PCATS: PRESSURE CORE ANALYSIS AND TRANSFER SYSTEM

Transcription

1 Proceedings of the 7th International Conference on Gas Hydrates (ICGH 2011), Edinburgh, Scotland, United Kingdom, July 17-21, PCATS: PRESSURE CORE ANALYSIS AND TRANSFER SYSTEM Peter Schultheiss, Melanie Holland, John Roberts, Quentin Huggett, Matthew Druce, Philip Fox Geotek Ltd. 3 Faraday Close, Daventry, Northants, NN11 8RD UNITED KINGDOM ABSTRACT PCATS has evolved into an essential component of pressure core analysis infrastructure for gas hydrate investigations. Cores up to 3.5 m long can be transferred from compatible pressure coring tools, nondestructive analyses performed, whole round subsamples of core cut and transferred into other chambers; all at in-situ temperatures and pressures up to 350 bar (35 MPa). Nondestructive analysis includes gamma density measurements, P-wave velocity measurements, and both linear X-ray images and 3-D X-ray computed tomography, providing data that has intrinsic scientific utility and is critical for the selection of subsamples. Cores can be cut into whole round subsamples using a variety of cutting techniques depending on the sediment type. Chambers to receive cut core can be relatively simple storage chambers (from 10 cm to 3.5 m long) or instrumented test cells for more advanced geotechnical or rock physics testing. Samples in storage chambers can be put back into PCATS for further analysis or subsampling as required. A newly developed combined triaxial test chamber and sample transfer mechanism even enables pristine samples of pressure core to undergo advanced resonant column testing. It can also perform more traditional triaxial tests coupled with mini production tests and direct permeability evaluation. Gas hydrate investigations generally require some cores to be cut and analyzed on board to determine the gas hydrate concentration from mini production tests, while others are stored for additional analysis on shore. PCATS was recently used on the Korean Ulleung Basin Gas Hydrate II (UBGH2) expedition in July-October 2010 where numerous onemeter-long pressure cores from a range of lithologies (muds to hydrate-cemented sands) were analyzed and cut into core samples as small as 5 cm. We anticipate that PCATS will be an integral component of gas hydrate investigations over the next few years. Keywords: pressure core, pressure analysis, automated measurement, P-wave velocity, X-ray CT, triaxial testing, resonant column, gas hydrate quantification INTRODUCTION It is recognized that gas hydrate formations are best studied in situ when possible; however, some analyses can only be performed on samples in the laboratory. Pressure cores recover gas hydrate preserved within the sedimentary matrix, without the disruption caused by gas hydrate dissociation or dissolved gas exsolution. They provide the least-disturbed samples of gas hydrate formations, and the best samples for laboratory tests, including geophysical measurements, geomechanical tests, and gas hydrate quantification. PCATS, the Pressure Core Analysis and Transfer System, is the interface between the pressure corer and investigators using pressure core samples. It provides the mechanism and infrastructure whereby pressure cores can be transferred from the individual coring autoclaves into a measurement Corresponding author: Phone: peter@geotek.co.uk

2 refrigerated infrastructure central laboratory refrigerated storage manipulator cutter analysis sensors storage chambers corer autoclave with core chamber, non-destructively analyzed providing fundamental geophysical data and X-ray images, subsampled, and transferred into customized pressure chambers for transport or further analysis. The purpose of this paper is to describe the current status and recent enhancements to the basic PCATS system and to introduce PCATS Triaxial, a new chamber for geomechanical testing of pressure core samples. PCATS OVERVIEW PCATS has taken on a variety of functions in the pressure coring workflow, from aiding coring logistics by quickly recycling corer autoclaves to providing basic scientific data such as P-wave velocity. PCATS operations have been described in detail elsewhere [1, 2, 3] but below is a list of primary functions, in the order they are generally undertaken. Operations under pressure with PCATS: Removal of core from coring tool Core quality assessment (i.e., is there a core and what is it like?) Nondestructive testing of core Transfer of core sections into and out of storage chambers Core motion control for third-party analyses Cutting core into sections Transfer of core sections into custom test chambers Gas hydrate quantification from depressurization PCATS IMPROVEMENTS PCATS was heavily used in the period [4, 5, 6], and little time was available for development. The break in field work after this intensive use, as well as the anticipated use in (see Upcoming Expeditions), provided the time and impetus for a suite of improvements to the system. Figure 1. Scale diagram of PCATS, showing the pressure housing inside three standard size 20-foot ISO containers. Corer autoclave shown contains a 3.5 meter core. 16 one-meter-long storage chambers are shown in the refrigerated storage container. Refrigerated infrastructure container contains (not