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doi:10.2204/iodp.proc.335.104.2012

Criteria for the siting of deep drill holes and considerations for achieving deep drilling objectives

Deep drilling into intact and rifted ocean crust has posed, and will continue to present, major technical and programmatic challenges to scientific ocean drilling. Only four holes, DSDP Hole 504B, ODP Holes 735B and 1256D, and IODP Hole U1309D (Figs. F5, F6; Table T1), have been cored deeper than 1 km into oceanic basement, and these penetrations are arguably the greatest technical achievements of scientific ocean drilling. All were “hard won” multiexpedition experiments. From the experiences of drilling these holes, there are important lessons to be learned for the siting, planning, and implementation of future deep drilling of the oceanic basement (Table T2). Other deep objectives may be targeted by future scientific ocean drilling (e.g., subvolcanic zones of large igneous provinces and arcs), for which these observations are also relevant. Here, we present a short review of deep drilling operations in the four >1 km basement holes penetrated by scientific ocean drilling, listed above. Although Holes 504B and 1256D drilled into intact ocean crust have been fraught with more drilling challenges than holes spudded directly into gabbro in oceanic core complexes (Holes 735B and U1309D), even those holes have proved troublesome to initiate (Hole U1309D) or maintain (Hole 735B).

Drilling deep holes in crustal hard rocks: tales of patience and perseverance

Difficulties encountered during Expedition 335 well illustrate the challenges faced by deep drilling of oceanic crust, especially while scientific ocean drilling operates in an expedition mode. On site at Hole 1256D, 93% of our time was spent on hole remediation and stabilization operations, with only 3–4 days spent coring (~4%). The interval cored eventually represents only ~4% of our initial depth objective for the time scheduled for Expedition 335. Several problems were encountered for the very first time in the history of scientific ocean drilling, and many lessons were learned or relearned (see detailed descriptions in “Operations” in the “Expedition 335 summary” chapter [Expedition 335 Scientists, 2012]). The main lesson is that patience and perseverance are required, and given that problems are always encountered, in some cases major problems, when drilling deep holes in intact crust, this must be taken into account at the program scheduling stage to achieve success in drilling deep in the ocean crust.

Here we summarize the operational challenges encountered during this expedition, together with past hard rock drilling experience and difficulties, in particular when drilling deep in intact oceanic crust. This section addresses one of the recommendations made at the MoHole workshop in Kanazawa, Japan, in June 2010 (Ildefonse et al., 2010a), which is to assess the past experience in scientific ocean crustal drilling for optimizing the engineering development and drilling operations for a future MoHole project. Although the various events that led to tool or pipe failure and equipment loss in various drill holes have been reported in past leg and expedition reports and partially assessed by ODP and IODP, there is no directly available self-consistent documentation of drilling challenges in deep ocean crustal boreholes. This section compiles the history of problematic and sometimes traumatic events in the four deepest holes drilled to date in the ocean crust.

Among the four boreholes deeper than 1000 m in basement (Table T1; Figs. F5, F6), two of them, Holes 504B and 1256D, were drilled in the Pacific Ocean crust and penetrated through the upper crustal lavas and into the underlying sheeted dike complex.

DSDP/ODP Hole 504B

Hole 504B is located in the eastern equatorial Pacific (1°13.611′N; 83°43.818′W; Fig. F7) and is the deepest hole (2111 mbsf) ever drilled by scientific ocean drilling programs since the launch of DSDP in 1968 (e.g., Becker et al., 1989; Alt et al., 1996). Operations in Hole 504B were carried out over eight legs (DSDP Legs 69, 70, 83, and 92 and ODP Legs 111, 137, 140, and 148) between 1979 and 1993 (only seven of these eight legs were coring legs; Leg 92 returned to Hole 504B for downhole logging operations). The detail of operations can be consulted in the Site 504 chapters of these eight leg reports (Cann, Langseth, Honnorez, Von Herzen, White, et al., 1983; Honnorez, Von Herzen, et al., 1983; Anderson, Honnorez, Becker, et al., 1985; Leinen, Rea, et al., 1986; Becker, Sakai, et al., 1988; Becker, Foss, et al., 1992; Dick, Erzinger, Stokking, et al., 1992; Alt, Kinoshita, Stokking, et al., 1993). The full suite of operations in Hole 504B is summarized in Table T3, and major perturbing events are reported in Figure F8. All together, the time spent in experiencing various hardware failures and subsequent remediation represents ~28% of the total time spent drilling, coring, logging, and sampling in Hole 504B (~205 days). During Leg 148, the coring bottom-hole assembly (BHA) became so thoroughly stuck at the bottom of the hole that it was necessary to sever the pipe. Subsequent operations recovered part of this material and milled much of the remainder, but the hole was abandoned with the coring bit, the float valve, and the lower support bearing remaining at the bottom (Alt, Kinoshita, Stokking, et al., 1993). It should be noted that because Leg 148 directly followed ODP Leg 147 to Hess Deep (Gillis, Mével, Allan, et al., 1993), during which significant equipment was consumed because of coring and fishing operations, Leg 148 sailed without the full complement of fishing and milling equipment, and new equipment, materials, and personnel needed to be sent from shore to try to resurrect the hole (e.g., a fishing expert and drilling jars/intensifiers). The scheduling of back-to-back, independent hard rock expeditions can put major stress on implementation organization resources.

