Towards an IODP Depth Standard

1. Towards an IODP Depth Standard Peter Blum CDEX Core-Log-Seismic Integration (CLSI) Workshop Tokyo 3-4 October, 2005

2. Goals of CLSI • Integrate and splice discontinuous data sets acquired in discontinuous intervals to construct more complete and/or continuous depth or time series • Integrate equivalent data from multiple runs or intervals • Integrate different types of data unique to their method or environment of acquisition • Core data • In-situ (formation) data • Remote sensing data

3. Goals of Depth (and Age) Scale Standards • Provide an infrastructure for effective use and integration of all project data by • Establishing an extensible set of scale definitions and their constraints in an accessible repository. • Defining a set of standard correlation procedure for routine use, such as core or wireline composite depths and splices. • Facilitating development of custom software tools for routine data integration for science party collaborative efforts. • Providing access to multiple standard scale maps as part of IODP data retrieval applications.

4. Why Do We Care? • Three IODP Implementing organizations, as well as industry and other academic organizations, are doing CLSI; however: • Use different process management • Use different data management systems • Use different tools • Use different nomenclature • Use (processing, integration) of data and publication of results is compromised by the lack of data standards.

5. 1995 Depth Workshop

6. 1995 Depth Workshop (cont.) • Results: • Review of present depth types and processing • Three prime depth types (drilling, logging, curation) • Three shipboard and one post-cruise processed depth types • Detailed description of logging depth processing • Recommend additional core depth data acquisition • Add "Subsections" to Corelog program to record voids and exotic material in section liner • Recommend "corrected core depth" utility • Provide utility to correct for voids and exotic materials (from subsection records) when calculating depth, and to normalize recovery to 100% • Recommend integration of composite section utility • Provide for "Splicer" program (in development at BRG/LDEO) to become an integrated module of the new Corelog program • Miscellaneous recommendations to improve accuracy and efficiency of depth data acquisition and management. • Syn-cruise log processing • Routine Corelog data quality control • Consistent depth data reporting, relational database

7. 1995 Depth Workshop (cont.)

8. 1995 Depth Workshop (cont.)

9. 1995 Depth Workshop (cont.)

10. 2003 Memo

11. 2003 Proposed Depth Types

12. Definitions • “Quantity” • Fundamental physical phenomenon that can be quantified with measurement methods. • Quantities used as independent variables for integrating core, log, and seismic data length and time. • “Unit” • Length: meter [m] • Time: second [s], year (derived) • “Scale” • A series of independent variables for the data of interest. • Depth, seismic travel time, and geologic age are the most commonly used types of scales in our business.

13. Definitions (cont.) • “Depth” • Special case of length • originating at a process-specific reference such as the seafloor, sea level, rig floor, etc.; • directed towards the center the Earth • ending at a magnitude defined by the target objective, such as a stratigraphic horizon. • The unit of depth is the meter, the IS unit of length. • The reference from which the depth is estimated has nothing to do with the unit of measurement, which is why the “mbsf unit” is nonsensical. • Each depth measurement method assumes that its scale units correspond exactly to the meter. • No estimate of depth should be considered the “True Depth”; each estimate of depth has an uncertainty associated with the measurement tool and procedure. • Uncertainties of depth estimates can be evaluated based on independent measurements of a target horizon at the same geographic location

14. Original Sample Depth Definition • Recovered core is always “hung” from the top of the cored interval, as referenced by the driller • This convention is represents the best practice in absence of additional core position data Seafloor Seafloor zero reference is defined by Mudline core or tagging with bit Core top depth Defined by drill pipe advance Cored Interval (e.g., 9.6 m) Section 1 Core 2 Driller’s Core Top + Section 1 length + Section 2 length + interval below top of Section 3 ------------------ = Sample depth Section 2 Section 3 65% Recovery

15. Problem 1 with Sample Depth Definition • Low Recovery • RCB coring typically yieds incomplete core recovery (<100%) • Position of recovered core intervals is therefore associated with significant uncertainty even if the core top datum is accurate and precise Seafloor Seafloor zero reference is defined by Mudline core or tagging with bit Core top depth Defined by drill pipe advance Cored Interval (e.g., 9.6 m) Section 1 Core 2 Driller’s Core Top + Section 1 length + Section 2 length + interval below top of Section 3 ------------------ = Sample depth Section 2 Section 3 65% Recovery

16. Problem 2 with Sample Depth Definition Interval depth Quasi-continuous depth • 106% Recovery! • With the APC, it is common to achieve a nominal recovery of >100% • Result of core expansion largely due to elastic rebound and gas expansion • Problem: Core overlaps and stratigraphic reversals Seafloor Cored Interval 1 Cored Interval 2 Cored Interval 3 Cored Interval 4 Cored Interval 5

17. Coring Gaps • Multiple hole coring with the APC during the late DSDP offered the first opportunities to accomplished hole-to-hole • Used black and white core photographs. • Splices were constructed on the light table. • The results revealed that coring gaps are a common feature • These successes with stratigraphic correlation led to the development of shipboard applications that use petrophysical core logging data for more precise and routine correlation.

