERS would have to be lowered 5.8 m to relatch (Fig. F28C). In this situation, the ERS would be lowered inside the OBS a distance of 2.8 m to reach the RS fishing neck (Fig. F28E). The ERS can reach a maximum of 4.92 m inside the OBS before the wider diameter electronics housing of the ERS reaches the landing shoulder (Fig. F29). After relatching, the wireline is raised, paying close attention to the wireline tension and ensuring that the tension rises to the predeployment value. Once latching is confirmed, the IBS and penetrometer are pulled from the formation into the OBS (Fig. F28F), where they are well protected during the trip out of the hole. If the probe is embedded so firmly into the formation that the wireline cannot pull it from the formation, then the BHA can be raised to dislodge the probe from the bottom. The MDHDS is retrieved by wireline. On deck, it is laid out as a normal core barrel would be. The flapper tube is removed, allowing access to the T2P, which is then detached from the IBS by disconnecting a quick release connection. The MDHDS latch is then reset in preparation for the next deployment. During this time (if necessary), the hole can be washed down several meters in preparation for another deployment.

Deployment results

Deployment 1

After a 2 day transit from Bermuda, the JOIDES Resolution arrived at Site U1402 at 1542 h ship time on 6 June 2012 (Table T8). During the first test, we chose to deploy the MDHDS within the drill string before we had spudded the hole but after the drill string had been deployed to near the seafloor. We planned to lower the MDHDS with the T2P attached, without the tether, stopping during the descent at 200 and 400 m DRF and once again near the mudline. We would then unlatch the MDHDS, record in situ pressure and temperature briefly, and then bring the MDHDS back to the surface. During a brief team discussion prior to deployment, we decided to run the initial deployment with the tether attached. This decision was influenced by the fact that we’d arrived at Site U1402 nearly 12 h later than expected because of high seas, and we were concerned that we would not have sufficient time to run our entire testing plan. Because we had not spudded the hole, we installed a locking collar on the IBS to limit the distance it could be advanced to 1.5 m. Otherwise, the IBS would fully extend and the ERS would not be able to reach the distance inside the OBS to retrieve it.

The drill string was deployed to 650 m DRF and we started recording data with the T2P at 0115 h on 7 June (Table T9). With the T2P installed on the MDHDS, we ran a communications test between the T2P and the ERS/MFTM prior to deploying in the drill string. Despite several attempts, we were unable to receive the T2P data stream. We received some data, but it was badly distorted and indiscernible. The deployment proceeded without connecting the tether to the ERS.

We proceeded with the deployment, latching the ERS to the RS fishing neck, removing the MDHDS lifting clamp, and lowering the wireline into the drill string. As the MDHDS and T2P were lowered into the drill string (at 0436 h), there was audible chatter in the drill string, as if the drill string was vibrating; acceleration data recorded by the T2P confirmed a bumpy descent (Fig. F30). At 0450 h, while resting the T2P at ~200 m DRF, the ERS prematurely released the MDHDS, dropping it ~450 m. The pressure gradient as the tool fell was 0.02 MPa/s, which equates to ~2 m/s. The premature release of the MDHDS is recorded by the decrease in wireline tension at 2887 s (Fig. F31). From this point in time, the tip and shaft pressure rose linearly until 13,074 s, when pressure once again reached a constant of 5.97 MPa. We interpret that the modest descent rate was caused by the narrow space between the outer diameter of the OBS and the inner diameter of the drill string.

During the next several hours, we attempted to retrieve the MDHDS with the ERS. We did this by repeatedly raising and lowering the ERS. We tried to completely close the latch before we lowered the ERS. We also tried to close the latch while the ERS was lowered and resting on the RS fishing neck. Every time we picked up on the wireline, there was no increase in tension, indicating that we had not picked up the MDHDS.

We next attempted to unlatch the MDHDS with drill string pressure (Fig. F32). We repeatedly raised the drill string pressure to 8–12 MPa (1160–1749 psi) and held it for ~2 min. When the pressure was reduced, the standpipe pressure never dropped to less than ~20 psi (dashed line in Fig. F32). We later surmised that the standpipe pressure was not reduced enough to allow the spring to expand against the hydrostatic pressure within the drill string and allow the tool to unlatch. We could not actively monitor the penetrometer position during this sequence because the tether was not attached. However, we know that if the MDHDS unlatched, the circulation would be reestablished after the T2P deployed 2.9 m (Fig. F28C). The circulation was never reestablished; we surmised that the MDHDS had not deployed.

We then retrieved the ERS and went back into the hole with a mechanical RS. The mechanical RS appeared to latch. However, when the wireline was raised, the weight was not maintained. When the mechanical RS was brought back to the rig floor, we discovered that it parted at its midpoint. At this point, we decided to recover the entire drill string in order to retrieve the MDHDS.

