-
UQ
-CC
SG
Centre for C
oal Seam
Gas
Dynamics of reservoir pressure and the influences
on coal seam gas production
Rui Li a,b, Victor Rudolpha, Tom
Rufforda
aSchool of Chemical Engineering, University of Q
ueensland; bFaculty of Earth Resources, China University of Geosciences
Assuming conditions:
CSG reservoir is flat;
Thickness of CSG reservoir is uniform
;
Boundary of CSG reservoir is closed;
Isothermal during CSG reservoir depletion.
Fig.1 CSG reservoir model
Results and discussion
Fig.3 Variations of reservoir pressure and BHP
Fig.4 Variations of pressure differencesBased
onthe
productiondata,
theCSG
recoveryrate
duringproduction
canbe
computed
as:
i
scVh
R Q
2
Inaccordance
with
theLangm
uircurve,the
gasrecovery
ratecan
alsobe
calculatedasfollow
s:
Ifapplying
Eq.(2)into
theprocess
ofgas
production,itm
eansP
(abandonment
pressure)becom
esa
dynamic
reservoirpressure.
Theoretically,thegasrecovery
basedon
theproduction
data,which
isbasedon
theLangm
uircurveare
equal:
P
PP
PP
P
Lcd
cdL
1
(1)
(2)
(3)
Solving for the dynamic reservoir pressure, it is expressed as:
Forthe
pseudosteady-stateflow,
thedeliverability
equationin
metricunitsisasfollow
s(Liao2012):
)75.0
(10
31.1
)(
)(
3
Sr R
Inh
KT
qP
mP
mw
g
scw
f
Solving for the BHP,
)75.0
(10
31.1
32
2S
r RIn
hK
TZq
PP
wg
scg
wf
Where
Risexternalradiusofdrainage
boundary,m;h
isthicknessofCSG
reservoir,m
;ρ
isdensity
ofcoal,
t/m3;
Qsc
istotal
gasproduction,
m3;
Pis
reservoirpressure,
MPa;
PL
isLangm
uirpressure,M
Pa;Pcd
iscriticaldesorption
pressure,MPa;P
wf is
BHP,M
Pa;qsc is
gasflow
rate,m3/d;K
g isgas
permeability,m
D;Tis
coalseam
temperature,K;
rwis
wellbore
radius,m;
sis
wellbore
skinfactor;μ
g isgasviscosity,mPa·s;and
Zisgasdeviation
factor.
(4)
(5)
(6)
1)There
aresim
ilarvariation
trendsbetw
eenthe
reservoirpressure
andBHP
with
calculationthatboth
showed
aslow
-fast,and
slowvariation
pattern.While
theBHP
inpractice
isevidentlylow
ercompared
with
BHPw
ithcalculation
.2)
Thereare
similar
variationtrends
between
thepressure
differencew
ithcalculation
andgas
productionrate.
Butthe
pressuredifference
inpractice
isevidentlyhighercom
paredw
ithpressure
differencew
ithcalculation
.3)
Thecontrolling
ofBHPofW
ellX1should
adaptthevariationsof
reservoirpressure.
1.LiR,W
angSW
,ChaoW
W,W
angJC,Lyu
SF,2016.Analysis
ofthe
transferm
odesand
dynamic
characteristicsof
reservoirpressure
duringcoalbed
methane
production.InternationalJournalofRock
Mechanicsand
Mining
Sciences,87,129-138.2.
SeidleJ,2011.Fundam
entalsofcoalbed
methane
reservoirengineering.Tulsa:PennW
ellBooks.
3.Liao
RQ,Zeng
QH,Yang
L,2012.Naturalgasproduction
engineering.Beijing:PetroleumIndustryPress.
Bibliography
iL
sccd
sci
Lcd
Vh
RP
QP
QV
hR
PP
P
2
2)
(
Fig. 2 Gas and water production of w
ell X1 in QinshuiBasin. Ⅰ
Single-phase water production stage; Ⅱ
Two-phase gas-w
ater production stage; ⅢStable gas production stage; Ⅳ
Declining gas production stage.
IntroductionCoal
seamgas
(CSG)is
known
asan
important
unconventionalnaturalgas
resourceand
them
itigationand
utilizationofCSG
cansignificantly
reducethe
gas-relatedm
ininghazards
suchas
gasexplosion
andgas
outburstand
reducegreenhouse
gasem
ission.The
dynamics
ofreservoir
pressureare
keyfactors
indeterm
iningthe
effectivedesorption
range,theinterw
ellinterference,andgas
productivity.Theobjectivesofthisstudy
areto
establisha
modelto
calculatethe
dynamics
ofreservoir
pressureand
bottom-hole
pressure(BHP)during
CSGproduction
andon
thisbasis,to
analysethe
influencesof
reservoirpressure
dynamics
onCSG
production.Firstly,a
newm
ethodw
asproposed
tocalculate
thedynam
icsof
reservoirpressure
with
considerationsof
CSGsorption
andproduction
data.Then,
with
thedeliverability
equationunder
pseudosteady-stateflow,the
variationsofBHP
were
analysedand
compared.
Methods
CCSG A1 Posters 2016.indd 3 11/08/2016 4:46 PM
