Specimen collection via pressure core, and maintenance of high pore pressures throughout the specimen collection and testing process, is required because these are gassy sediment that potentially contain gas hydrate. Allowing these specimens to depressurize prior to testing would allow gas bubbles to form, expand, and disrupt the sediment fabric that determines the in situ moduli, permeability and strength reported in this data release.
Both chambers yield the void ratio dependence on vertical effective stress, but not all measurements are possible in the two chambers used in this study. The Direct Shear Chamber (DSC) can be used for compressional wave velocity measurements (Vp) and thus for calculating the constrained moduli from Vp as well as from the void ratio dependence on vertical effective stress. The DSC is also used to obtain direct shear strength measurements (See the NGHP02_AreaC_Direct_Shear_Data dataset in this data release). The Effective Stress Chamber (ESC) only provides the constrained modulus via the consolidation data, but the ESC can also measure permeability (See the NGHP02_AreaC_Permeability_Data dataset in this data release). Blank entries within a column of measured data occur because that measurement is not possible for the given vertical effective stress or in the given measurement chamber.
Process_Step:
Process_Description:
Deployment sample collection: This study used sediment from pressure core NGHP-02-08-30P, collected from Site NGHP-02-08 in Area C of the Bay of Bengal offshore Eastern India. Pressure core collection requires the rotary corer to retract the core through a ball valve and into an autoclave at the in situ coring depth. Once retracted into the autoclave, the ball valve at the base of the autoclave can be closed, sealing the core within the autoclave. A connected high-pressure nitrogen canister provides pressure stabilization as the autoclave is brought through different thermal regimes on the trip to the rig floor. Once the autoclave is recovered, it is chilled in an ice bath to stabilize the core contents, then transferred to a temperature-controlled unit for core manipulation. During NGHP-02, depth below sea floor was based on the continuous downhole log of the drill pipe length. The sea floor depth reference (mudline) was determined from a combination of noting when the drill string contacted the sea floor and increased the measured weight-on-bit, and visual verification of the drill bit position using an ROV. Here, depth is reported using the IODP standard depth terminology CSF-B (total depth from sea floor to target sediment, after all gas expansion gaps have been removed).
Process_Date: 20150703
Process_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: U.S. Geological Survey
Contact_Person: William F. Waite
Contact_Position: Research Geophysicist
Contact_Address:
Address_Type: mailing
Address: 384 Woods Hole Road
City: Woods Hole
State_or_Province: Massachusetts
Postal_Code: 02543-1598
Country: USA
Contact_Voice_Telephone: 508-548-8700 x2346
Contact_Electronic_Mail_Address: wwaite@usgs.gov
Process_Step:
Process_Description:
Core preparation and transport: Note that throughout the core preparation, transport and testing stages, the hydrostatic pressure is maintained at or above in situ values to maintain the stability of the core contents and avoid the formation of gas bubbles. Once the core-filled autoclave was brought to the rig floor and its temperature was stabilized, the autoclave was transferred to a shipboard analysis laboratory. In the laboratory, a pressurized system extracted the core from the autoclave, cut the core to a prescribed length (1.2 meters for the NGHP-02-08-30P core described here), and inserted the 1.2 m-long section into a pressurized storage chamber. The storage chamber can then be isolated via a ball valve closure and, ultimately, shipped in a Department of Transportation-approved, refrigerated overpack system to the U.S. Geological Survey’s Woods Hole Coastal and Marine Science Center for analysis (WHCMSC).
Process_Date: 2015
Process_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: U.S. Geological Survey
Contact_Person: William F. Waite
Contact_Position: Research Geophysicist
Contact_Address:
Address_Type: mailing
Address: 384 Woods Hole Road
City: Woods Hole
State_or_Province: Massachusetts
Postal_Code: 02543-1598
Country: USA
Contact_Voice_Telephone: 508-548-8700 x2346
Contact_Electronic_Mail_Address: wwaite@usgs.gov
Process_Step:
Process_Description:
Pressure Core Characterization Tool (PCCT) Core Manipulation: Once the core storage chamber arrived at WHCMSC, it was moved into a refrigerated core storage facility to maintain the core’s temperature stability. The core was subsequently tested in the WHCMSC High Pressure Core Analysis Laboratory (HyPrCAL) using the PCCTs (see the browse graphic for this data releases primary landing page). Similar to the shipboard setup, the core was first retrieved, at pressure, from the storage chamber, then individual specimens were cut and inserted into either the Direct Shear Chamber (DSC) or Effective Stress Chamber (ESC). The core manipulation and transfer into the testing chambers was accomplished at a hydrostatic pressure between 10-11 MPa (Megapascal).
