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THD LOGS
If Technical Hole Deviation
(THD) in general is new for you, we kindly suggest you first read this.
This document contains the following sections.
TECHNICAL HOLE DEVIATION LOGS INTRODUCED
A powerful, visual way in which to present Technical Hole Deviation is with a well
log. A "Technical Hole Deviation
Log" is a well log that conveys the directional well plan and the actual associated geometric
deviations. THD logs equip the operator with a superior mechanism for monitoring and/or
"grading" directional control performance, and they provide
directional drillers with critical information for rationalizing tool settings
while drilling.
As would be expected, THD values are plotted versus
actual measured depth. The Vertical Technical Hole Deviation Log addresses
deviations in the "vertical" sense. It presents planned and actual
values of well bore inclination and dogleg-severity, and THD components msVD™, RCVD™,
msID™, and RCID™.
The Horizontal Technical Hole Deviation Log addresses
deviations in the "horizontal" sense. It presents planned and actual
values of well bore azimuth and dogleg-severity, and THD components
msHD™, RCHD™,
msAD™, and RCAD™.
THD logs can be created prior
to drilling in order to present the plan, just like standard directional plots.
Then, as drilling commences, the "actual part" of the THD logs are
plotted and the directional control performance unfolds. The footer section of a
THD log contains standard vertical section and plan view directional plots.
Regardless of the planned
well path linear/curved 3D/2D complexity, the target path is always
a single vertical green zero line on the Technical
Hole Deviation log tracks.
THD
WELL LOG HEADERS
Besides measured depth, the commonality between the Vertical
THD Log and the Horizontal THD Log is the inner left track. Here, planned
and actual dogleg-severities (DLS) are graphed. Circular unfilled markers on the
actual DLS curve convey depths with directional surveys. Circular filled markers
on the planned DLS curve convey critical-point changes in the well plan (e.g.,
curved to straight).
Vertical Technical Hole Deviation Log
Header
The upper THD log header
section contains basic summary statistics. These include:
- Excess Measured Depth
- amount of actual hole drilled subtracted by the corresponding planned
measured length of drill hole. This value typically indicates the
"cost" of oscillating about the planned path. However, in special
cases this value can be negative. Such may be observed, for example, when
dropping a well bore to vertical with actual dogleg-severities exceeding
planned dogleg-severities.
- Average Absolute msVD
- average absolute value of vertical deviation (msVD™) associated with real
survey stations over the length of drill hole for which the THD log was
created. A smaller value usually indicates better directional control
performance.
- Average Absolute msID
- average absolute value of inclinational deviation (msID™) associated with
real survey stations over the length of drill hole for which the THD log was
created. A smaller value usually indicates better directional control
performance.
- THD Grid Values -
conveys the grid values of the THD tracks, as a result of auto-scaling. For
the example header below, the "20~2" means the grid value for the
msVD™ track is 20 feet, and the grid value for the msID™ track is 2 degrees.
The outer left track graphs planned and actual well bore
inclination. Hole deviation in the "vertical" sense is displayed on
the two right tracks. The inner right track displays vertical deviation (msVD™-blue)
and the relative change in vertical deviation (RCVD™-red).
The outer right track displays inclinational deviation (msID™-blue)
and the relative change in inclinational deviation (RCID™-red).
A zero line (green) centers each of the two
THD tracks. For the actual drill path to follow the planned path in the
vertical sense, msVD™, RCVD™, msID™, and RCID™ must trace their respective zero
lines.
Horizontal Hole Deviation Log
Header
The upper header section of
the Horizontal THD log contains the same Excess Measured Depth values and other
basic summary statistics including:
- Average Absolute msHD™
- average absolute value of horizontal deviation (msHD™) associated with real
survey stations over the length of drill hole for which the THD log was
created. A smaller value usually indicates better directional control
performance.
- Average Absolute msAD™
- average absolute value of azimuthal deviation (msAD™) associated with real
survey stations over the length of drill hole for which the THD log was
created. A smaller value usually indicates better directional control
performance.
The outer left track graphs planned and actual well bore
azimuth. Hole deviation in the "horizontal sense" is displayed on the
two right tracks. The inner right track displays horizontal deviation (msHD™-blue)
and the relative change in horizontal deviation (RCHD™-red).
The outer right track displays azimuthal deviation (msAD™-blue)
and the relative change in azimuthal deviation (RCAD™-red).
A zero line (green) centers each of the two
THD tracks. For the actual drill path to follow the planned path in the
horizontal sense, msHD™, RCHD™, msAD™, and RCAD™ must trace their respective zero
lines.
PROJECTIONS
Forecasts of the msVD™ and
msHD™ profiles are shown as thick black lines that extend from the last survey
station. These THD projections are helpful for directional drillers while
they rationalize directional tool setting adjustments, during drilling
operations.
EXAMPLE
THD WELL LOGS
THD well logs for three wells
are presented below. These logs were created with
SES
and then converted to JPEG graphics files. Click a thumbnail to enlarge. All
data is from real wells.
| 3D
Sidetrack Horizontal |
3D
Sidetrack Horizontal |
2D
Sidetrack Directional |
| 3
in. / 1000 ft |
5 cm / 300
m
|
1.5 in. /
1000 ft
|
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