<br><font size=2 face="sans-serif">Ditto. Thanks. Very interesting.</font>
<br>
<br>
<br>
<br>
<table width=100%>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">From:</font>
<td><font size=1 face="sans-serif">"Noel Zinn" <ndzinn@comcast.net></font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">To:</font>
<td><font size=1 face="sans-serif">"'PROJ.4 and general Projections
Discussions'" <proj@lists.maptools.org></font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">Date:</font>
<td><font size=1 face="sans-serif">06/14/2010 04:50 PM</font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">Subject:</font>
<td><font size=1 face="sans-serif">Re: [Proj] Deepwater Horizon. Where
is the bottom of the well?</font>
<tr valign=top>
<td><font size=1 color=#5f5f5f face="sans-serif">Sent by:</font>
<td><font size=1 face="sans-serif">proj-bounces@lists.maptools.org</font></table>
<br>
<hr noshade>
<br>
<br>
<br><tt><font size=2>A lot of science goes into wellbore surveying nowadays,
and that applies to<br>
assessing the quality of the survey, too. Wells are surveyed while
drilling<br>
(MWD, measurement while drilling) with instruments in the bottom hole<br>
assembly (BHA) that includes the drill bit. Typically, those instruments<br>
are magnetometers (magnetic azimuth) and accelerometers (inclination).<br>
Wells are also surveyed when the BHA has "tripped out" with instruments<br>
(typically gyros for true azimuth and accelerometers) that are lowered
on a<br>
wire line. Distance along the wellbore trajectory (measured depth,
MD) is<br>
determined by drilling pipe tally or wire line length. All these<br>
instruments have biases that must be compensated and different random errors<br>
that must be propagated from surface to TD (total depth). Stochastic
models<br>
for MWD and gyro surveys have been published by the Industry Steering<br>
Committee for Wellbore Survey Accuracy (ISCWSA), which is now the Wellbore<br>
Survey Accuracy Technical Committee of the Society of Petroleum Engineers<br>
(SPE). BP provided early leadership of the ISCWSA. For more
information<br>
follow this link => </font></tt><a href=http://www.iscwsa.org/><tt><font size=2>http://www.iscwsa.org/</font></tt></a><tt><font size=2>.
Given all this technology,<br>
there are also geodetic and cartographic corrections that must be applied,<br>
especially with deviated, extended-reach wells, which are common in deep<br>
water. <br>
<br>
Regards,<br>
Noel Zinn, Principal<br>
Hydrometronics LLC, Consultancy and Technical Software<br>
+1-832-539-1472, noel.zinn@hydrometronics.com<br>
</font></tt><a href=http://www.hydrometronics.com/><tt><font size=2>http://www.hydrometronics.com</font></tt></a><tt><font size=2><br>
<br>
<br>
-----Original Message-----<br>
From: proj-bounces@lists.maptools.org<br>
[</font></tt><a href="mailto:proj-bounces@lists.maptools.org"><tt><font size=2>mailto:proj-bounces@lists.maptools.org</font></tt></a><tt><font size=2>]
On Behalf Of Karney, Charles<br>
Sent: Monday, June 14, 2010 1:09 PM<br>
To: PROJ.4 and general Projections Discussions<br>
Subject: [Proj] Deepwater Horizon. Where is the bottom of the well?<br>
<br>
Here are some questions related to the Deepwater Horizon accident and<br>
the drilling of relief wells for the readers of this list in the oil<br>
industry.<br>
<br>
(1) What is the method of determining the position of an instrument 3km<br>
down a well? Is it seismic, dead reckoning, or what?<br>
<br>
(2) What is the typical absolute accuracy of the measured position,<br>
horizontally and vertically (and, if possible, specifically with<br>
reference to the leaking well)? What is the *relative* accuracy?<br>
(I.e., I can imagine that the absolute accuracy is poor because of the<br>
unknown properties of the intervening rock. However, it might be<br>
possible to "find" the same position when drilling the relief
well if<br>
the same method is used.)<br>
<br>
(3) Is the drill bit instrumented to return the position? How? Or
does<br>
a separate logging package need to be inserted into the well? At
what<br>
frequency would this be done?<br>
<br>
I can piece together some of the answers from wikipedia. However,
maybe<br>
I can get more autoritative and more specific answers from this list.<br>
<br>
--Charles<br>
<br>
-- <br>
Charles Karney <ckarney@sarnoff.com><br>
Sarnoff Corporation, Princeton, NJ 08543-5300<br>
<br>
Tel: +1 609 734 2312<br>
Fax: +1 609 734 2662<br>
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