shown) chillers, heat exchangers, pumps, manifolds. Central laboratory additionally contains motor control electronics and computers. Expansion in variety of cores accepted Upcoming expeditions will use pressure coring systems developed by Aumann Associates to interface with PCATS, which can recover 3.5- meter-long cores. PCATS has been redesigned to accept both Fugro pressure coring systems and the longer Aumann systems without any modifications apart from a change of core adaptor. (A simple core adaptor is used to join the cores to the PCATS core motion system; these adaptors are customized for each coring system.) Currently PCATS can accept cores with a plastic liner that is up to 63 mm in outer diameter, with a wall thickness of up to 4 mm and up to 3.5 meters long. Pressure coring tools must of course be adapted to interface with PCATS and special provisions made for the PCATS manipulator to extract the core from the coring tool under pressure. Fully containerized system Previous PCATS systems were deployed in a single refrigerated container to maintain the low temperatures needed to preserve gas hydrate. The corer autoclave passed through an opening in the end of the cold container and connected to the PCATS. The new PCATS has been completely redesigned to accommodate the much longer cores and expanded specification, which has necessitated an approximate doubling of the length of the overall system. It is now housed in a linear array of three 20-foot custom laboratory containers (Fig. 1). This fully containerised system is based on

3 standard ISO 20-foot containers with DNV classification, enabling the system to be easily shipped to mobilization ports and lifted on to offshore platforms as required. If logistically necessary, the units can also be air freighted. The PCATS itself, together with much of the control infrastructure, is housed in the left-hand refrigerated container and the central airconditioned laboratory container (Fig. 2). The refrigerated right-hand container enables the corer autoclave to be attached to PCATS through an opening between the central and right-hand containers. This right-hand unit is also used as temporary storage for cores recovered and held in pressure vessels. During shipping, the manipulator can be disconnected from the central laboratory and stored in the left-hand container. The containers are fitted with overhead hoists simplifying the movement of heavy components and making quick transfers of core substantially easier than on previous expeditions. Figure 2. Photo of inside of PCATS central laboratory showing insulated manipulator and cutter assembly. Redesign of linear manipulator Precise, computer-controlled core motion is at the heart of PCATS and is critical because the pressure housing prevents either visual inspection or manual intervention. The original PCATS had a long leadscrew-based manipulator, which worked in series with the core enabling precise motion for transfer and analysis of one-meter long cores. However, a simple scaling up of this serial-concept manipulator for a 3.5 meter core would have necessitated an impractically long system manipulator and overall system. The manipulator has been completely redesigned using a ballscrew mechanisms which operates in parallel with the core. When the core is fully retracted into PCATS, it lies parallel alongside the ballscrew, greatly reducing the overall length of the system. (Note that the conceptual diagrams in this paper resemble the old serial manipulator, rather than the new parallel manipulator, for clarity.) This redesign had two large advantages: it significantly reduced the length of the overall system and reduced the length of the ballscrew itself. However, at over 5 meters long, the ballscrew is still long enough to require traveling supports inside the pressure tube to prevent excessive deformation under its own weight! Core rotation The original design of PCATS only enabled linear core motion. Subsequently, a modification using an auxiliary system enabling core rotation was introduced. This new rotational ability proved invaluable when looking at fine scale structures revealed from the X-ray images. For the new redesigned manipulator, core rotation was an integral part of the new specification. Core rotation mechanisms are now essential infrastructure in PCATS, as the core subsectioning and the X-ray imaging depend on core rotation. PCATS now has two rotational mechanisms: one is part of the manipulator, and the other is a separate subsystem that grips the core liner. The gripping mechanism will be mainly used for cutting core into sections, so a significant amount of torque may be transferred to the liner. However, for X-ray purposes, which only require precise motion without any high driving torque, the rotation via the manipulator will be more appropriate. X-ray CT With PCATS equipped for accurate core rotation, the addition of X-ray computed tomography (CT)

