CHAPTER-III

LIGHT HYDROCARBON GEOCHEMISTRY

Introduction

Hydrocarbon distribution and its evaluation in soil gases

Results and discussion

Conclusions

________

3.1 Introd

Adsorbed

light hydr

grained p

amounts o

to present

oil and ga

from a so

not have

essential

geologica

they are n

presence

integrated

about the

hydrocarb

Hydrocarb

migrated

as a gas

sediment

minerals,

LIGHT___________

duction

d soil gas su

rocarbons oc

portion of so

of light hydr

t day subsur

as reservoir

ource rock m

to be trap a

components

al studies. A

not employed

or absence o

d with geolo

structures a

bon generatio

bons reside

from the de

dissolved i

matrix or

such as calc

T HYDR__________

urvey is a dir

ccurring in th

oil or incorp

rocarbons co

rface fluid c

(Gervitz, 20

might show su

and reservoir

s for a comm

As far as Su

d independe

of hydrocarb

ogical and g

and types of

on and entra

in the near

epth. Free g

in an aqueo

contained

cite or oxide

OCARB___________

rect techniq

he pore spac

porated in so

ollected near

composition

002). A stea

urface geoch

r below. Ho

mercial depo

urface geoch

ently for exp

bons in an ar

geophysical

f rocks prese

apment.

r surface as

ases occur a

ous solution

within the

e coatings, (

ON GEO__________

que, in which

ce of soil and

oil cements

r the earth’s

and migrat

dy stream o

hemical ano

owever, trap

osit and thes

emical anom

loration nee

rea. Neverth

studies wh

ent at depth w

free and bo

as either vap

n. If the ga

interstices

Hunt, 1981;

CHAPT

OCHEMI___________

h the trace a

d adsorbed o

are analyze

surface prov

tion from de

or rising hyd

malies and t

and reservo

e can be kn

malies are co

ds as they su

heless, they h

hich give in

which are su

ound gases w

pour in pore

as is attach

of rocks o

Jones et al.

81

TER-III

ISTRY ________

amount of

on the fine

ed. Trace

vide clues

eep seated

drocarbons

there does

oir are the

own from

onsidered,

uggest the

have to be

nformation

uitable for

which are

spaces or

hed to the

or certain

., 2000) is

82

consi

gases

from

depth

migra

indig

rocks

therm

sourc

1993

sourc

meth

Hydr

vary

(Burt

et al

appea

produ

anaer

the n

and B

sourc

butan

Comp

idered to be

s. The boun

the biologi

h (Jones et

ated through

enous gases

s). Gases tha

mogenic and

ces (Horvitz,

, 1999). N

ces but may

ane (Waples

rocarbon con

with time be

tell, 1989; Jo

., 2000). B

arance of so

uce anaerob

robic conditi

near surface

Baldassare,

ce of C1, s

ne) should

position and

e bound. B

nd gases we

cal oxidatio

al., 2000).

h the rock

s (syngenetic

at have reac

d/or abiogen

, 1969, 1972

Near surface

also contain

s, 1985; Dick

ncentration

ecause of dis

ones and Bur

Bacteria in

me soil gas

bic methane

ions prevail

under oxid

1998). To

some other

be measu

d concentra

Bound gases

ere trapped w

on of free ga

Sediments

soil matrix

c gases form

ched the soi

ic gases tha

2, 1980; Sta

e free gases

n gases forme

kinson and M

in the very

splacement b

rtell, 1996; L

the near s

seepage dat

e (C1) in t

, however, o

izing condit

minimize t

hydrocarbo

ured (Matth

ation of soi

s include ad

within autho

ases and oil

s may conta

x after sed

med at the sa

il horizon m

at migrated

ahl et al., 19

are domina

ed during di

Matthews, 19

near surfac

by wind, rain

Laughrey an

surface may

ta. Certain b

the near su

other stains

tions (Schoe

the influenc

on constitue

hews, 1996

il gas const

dsorbed and

ogenic carbo

ls that had m

ain epigenet

iment depo

ame time as

may also con

to the surfa

81; Saunder

ated by gas

agenesis, su

993; Jenden

ce environm

n and barom

nd Baldassar

y contribute

bacteria have

urface enviro

consume hy

ell et al., 19

ce of biogen

ent (ethane,

6; Jones et

tituents are

d chemisorb

onates form

migrated fro

tic (gases th

sition) and/

the enclosin

ntain biogen

ace from de

rs et al., 199

ses from de

uch as biogen

et al., 1993)