ODP/IODP Hole 1256D

Hole 1256D is located in the Guatemala Basin on the Cocos plate, eastern Pacific (6°44.16′N; 91°56.06′W; Fig. F7), and is the only hole to date that reached the transition zone between the sheeted dike complex and the lower crustal gabbros in fast-spreading, intact ocean crust (Wilson et al., 2006). The first contact between dike and gabbros was recovered at 1406.5 mbsf on 13 December 2005 at 1400 h UTC. The detail of operations in Hole 1256D can be consulted in the Site 1256 chapters of the ODP Leg 206 Initial Reports volume (Wilson, Teagle, Acton, et al., 2003) and the Expedition 309/312 Proceedings volume (Teagle, Alt, Umino, Miyashita, Banerjee, Wilson, and the Expedition 309/312 Scientists, 2006). The full suite of operations in Hole 1256D is summarized in Table T4, and major perturbing events are reported in Figure F9. Most of our operation time during Expedition 335 (see “Operations” in the “Expedition 335 summary” chapter [Expedition 335 Scientists, 2012] for a detailed narrative) was used for (1) reopening the hole to the bottom and (2) cleaning the bottom of the hole after losing most of the first coring bit used. The three previous scientific ocean drilling expeditions required to build the upper crustal infrastructure for deep drilling and then advancing Hole 1256D to >1500 mbsf represent a significant investment for the ocean drilling community. Consequently, determined efforts have been made to resuscitate Hole 1256D and prepare and preserve it for future deepening during Expedition 335. The first problem was encountered in the 920–950 mbsf interval, where an obstruction encountered on the initial reentry prevented penetration to the bottom of the hole. Coring started 15.3 days after our first reentry in Hole 1256D. Our second major problem occurred shortly after that, when our first coring C9 bit disintegrated after cutting two cores. A long period of reaming and fishing continued until the end of the expedition, which concluded with logging operations, the retrieval of a final core (335-1256D-239R), and cementing activities to stabilize the hole for a future return to Hole 1256D.

Gabbro drilling at oceanic core complexes at slow-spreading ridges: Holes 735B and U1309D

The two other deep holes (Hole 735B at the Southwest Indian Ridge and Hole U1309D at the Mid-Atlantic Ridge) were drilled in gabbroic plutons in the footwall of oceanic core complexes in slow-spread crust. They were initiated in bare rock (with only a few meters of soft sediment for Hole U1309D). The uppermost 20 m of Hole U1309D was cased using a hammer-in-casing technique to provide a safe and viable reentry system for a deep hole. Hole U1309D was drilled over two back-to-back expeditions in 2005 (Blackman, Ildefonse, John, Ohara, Miller, MacLeod, and the Expedition 304/305 Scientists, 2006), whereas Hole 735B was drilled during two ODP legs 10 years apart (in 1987 and 1997; Robinson, Von Herzen, et al., 1989; Dick, Natland, Miller, et al., 1999). Both holes were drilled to their terminal depth (1508 and 1415.5 mbsf for Holes 735B and U1309D, respectively) without major trouble related to drilling or coring. Gabbro has been the easiest lithology to drill and core in oceanic crust so far.