Process_Date: 2017
Process_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: U.S. Geological Survey
Contact_Person: Junbong Jang
Contact_Position: Geophysicist
Contact_Address:
Address_Type: mailing and physical
Address: 384 Woods Hole Road
City: Woods Hole
State_or_Province: Massachusetts
Postal_Code: 02543-1598
Country: USA
Contact_Voice_Telephone: 508-548-8700 x2278
Contact_Facsimile_Telephone: 508-457-2310
Contact_Electronic_Mail_Address: jjang@usgs.gov
Process_Step:
Process_Description:
Testing Chamber Overview: Once a test specimen is isolated in one of the testing chambers, the sediment is extruded from the plastic core liner using a plunger that will eventually serve as the specimen’s top endcap once the specimen is pushed all the way out of the liner and into the primary testing space. The plunger is then used to apply a vertical effective stress, returning the specimen to its in situ state of effective stress (approximately 2 MPa). Additional vertical effective stress can be applied to test the specimen response to the increasing effective stress that will occur in situ when the formation is depressurized to extract methane from gas hydrate. In this study, vertical effective stress is increased in steps, with each step held long enough for the specimen to consolidate. The consolidation (specimen shortening) is monitored via a linear voltage displacement transducer (LVDT) and reported here in terms of the void ratio. The void ratio is calculated according to the derivation in ASTM D2435 [ASTM, 2011]. Void ratio is unitless, and is reported here with an accuracy of 0.0005. Vertical stress is measured via a load cell, and reported here with an accuracy of 5 kPa (kilopascal). Once the specimen is consolidated to the peak effective vertical stress and all high-stress testing is complete, the vertical effective stress is released (again, in steps). Once the specimen is back at its in situ effective stress state, the specimen is depressurized by reducing both the pore pressure and vertical effective stress together to retain the in situ vertical effective stress. If there is any gas hydrate in the specimen, this step breaks that gas hydrate down, releasing the methane and water. Additional consolidation testing is done after depressurization.
ASTM D2435 / D2435M-11, Standard Test Methods for One-Dimensional Consolidation Properties of Soils Using Incremental Loading, ASTM International, West Conshohocken, PA, 2011, www.astm.org , DOI: 10.1520/D2435_D2435M-11.
Process_Date: 2017
Process_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: U.S. Geological Survey
Contact_Person: Junbong Jang
Contact_Position: Geophysicist
Contact_Address:
Address_Type: mailing and physical
Address: 384 Woods Hole Road
City: Woods Hole
State_or_Province: Massachusetts
Postal_Code: 02543-1598
Country: USA
Contact_Voice_Telephone: 508-548-8700 x2278
Contact_Facsimile_Telephone: 508-457-2310
Contact_Electronic_Mail_Address: jjang@usgs.gov
Process_Step:
Process_Description:
Direct Shear Chamber (DSC): The DSC and its operations are described in Santamarina and others (2012, 2015). Briefly, the DSC applies a vertical stress to a core specimen held in a three-layer specimen chamber bounded at either end by endcaps containing compressional wave velocity transducers. The middle layer can be horizontally moved, shearing the specimen along the top and bottom of the middle layer. In this data release, the following parameters are reported as functions of the applied effective vertical stress: void ratio, compressional wave velocity, and constrained modulus. The derivations of compressional wave velocity and constrained modulus are given as follows:
Compressional Wave Velocity, Vp: Throughout the consolidation process, compressional waveforms are collected in the axial direction, with results reported here in terms of wave velocity (waveform travel time divided by specimen length). The uncertainty in Vp is 1.5 percent.
Constrain Modulus, M: The constrained modulus is calculated two different ways, representing the specimen stiffness for deformation at two different length scales. The first method recovers the small-strain constrained modulus, Mvp (stiffness for microscopic strains induced by the compressional wave transducers). The formula is Mvp = (specimen density)x((Vp)^2).
The second method recovers the constrained modulus for consolidation, Mconsol (macroscopic deformation) via the formula Mconsol = -(1+ei)x(change in vertical effective stress)/(change in e), where e is the void ratio, and ei is the void ratio at the beginning of the effective vertical stress step increase. The specimen is much stiffer for microscopic deformations than macroscopic deformations, so Mvp is larger than Mconsol. The uncertainty in both constrained moduli is 3 percent.