ment may al

metric pumpin

re, 1998; Jon

to the noi

e the ability

onment wh

ydrocarbons

993; Laughr

nic or anoth

propane an

t al., 2000

the princip

bed

med

om

hat

/or

ng

nic,

eep

91,

eep

nic

).

lso

ng

nes

isy

to

hen

in

rey

her

nd

0).

pal

parameter

irrespectiv

of the ear

(microsee

hydrocarb

1986, Jo

commonly

signature

Richers et

al., 2002)

from mu

Composit

accumula

whereas

condensat

using rati

percent m

Drozd, 19

al., 1993;

quantify t

may have

gases (Ho

and Drozd

al., 2000)

rs used to r

ve of their o

rth because

eps) detecte

bon reservoi

nes and D

y associated

of the gas,

t al., 1986; K

). An except

ultiple sour

tional analys

ations presen

oil reservoi

te (liquid hy

os of hydroc

methane (%C

983; Richers

; Laughrey

the composit

e an effect on

orvitz, 1969,

d, 1983; Ma

). Fractures

recognize an

origins, are m

of pressure

ed in the

ir or other so

Drozd, 1983

d subsurface

gas condens

Klusman, 19

tion may oc

rces (Jones

sis reveals t

nt. Gas rese

irs common

ydrocarbons

carbon cons

C1) and the p

s et al., 1986

and Baldss

tional signat

n the magni

1972, 1980

atthews, 198

provide pat

nomalous o

mobile and te

and buoyan

near surfac

ource in the

). The co

source and

sate and oil

993, 2002; K

ccur if the n

and Drod

the type or

rvoirs are co

nly contain

s dissolved

stituents dete

percent gas w

6; Dickinson

sare, 1998;

ture of a soil

tude and com

; Stahl et al.

5; Saunders

thways so th

ccurrences.

end to migra

ncy effects

ce, indicate

subsurface

omposition

generally pr

at depth (Jo

Klusman and

nearsurface s

d, 1983; J

types of sub

ommonly do

a higher p

in the gas)

ected in the

wetness (Hor

n and Matth

Jones et al

l gas. Faults

mposition of

, 1981; Rich

et al., 1991,

hat permeab

Light hyd

ate toward th

(Hunt, 1995

the presen

(Richers et

of microse

rovides a geo

nes and Dro

d Saeed, 199

soil gases ar

ones et al

bsurface hyd

ominated by

ercentage o

or oil is d

soil gas sam

rvitz, 1980;

hews, 1993;

., 2000) ma

s and fractur

f the near su

hers et al., 19

, 1993, 1999

bility is enha

83

drocarbons

he surface

5). Leaks

nce of a

al., 1982,

eep gases

ochemical

ozd, 1983;

96; Rice et

re formed

l., 2000).

drocarbon

y methane,

of heavier

etermined

mple. The

Jones and

Jenden et

ay further

re systems

urface soil

982; Jones

9; Jones et

anced and

84

there

hydro

Droz

3.2 H

Nume

been

offsh

been

surfa

light

(C2),

direct

hydro

sedim

3.3 R

Adso

gas c

(alkan

billio

adsor

param

stand

histog

fore more g

ocarbons (Li

d, 1983).

