geological desciption(simple way to describe)..special
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How to Describe sample while on wellsite job:
First we need to tell about the rock type then we have to follow the trend as per client requirement. Here are
some common rock types.
CLS/MDST/SLST
1. COLOUR
I.e. me ! "#$! "#% ! "# br$! "#% lt "#% ! brn% bl!% bl&% brn% clss% cr 'cream(% "o% "rn% op 'opa)&e(%
or% p!% p&rp% re% *i% wh% #el% *aricol% mot.
+. H,RD-SS 'CO-SOLD,TO-(
s0t soft Grains offer no resistance when prodded
0rm firm Gns bk apart easily
mo h mod hard Gns bk with some difficulty
h Hard Grains diff to bk
brit brittle (bk easily along fracture planes) ie !oal or salt
cons consolidated&ncons
ol
unconsolida
ted
plas plastic Fle" without breaking
. 2R,CTUR '3R,4(
bl!# blocky #reak into rectangular fragments
an" angular $a%ority of corners are less than &' deg
splt# splintery ointed elongated cuttings
0is fissile Fine grained sediments tend to divide readily along
well developed laminar or platy structure
s&b0is subfissile *s above+ but not so well pronounced
amor amorphous ,o form - commonly to describe soft cuttings
conch conchoidal !urved ribbed surface+ like a shell
cr&mb crumbly crumbles
. T5TUR 'to escribe *is&al appearance(
erth# earthy
homo" homogenou
s
/ock with a uniform appearance ie 0plain mudstone1
hetero" heterogeneo
us
Ie 0sandy mudstone1 or 0conglomerate1
*esic vesicular 2mall s pherical cavities+ like an aero.
amor amorphous ,o form - commonly to describe soft cuttings
ch!# chalky *ppears chalky
6ln crystalline *ppears "ln
s&c sucrosic *ppears sugary
w6# wa"y *ppears wa"y
0ri friable !an be disintegrated into individual grains by finger
pressure
lam laminated *ppears laminated
w6# wa"y
0ri friable
3. SLT CO-T-T
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ie sl slt#% loc slt# or w occ *0 )t7
*renaceous !425 that has a recognisable sandy content -
appearance - te"ture
8. C,R3O-,T CO-T-T 'cr&sh c&ttin"s(
non% sl% * or occ sl
calc
calcareous 5he way in which a cutting reacts in 6'7
H!4
dolomitic /eacts only after several mins immersion
i.e. occ sl calc or * ol
-.3. an oil base m& inhibits reaction% so cr&sh c&ttin"s to e6pose 0resh s&r0aces.
9. SLL-;
swl" / non swl" 2well 8 (,# hydro 9 hygro used with same meaning)
H#"t Hydroturgid 8 swelling in a random manner- imm
e"pands-throughout sampleH#"clst Hygroclastic 8 bits break off in water - patchy swelling
H#"0is Hydrofissile 8 swells into sm flakes :sl;+ :mo; or :*;
Cr#ptt !ryptoturgid 8 swells in dilute H!4 hot water
Cr#pt0is !ryptofissile 8 as 0Hygro1 but induced by 6'7 H!4
<. ,CCSSOR= COM>O--TS (2mall quant1s of other minerals present)
issem 8 fine grains throughout
no 8 crystalline mass
r tr 8 rare trace of ab&n 8
abundantloc 8 locally occ 8
occasionally
mica
"la&c
micromic 8 micromicaceous
SST
1. -,M O2 ROC4 225 (cemented sand grains) or 2,< (sand)
+. COM>OSTO-... =5>+ ark (sig quantities of Feldspar)+ lith (sig rock fragments)
<! bits churn wellcemented sandstone into /k Flr+ so acid test may look like 425. 4ook for grains ofsand trapped within the paste.
If predominantly recovered as /ock Flour then start with SST: rec as R! 2lr%
If predominantly 225 then start with SST: and state finally also rec* as R! 2lr% (if applic).
If predominantly grains and some /k flr then start with SST: lse )t7 "ns?..also rec* as R! 2lr.
