-
Gamma Ray and Spontaneous PotentialSchlumberger
2-1
GR
Gamma Ray Corrections for Hole Size and Mud WeightFor 338-in.
and 11116-in. SGT wireline gamma ray tools GR-1
0 5 10 15 20 25 30 35 40
10.0
7.0
5.0
3.0
2.0
1.0
0.7
0.5
0.3
t (g/cm2)
Corre
ction
facto
r
33 8-in. to
ol, centere
d
11116-in. tool, c
entered
11116-in. tool, eccentered
338-in. tool, eccentered
Schlumberger
Log interpretation Charts GR-1 and GR-2, replacing Chart
Por-7,are based on laboratory work and Monte Carlo calculations
toprovide improved corrections for 338- and 11116-in. SGT gammaray
tools. The corrections normalize the response of both tools
toeccentered positions in an 8-in. borehole with 10-lbm mud.
ChartGR-2 provides a correction for barite mud in small
boreholes.
Although these charts are more difficult to use than the
onesthey replaced, the results are more exact since they are
normal-ized to current tools, no interpolation is required, and the
rangesare extended.
The input parameter, t, in g/cm2, is calculated as follows:
The correction for standoff is
CF m is the correction factor for centered tools, while CF o is
thecorrection factor for eccentered tools. Both are corrected
forbarite if it is present in the borehole. S is the actual
standoff, andSm is the standoff with the tool centered.Example: GR
reads 36 API units, dh is 12 in., and mud weight
is 12 lbm/gal. The tool is 338 in. and centered.Therefore, t =
15.8 g/cm2, resulting in a correction factor of 1.6.
The corrected GR = 58 API units.
CF CF CF CF = +
m o m
mm
S SS( ) .
2
t W d dmud hole sonde=
8 345
2 542
2 542.
. ( ) . ( ) .
-
David Garcia3
David Garcia
David Garcia
David Garcia
David GarciaHERRAMIENTA CENTRADA
David Garcia
David GarciaGRmincorregido=(1.6)(33)=52.8API
David Garcia
David Garcia8.2
David Garcia1.6
David GarciaGR(12)=(1.5)(44)=66API
David GarciaGRmnaxcorregido=(1.5)(92)=138API
David Garciaish=66-52.8/238-52.8=0.15
3aproximacion
David Garcia
David Garcia
-
David Garcia
David Garcia
David Garcia
David Garcia
-
David Garcia
David Garcia
David Garcia
David Garcia1
David Garcia
David Garcia
David Garcia
David GarciaGR MAX
David GarciaGR MIN
David Garcia
David Garcia8`MIDE EL CALIPER
-
David Garcia2
David Garcia0.18
David Garcia
David Garcia
David Garcia0.07
David Garcia
David Garcia0.06
David Garcia
David Garcia0.16
-
David Garcia
David Garcia
David Garcia
David Garcia27 API
David Garcia
David Garcia
David Garcia
David Garcia0.88 PPMGGR=GR-U=27-8(0.8)=20.6 API
David GarciaTexto
David Garcia
David Garcia
David GarciaGR MIN= 10 API
David Garcia
David GarciaU=2 PPMGRmin =10-8(2)=-6=0
David Garcia
David Garcia
David GarciaGR Max= 8610 API
David Garcia
David Garciau=1.5ppm=86-8(1.5)=74API
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Crossplots for Porosity, Lithology and
SaturationSchlumberger
4-30
CP
Radioactive minerals often occur in relatively small
concentra-tions in sedimentary rocks. Even shales typically contain
only30 to 70% radioactive clay minerals.
Unless there is a complex mixture of radioactive mineralsin the
formation, Chart CP-19 can be used to identify the morecommon ones.
The ratio of thorium to uranium activitythe
thorium/potassium ratio, Th/Kdoes not vary with
mineralconcentration. A sandstone reservoir with varying amounts
ofshaliness, with illite as the principal clay mineral, usually
plotsin the illite segment of the chart, with Th/K between 2.0 and
2.5.Less shaly parts of the reservoir plot closer to the origin,
andmore shaly parts plot closer to the 70% illite area.
Mineral Identification fromNGS* Natural Gamma Ray Spectrometry
Log CP-19
0 1 2 3 4 5
Potassium (%)
25
20
15
10
5
0
Thor
ium (p
pm)
Mixed layer
clay
IlliteMicas
Glauconite
Potassium evaporites, ~30% feldspar
~30% glauconite
~70% illite
100% illite point
~40% mica
Montm
orillon
ite
Chlorite
Kaolinite
Possible 100% kaolinite, montmorillonite, illite clay line
Th/K
: 25
Th/K:
12
Th/K: 3.5
Th/K: 2.0
Th/K: 0.6
Th/K: 0.3Feldspar
Heav
y tho
rium-
bear
ing m
inera
ls
*Mark of Schlumberger Schlumberger