Hydrocarbon

erous analy

devised an

hore explorat

based on th

ce reaction p

hydrocarbon

Propane (C

tly from a h

ocarbons mi

ments (Sokol

Results and D

orbed soil sa

chromatogra

ne series: C

on (ppb) of

rbed soil sam

meters of the

dard deviatio

grams are

gas reaches

ink, 1952; H

n distributi

ytical metho

nd applied b

tion. The su

he direct dete

products resu

ns is primari

C3), butane

hydrocarbon

igrate easily

lov et al., 19

Discussion

amples were

aphy. The

C1, C2 and C

gas in the

mples of the

e variables v

on of light h

prepared ba

the surface

Horvitz, 197

on and its e

ds that mea

by the petro

urface geoch

ection of see

ulting from m

ily based on

(iC4 & nC4

reservoir (K

y than the l

70).

e analyzed f

magnitude

C3) were mea

soil gas mi

study area a

viz. minimum

hydrocarbon

ased on the

e above a re

2; Jones and

evaluation in

asure these

oleum indus

hemistry for

epage, or on

microseepag

measuremen

4) and pent

Klusman, 20

larger liquid

for the light

of each of

asured and a

ixture. The

are shown in

m, maximum

ns are summ

e mean and

eservoir or

d Thune, 19

n soil gases

hydrocarbo

stry to both

petroleum e

n the measur

ge. The dire

nt of methan

tane (iC5 &

002). These

d hydrocarb

hydrocarbo

f the organi

are expresse

e analytical

n Table 3.1.

m, mean (bac

marized in Ta

d standard

strata bearin

982; Jones an

n traces ha

h onshore an

xploration h

rement of ne

ct detection

ne (C1), etha

nC5) deriv

e light gaseo

bons in rece

on gases usin

c constituen

ed in parts p

results of t

The statistic

ckground) an

able 3.2. T

deviation f

ng

nd

ave

nd

has

ear

of

ane

ved

ous

ent

ng

nts

per

the

cal

nd

The

for

samples.

soil gases

Histogram

distributio

and anom

distributio

graph of G

towards n

can be ske

Data skew

common

representa

population

skewness

Figures 3

3.3.1 Met

The meth

1582 ppb

value (me

present in

shows as

associated

The hydro

s have shown

ms are one

on of hydro

malous sam

on that has

Gaussian is a

negative (left

ewed to eith

wed to the r

form of hi

ative of ba

n (Tedesco,

. Histogram

.1 to 3.3.

thane (C1)

hane (C1) co

with mean

ean + Standa

n all the sa

symmetrical

d with surfac

ocarbon distr

n the presenc

of the stat

ocarbon com

mples. Norm

bell shaped

a characteris

ft) and positi

her the right

right are ter

istogram in

ackground p

, 1995). Da

ms of metha

oncentration

of 293 ppb,

ard deviation

amples (100%

curve wit

ce geochemi

ribution patt

ce of methan

tistical comp

mponents di

mal distribu

d curve know

stic symmetr

ive (right). D

or the left, w

rmed a posit

petroleum

population

ata skewed t

ane, ethane

in the study

standard de

n) of 566 ppb

%) in study

th positive

ical data in p

tern clearly

ne to propan

ponents in

fferentiates

ution is co

wn as Gauss

ric ‘bell curv

Data contain

which gives t

tive skewne

exploration

rather than

to the left a

and propan

y area range

eviation of 2

b. The resul

y area. The

skewness

petroleum ex

indicates th

e.

which the

between ba

ontinuous p

sian distribu

ve’ shape tha

ing anomalo

the impressi

ess. This is

with the d

n of the a

are called a

ne are show

es between

273 ppb and

lts show tha

e histogram

which is c

xploration.

85

hat all the

frequency

ackground

probability

ution. The

at falls off

ous values

ion of tail.

the more

data more

anomalous

a negative

wn in the

14 ppb to

threshold

at the C1 is

m (Fig.3.1)

commonly

86

3.3.2

Ethan

mean

(mean

Ethan

surfa

3.3.3

Propa

with

ppb.