Santamarina, J.C., Dai, S., Jang, J., and Terzariol, M., 2012, Pressure core characterization tools for hydrate-bearing sediments: Scientific Drilling, v. 14, p. 44-48.
Santamarina, J.C., Dai, S., Terzariol, M., Jang, J., Waite, W.F., Winters, W.J., Nagao, J., Yoneda, J., Konno, Y., Fujii, T., and Suzuki, K., 2015, Hydro-bio-geomechanical properties of hydrate-bearing sediments from Nankai Trough: Marine and Petroleum Geology, v. 66, p. 434-450.
Process_Date: 2017
Process_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: U.S. Geological Survey
Contact_Person: Junbong Jang
Contact_Position: Geophysicist
Contact_Address:
Address_Type: mailing and physical
Address: 384 Woods Hole Road
City: Woods Hole
State_or_Province: Massachusetts
Postal_Code: 02543-1598
Country: USA
Contact_Voice_Telephone: 508-548-8700 x2278
Contact_Facsimile_Telephone: 508-457-2310
Contact_Electronic_Mail_Address: jjang@usgs.gov
Process_Step:
Process_Description:
Effective Stress Chamber (ESC): In the primary testing chamber of the ESC, a thin latex sleeve can be pressed against the cylindrical sides of the specimen, and the upper and lower specimen endcaps have porous stones connected to fluid flow lines that enable flow-through vertical permeability measurements to be made in the ESC. The ESC and its operations are described in Santamarina and others (2012, 2015). A sample permeability measurement is provided in the permeability section of this data release, accessible from the primary landing page. In this portion of the data release, only the consolidation data and associate constrained modulus, Mconsol, are reported, again with an uncertainty of 3 percent. The consolidation procedure follows that of the DSC given above.
Santamarina, J.C., Dai, S., Jang, J., and Terzariol, M., 2012, Pressure core characterization tools for hydrate-bearing sediments: Scientific Drilling, v. 14, p. 44-48.
Santamarina, J.C., Dai, S., Terzariol, M., Jang, J., Waite, W.F., Winters, W.J., Nagao, J., Yoneda, J., Konno, Y., Fujii, T., and Suzuki, K., 2015, Hydro-bio-geomechanical properties of hydrate-bearing sediments from Nankai Trough: Marine and Petroleum Geology, v. 66, p. 434-450.
Process_Date: 2017
Process_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: U.S. Geological Survey
Contact_Person: Junbong Jang
Contact_Position: Geophysicist
Contact_Address:
Address_Type: mailing and physical
Address: 384 Woods Hole Road
City: Woods Hole
State_or_Province: Massachusetts
Postal_Code: 02543-1598
Country: USA
Contact_Voice_Telephone: 508-548-8700 x2278
Contact_Facsimile_Telephone: 508-457-2310
Contact_Electronic_Mail_Address: jjang@usgs.gov
Process_Step:
Process_Description:
Data archiving: Microsoft Excel version 15.33 was used to consolidate all data in a spreadsheet. Measured interface heights and elapsed times were arranged by sediment and pore fluid type. Results were then exported to a comma-separated values (csv) file format.
Process_Date: 2017
Process_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: U.S. Geological Survey
Contact_Person: Junbong Jang
Contact_Position: Geophysicist
Contact_Address:
Address_Type: mailing
Address: 384 Woods Hole Road
City: Woods Hole
State_or_Province: Massachusetts
Postal_Code: 02543-1598
Country: USA
Contact_Voice_Telephone: 508-548-8700 x2278
Contact_Facsimile_Telephone: 508-457-2310
Contact_Electronic_Mail_Address: jjang@usgs.gov
Process_Step:
Process_Description:
Added keywords section with USGS persistent identifier as theme keyword.
Process_Date: 20200806
Process_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: U.S. Geological Survey
Contact_Person: VeeAnn A. Cross
Contact_Position: Marine Geologist
Contact_Address:
Address_Type: Mailing and Physical
Address: 384 Woods Hole Road
City: Woods Hole
State_or_Province: MA
Postal_Code: 02543-1598
Contact_Voice_Telephone: 508-548-8700 x2251
Contact_Facsimile_Telephone: 508-457-2310
Contact_Electronic_Mail_Address: vatnipp@usgs.gov