. COLOUR
I.e. clss% clr to transl% transp$transl% loc pale "r# or pale "r# brn% 0rst
(abraded outer surface)
?. H,RD-SS 'CO-SOLD,TO-(
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0ri friable (in place of soft or firm)
lse loose @here 0only1 sand grains are observed
brit brittle (bk easily along fracture planes) i.e. !oal or salt
cons consolidated
&nconso
l
unconsolida
ted
@. 2R,CTUR / 3R,4 ' to escribe morpholo"# o0 c&ttin"s(
bl!# blocky #reak into rectangular fragments
an" angular $a%ority of corners are less than &' deg
splt# splintery ointed elongated cuttings
0is fissile Fine grained sediments tend to divide readily along well
developed laminar or platy structure
s&b0is subfissile *s above+ but not so well pronounced
amor amorphous ,o form - commonly to describe soft cuttingsconch conchoidal !urved ribbed surface+ like a shell
cr&mb crumbly * cutting of irregular outline
8. ;R,-S
Grain type (if
app)
Asually =uartB+ Ccc *rkosic (sig quantities of F-spar difficult
to spot) or 4ithic (sig rock fragments)
Grain 2iBe *0% 0% me% c% *c ie A *0 to occ mB
Grain !olour
(if applic)
wh% clss% transl% transp% #el% or % 0rst (abraded outer surface).
Grain 2hape
(or roundness)
an"% s&ban"% rn% s&brn% well rn ie As&ban" to s&brn% loc
rnB
Grain
2phericity
sphr% s&bsphr% elon"% s&belon" ie As&ban" to s&bsphrB
Grain 2orting 'Little *ar well srt(% mo srt% pr srt% bimo srt ie @/@ Apr
srtB
9. CM-T,TO- 'in terms o0 e"ree an t#pe(
!ement
type
0how
easily canthe bond
be
brokenD1
quals areE
r% occ% pr%
mo%
well% str
Lse loose ,o cement
Sili 2ilica no react with
H!4
r sili cem% loc slt#
Cal !alcite usual reaction occ with str calc cemDol
<olomite
dolomitic
reaction
<. MOD2RS
2and is *rgillaceous
ar"
,on !425 with a recognisable clay content
!lst is *renaceous
aren
,on 225 i.e. !425 that has a recognisable sandy
content - appearance - te"ture
!onglomeratic 225
225= =uartB
225* *rkosic ar! (sig quantities of Feldspar)
2254 4ithic li (sig rock fragments)
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2mall
quant1s of
other
minerals
present
tr p#r $ight be issem (fine grains throughout) or no
(crystalline mass) ie 0
Cther e"amples are? rtr mica or ab&n mica an "la&c or occ
mica or loc "la&c or no "la&
E. >OROST= 0e"tremely sub%ective1
*is por visible porosity Ie 0" *is poroB or 0no *is poroB
int6ln Intercrystalline
intra6l
n
Intracrystalline
int"ran Intergranular
intra"r
an
intragranular
TH- ;O O-TO SHOSF
LST (wash salts with base oil only to avoid dissolving)
!*/#C,*5S (composed of lime mud and-or biogenic debris)*C/I52 (ie Gypsum-*nhydrite)
,0ter etchin" can place sample in col ,la7arin Re 0or a 0ew mins. LMST eep re% DOL
&na00ecte
+. COLOUR (specifically the colour of the rock)
I.e. lt brn "r% brn "#% bl&/wh% "#$o00 wh.