an as

with

In M

positi

the ri

distri

high

Ethane (C2

ne (C2) in so

n value of 16

n + standard

ne histogram

ce geochemi

Propane (C

ane (C3) con

mean value

C3 is presen

symmetrical

surface geoc

Methane, Eth

ive skewnes

ight side is l

bution is sk

concentratio

2H6)

oil sample of

6 ppb with s

d deviation)

m (Fig 3.2) i

ical data for

C3H8)

ncentration i

e of 6 ppb, s

nt in 77% of

curve with

chemical dat

hane and Pr

ss is observe

long and the

kewed to the

ons.

f the study a

standard dev

of 30 ppb.

s positively

hydrocarbo

in the study

standard dev

f the sample

positive ske

ta in petroleu

ropane histo

ed. A positiv

e bulk of va

e right side

area ranges f

viation of 14

C2 is presen

skewed wh

n exploratio

area varies

viation 6 pp

s. The C3 h

ewness whic

um explorati

ograms, an

ve skewness

alues lie to th

i.e., less nu

from 0 to 97

4 ppb and th

nt in 99% o

ich is comm

n (Tedesco,

between 0 p

pb and thres

histogram (F

h is commo

ion.

asymmetric

s indicates th

he left of th

umber of sam

7 ppb having

hreshold val

of the sample

monly found

1995).

ppb to 33 pp

shold value

Fig. 3.3) show

only associat

al curve wi

hat the tail

he mean. T

mples bearin

g a

lue

es.

in

pb

12

ws

ted

ith

on

The

ng

Fig. 3.1 H

Fig. 3.2 H

0

10

20

30

40

50

60

No.

of s

ampl

es

0

10

20

30

40

50

60

No.

of s

ampl

es

Histogram sh

Histogram sh

48

200

52

14

howing the d

howing the d

27

15

400 600

118

18 21

distribution o

distribution o

6

0 800

Methane

8

25

Ethane

of yield valu

of yield valu

1 1

1000 12

e (ppb)

7 7

30 3

(ppb)

es for Metha

es for Ethan

1 1

200 1300

7 6

37 45

87

ane (ppb)

ne (ppb)

1

1583

1

97

88

Fig. 3

3.3.4

The d

gases

cross

effect

activi

The

ethan

const

for al

const

prom

No.

of s

ampl

es

3.3 Histogram

Genetic cor

data sets hav

s using the c

plots of the

t of secon

ity and mult

cross plots

ne-propane (

tituents (Fig

ll the compo

tituents in m

minent secon

57

0

10

20

30

40

50

60

6

m showing t

rrelation of

ve been advo

cross plots

e yield data o

dary alterat

iplicity of so

of methane

(C2-C3) indi

gs. 3.4 to 3.9

onents (R > 0

microseeps a

dary alterati

7

20

10

the distributi

f Hydrocarb

ocated for th

and Pearson

of different h

tions like b

ource.

e-ethane (C

cates linear

9) and the P

0.8) suggest

are from the

ions during

14

15

Pro

ion of yield

bon constitu

he genetic ch

n correlation

hydrocarbon

biodegradati

C1-C2), meth

relationship

Pearson corr

ts (Table. 3.3

same origin

the path of

6

18

opane (ppb)

values for P

uents in adso

haracterizatio

n coefficient

n component

ion, degass

hane-propane

p among the

relation coef

3) that all th

n (cogenetic

f migration

2

24

ropane (ppb

orbed gases

on of adsorb

t matrix. T

s represent t

sing, bacter

e (C1-C3) an

e hydrocarb

fficient matr

e hydrocarb

c) without an

to the surfa

1

33

b)

s

bed

The

the

ial

nd

on

rix

on

ny

ace

and their

light gase

source be

compositi

nature of

Fig. 3.4 C

0

20

40

60

80

100

120

Etha

ne (p

pb)

subsequent

eous hydroc

ecause of th

ion trend C1

microseeps.