4 was an obvious next step. Previously, pressure cores had been subjected to X-ray CT analysis using hospital scanners [7], but the ability to perform CT scans at sea inside PCATS would provide obvious immediate benefits. X-ray images in PCATS are already collected using a variable intensity, microfocal X-ray source (130 kv max) and a digital flat-panel detector. The combination of microfocal source and high resolution flat-panel detector enables images to be collected with typical spatial resolutions of 100 microns, which allows X-ray CT reconstructions with a similar resolution to an industrial X-ray CT scanner (hydrate-bearing example of CT reconstruction shown in Fig. 3). Currently data for X-ray CT reconstruction is collected using a rotational motion for short sections of core but in the future a helical motion for the complete length of a core section will provide greater efficiency. Reconstructions are generated using appropriate algorithms suitable for rotational or helical scans in a cone beam. To ensure that the core remains aligned with the axis of rotation, mechanical centralizers are used on either side of the X-ray detector. Figure 3. X-ray CT reconstruction of core taken on Expedition UBGH2. Dense material (sediment) is dark; less dense material (gas hydrate) is light. Active temperature control Previous incarnations of PCATS were deployed inside a refrigerated container laboratory to maintain the system at low temperatures. To increase flexibility (and operator comfort!), direct temperature control of the pressure chambers was instigated through refrigeration and circulation of the pressurizing fluid. A custom heat exchanger is used to chill the circulating, high-pressure fluid (seawater or fresh water, depending on the application). The pressure chambers comprising PCATS are thoroughly insulated to allow the central laboratory container to be maintained at room temperature. Improvement of pressure rating PCATS will be used on the upcoming Gulf of Mexico Gas Hydrates Joint Industry Project expedition, scheduled to begin in Some of the target gas hydrate formations are at depths exceeding 2500 meters below sea level. To ensure that the pressure cores can be maintained at in situ pressures, the pressure chambers and all the components that make up PCATS were redesigned, and their maximum working pressure was increased from 25 MPa to 35 MPa. This specification change involved a substantial number of design modifications in both materials and concepts. Core subsampling The facility to subsample cores under pressure, and transfer these samples into analysis cells for specialized analyses, has long been a goal for PCATS. This ability to distribute samples to the interested scientific community would fulfill a promise of pressure coring: that of providing experimenters with never-depressurized gashydrate-bearing sediments. This goal and promise has been realized with the development of the PCATS core cutting subassembly. To cut the core, the PCATS core cutter first parts the core liner and then slices the sediment within. The liner is cut with a rotating wheel, similar to a pipe-cutting tool. The cutter is pressure-balanced and advanced under manual control, enabling the operator to feel the cutter moving through the core liner. Once the core liner is parted, the operator uses the thin stainless steel of a guillotine to slice the sediment. While this system for cutting samples works well on hydrate-bearing clay sediments (64 cuts during Expedition UBGH2, including 20 GHOBS samples), there is an anticipated problem cutting gas-hydrate-cemented sands. The guillotine mechanism will encourage these sediments to part along preferred cleavage planes, and the fractured surface may not be orthogonal to the core axis or flat. It is essential for some types of geomechanical studies for samples to have flat,

5 squared-off faces. Both the GHOBS and PCATS Triaxial require that the samples have clean faces orthogonal to the core axis. To ensure that flat-faced samples of hydratecemented sands can be placed in geomechanical cells under pressure, a second cutting system is under development to enable harder, friable material to be cleanly sub-sampled. SPECIFICATION OF IMPROVED PCATS Compatible coring tools: Fugro FPC & FRPC, Aumann HPTC and Hybrid PCS (see below) Maximum core length: 3.5 m Core liner specifications: OD up to 63 mm, liner thickness up to 4 mm Maximum operating pressure: 35 MPa Operating temperature range: 4-30 C Linear core motion: ±0.1 mm Rotational core motion: ±0.1 Gamma density sensor: 137-Cs 10 mci source and NaI detector P-wave velocity sensor: Geotek 250 khz transducers X-ray imaging: 130 kv microfocal source & 14- bit digital flat-panel detector (1920 x 1536 pixel); image resolution 100 microns System length: 18.3 m (3 x 20-foot standard shipping containers) System weight: approx 24 tons CURRENT FUNCTIONS OF PCATS This section briefly describes the primary functions of PCATS as used in its new extended configuration. Core transfer and quality control PCATS allows core transfer out of the coring tool autoclave and quick visualization of the contents for quality control (Fig. 4). Currently, the compatible borehole wireline coring tools include the Fugro Pressure Corer (FPC), the Fugro Rotary Pressure Corer (FRPC), the Aumann Associates Hybrid Pressure Coring System (Hybrid PCS), and the Aumann Associates High Pressure Temperature Corer (HPTC). A compatible sealed pressure corer autoclave containing a core liner up to 3.5 meters long is connected to PCATS, and the PCATS manipulator rod is extended to latch on to