Page 17 - The Geological Interpretation of Well Logs

- INTRODUCTION -

LWD tools are much used in highly deviated and 1.7 The logging companies
horizontal wells where they help to direct the drilling and
The wireline well-logging world is dominated by one,
function in conditions very difficult for standard wireline
extremely successful, giant international company —-
tools. Also, it is found that multiple passes with the
Schlumberger. In America a number of other companies
LWD tools, combined with the wireline log results, give a
exist but in many parts of the world Schlumberger has a
very accurate picture of fiuid movement in the period
quasi-monopoly. The reasons for this domination are
following drilling (Chapter 6). Case studies suggest that
partly historical: it was the fréres Schlumberger, Conrad
often wireline logs are not run at the best time in terms of
and Marcel, who created the original SPE (Société de
borehole conditions (Cunningham et al., 1991).
Prospection Electrique) in 1926, the precursor of the
LWD logs are clearly going to be used more and
modern Schlumberger. The brothers, along with H.G.
more, partly as a replacement to the open hole logs and
Doll, were the creators of the well-logging technique.
partly as an addition, especially in horizontal or highly
The international forum is becoming more competi-
deviated wells (Walsgrove er al., 1992). However, the
tive, and in America smaller companies are active.
interpretation of LWD logs involves problems rather
However, two names stand out in the general logging
specific to the LWD technique and tool types involved.
field apart from Schlumberger: Western Adas Logging
At present we are still at the stage of comparing LWD
Services, which was called Atlas Wireline Services (ex-
with wireline logs, expecting the latter to be the ‘stan-
Dresser Atlas) and Halliburton Logging Services
dard’. Very soon the reverse will be true since the slower
(ex-Gearhart and incorporating Welex). B.P.B. Wireline,
logging speed of the LWD technique offers the potential
originally the logging arm of British Plaster Board, is an
for a better reading. But, in order to keep this book at a
additional, smal] player.
relatively straightforward level, the LWD logs are used
occasionally as examples, but are not considered further,
per se.
Table 1.2 Principal uses of open-hole wireline logs.

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5 S/8 €/$/sl2/Els|sisl2 ele lE|F\ sl 2/2

3 | Temperature - + -

4 | Caliper - -

5 |SP - - - + *

6 Resistivity ~ - _ _ + + + + - _ * _

7 |Gammaray | - | - + | - - | - +- +

7 8 | Sonic + - | + - + - - - - - | + + * _ * >
|SpectralGR | -

+ - - - ~ - - + - - ~ * * + _ + _ _ dip *

+
- | +
9 | Density

9 | Photoelectric | +

-
-
-
+
10] Neutron
-

12| Dipmeter
~
13] Image logs

- Essentially) qualitative use - - - + dip
+ Semti-quantitative and quantitative uses
* Strictly quantitative