When the MDHDS was retrieved, the T2P was removed and the data downloaded. At 13,658 s, data acquisition terminated (Fig. F30). When the T2P was opened, it was found that the MDM nine-pin (power) connector on the CDAQ board had dislodged. In addition, the fishing neck on the top of the IBS had several deep gouges. We interpreted that the ERS latch had repeatedly struck the RS fishing neck in attempts to recover it. One of these impacts caused the damage to the MDM nine-pin connector, causing the T2P to lose power and terminating data collection (Fig. F30). At this point, we observed that the ERS was in an overlatched position. We also observed that several screws on the latch motor cover were missing and had likely vibrated out. It was decided that in the next deployment the ERS and T2P would be replaced and that connections would be sealed with a temporary bonding agent (Loctite or similar) to reduce the likelihood of losing screws.

Deployment 2

At 1900 h, Hole U1402A had been washed to 96.4 m DSF (Table T10). The T2P was attached to the MDHDS, and a communications test between the Schlumberger wireline and the tool string components was successful. At 2115 h, the MDHDS was deployed by wireline into the drill string. The wireline was held and the pumps turned off at 285 m and at the mudline for pressure calibration (B and C in Fig. F33; Table T11). At 2227 h, the MDHDS reached the BHA and was released by the ERS (A in Fig. F33; Table T11).

There were three attempts to unlatch the MDHDS, and these are recorded by increases in the standpipe pressure (Fig. F34). The first pressurization sequence began at –958 s, lasted 61 s, and reached a peak pressure of 9.18 MPa (1331 psi). The second attempt began at –782 s, lasted 22 s, and reached a peak 9.23 MPa (1339 psi). The third pressurization sequence began at –598 s, lasted 147 s, reached a peak pressure of 10.49 MPa (1521 psi). After this last pressurization, when the standpipe pressure was reduced, there was an abrupt increase in both tip and shaft pressure in the T2P (approximately –375 s; D in Figs. F24, F33; Table T11). This is interpreted to record the tool penetrating the formation under its own weight after the MDHDS unlatched.

The first two attempts to unlatch the MDHDS failed. We interpret that in these cases, the drill string pressure was not lowered enough to allow the spring within the MDHDS to overcome the seal friction and expand. In the last pressurization, we pressured to our highest value (1521 psi) and held this pressure for the longest amount of time (147 s; Fig. F34). We interpret that in this case, the head in the standpipe decreased enough to allow the spring to expand.

The drill string was pressurized once more to drive the T2P into the formation (–210 s; Fig. F35). The pump rate was increased to ~60 strokes per minute (spm) over ~18 s (–218 to –200 s), and then the pump rate was reduced to ~30 spm. Tip pressure changed very little at this time; however, shaft pressure jumped abruptly at approximately –180 s (F in Fig. F35; Table T11). Simultaneously, tip temperature increased (E in Figs. F33, F36; Table T11). We interpret that the tip pressure was already high because it had previously entered the formation when it fell by its own weight. However, when the pump rate was increased, the tool was driven further into the formation, and this was recorded by the increase in shaft pressure and the increase in tip temperature caused by frictional heating. Circulation was held at just below 30 spm for ~2 min until 0 s (the start of dissipation; F in Figs. F33, F35). When the pumps were shut off, the pressures in both tip and shaft dropped abruptly over ~10 s. This drop in pressure is interpreted to be from the unloading caused by the reduction in pressure within the drill string.

From 0 to ~2000 s, the tip and shaft pressure and the tip temperature record smooth declines that are characteristic of dissipation. During this period, the accelerometer records no movement, despite the presence of significance ship heave (Fig. F36).

At 2046 s (~34 min), circulation was initiated (Fig. F37). Initially, circulation was increased to >50 spm, with only a small (0.33 MPa) pressure increase in the standpipe. Circulation was terminated and then restarted at 2154 s. It was increased to 37 spm, at which point (2170 s) the standpipe pressure began to rise rapidly to 5.6 MPa (812 psi) at 2188 s. As the standpipe reached the peak pressure, the T2P experienced a slightly vertical jarring force, visible in the acceleration jump at 2179 s (H in Figs. F33, F37; Table T11). At this point, communication with the T2P ceased.

We attempted to retrieve the MDHDS and T2P with the ERS. The ERS successfully latched onto the RS fishing neck of the MDHDS. However, when we pulled on the wireline, the tool would not come free, as is recorded by the successive cycles of increasing wireline tension (I in Figs. F33, F38; Table T11). We also raised the BHA until we were sure that the penetrometer was no longer in the formation and then once again tried to pull on the wireline (J in Figs. F33, F38; Table T11). However, the MDHDS would not separate from the BHA. The team concluded that the MDHDS was stuck inside the BHA, and the decision was made to trip out of the pipe. Upon recovering the tool string, it was discovered that the BHA was filled with sediment, and shredded pieces of the communications tether were wedged between the BHA and OBS, binding the tool string within the BHA.

