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XMML Borehole description


Contents

Related pages

The XMML Borehole model is provisional, pending alignment with the requirements of the GeoSciML participants. The model shown here is a streamlined version of models developed in the XMML Project. Future revisions are likely to lead to greater harmonization with PPDM.

Schema documents

XMML borehole is implemented using components from 2 specialised schema documents (on top of the generic XMML and GML schemas):

  • XmmlSVN:trunk/XMML/coverage.xsd - generic method for mapping values to position
  • XmmlSVN:trunk/sampling/0.1.0/site.xsd, XmmlSVN:trunk/sampling/0.1.0/extensiveSite.xsd - stations, sections etc
  • XmmlSVN:trunk/XMML/borehole.xsd

Example Instances

  • XmmlSVN:trunk/GeoSciML/draft/instances/XMMLBRGMBorehole_1.xml, bh_1.xml

Borehole

Model

borehole.PNG

Explanation

XMML Borehole is an extension of sa:Profile, and inherits most of its key properties from there.

The following properties are added:
  • drillMethod indicates the construction method
  • collarDiameter gives a measure of the hole size at the collar

The gml:Point that is the value of the xmml:begin property (inherited from xmml:Section) will normally be the hole collar-location.

Position within a Borehole

Positions in a hole are constrained to lie along the 1-D geometry corresponding to the axis of the hole, and locations in a borehole are conventionally described using the offset arc-length from the collar. These offsets may be interpreted formally as "direct positions" in a 1-D CRS, whose basis is the centre-line of the hole, with the origin at the hole collar. Thus, only a single coordinate is required for each position.

For example, a position 35.23m down a borehole can be recorded using a generic GML position as follows:
<gml:pos srsName="BoreholeAxis" srsDimension="1" axisLabels="offset" uomLabels="m">35.23<gml:pos>

(Note that all of the XML attributes are optional: the srsName is often inheritted from context, and the other attributes are provided for client convenience only.)

The origin from which the offsets are measured is the datum of the coordinate reference system, and would usually be a collar location at the surface where the drill-rig sat, or it may be an underground location where the hole of interest splays from a primary hole. Note that in the latter case the position of the origin may again be expressed as a 1-D coordinate relative to the CRS defined by the axis of the parent hole.

Borehole survey

The primary means for describing the shape of a borehole is the shape property inherited from Section (see SitesAndSpecimens). However, it is common for both traverses and boreholes to have a "survey" captured as a set of (position, orientation) pairs, or as waypoints and headings. It is often made using a wireline tool simultaneously with other observational logs.

Transformation of survey information into an explicit curve registered to a conventional 3-D cartesian reference system is commonly known as de-surveying.

To maintain the integrity of the survey information, it may be necessary to transfer the survey observations themselves. The survey may be recorded as a point-log using the standard XMML components. However, since the survey is one log type common to every borehole, it is convenient to promote it to a specialised element, the CurveSurvey, with various properties fixed to be those necessary for surveys - see XmmlCoverage#Specialised_coverages.

Logs

The various log types are described in XmmlCoverage#Specialised_coverages.

A PointLog is a set of values (observations) at discrete points distributed along a 1-D spatiotemporal axis. In the context of a Borehole, the points of interest are distributed along the hole. The model for a PointSetCoverage is used.

A IntervalLog is a set of values assigned to discrete intervals distributed on a 1-D spatiotemporal axis. The model for an IntervalSetCoverage is used. In the context of a Borehole, the intervals of interest are distributed along the hole. IntervalLog describes a piecewise-constant field, where the values are fixed in each interval. Other coverages may be defined where the value varies, e.g. linearly within intervals between sampled end-points. Note that the latter is not an Interval Log, but is rather a continuous log with a specified interpolation method, in which a discrete Point Log provides the control points.

A ContinuousLog is a set of values assigned to regularly spaced points distributed on a 1-D spatiotemporal axis. The model for a RectifiedGridCoverage is used. In the context of a Borehole, the grid-points are distributed along the hole.

Interpolated values

The log types described refer to discrete ("sampled") coverages, where the value of the property of interest is constant in each element of the domain. The value for the property at unsampled locations within the convex hull of the domain requires interpolation.

Communication of the interpolation method for coverages is not (yet) handled formally in XMML. However, the MappingRule option of the coverageFunction property allows a string value, or a link to an external explanation, that may be used by a data provider to indicate the recommended method for generating values continuously.


For more discussion, see IssuesAndRequests.

Issues and change requests

Readers are invited to add issues to this table - select [Edit Table] below. It is not mandatory to enter a solution, but change requests are more likely to be implemented if a concrete solution is proposed.

%EDITTABLE{ header="| # | By | Timestamp | Component(s) | Description of issue | Proposed solution | Resolution |" format="| row, -1 | text, 25, Unknown | label, 0, 21 Sep 2017 16:45 | textarea, 3x25, Component(s) | textarea, 3x25, Description | textarea, 3x25, Proposal | select, 1, Unaddressed, Progressing, Resolved |" changerows="on" }%
# By Timestamp Component(s) Description of issue Proposed solution Resolution
1 My org 14 May 2004 collar location A big whinge a proposed solution Unaddressed
Topic attachments
I Attachment Action Size Date Who Comment
borehole.PNGPNG borehole.PNG manage 6.9 K 07 Nov 2005 - 13:14 SimonCox Revised borehole model
borehole.pngpng borehole.png manage 27.0 K 09 Apr 2004 - 12:44 SimonCox  
Topic revision: r47 - 15 Oct 2010, UnknownUser
 

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