In Hole U1309D the only major difficulty encountered was related to the installation of the casing using the hammer-in-casing technique (see Blackman, Ildefonse, John, Ohara, Miller, MacLeod, and the Expedition 304/305 Scientists, 2006, for further details regarding the casing operations). The casing operation succeeded in Hole U1309D after a failed first attempt (IODP Hole U1309C). However, the casing could not penetrate deeper than 20.5 mbsf, leaving 4.5 m standing above the seafloor. The reentry cone was deployed at that point, and coring operations proceeded without noticeable incident until the end of Expedition 305, with an average total recovery of ~75%. Hole U1309D remains open for potential reentry and future deepening. The minimum temperature at the bottom of the hole is 110°C (Blackman, Ildefonse, John, Ohara, Miller, MacLeod, and the Expedition 304/305 Scientists, 2006).

Hole 735B was similarly easy to drill, and the recovery at ~86% is the highest achieved in oceanic hard rocks to date. It is the second deepest hole in oceanic basement after Hole 504B (1836.5 m) and the deepest penetration into slow-spread crust. The only major incident that unfortunately resulted in losing the hole occurred 12 days before the end of Leg 176, a few hours after coring had resumed following ~1 day of interrupted operations due to bad weather conditions (see Dick, Natland, Miller, et al., 1999, for a detailed narrative of the incident). The drill string failed following contact with a ledge in the hole when the vessel heaved down during a pipe connection make-up, and the BHA and 1403 m of drill pipe were lost in the hole. The first fishing attempt retrieved 497 m of drill pipe; the hole was abandoned at the end of Leg 176 after a total of eight unsuccessful fishing attempts, alternated with several milling runs. A combination of bad weather and bad luck was, in this case, the cause of failure.

Hess Deep, ODP Leg 147: a tectonic window into fast-spread lower oceanic crust

Another historical record of hard rock drilling challenges and incidents is Leg 147 to Hess Deep in the eastern Pacific (Fig. F7) (Gillis, Mével, Allan, et al., 1993). The westward propagation of the tip of the Cocos-Nazca plate boundary into crust formed ~1 m.y. ago on the eastern side of the East Pacific Rise has resulted in the exposure of lower ocean crust and serpentinized upper mantle (e.g, Francheteau et al., 1992; Karson et al., 1992; Karson, 2002). This tectonic window provides an alternative approach to drilling through intact ocean crust (e.g., Holes 504B and 1256D), but to date drilling into Hess Deep gabbros and serpentinized peridotites has been very difficult to achieve, partly because of the very rugged topography and complex tectonic settings, resulting in boreholes probably intersecting numerous fault zones. A series of problems was encountered at the two sites, including difficulties to set up a three-legged hard rock base (HRB) designed for handling slopes as steep as 35°, hole deviation, and lost BHAs (see Gillis, Mével, Allan, et al., 1993, for a complete narrative of these events).

Drilling young unsedimented lavas

Drilling young basalt has also proved very difficult, especially when holes are spudded directly into bare rocks. All basaltic holes reported in Table T1 and Figure F6 were drilled in areas with a significant sediment cover that assists in the initiation, stabilization, and progress of the boreholes. Drilling in zero-age basaltic crust during DSDP (Leg 54) and ODP (Leg 142) at the East Pacific Rise was unsuccessful (Rosendahl, Hekinian, et al., 1980; Storms, Batiza, et al., 1993). More recent attempts have also had relatively limited success, recovering at best a few tens of centimeters before the holes had to be abandoned, such as at several sites attempted during Leg 209 at the Mid-Atlantic Ridge in the 15°20′ Fracture Zone area (Kelemen, Kikawa, Miller, et al., 2004). Initiating and progressing a hole deeper than ~20 m (with very poor recovery) in the young basaltic hanging wall of the Atlantis Massif Core Complex also failed in spite of 11.5 days of continuous efforts, despite using the hard rock reentry system and rotary core barrel (RCB) coring successfully deployed to drill into gabbros during the same expedition (Expedition 304/305; Blackman, Ildefonse, John, Ohara, Miller, MacLeod, and the Expedition 304/305 Scientists, 2006).

Considerations for the location of scientific wells with deep objectives

Location

Although the overriding justification for the siting of drill holes must be scientific grounds, there is no doubt that geographic location plays a major role in the successful scheduling of operations at sites that require multiple visits to accomplish objectives. The proximity of a site only a few days steaming from a major port where resupply can occur greatly reduces expensive and fuel-consuming transit days and provides maximum operational days on site. This siting also reduces transport distances for equipment dispatch should unanticipated drilling situations occur (e.g., the dispatch of drilling jars/intensifiers and a specialist engineer to Hole 504B during Leg 148; Alt, Kinoshita, Stokking, et al., 1993) (Table T3). Proximity to shipping routes frequently transited by the drillship (e.g., the Panama Canal) facilitates repeated scheduling at higher frequencies than more remote locations. A benign 12 month weather window allows maximum flexibility for the scheduling of return visits and the efficient arrangement of expeditions to locations with more restricted weather conditions.