Cross plot of

0

0

0

0

0

0

0

0

adsorption

carbons migh

he presence

1>C2>C3 in

f adsorbed ga

500

on the soil

ht have bee

of C2 & C

the study ar

as componen

100

Methane

(Gervitz an

en generated

C3 componen

rea is indica

nts Methane

0

e (ppb)

d Carey, 19

d from a the

nts. The hyd

ating the pet

vs. Ethane

1500

89

983). The

ermogenic

drocarbon

troliferous

R = 0.89

2000

90

Fig. 3

Fig. 3

Prop

ane

(ppb

)∑C

2+(p

pb)

3.5 Cross plo

3.6 Cross plPropan

0

5

10

15

20

25

30

35

0 2

0

20

40

60

80

100

120

140

0

2

ot of adsorbe

lot of adsorbne).

200 400

200 400

ed gas comp

bed gas com

600 800

Met

600 80

Me

ponents Meth

mponents Me

0 1000 1

hane (ppb)

00 1000

ethan (ppb)

hane vs. Prop

ethane vs. ∑

1200 1400

1200 1400

pane.

∑C2+ (Ethane

R = 0.

1600 18

R = 0.

1600 18

e +

83

00

88

00

Fig. 3.7 C

Fig. 3.8 C(E

0

5

10

15

20

25

30

35

40

45

Prop

ane

(ppb

)

Cross plot of

Cross plot of Ethane + Pro

0 2

0

20

40

60

80

100

120

140

160

0

∑C2+

(ppb

)

f adsorbed ga

f adsorbed gaopane).

20 40

20

as componen

as componen

0 60

Ethane (

40

nts Ethane vs

nts Methane

80

(ppb)

60

Ethane (ppb

s. Propane.

vs. ∑C2+

100

80

b)

91

R = 0.96

120

R = 0

100

0.99

120

92

Fig. 3

3.3.5

The

devel

gas o

condi

proba

Droz

to det

reserv

volum

gener

∑C2+

(ppb

)

3.9 Cross plo (Ethane +

Hydrocargeneratio

use of ligh

loped as a w

or oil) and

itions. Val

able source

d, 1983; Ma

termine the

voir (Yasnev

mes of heav

rally imply e

0

20

40

60

80

100

120

140

0

2

ot of adsorbe+ Propane)

rbon ratioson

ht hydrocarb

way to predic

d as a filte

lues of ratio

of light hyd

atthews, 198

potential co

v, 1986; Wi

vy hydrocarb

economic via

5

ed gas comp

s and its

bon ratios i

ct the type of

er to elimin

os of hydro

drocarbons (

5; Jones et a

ommercial or

illiam Harbe

bons and sm

ability.

10 15

Pro

ponents Prop

evaluation

in hydrocarb

f oil/gas pres

nate false in

ocarbons ma

Richers et a

al., 2000). R

r non-comm

ert et al., 200

maller ratios

5 20

opane (ppb)

pane vs. ∑C2

for predi

bon data ev

sent at depth

ndications o

ay also indi

al., 1982, 19

Ratios have a

mercial nature

05). It is fo

s of lighter

25

2+

icting oil/g

valuation w

h (wet gas, d

of anomalo

cate the mo

986; Jones an

also been us

e of petroleu

ound that lar

hydrocarbo

R = 0.98

30

gas

was

dry

ous

ost

nd

sed

um

rge

ons

35

With reg

samples a

C2+ gases

Soil samp

content is

Oung et a

presence

thermogen

thermogen

ethane, pr

al., 2006)

Jones an

hydrocarb

According

C3/C1X10

microseep

derived ra

various ra

suggests t

pools.

Pixler (19

ethane (C

geochemi

gard to the

analyzed. Th

s including e

ples from Sh

s used to dist

al., (2006) r

of thermog

nic gas ge

nic gas and

ropane, buta

.

nd Drozd (

bons in soil

g to Jones

000 ratios re

ps. The sta

atios of Jon

atios within

that the soil

969) defined

C1/C2) and

ical signatur

chemical c

he hydrocarb

ethane and p

hri Ganga Na

tinguish the

reported that

genic gas. T

enerated fro

microbial g

ane and pent

(1983) repo

gas as indic

s and Dro

veal that the

atus of vario

nes and Dro

the threshol

l gases are d

d the compo

methane to

e (oil, oil/ga

composition,

bon gases wi

propane are

agar show hi

origin of the

t C2+ concen

The sample

om mature

gas. The pre

tanes sugges

orted empir

cative of the

zd (1983),

e general inc

ous ratios in

zd is given

d value in la

derived by m

ositional sig

o propane r

as, gas). Acc

, methane w

ith higher ca

detected in

igh concentr

e hydrocarbo

ntration arou

e containing

sediments

esence of a

st its thermo

rically deriv

nature of a

C1/C2, C1

cidence indic

n the study a

in Table 3.

