| enumeration |
ground surface |
Natural or existing ground surface at the location of the
feature. Common reference for boreholes, CPT soundings, test pits,
and other subsurface investigations.
|
|
| enumeration |
kelly bushing |
Kelly bushing on a drilling rig, typically the reference
point for measured depth in rotary drilling operations.
Located at the top of the kelly drive system.
Note: See also 'rotaryBushing' which is the preferred term.
|
|
| enumeration |
rotary bushing |
The bushing seated in the rotary table through which the kelly
or drill string passes during drilling operations. The elevation
of the rotary bushing (often referred to as RKB - Rotary Kelly
Bushing) is a common datum reference for measuring drilled depths
and is typically a few feet above the drill floor elevation.
This is the preferred term over 'kelly bushing'.
|
|
| enumeration |
rotary table |
Rotary table on a drilling rig, alternative reference point
for measured depth measurements. The rotating platform through
which the drill string passes.
|
|
| enumeration |
crown valve |
The valve assembly located at the crown of the derrick or mast,
typically at or near the crown block. Used as a reference datum
for depth measurements in drilling operations, representing one
of the highest fixed points on the rig structure.
|
|
| enumeration |
derrick floor |
Derrick floor or rig floor elevation, sometimes used as
alternative to kelly bushing or rotary table. The main working
platform of the drilling rig.
|
|
| enumeration |
mudline |
River or lakebed surface in over-water drilling operations.
The sediment-water interface in non-marine aquatic environments.
|
|
| enumeration |
sea floor |
Seafloor surface, used in marine geophysical and geotechnical
surveys. Typically the reference for measured depth in subsea
wells and offshore boreholes.
|
|
| enumeration |
mean sea level |
Mean sea level, used as vertical datum reference in marine
and coastal environments. The arithmetic mean of hourly water
elevations observed over a specific 19-year cycle (National
Tidal Datum Epoch).
|
|
| enumeration |
lowest astronomical tide |
The lowest tide level over the duration of the National Tidal
Datum Epoch (19 years). Used as a low-water datum in some
coastal applications.
|
|
| enumeration |
mean higher high water |
A tidal datum. The average of the higher high water height of
each tidal day observed over the National Tidal Datum Epoch
(19 years). Applicable in areas with mixed tidal regimes.
|
|
| enumeration |
mean high water |
A tidal datum. The average of all the high water heights observed
over the National Tidal Datum Epoch (19 years).
|
|
| enumeration |
mean lower low water |
A tidal datum. The average of the lower low water height of each
tidal day observed over the National Tidal Datum Epoch (19 years).
Common datum for nautical charts in the United States.
|
|
| enumeration |
mean low water |
A tidal datum. The average of all the low water heights observed
over the National Tidal Datum Epoch (19 years).
|
|
| enumeration |
mean tide level |
A tidal datum. The arithmetic mean of mean high water and mean
low water. Same as half-tide level.
|
|
| enumeration |
top of casing |
Top of protective casing in a borehole or well. May be used
as reference for depth measurements in monitoring wells and
environmental boreholes.
|
|
| enumeration |
bottom of casing |
Base of protective casing in a borehole or well. Marks the
transition from cased to open hole.
|
|
| enumeration |
casing flange |
A flange affixed to the top of the casing string used to attach
production equipment. Common reference in oil/gas wells.
|
|
| enumeration |
kickoff point |
Point at which a borehole deviates from vertical in directional
drilling operations. Important reference for deviated well paths
and horizontal drilling.
|
|
| enumeration |
top of hole |
The top of a drilled hole - generally synonymous with ground
surface unless drilled within an excavation or from a platform.
|
|
| enumeration |
bottom of hole |
Terminal end of a borehole or well at maximum penetration depth.
Total depth (TD) of the hole.
|
|
| enumeration |
top of core |
The defined top of a core sample. Used when referencing positions
within core samples that may be handled separately from the parent
borehole. Common anchor point for core sample linear referencing.
|
|
| enumeration |
bottom of core |
The defined base of a core sample. Used for core recovery
calculations and sample referencing. Often provides a better-defined
reference than top of core when slough is present at the top of
cored interval. Common anchor point for bottom-up core logging.
|
|
| enumeration |
line start |
Starting point of a geophysical trackline or survey transect.
Corresponds to first coordinate in LinearExtent. Common reference
for distance along survey lines.
|
|
| enumeration |
line end |
Ending point of a geophysical trackline or survey transect.
Corresponds to last coordinate in LinearExtent.
|
|
| enumeration |
intersection |
Intersection point where this linear feature crosses another
linear feature. Common in grid-based geophysical surveys where
perpendicular survey lines create a network of tie points.
|
|
| enumeration |
benchmark |
Surveyed benchmark used as elevation reference for the feature.
A monumented point with known coordinates in a geodetic reference
system.
|
|
