Crains Shale Voulme GR Log Models

8/11/2019 Crains Shale Voulme GR Log Models

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SHALE VOLUME FROM GAMMA RAY LOG MODELS

!hisPa"e

#orehole Correction $sh %ro& 'R S(ectral 'R Ea&(le

)on-*inearCorrections

See+lso

S(ontaneousPotential

Calibration Courses Site Ma(

#OREHO*E CORREC!O)S %OR '+MM+ R+!he two &ost co&&on shale indicatin" lo"s are the "a&&a ray 'R/ and s(ontaneous(otential SP/ lo"s. !he units of &easure&ent for 'R are +P units or counts (er second,and for SP are &illivolts.

!he resistivity, neutron, and sonic are so&eti&es used individually, and the se(arationbetween density (orosity and neutron (orosity is also widely used. More rarely, theelectro&a"netic (ro(a"ation attenuation curve is available and is an ecellent shaleindicator, es(ecially in thin bedded la&inated/ sand-shale se0uences.

!here are several flavors of "a&&a ray lo"s. !he conventional natural "a&&a ray lo" isusually abbreviated 'R or S'R and is the curve &ost co&&only available. !he natural

"a&&a ray s(ectral lo" (roduces the sa&e total "a&&a ray curve, usually abbreviatedS'R. + second "a&&a ray curve, called C'R, has the "a&&a rays fro& uraniu& filteredoff. !hus C'R is always less than or e0ual to S'R. f a C'R is available, it should be usedin (reference to the S'R or 'R lo"s.

f the hole si1e varies between intervals within the 1one to be analy1ed, or the shale 1oneused to (ic2 the 'Rl33 value, then hole si1e correction to the 'R is needed. Correctionsfor the SP are seldo& used even thou"h so&e effect of hole si1e and &ud (ro(erties &aybe seen. Co&(le correction charts are available in the literature, but are not usuallyincluded in co&(uter (ro"ra&s or hand analysis.

'R4C - '+MM+ R+ CORREC!ED %OR #OREHO*E E%%EC!

56 % DEP!H7)!8 9: ;ME!RC; l ? 3.3@ > MA! - B.// > l ? 3.3 > C+* - B// 6 % DEP!H7)!8 = ;ME!RC; @6 !HE) 'Rc = 'R > 5 ? 3.333 MA! - 5333// > 5 ? 3.33 C+* -


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#orehole Corrections for 'a&&a Ray

SH+*E $O*7ME %ROM !HE '+MM+ R+!he res(onse e0uation for the "a&&a ray lo" follows the classical for&6

536 'R = PHe > So > 'Rw water ter&/ ? PHe > 5 - So/ > 'Rh hydrocarbon ter&/ ? $sh > 'Rsh shale ter& ? 5 - $sh - PHe/ > Su& $i > 'Ri/ &atri ter&/


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AHERE6 'Rh = lo" readin" in 533J hydrocarbon 'Ri = lo" readin" in 533J of the ith co&(onent of &atri roc2 'R = lo" readin" 'Rsh = lo" readin" in 533J shale 'Rw = lo" readin" in 533J water PHe = effective (orosity fractional/ So = water saturation in invaded 1one fractional/ $i = volu&e of ith co&(onent of &atri roc2 $sh = volu&e of shale fractional/

#oth 'Rw and 'Rh are 1ero. 'Ri is e0ual to the bac2"round radiation in non-shaly roc2and is called 'R3 in this boo2. 'Rsh is the lo" readin" in shale, called 'R533 here. !heeffect of (orosity is very s&all, so that ter& also is assu&ed to be 1ero. !he res(onsee0uation thus reduces to6

556 'R = $sh > 'R533 ? 5 - $sh/ > 'R3

Ahen solved for $sh, this e0uation beco&es6

$SH4'R - SH+*E $O*7ME %ROM '+MM+ R+ 5


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$SH4*) )O)- *)E+R +DL7S!ME)!S !O SH+*E $O*7MESchlu&ber"er Clavier e0uation. 56 % )O)*)SA!CH8 = ;C*+$ER; 5@6 !HE) $shc = 5.G - .B - $sh ? 3.G/ N < N .G > $sh/ - 5/

Dresser older roc2 e0uation. 5G6 % )O)*)SA!CH8 = ;O*DERROCIS; 5B6 !HE) $shc = 3. > < N < > $sh/ - 5/ 56 O!HERASE $shc = $sh

AHERE6 $sh = shale content fro& 'R or SP fractional/ $shc = shale content corrected for non-linear effects fractional/

COMME)!S6$sh &ust be within the ran"e of 3.3 to 5.3 before a((lyin" these for&ulae. !he Claviere0uation is a "ood co&(ro&ise between the tertiary and older roc2 e0uations. !he "ra(hbelow illustrates these curves.


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)on-*inear +dKust&ents to Shale $olu&e

RECOMME)DED P+R+ME!ERS6)one.

SH+*E $O*7ME %ROM !HE SPEC!R+* '+MM+ R+ *O'!he al"ebraic for&ula to solve for shale volu&e fro& the "a&&a ray s(ectrolo" is in thesa&e for& as the nor&al "a&&a ray.

$SH4!H - SH+*E $O*7ME %ROM !HE '+MM+ R+ SPEC!RO*O'!HOR7M


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!H533 = "a&&a ray thoriu& readin" in 533J shale ((&/ $shth = shale volu&e fro& thoriu& curve of "a&&a ray s(ectrolo" fractional/

COMME)!S6!he "a&&a ray s(ectrolo" thoriu& curve for shale volu&e is (referred in dolo&ites andsandstones which are radioactive due to uraniu& content, and 1ones which contain

felds(ar and its derivatives, such as 2aolinite.

$SH4I - SH+*E $O*7ME %ROM !HE '+MM+ R+ SPEC!RO*O'PO!+SS7M


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)7MERC+* E+MP*E

'R = G +P units !H = ((&'R3 = @ +P units !H3 = 3 ((&'R533 = 5 +P units !H533 = 53 ((&

SP = -3 &v I = 5. JSP3 = -3 &v I3 = 3 JSP533 = 3 &v I533 = .3 J

PH) = 3.

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Crains Shale Voulme GR Log Models