arge percent

microseepag

gnatures disp

ratios (C1/C

cording to Pi

was domina

arbon numbe

majority of

ration of C2+

on gas.

und 3% ind

g C2+ is reg

or as a m

significant a

genic origin

ved ratios

a subsurface

1/C3, C2/C3

cates the ori

area with em

.4. The inc

ages in the s

e from subs

played by m

C3) to deter

ixler, which

93

ant in all

er, i.e., the

f samples.

+. The C2+

dicates the

garded as

mixture of

amount of

n (Oung et

for light

reservoir.

X10 and

igin of the

mpirically

cidence of

study area

surface oil

methane to

rmine the

has C1/C2

94

ratio

conde

C1/C3

indic

on th

zones

plotte

conde

The g

therm

could

of C2

1977)

isotop

sectio

petro

is up to 5

ensate zone

3 are given a

ated that the

he Pixler plo

s) but major

ed in the Pix

ensate zone.

generation o

mogenic proc

d yield C2 an

2 and C3 are

) and the rat

pic ratios o

on 4.6), an

liferous orig

considered

and up to 5

as 14, 33, an

e deposits w

ot (Fig 3.10)

rity of samp

xler diagram

Remaining

of higher hy

cess as the n

nd C3 in sma

useful in pr

tios obtained

of methane,

nd the high

gin.

as oil zone

0 considered

nd 80 respec

ere of no-co

), the sampl

ples belong

m shows that

samples fall

ydrocarbon g

normal micro

all amounts.

redicting the

d here also s

ethane and

er ratios of

e, up to 18

d as dry gas

ctively. Ratio

ommercial im

les fall in tw

s to oil &

t 90% of sam

l in gas zone

gases (C2 an

obial decom

. However,

e origin of e

suggest a th

propane ar

f C2 and C

considered

s zone. Simil

os below ~2

mportance or

wo zones (o

gas and Ga

mples fall in

e.

nd C3) is no

mposition of o

the carbon

ethane and p

ermogenic s

re reported

C3 further s

as oil & g

larly ratios f

2 or above 2

r value. Bas

oil/gas and g

as zones. Da

n the oil & g

ot restricted

organic matt

isotopic rati

propane (Fue

source (carb

in chapter-I

suggests the

gas

for

00

sed

gas

ata

gas

to

ter

ios

ex,

on

IV

eir

Fig. 3.10

Pixler plot fC1/C2 and C

for discriminC1/C3 ratios

nating Oil, O(Pixler, 196

Oil & Gas an9).

nd Gas wind

95

dow using

96

3.3.6

The i

of the

that a

and a

using

given

samp

calcu

classe

conce

show

calcu

map

displa

samp

ethan

[gas]

(Figs

[Stan

The a

hydro

Hindu

Moha

Distributio

identification

ese sites sug

are indicativ

anomaly dis

g Arc GIS 9

n in a way to

ples in an a

ulated based

es. Contour

entration ran

w the anomal

ulated backgr

is calculate

ay of the g

ples in the st

ne, propane a

-[Mean gas]

. 3.15 to 3

ndard deviati

anomaly dist

ocarbon a

umalkotraod

anpura, Chak

on and delin

n of high con

ggest clear t

e of oil/gas

stribution m

9.3.1 version

o show visua

area posses

on mean of

r colors ar

nge of each

lous concent

round value

d based on

geographic

tudy area.

and C2+ are

]. The gas an

3.18) are ca

ion]).

tribution ma

anomaly

d with anot

k12Q and th

neation of su

ncentration s

trends involv

charged sub

maps of indiv

n software.