. CO-SOLD,TO-
s0t soft Grains offer no resistance when prodded
0rm firm Gns bk apart easily
mo h mod hard Gns bk with some difficulty
h hard Grains diff to bk
brit brittle (bk easily along fracture planes) ie !oal or salt
cons consolidated
&ncons
ol
unconsolida
ted
plas plastic Fle" without breaking
lse loose 4oose
0ri friable asily crumbled
?. 2R,CTUR SH,> 'to escribe morpholo"# o0 c&ttin"s(
bl!# blocky #reak into rectangular fragments
an" angular $a%ority of corners are less than &' deg
splint splintery ointed elongated cuttings
0is fissile Fine grained sediments tend to divide readily along well
developed laminar or platy structure
s&b0is subfissile *s above+ but not so well pronounced
amor amorphous ,o form - commonly to describe soft cuttings
conch conchoidal !urved and ribbed surface+ like a shell
cr&mb crumbly !rumbles
@. T5TUR 'to escribe *is&al appearance(
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micro6l
n
$icrocrystall
ine
Cnly visible under microscope
6ln crystalline asily visible crystal structure
cr#pto6
ln
cryptocrystall
ine
!rystalline in appearance but no visible structure
(commonly applied to !hert)
s&c sucrosic Fine grained rock with sugary appearance
ool oolitic @hen contains spheroids of algal origin
erth# earthyhomo" homogenous /ock with a uniform appearance ie 0plain mudstone1
hetero" heterogeneou
s
Ie 0sandy mudstone1 or 0conglomerate1
*es vesicular 4ike an aero
amor amorphous ,o form - commonly to describe soft cuttings
ch!# chalky *ppears chalky
lam laminated *ppears laminated
@'a(. DU-H,MS CL,SS2C,TO- '2OR LMSTO-S(
3,SD O- >RO>ORTO-S O2 LM MUD TO S4LT,L 2R,;M-TS
$udstoneMst
!omposed of lime mud ('m) 9 less than 6'7 grains. $udsupported
@ackestone
!st
:!C*/2 G/*I,2 F4C*5I,G I, $*5/IJ; !omposed
mainly lime mud w more than 6'7 grains (K'm). $ud suptd
ackestone
>!st
:G/*I,2 I, !C,5*!5 @I5H $*5/IJ; !omposed mainly
grains 9 grain suptd. K6'7 interstitial mud matri" 9 occ sparry
calcite or pore space
Grainstone
;rst
:G/*I,2 @I5HCA5 $*5/IJ; !omposed of grains 9 grain
supported. 4ess than 6'7 interstitial mud matri"
#oundstone
3st
Criginal constituents bound 9 suptd by organic growth
!rystalline
5ln
*ll orig te"tures lacking due to recrystallisation. <istinct
crystal faces
8. MOD2RS
*rgillaceous
ar"
,on claystones with a recognisable clay content
*renaceous ,on claystones with a recognisable sandy content
<olomitic ol
*nhydrite anh#
2iliceous sili
9. ,CCSSORS
2mall quant1s
of other
minerals
present
tr
p#r
$ight be issem (fine grains throughout) or no
(crystalline mass)
Cther e"amples are? rtr mica or ab&n mica an "la&c or occ
mica or loc "la&c or no "la&c
*nhydrite
<olomite
4imestone often contains carbonaceous lamination of algal origin
<. >OROST= 0usually isible or stimated1(visual estimation is very sub%ective)
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*is por visible porosity Ie 0nil (or pr+ or fr or mod or gd or v gd or e"c) vis
poro1
int6ln Intercrystalline
intra6ln Intracrystalline
int"ran Intergranular $ay be seen in oolitic limestones
intra"ra
n
Intragranular
0r Fracture Is the principal type*&" uggy @here elements of original fabric have been
leached away by ground water
E. OOLTS/>LODS
S>H% SU3S>H+ (2!IFL 2I> /*,G)
SHOS
1. ST,-
If free oil in sample then give 7
is there an oily smellD"amine cuttings for oil staining under microscope (what colour in sample tray).
!ould beE spty+ streaky+ pch+ uniform. Ie 01G spt# stn1 or 0no *is stn1 or 0@G pch stnB or 0"enerall#
wea! 1 or 0wea! to 0airB or Apale br oil stain% &ni0ormFbrt bl&ish white 0l&orB
+. 2LUORSC-C 'nat&ral(
"amine washed cuttings under A light and describeE
'a( ,mo&nt: in 7
'b( ntensit# o0 0l&orescence: v dull+ dull+ mod+ bright
' c( Colo&rsE :bluish white condensate;+ :white;+:yellow;+ :gold;+ :green;+ :orange heavier oil;+ :brown
heavier oil;+ :black in bitumen 9 dead oil;
,oteE base oil gives off a pale blue fluorescence (keep a sample in A bo")ie A<G &ll #el fluor1 or AEG brt #el wht 0l&orB
'( Distrib&tion: i.e. patchy+ evenly.
lace representative cuttings in spot tray to check they are 225 and not !a!CM
. SOL-T ACUTB (should really list type ie normal+ dried+ acid+ water)
2pot tray back in A and (while watching) immerse cuttings in trichloroethane+ describeE (as it is leached
from rock)
'a( Rapiit# 8 instant+ fast+ mod fast+ mod+ mod slow+ slow
'b( Character 8 diffuse+ blooming+ streaming
'c ( Colo&r 8 br+ orange+ gold+ bright yellow+ gy yel+ yel wht+ blu wht.