the pressure corer piston assembly at the top of the liner. (Note that the conceptual diagrams [Figs. 4-6] do not strictly represent the operation of the redesigned manipulator.) As the core is withdrawn from the autoclave into PCATS, an X-ray image is collected to determine whether a good quality core has been recovered. Once the core is fully inside PCATS, the autoclave is removed and returned to the rig floor for tool redressing. A B C D manipulator PCATS PCATS sensors mechanical assembly ball valve core corer autoclave Figure 4. Conceptual diagram showing operation of removing pressure core from corer autoclave using PCATS: A) connecting the autoclave, B) using the manipulator to latch onto the core, C) withdrawing the core whilst acquiring an X-ray image and D) removing the autoclave. Reproduced from [1]. Geophysical analyses A set of fundamental measurements is collected on every core (Fig. 4). These measurements provide the basis for further analyses and sampling. Gamma density and P-wave velocity are typically collected every centimeter along the core, aligned with linear X-ray images of the core at multiple angles. A low-resolution (0.5-mm-per-side voxel) computed tomographic X-ray scan may be collected at this stage as well in the future. The complete data set gives investigators enough information to create a detailed analysis and sampling plan for each core. While gamma density and P-wave velocity are intrinsically important quantitative parameters for sediment material, they also provide important gas-hydraterelated information. Though many gas hydrate features in clays are clearly visible in the X-rays, gamma density provides an absolute reference and aides in distinguishing sands/silts from clays and massive hydrate from water. The P-wave velocity is a very sensitive indicator of gas-hydratecemented sediments, which can be difficult to distinguish by density alone. Velocities can

6 increase from around 1.5 km/s in soft sediments to over 3 km/s in gas hydrate cemented sands. Temporary core storage Often during expeditions, the fate of an earlier core is dependent on the contents of cores collected later in the expedition. For that reason, when the initial core measurements have been completed, the core can be stored until investigators are ready for further analyses or subsampling. The core is cut free from the pressure corer piston assembly and pushed into a storage chamber, which can be stored in the cold until required again. The pressure corer piston assembly is returned to the tool operators for redressing the coring tool. At any time the storage chamber can be connected to PCATS and the core removed for further analysis and subsampling. Precise motion to support third-party analyses PCATS has extremely precise linear (±0.1 mm) and rotational (±0.1 ) motion to enable its own analyses to be performed (e.g., CT scans). These computer-controlled operations can be used to move core through third-party devices. PCATS has been used to move core through the Instrumented Pressure Testing Chamber (IPTC) [8, 9], where holes are drilled in the liner and cores must be accurately moved so these holes can be reentered by multiple probes situated along the length of the instrument (Fig. 5). A B C D manipulator PCATS core PCATS sensors ball valve extension chamber third-party device Figure 5. Conceptual diagram showing nondestructive and third-party measurements with PCATS: A) connecting the extension tube, B) logging the core (X-ray imaging, density and P- wave measurements), C) attaching third party measurement device (e.g., IPTC) and D) making measurements with the third-party tools. Reproduced from [1]. Subsampling under pressure PCATS non-destructive analyses provide important information, but it is only when samples of core under pressure can be made available to the entire scientific community that the promise of pressure coring is truly realized. PCATS can cut whole-round samples of any length from a sediment core, first parting the plastic core liner and then slicing the sediment material (Fig. 6). These samples can be pushed into storage vessels or specialized cells, such as the Gas Hydrate Ocean Bottom Simulator [10], for further testing under pressure. A B C D E manipulator PCATS core core cutter ball valve pressure vessel Figure 6. Conceptual diagram showing the subsampling of a pressure core and transferring of the sample into a custom pressure vessel (analysis or storage cell) using PCATS: A) connecting the sample cell, B) cutting the sample at a precise location, C) pushing the sample into the sample cell, D) withdrawing the manipulator and E) isolating the sample and removing the sample cell with the sample at full pressure. Reproduced from [1]. Depressurization experiments One ancillary feature of PCATS is the ability to slowly depressurize a core within the system, quantifying the methane and other gases for use in methane mass balance calculations of gas hydrate concentration (e.g., [4, 5]). These depressurization experiments (or mini-production tests ) can be performed while making measurements with the PCATS sensors or third-party apparatus [e.g., 9]. Alternately, a small portion of core can be transferred to a low-volume pressure vessel for offline depressurization analysis.