Sediment cover

Presently there is no effective technology to routinely initiate deep (or even shallow) holes in volcanic rocks directly exposed at the seafloor (e.g., Legs 54 and 142 and Expedition 304; see “Drilling young unsedimented lavas”). Even a small amount of sediment greatly stabilizes the drill bit and assists in the initiation of drilling (e.g., ODP Leg 187 and IODP Expedition 329). Deep drilling of volcanic and deeper rocks of the oceanic basement requires the installation of a reentry cone and subsurface casing, but presently this infrastructure can only be set successfully in volcanic rocks where there is thick sedimentary cover. The installation of a reentry cone has not been successfully attempted in a bare rock environment, with the exception of Hole U1309D in gabbroic basement (see “Gabbro drilling at oceanic core complexes at slow-spreading ridges: Holes 735B and U1309D”). This lack of success has led to a bias toward operations in regions of anomalously thick sediment cover, such as crust formed in the equatorial high-productively zone (±1° of the Equator; e.g., DSDP Holes 504B and 896A and ODP Hole 1256D), on ocean crust very close to the continental margin (e.g., Juan de Fuca Ridge, ODP Leg 168 and IODP Expeditions 301 and 327), or in very old crust (e.g., DSDP Holes 417D and 418A and ODP Hole 801C; Donelly, Francheteau, Bryan, Robinson, Flower, Salisbury, et al., 1980; Lancelot, Larson, et al., 1990; Plank, Ludden, Escutia, et al., 2000). The deepest hole spudded into bare volcanic rock is only 50 m deep, and drilling was fraught with equipment failure and poor hole conditions (ODP Hole 648B, Mid-Atlantic Ridge; Detrick, Honnorez, Bryan, Juteau, et al., 1988). Generally at least 100 m of sedimentary overburden is required to mount a reentry cone supported by 20 inch casing, the minimum upper hole infrastructure recommended for deep drilling (e.g., Hole 1256D).

Seismic velocities and alteration

Young lavas are highly fractured, and it has proven difficult to initiate, maintain, and progress drill holes in young volcanic rocks. At the ridge axis, lava commonly flows beneath a thin, brittle carapace of quenched magma. These fragile surfaces collapse beneath subsequent lava flows, resulting in layers of poorly consolidated volcanic materials (e.g., Gregg and Fink, 1995; Gregg and Chadwick, 1996; Umino et al., 2000). Even more massive flows tend to have rubbly flow tops composed of glassy material that makes up substantial portions of the flows. Low-temperature hydrothermal alteration that occurs on the ridge flanks for millions of years leads to the precipitation of clays, principally Mg saponite, and other secondary minerals (e.g., celadonite, minor iron oxyhydroxides, calcium carbonate, and zeolites; Alt et al., 1986a) that replace mesostasis, fill fractures, and form breccia cements. Secondary mineral precipitation provides greater cohesion within the lava pile. This cohesion is reflected at a regional scale by increased seismic P-wave velocities (e.g., Carlson, 1998; Christeson et al., 2007) compared to younger crust closer to the spreading axis. However, these secondary minerals provide only weak bonding to fractured rocks. At any particular crustal age or region, relatively high seismic velocities probably reflect thicker or a greater abundance of massive lava flows relative to sheet flows, pillow lavas, or hyaloclastites. These latter lava morphologies are likely to be more highly fractured and include greater proportions of voids that present drilling hazards. Targeting areas with relatively higher seismic velocities will increase the probability of encountering stable formations in the uppermost basement, greatly increasing the chances of initiating a stable deep borehole, as demonstrated by the siting of Hole 1256D. However, drilling only more massive lavas may lead to a bias against more permeable and more altered oceanic crust, underestimation of hydrothermal exchanges between the oceanic crust and seawater, and overestimation of in situ physical properties (e.g., discrete sample P-wave velocities).