ie Amo$0st strm"%bl& wht c&t 0l&orB
?. CRUSH CUT
If leaching is v slow+ then crush cuttings and observe changes in fluorescence.
could use fresh sample
@. Resi&al Rin" <escribe colour of oil stained solvent under natural light
allow solvent to evaporate and describe colour of residual ring
ie Ath! res rn"% abnt O in m&% str pet orB OR Ano res rn"% mo O in m&% no pet oBor Aocc pale br
resi&eB
residual ring 8 none+ trace+ thin rng+ mod rng+ thick ring+ thin film+ thick filmoil in mud 8 trace+ mod+ abnt
odour 8 str+ mod+ tr+ none
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CHEMICAL TESTS
ith 1G HCL etch
4imestone 8 instant 9 violent - float 9 move around - comp dissolve in mins - leaves acid frothy
<olomitic 4imestone 8 immediate reaction - moderate 9 continuous - move from top to bottom of acid
!alcitic <olomite 8 slowly 9 weakly - accelerates to continuos reaction after few mins - some bobbing on
bottom
<olomite 8 slow 9 hesitant - bubbles evolve one at a time - may have to warm acid for reaction to proceed -
leaves acid milky.
ith ,la7arin Re etch 'a0ter HCL( leave in cold *laB /ed for a few minutes
4imestone 8 <eep red
<olomite 8 Anaffected
!alcite 8 /ed
Ferrous !alcite 8 $auve
Fe rich !alcite 8 urple
Fe dolomite 8 4ight #lue
ith 3ari&m Chlorie test (#a!4) (for evaporates)
6. lace several cuttings in bottle and fill with distilled water.
. *gitate and pour off water.
M. /efill and repeat.
. Half fill with distilled water+ add M drops of H!4 and agitate.
3. *dd drops #a!4
N. ,ote discoloration if any.
*nhydrite 8 white precipitate
Gypsum 8 pearly white discoloration
>henolphthalen 8 redcement
Heatin" will cause
<olomite !laystone to effervesce when heated but will produce lots of particles and the cement dissolves.
<olomite will stay solid and bubble.
T#pes..
er# er# 2ine Cla#stone less than 6-Mrd 2ilt
er# 2ine M&stone between 6-Mrd 9 -Mrds 2ilt:less than m; e"tremely fine grain+ homogenous appearance+ smooth 9 fine+ feels greasy to touch+ not gritty
between teeth. $ :greater than 3'7 !lay then *rgillaceous;
Shale a 0catchall1 category where there is more than 6-Mrd !lay and unknown quantity of 2ilt. *lso when a
fine sediment becomes laminated. :less than m;
2ine Siltstone more than -Mrds 2ilt
less than M7 clay+ more than NO7 silt siBe perticles :N'm;
grainy+ though generally grains are not vis to naked eye+ feels gritty between teeth+ has greater than 3'7 2ilt
content. !rush few crumbs with pencil in dish. If feels grainy is silt
,r"illaceo&s Roc!s 0the most abundant sediment1
primarily marine depositional+ though can be lacustrine or f-water
Shales+ well compacted and fissile
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Cla#s+ soft and amorphous
Marls(!arbonate bearing clays).calcareous shale
Siliceo&s Roc!s 0small 7 of seds1
Siltstones smaller than the smallest sst grains
Sans silica grns+ fldsprs P other minerals
Sanstones
Cla#stone/M&stone
e"tremely fine grain+ homogenous appearance+ smooth 9 fine+ feels greasy to touch+ not gritty between teeth.
:less than m;
:greater than 3'7 !lay then *rgillaceous;
If becomes laminated then is Shale :less than m;
Siltstone :N'm;
grainy+ though generally grains are not vis to naked eye+ feels gritty between teeth+ has greater than 3'7 2ilt
content
Sanstone (coarse) crush few crumbs with pencil in dish. If feels grainy is silt
Cr#stal 2orms
*nhedral no visible crystal form
2ubhedral partly developed crystal form
uhedral well developed crystal form
Clastic Roc! T#pes
/udaceous 5ill?..Gravel
*ranaceous 2ilt?..2and
*rgillaceous $ud?..!lay