wellbore storage + skin
DESCRIPTION
Wellbore Storage + SkinTRANSCRIPT
4. Solusi Persamaan aliran radial silindris dibawah pengaruh Wellbore Storage dan SkinSelama sumur ditutup, tekanan reservoir akan menopang kolom fluida di lubang bor sebatas mana ditentukan oleh kesetimbangan antara tekanan formasi dan berat kolom fluida.
Apabila sumur tersebut diproduksikan dengan membuka kerangan di permukaan, mula-mula minyak yang diproduksikan hanya berasal dari apa yang ada di lubang bor, sedangkan laju produksi mula-mula dari formasinya sendiri sama dengan nol.
Dengan bertambahnya waktu aliran, laju aliran didasar sumur akan berangsur-angsur sama dengan laju aliran dipermukaan.
Fluid-Filled Wellbore - Unloading
Rat
e
Time
Bottomhole Rate
Surface Rate
wbwb
sfw
cVBqq
dtdp
24
q
qsf
q = laju alir di permukaanqsf = laju alir di muka formasi
Berdasarkan persamaan kesetimbangan materi di lubang sumur dan laju akumulasi fluida di lubang sumur adalah :
Dengan anggapan luas luabnag sumur sama disemua tempat dan faktor volume formasi konstan maka dapat dituliskan persamaan kesetimbangan :
Fluid-Filled Wellbore - Afterflow
Rat
e
Time
Bottomhole Rate
t=0
Surface Rate
wbwb
sfw
cVBqq
dtdp
24
q
qsf
dtdPC1qq w
Dsf
Pada saat persamaan diatas akan menjadi : 0qqsf
dtdPC1 w
D
atau DD tlogdPlogClog
Characterizing Damage and Stimulation
Characterizing Damage and StimulationInstructional Objectives
1. List causes of damage skin2. List causes of geometric skin3. Calculate skin from pressure drop4. Calculate flow efficiency from skin5. Calculate skin factor and wellbore radius 6. Convert skin to fracture half-length
Damage Caused by Drilling Fluid
Mud filtrateinvasion
Damage Caused by Production
p < pb p > pb
Damage Caused by Injection
“dirty”water
incompatiblewater
Reservoir Model of Skin Effect
Bulkformation
h
rw
ka
ra
k
Alteredzone
Reservoir Pressure Profile
500
1000
1500
2000
1 10 100 1000 10000Distance from center of wellbore, ft
Pres
sure
, psi
ps
Skin and Pressure Drop
spqB
hk00708.0s
Skin and Pressure Drop
skh
qB2.141ps
Skin Factor and Properties of the Altered Zone
w
a
a rrln1
kks
Skin Factor and Properties of the Altered Zone
wa
a
rrlns1
kk
Effective Wellbore Radius
w
warrlns
swwa err
Minimum Skin Factor
w
emin r
rlns
Minimum Skin Factor Example
3.75.0
745lnrrlnsw
emin
Geometric Skin - Converging Flow to Perforations
Geometric Skin - Partial Penetration
h
hp
Partial Penetration
hp
ht
h1
pdp
t sshhs
Partial PenetrationApparent Skin Factor
21
11
2ln1
2ln11
BA
hh
hrhs
pD
pD
pDDpDp
21
h
v
t
wD k
khrr
tppD hhh
tD hhh 11
41
1 pDD hhA
431
1 pDD hhB
Geometric Skin - Deviated Wellbore
sechh
sss d
Deviated Wellbore Apparent Skin Factor
100log
5641
865.1'06.2'Dww hs
wh
vw k
k tantan 1'
v
h
wD k
krhh
Geometric Skin - Well With Hydraulic Fracture
Lf
Skin Factor and Fractured Wells
2Lr f
wa
waf r2L
Completion Skin
dpdp ssss
d
R
dp
R
p
dp
pdp k
kkk
rr
nLhs ln
rdp
Lp
kR
kdp
kd
rp
rd
rw
After McLeod, JPT (Jan. 1983) p. 32.
Gravel Pack Skin
Lg
Cement
22 pgp
gRgp rnk
hLks
Productivity Index
wfppqJ
Flow Efficiency
wfswf
idealactual
f ppppp
JJE
Flow Efficiency and Rate
foldfnew
oldnew EEqq