Age-depth-temperature

For crust in all oceans, ocean depth and conductive heat flow are inversely proportional to the square root of the age of the ocean crust (e.g., Lister, 1972). Although older ocean crust is cooler at depth and lower basement temperatures should improve drilling and wireline tool performance, targets will be significantly deeper, increasing pipe trip and wireline times. Water depth and the total target depth are important considerations for the siting of a future riser drilling approach to core beyond the Moho and to a significant distance (hundreds of meters) into the upper mantle (e.g., Ildefonse et al., 2007b, 2010a, 2010b). Plans are being formulated for the development of an ultra-deepwater riser capability for the D/V Chikyu, but these enhanced capabilities are unlikely to be developed beyond ~4000 m water depth.

There is a discernible conductive heat flow anomaly out to ~65 m.y., indicating that the transport of heat by low-temperature hydrothermal circulation of seawater-derived fluids becomes on average negligible beyond this age (e.g., Stein and Stein, 1994). However, in individual regions, hydrothermal flow occurs wherever hydrological gradients can be established because of basement topography, variable sediment cover, or seamounts that penetrate the sediment overburden and provide pathways for the ingress of seawater and egress of basement fluids (e.g., Wheat and Fisher, 2008; Von Herzen, 2004). Whether this fluid flow is always accompanied by significant chemical reaction or microbial stimulus is as yet unconstrained. Dating of secondary minerals formed by low-temperature hydrothermal alteration remains challenging (e.g., Waggoner, 1993), but assessment of basement calcium carbonate veins, generally one of the latest phases to form, suggests that effective chemical exchange is complete within a few tens of millions of years of crustal formation (e.g., Coggon et al., 2010). There have been major changes in ocean chemistry since the Cretaceous and through the Tertiary (e.g., Stanley and Hardie, 1998; Lowenstein et al., 2001; Horita et al., 2002; Coggon et al., 2010). Hence ocean crust formed in the Cretaceous was altered in very different thermal and chemical (and biological?) regimes compared to the modern ocean (e.g., Alt and Teagle, 1999). To understand the role of ocean crustal formation and hydrothermal circulation in the global geochemical cycles of modern Earth, it would be sensible to target ocean crust formed in the past 20 to 30 m.y.

Program considerations for the attainment of deep targets by scientific ocean drilling

Establishing the ideal location for drilling is only part of the challenge of successfully drilling moderately deep holes (2–3 km) to recover the samples and data necessary to address long-standing primary goals of scientific ocean drilling. Experience from Holes 504B and 1256D indicates that such experiments require multiple expeditions to achieve their target depths. A total of ~500 m penetration per expedition is an upper limit for coring in the upper crust, with lesser advances and more frequent drilling challenges as these holes get deeper and rocks metamorphosed at higher pressures and temperatures are encountered (Figs. F8, F9, F10; Tables T1, T3, T4). Penetration and core recovery rates have been low to very low in the two sheeted dike complex sections drilled to date (Holes 504B and 1256D). Average rates of recovery and penetration in the dike section of Hole 1256D are 32% and 0.8 m/h, respectively. The average rate of recovery in the sheeted dike complex of Hole 504B was a miserly 11%. However, experience to date suggests that gabbroic rocks can be cored relatively rapidly at high rates of recovery (e.g., Hole U1309D: penetration rate = 2 m/h; recovery ≥75%), so when the dike–gabbro transition zone is breached, solid progress through the plutonic section can be anticipated.

Long uncased sections through lava flows can result in major problems with wall stability and clearing of drill cuttings as boreholes get deeper. Lava sections are commonly strongly enlarged and out of gauge (>20 inches) for long intervals because of continued spalling of fractured material from the borehole walls. Borehole wall damage is exacerbated by multiple passes of the drill string because of the numerous pipe trips needed to drill a deep hole (e.g., 93 reentries in Hole 504B and 62 reentries in Hole 1256D as of the end of Expedition 335; Tables T3, T4). Hole intervals with large diameters (>12 inches) greatly reduce the efficiency of high-viscosity mud sweeps to clear deep holes of fine cuttings. The hydraulic horsepower of the lifting fluid is reduced because of velocity decreases and fluid turbulence when mud sweeps leave regions of in-gauge hole and enter more cavernous zones. Hole enlargements also provide cavities where cuttings not swept from the hole can temporarily collect and subsequently become continuously recycled within the borehole.