7 These methane mass balance measurements have been routinely made on pressure cores collected on expeditions to date: on the Indian Expedition NGHP1 [5], 75% of the pressure cores were slowly depressurized, and on the recent Korean Expedition UBGH2, approximately 35% of the material recovered under pressure was slowly depressurized for gas hydrate quantification. These hydrate saturations are used as reference values to ground-truth other measurements (e.g., [11]) The quantification of gas hydrate through methane mass balance is currently the only method able to positively identify samples with NO gas hydrate. PCATS TRIAXIAL The PCATS Triaxial system is a newly-developed set of pressure chambers (Fig. 7) that will enable both small and large strain geotechnical tests on samples of pressurized cores, as well as direct flow measurements of permeability. Interchangeable drive heads within the test chamber provide options for testing: small strain tests are carried out using a resonant column head, while large strain tests use a more standard triaxial testing technique. Sample preparation is similar for both types of test. A pressure core subsample is extruded from the core liner into the test chamber while being enveloped by a standard impermeable rubber membrane. This entire process occurs under in situ pressure and temperature conditions, thereby preserving the structural integrity of the sample and any gas hydrate located within it. For small strain resonance testing, an electromagnetic drive unit excites the sample in either torsion or flexure, to obtain the natural frequency of the sample and attached drive mechanism. The shear and Young s moduli of the sample can be derived using wave propagation theory. Large strain behaviour of the sample is obtained using a standard triaxial testing technique, which allows the stress-strain behaviour of the sample to be determined. A progressive uniaxial load is applied to the sample with axial deformation recorded as a function of the applied load. The design of the pressure system allows the effective stress on the sample to be controlled through independent manipulation of both the confining pressure and pore water pressure. This independent control of pore pressure will allow the initial permeability of the sample to be determined as well as any changes in permeability or volume of the sample during shearing. motor piston resonant column drive head core sample in sleeve ball valve Figure 7. Diagram of PCATS Triaxial, showing core sample (in sleeve) held at both ends by pistons (lower piston & motor not completely shown). Resonant column drive head can be switched to triaxial cell drive head before loading sample into cell. The realization of providing high quality samples from PCATS into the PCATS Triaxial system will represent the culmination of an ambitious longstanding goal. This goal has been referred to before as the holy grail of gas hydrate sample testing. It consists of recovering, sub-sampling and transferring gas-hydrate-bearing sediments

8 into a sophisticated test apparatus for accurately determining the mechanical properties without significantly altering the hydrostatic pressure or temperature during the complete procedure. The information that can be obtained from pressure core samples tested in PCATS Triaxial or similar systems could be of significant benefit for larger scale engineering studies (e.g., where wellbores pass through gas-hydrate-bearing zones) and for detailed modeling of reservoir deformation during gas hydrate production. PCATS Triaxial would also be applicable to studies from many of the other unconventional oil and gas formations where undisturbed samples can only be obtained under pressure. These formations include tar sands, shale gas and oil, and coal-bed methane as well as gas hydrate. RECENT & UPCOMING INVESTIGATIONS In past offshore gas hydrate drilling operations, pressure coring and pressure core analysis has been a relatively minor component of the overall program [4, 5, 6]. As the technology matures (becoming both