The second deployment terminated at 0357 h on 8 June. A helicopter was scheduled to drop off shipboard technicians and pick up the MDHDS engineering team at 1000 h. With more than 6 h until the helicopter was scheduled to arrive, the science party requested that the ship be offset 20 m and core collected. This ended the MDHDS engineering tests. The MDHDS engineers departed the ship at 1010 h.

Results

In situ temperature and pressure

The pressure and temperature dissipation data were extrapolated using an inverse time approach (e.g., Flemings et al., 2008). These data were plotted against inverse time from 3900 to 4500 s. The extrapolated shaft pressure was 7.66 MPa, the extrapolated tip pressure was 7.53 MPa, and the extrapolated tip temperature was 9.61°C (Fig. F39). We interpret that the tip pressure is a more accurate measure of the two pressure measurements because it has undergone greater dissipation than the shaft pressure. The tip sensor is located on the narrow-diameter tip of the tool and thus induces a smaller pressure perturbation that undergoes a more rapid decline than the shaft pressure. The projected in situ pressure (7.53 MPa) is shown on a pressure depth diagram. The pressure is very slightly overpressured (Fig. F40). Similar results were predicted by Dugan and Flemings (2000) based on an indirect measurement based on bulk density.

MDHDS performance

The MFTM, ERS, and MDHDS worked well in this deployment. The tool successfully unlatched after drill string pressurization (Fig. F34). When the drill string was repressurized, the penetrometer was successfully driven into the formation (Fig. F35). After penetration, both the tip and shaft pressure sensors recorded smooth pressure dissipation profiles. The pressure records are characteristic of those recorded by successful T2P deployments (Flemings et al., 2008). The lack of any motion in the accelerometer (Fig. F36), although there was significant ship heave during the dissipation interval, is evidence that the drill string completely decoupled from the penetrometer. Finally, the penetrometer was undamaged when it was recovered, which indicates that it was driven straight downward and that there were no problems with the flapper valve at the base of the BHA.

We have illuminated the conditions under which the MDHDS latch will deploy (Fig. F24). We interpret that for the latch spring within the MDHDS to expand, the standpipe pressure must be significantly reduced. In particular, the static head must be lowered several meters below the 21.5 m that it is normally held at. We achieved this during the last pressurization during Deployment 2 (Fig. F34), but we never dropped the pressure low enough for the spring to expand during Deployment 1 (Fig. F32). We interpret that it is not necessary to raise the drill string pressure to >1000 psi to shear the shear pins. However, it may be necessary to hold this pressure for several minutes. Not surprisingly, there appear to be significant time lags between the measured surface pressures and the downhole pressures necessary for opening the latch. Without real-time telemetry, the only way that it will be possible to interpret a successful unlatching is by the establishment of circulation after the tool is advanced.

In the midst of the deployment, we circulated, as recorded by a pore pressure increase (H in Fig. F33). Afterward, we turned off circulation. The effect on the long-term pore pressure dissipation was minimal. We interpret that the reason for this is that circulation applies an undrained load on the formation that raises the pore pressure everywhere near the penetrometer. Because the increase in pore pressure is applied everywhere, it does not affect the process of dissipation (the spatial gradients in pressure are not changed). When the circulation is stopped, the load is removed and the dissipation continues. This is important because drillers get very uncomfortable when there is no circulation for prolonged periods. These data suggest that periodic circulation during a penetrometer deployment will not significantly affect the measurement.

Although real-time data were acquired through the tethered system, failure of the tether during circulation shows that a tethered real-time telemetry configuration is not ready for regular shipboard use.

Long-term application

Based on the outcome of this engineering test, the MDHDS, T2P, and MFTM have been certified for deployment onboard the JOIDES Resolution. Real-time telemetry will not be used until a more reliable communication system is developed. Without the need for a hollow barrel to house the tether system, the IBS has been replaced with an inner rod subassembly (Fig. F41). It has a smaller diameter, is solid, and is stronger. The 316 stainless steel spring has also been replaced with a stiffer Iconel X750. The new stiffer spring has a latch spring rate of 106.4 lb_f/inch. This generates 110 lb_f of overforce to start the piston moving once the drill string pressure is released. As a result, the standpipe pressure will only need to be bled down to <27 psi for the spring to begin moving the piston upward. This should simplify the unlatching process. Additionally, the new inner rod subassembly is designed with a long, large diameter at the bottom to create 2.5 m of stroke for the SET-P; this will not affect the 2.9 m stroke for the T2P.

Stress Engineering Services is completing final modifications to the ERS to improve its latching operation. Once the modifications are complete, the ERS will also be certified for onboard deployment by the USIO. The ERS will be used to deploy the SCIMPI tool during IODP Expedition 341S in May 2013.

We hope that the advances in tool delivery allowed by the MDHDS will result in rich pore pressure and temperature data sets for future expeditions and will engender the development of new downhole tools that can be deployed by the MDHDS. More information about the MDHDS can be found at www.ig.utexas.edu/research/facilities/downhole/mdhds.htm.

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