Although Hole 1256D was established with the infrastructure to install two more casing strings (13⅜ inches and 10¾ inches) within the 16 inch casing that was cemented into basement, drilling during ODP Leg 206 and IODP Expedition 309 proceeded quickly in the upper crust without an apparent need to case the lava sequences to maintain hole stability. However, as Hole 1256D has been drilled deeper, clearing cuttings from the hole to keep the drill bit clear of debris has become increasingly difficult. Large amounts of coarse-grained basaltic sand were recovered in the fishing tools and the BHA during three consecutive fishing runs while trying to retrieve the broken bit during Expedition 335 (see “Operations” in the “Expedition 335 summary” chapter [Expedition 335 Scientists, 2012]), attesting to the accumulation of cuttings in the hole.

Scientific ocean drilling has little experience in casing long sequences (hundreds of meters) of oceanic basement and a poor armory of underreaming tools for opening hard rock basement holes to the diameters required for the insertion of a casing. For example, the insertion of 13⅜ inch casing requires reaming an 18½ inch hole beneath 16 inch casing. Casing hundreds of meters of a deep borehole in igneous basement would be a high risk, costly, and ship-time consuming operation that would produce no new scientific output until completed and drilling was resumed. However, it would greatly improve the stability and hydrodynamics of deep basement boreholes. A regular drilling-then-casing approach to investigate the lower oceanic crust (target depth = 2–3 km) will require a long-term commitment by the scientific ocean drilling community to a particular site and experiment and as many as 10 expeditions to complete. The possibility that even such a highly engineered approach could still fail to reach its target would have to be acknowledged and accepted by the community. The development of untethered casing sleeves or targeted wall rock cementing (as tested for the first time during Expedition 335) are options that should be considered. Such approaches might be effective at securing unstable formations and more palatable to a multidisciplinary program with competing science drivers and constant assessment of the outputs. Nevertheless, the potentially transformative science that could be yielded by a deep borehole through the upper crust and down into cumulate gabbro is going to require long-term commitment and investment in time on site, as well as technology and external expertise (e.g., consultant drilling engineers and casing, fishing, cementing, and hardware experts).

It is very unlikely that without significant good fortune deep targets in intact ocean crust can be achieved in the current science advisory configuration. The peer-review system that has overseen the progress of both Holes 504B and 1256D has required the reevaluation of new proposals following the successful completion of each drilling increment. A system similar to the “complex drilling proposals” used for riser experiments must be extended to riserless targets that require multiple expeditions to achieve important scientific goals.

Such is the capriciousness of hard rock coring that scientific ocean drilling may have to consider new approaches if it is to ever successfully address some of the major science questions that remain unanswered after more than 50 years. There are unlikely to ever be “quick wins” with targets that require multiexpedition deep boreholes. Expedition 335 was initially scheduled by the IODP-MI Operation Task Force as a short cruise (~4 weeks), despite the explicit recommendations of the postexpedition 309/312 Operational Review Task Force “to maximize on-site time for deep drilling expeditions” (Recommendation 309/312-03; see 309_312_ORTF.PDF in REPORTS in “Supplementary material”). Flexibility in expedition scheduling may be a low-impact means to achieve deep objectives. Back-to-back expeditions to a single target could be scheduled. This approach was successful at drilling Hole U1309D deeper than 1400 mbsf during Expeditions 304 and 305. Commonly, the ship has been moved off a deep hole after the significant investment in engineering and cleaning operations that have succeeded in preparing the hole for deep drilling. For example, Expedition 312 drilled >100 m of the dike–plutonic transition zone in Hole 1256D following significant hole remediation operations but left an open clean deep hole. Five years later, most of Expedition 335 scheduled time was spent on hole remediation. Mechanisms are needed for revising expedition schedules so that drilling can continue in deep boreholes when progress is actually being made. This would require the movement of crew, scientists, and supplies to and from the rig so that drilling and hole cleaning can continue, as well as the temporary postponement of the immediately following expeditions. Clearly, this would be a major departure from the standard operating style of the JOIDES Resolution within ODP and IODP and a challenge to the science advisory and scheduling structure. It would require community acceptance that could be difficult to achieve. However, the present standard “1 proposal = 1 expedition” approach is not an effective process to reach targets that require multiple expedition deep drilling. Unless the community and the drilling program are able to develop new approaches to achieving deep targets, the lack of closure on science questions that can only be addressed by deep drilling will continue to stain future renewal documents with a perceived lingering staleness due to a continued recycling of unaccomplished goals.