more reliable and capable) and the value of the techniques become better recognised and appreciated, it is clear that pressure coring and pressure core analysis will be the major component of some forthcoming operations especially where potential gas hydrate reservoirs need to be evaluated. When pressure coring becomes a continuous operation (for example, through a thick reservoir sequence) the time taken to analyse the core material in PCATS can be much longer than the time it takes to collect the core. Consequently, it is critical to operate PCATS in a rig-time-efficient fashion when continuously pressure coring. The operational procedures in the field must focus on a rapid evaluation to check the quality of the core obtained before saving it for later processing. In this quick mode it is possible to have a turn around time comparable to the turn around of the coring systems (2-3 hours). When the pressures of time are reduced, further detailed analysis and cutting/transferring of subsamples can take place. Because each highquality 3.5-meter core could take more than a day to analyse and process, it is very likely that a companion onshore PCATS operation will need to be scheduled to complement continuous pressure coring operations. PCATS use on Expedition UBGH2 PCATS was extensively used on Korean Expedition UBGH2 in 2010 on board D/V Fugro Synergy [12], using Fugro pressure coring tools which collect 1-meter cores. This was the second use of the core cutting subsystem [10], and the first use of the X-ray CT capability. On Expedition UBGH2, 22 pressure cores were collected, and from these cores 20 GHOBS samples were cut, along with 22 samples for quantitative depressurization in low dead-volume cells for gas hydrate quantification. X-ray CT analysis was performed on some of the more interesting core as time allowed (e.g., Fig. 3). PCATS and MH21 The Japanese Research Consortium for Methane Hydrate Resources in Japan (MH21) program has the world s first offshore methane hydrate production test scheduled in 2013 [13]. As part of the program leading up to this test, the methane hydrate reservoir will be continuously pressure cored using an Aumann Associates pressure corer and the cores analyzed and transferred using PCATS. This expedition is scheduled to take place in early PCATS and the GOM-JIP The Gulf of Mexico Gas Hydrate Joint Industry Project (GOM-JIP) is also evaluating the reservoir potential of gas hydrate formations [14, 15]. Again, towards that goal, the methane hydrate reservoir will be continuously pressure cored using the Aumann HPTC and the cores analyzed and transferred using PCATS. This expedition is currently scheduled to take place in the first half of PCATS and IODP Expedition 337 The Integrated Ocean Drilling Program (IODP) has a expedition arranged to drill into a methanerich system off Shimokita, Japan. Expedition 337, Deep Coalbed Biosphere off Shimokita: Microbial Processes and Hydrocarbon System Associated with a Deeply Buried Coalbed in the Ocean, was scheduled to take place on D/V Chikyu during April and May However, the devastating tsunami in March 2011 damaged the Chikyu, and the expedition was postponed. If the expedition is reinstated as planned, there will be pressure coring of some hydrate-bearing

9 formations using the Aumann Hybrid PCS, and PCATS will be installed on the aft deck of the Chikyu to analyze and transfer the pressure cores. CONCLUDING REMARKS Handling and analysis of cores recovered at high hydrostatic pressures is maturing into a proven technology using PCATS, and pressure core analysis with PCATS as infrastructure is now planned as part of gas hydrate reservoir evaluations. Cores up to 3.5 m long can be manipulated, non-destructively analysed and cut into subsamples, all at pressures up to 35MPa. The full potential of these capabilities will not be fully realized until more third-party equipment is designed and built to accept never depressurized samples. However, the triaxial and consolidation cells that have been/are being built are a significant step