18. Core Logging Data for Scale Mapping • Whole-round multisensor track: • Magnetic susceptibility • Bulk density • Natural gamma radiation Archive-half multisensor track - Color reflectance - Magnetic susceptibility

19. Core Composite Depth Scale Example: Natural gamma radiation data from Site 1146

20. Composite Composite Depth Scale Hole B Hole A • Each core has its own internal deformation • Stretched intervals • Squeezed intervals • Shipboard stratigraphic correlation only shifts entire cores based on one-point correlation • Other intervals may not be perfectly correlated • This is a pragmatic procedure that can be accomplished in the given time and eliminates >95% of the depth error Seafloor B1 A1 B2 A2 ? B3 A3 B4 A4 B5 A5

21. Core Composite Depth Scale

22. Core Composite Scale Characteristics • Construction of a common depth scale for all cores from multiple holes at a site using high-resolution core logging data • Squeezing and stretching within cores is not corrected, which results in residual depth discrepancies • Each core has a differential offset of typically 0.5-2 m as a result of core expansion. • Cumulative offset, or growth, at any depth is typically 10-20% (growth factor of 1.1 to 1.2) • If correlation is not possible over certain intervals (incomplete stratigraphic section), the composite depth can be constructed/continued in one of two ways: • Append based on recovered/drilled interval • Apply adjacent mcd growth factor of adjacent, correlated interval • Composite depth scale is generally not a continuous depth scale

23. Splice at Composite Depth Scale Splice Hole B Hole A • Each core has its own internal deformation • Stretched intervals • Squeezed intervals • Shipboard stratigraphic correlation only shifts entire cores based on one-point correlation • Other intervals may not be perfectly correlated • This is a pragmatic procedure that can be accomplished in the given time and eliminates >95% of the depth error Seafloor B1 A1 B2 A2 ? B3 A3 B4 A4 B5 A5

24. Spliced Stratigraphic Section Example of spliced stratigraphic section: Natural gamma radiation data from Site 1146

25. Core Splice Characteristics • A splice is a stratigraphically representative, complete sediment section • In intervals where correlation is impossible and overlap cannot be documented, adjacent sections are “appended” • A “sampling splice” is a continuous core scale only for those intervals that are part of the splice. • Selection of tie points is subjective • The shipboard splice is used for postcruise sampling • Additional splices can be constructed, and they may or may not have the same composite depth scale.

26. Refined (Revised) Composite Scales • Non-splice core intervals are mapped to the primary splice • If completed for all core intervals at a site, core data can now be displayed against a common, continuous depth scale • This scale is presumably the most useful for core-log integration. • If used to define core sampling programs, the proposed sampling position must be mapped back to the curatorial scale.

27. Depth Scale Classes • Based primarily on the composite depth and splice experience, and to a limited degree on core-log integration experience, the many possibly useful depth scales fall into four classes: • Class 1: Measurement scales • Intrinsically linked to method of data acquisition such as drill string, wireline, time, etc. • Includes current “mbrf” types • Class 2: Referenced scales • Measured scales are referenced to sea level, sea floor, etc. • Includes current “mbsf” types • Class 3: Composite scales • Data from multiple holes are runs are correlated, thus construction a composite scale that integrates all associated data. • Includes current “mcd” type • Class 4: Scaled scales • Referenced and composite scales are mapped to each other using equivalent data types • Includes current “rmcd” and “eld” types

28. Depth/Time Scale Types Original measurement scales: few specialists access these raw data Interval Scales Many possible types depending on application

29. Depth Scale Definitions • Depth Scale Class 1: Original Depth Measurement scales

30. Depth Scale Definitions • Depth Scale Class 2: Referenced Depth Scales Discontinuous “interval” scales

31. Depth Scale Definitions • Depth Scale Class 3: Composite Depth Scales

32. Depth Scale Definitions • Depth Scale Class 4: Scaled Depth Scales

33. Towards an IODP Depth Standard • Planning • Need an IODP task force to develop a detailed plan and implementation process • Potential Implementation • Define data model that incorporates scale definitions and scale repository • Provide IODP data access systems to return any data set against the user-selected depth scale (or age) • Choice of multiple scale types • Choice of multiple scales for any one scale type as appropriate

34. Scope of CLSI Scale Standards IODP Standard Scale Type Look-Up Scale processes Look-Up Scale Map Repository Scale Selection User Interface Graphical and Tabular Data Reports Scale Mapping Tools Data Repository Data Capture/Entry Tools

35. Scope of Standard (cont.) SCALES scale_id scale_name scale_type scale_description SCALE MAP METADATA map_id scale_id_source scale_id_target date_time_submitted map_author_name process_id comments SCALE MAP DATA map_id source_depth target_depth SCALES PROCESSES process_id process_name process_description Look-up tables for standard definitions Standard scale maps

36. Tools • Application tools are not part of standard • Best available tool should be used for scale mapping • In cases where custom tools are desired, the standards help custom tool builders because they define input and output data types and formats • A broad range of tools may be used: • Generic analysis tools, e.g., Excel, Kaleidagraph, Matlab, IGOR… • Customized for generic process, e.g., Analyseries, ARAND… • Customized for process, e.g., Splicer, Sagan, Nclip, Age-Depth Modeler…

37. Tools • Some scale mapping tools have operational relevance and are therefore highly customized - they may become quasi-standard tools • Example: Composite depth construction tool • may guide coring depth adjustments in real time and improve coverage of coring gaps in multiple holes. • May avoid coring in third and fourth holes at a site and thus save valuable operations time. • requires that core logging data are collected and correlated as quickly as possible • Some scale mapping tools require specialized data input and/or expert knowledge, and therefore are highly customized • Example: Age-depth modeling