ally, the part

sses. In the

f the obtain

re not iden

h class. Whe

trations of h

s. Here the

Mean plus

distribution

The concent

illustrated i

nomaly valu

alculated on

aps of light g

between

ther trend o

he area south

urface hydr

sample sites

ving individ

b surface stru

vidual hydro

Concentrati

ticular conce

se maps th

ned data and

ntical in or

ereas, the an

hydrocarbons

e background

Standard D

of the hig

tration distr

in Figs. 3.11

ues used in a

n the basis

gaseous hydr

Mirzawala

of high hyd

h east to Kesr

ocarbon an

and the a re

dual site or g

uctures. The

ocarbons are

ion distribut

entration ran

he classes/b

d kept identi

rder to dif

nomaly dist

s in an area

d for anoma

Deviation.

gh concentra

ibution map

1 to 3.14 wit

anomaly dist

of [gas]-([

rocarbons ide

a, Prithvi

drocarbon si

risinghpur.

omalies

eal distributi

groups of sit

concentrati

e prepared b

tion maps a

nge each of t

in values a

ical for all t

fferentiate t

tribution ma

deducting t

aly distributi

It provides

ation anoma

ps of methan

th backgroun

tribution ma

[Mean gas]

entify a stron

ragpur an

ignatures ne

on

tes

on

by

are

the

are

the

the

aps

the

on

s a

aly

ne,

nd

aps

+

ng

nd

ear

Fig. 3.11 Conncentration distrribution map of adsorbed gas mmethane (ppb).

97

98

Fig. 3.12 Concentration distribution map of adsorbed gas Ethane (ppb).

Fig. 3.13 Conncentration distriibution map of aadsorbed gas Prropane (ppb).

99

100

Fig. 3.14 Concentration distribution map of adsorbed gas C2+ (Ethane+Propane) (ppb).

Fig. 3.15 Anommaly distributionn map of adsorbbed gas Methane (ppb).

101

102

Fig. 3.16 Anomaly distribution of adsorbed gas Ethane (ppb).

Fig. 3.17 Anoomaly distribution map of adsorrbed gas Propanne (ppb).

103

104

Fig. 3.18 Anomaly distribution map of adsorbed gas C2+ (Ethane+Propane) (ppb).

3.4 CONC

The anom

the study

from the s

1. Th

co

2. Th

su

by

to

3. Di

th

4. Th

de

fa

5. Th

co

M

hi

so

CLUSIONS

malous conce

area. Based

study area fo

he adsorbed

oncentrations

he linear co

uggests that

y secondary

surface and

ifferent ratio

e most of th

he Pixler pl

erived from

llen in oil/ga

he anomaly d

ompositional

Mirzawala, Pr

gh hydrocar

outh east to K

S

entrations in

d on the ligh

ollowing sum

d soil gas an

s of methane

orrelation ob

these gases

alteration ef

d are thermog

os between l

e samples fa

lot illustrate

the oil/gas

as condensat

distribution

l ratios iden

rithviragpur

rbon signatu

Kesrisinghpu

ndicate series

ht hydrocarb

mmary is dra

nalyses show

e, ethane and

btained for

are cogenet

ffects during

genic in natu

light hydroca

all in oil and

es that the l

condensate

te zone)

maps of ligh

ntify a stron

and Hindum

ures near Mo

ur.

s of large ma

bon geochem

awn:

w presence

d propane.

C1-C2, C1-C

tic and have

g their migra

ure.

arbon gases

gas condens

light gaseou

zone. (majo

ht gaseous h

g hydrocarb

malkotraod w

ohanpura, C

agnitude ano

mistry of soi

of high to

C3, C2-C3 an

e not been i

ation from s

indicate /su

sate zone.

us hydrocarb

ority of sam

hydrocarbons

bon anomaly

with anothe

Chak12Q and

105

omalies in

il samples

moderate

nd C1-C2+

influenced

subsurface

uggest that

bons were

mples were

s and their

y between

er trend of

d the area