forward, illustrating what can be achieved. Pressure coring operations and the use of PCATS to date have been exclusively used for gas hydrate bearing formations (science and industry). Other unconventional oil or gas formations that are difficult to core conventionally due to gas disruption, and hence are difficult to assess accurately, would benefit from pressure coring and pressure core analysis. REFERENCES [1] Schultheiss PJ, Aumann JT, Humphrey GD. Pressure Coring and Pressure Core Analysis for the Upcoming Gulf of Mexico Joint Industry Project Coring Expedition. OTC 20827, Offshore Technology Conference, Houston, Texas, May See also: papers/papers.html [2] Schultheiss P, Holland M, Humphrey G. Wireline Coring and Analysis under Pressure: Recent Use and Future Developments of the HYACINTH System. Scientific Drilling, March 2009, pp See also: scientific-publications/ [3] Schultheiss PJ, Francis TJG, Holland M, Roberts JA, Amann H, Thjunjoto, Parkes RJ, Martin D, Rothfuss M, Tuynder F, Jackson PD. Pressure Coring, Logging and Sub-Sampling with the HYACINTH system. In Rothwell G (Ed.), New Techniques in Sediment Core Analysis, Geol. Soc. London, Spec. Pub pp [4] Riedel M, Collett TS, Malone MJ, and the Expedition 311 Scientists. Proc. IODP, Exp. Repts., 311: College Station, TX (Ocean Drilling Program), See also: publications.iodp.org/proceedings/311/311toc.htm [5] Collett T, Riedel M, Cochran J, Boswell R, Presley J, Kumar P, Sathe A, Sethi A, Lall M, Sibal V, and the NGHP Expedition 01 Scientists Indian National Gas Hydrate Program Expedition 01 Initial Reports. Indian Directorate General of Hydrocarbons, New Delhi, India. [6] Zhang H, Yang S, Wu N, Su X, Holland M, Schultheiss P, Rose K, Butler H, Humphrey G, and the GMGS-1 Science Team. Successful and surprising results for China s first gas hydrate drilling expedition. Fire in the Ice (U.S. DOE NETL newsletter) Fall 2007, 6 9. See also: publications/hydrates/newsletter/ HMNewsFall07.pdf [7] Holland M, Schultheiss P, Roberts J, Druce M. Observed Gas Hydrate Morphologies in Marine Sediments. 6th ICGH conference in Vancouver, July 6-10, See also: handle/2429/1201. [8] Yun TS, Narsilio G, Santamarina JC, Ruppel C. Instrumented pressure testing chamber for characterizing sediment cores recovered at in-situ hydrostatic pressure. Marine Geology : [9] Park K-P, Bahk J-J, Holland M, Yun TS, Schultheiss P, Santamarina C. Improved Pressure Core Analysis Provides Detailed Look at Korean Cores. Fire in the Ice (US DOE NETL newsletter) Spring 2009, p See also: publications/hydrates/newsletter/ MHNewswinter09.pdf. [10] Lee J-Y, Schultheiss P, Druce M, Lee JY. Pressure Core Sub Sampling for GH Production Tests at In Situ Effective Stress. Fire in the Ice (US DOE NETL newsletter) Fall 2009, p See also: publications/hydrates/newsletter/ MHNewsFall09.pdf. [11] Lee MW, Collett TS. Gas hydrate saturations estimated from fractured reservoir at Site NGHP-01-10, Krishna-Godavari Basin, India. J. of Geophy. Res., 2009, 114, B071102, doi: /2008JB [12] Gas Hydrate R&D Organization, Korea. 2nd Ulleung Basin Gas Hydrate expedition (UBGH2) Fire in the Ice (US DOE NETL newsletter) March 2010, p.18. See also: technologies/oil-gas/publications/hydrates/ Newsletter/MHNews_2010_03.pdf [13] Masuda Y, Yamamoto K, Tadaaki S, Ebinuma T, Nagakubo S. Japan s Methane Hydrate R&D Program Progresses to Phase 2. Fire in the Ice

10 (US DOE NETL newsletter) Fall 2009, p.1-6. See also: publications/hydrates/newsletter/ MHNewsFall09.pdf. [14] Gulf of Mexico Gas Hydrate Drilling and Logging Expedition Underway. Fire in the Ice (US DOE NETL newsletter) Spring 2009, p.1-6. See also: oil-gas/publications/hydrates/newsletter/ MHNewsSpring09.pdf. [15] Boswell R, Collett T, McConnell D, Frye M, Shedd B, Mrozewski S, Guerin G, Cook A, Godfriaux P, Dufrene R, Roy R, Jones E. Joint Industry Project Leg II Discovers Rich Gas Hydrate Accumulations in Sand Reservoirs in the Gulf of Mexico. Fire in the Ice (US DOE NETL newsletter) Summer 2009, p.1-5. See also: publications/hydrates/newsletter/ MHNewsSummer09.pdf.