the spe foundation through member donations and a ... · pvt report – an old hat? yes decades of...
TRANSCRIPT
Primary funding is provided by
The SPE Foundation through member donations
and a contribution from Offshore Europe
The Society is grateful to those companies that allow their
professionals to serve as lecturers
Additional support provided by AIME
Society of Petroleum Engineers
Distinguished Lecturer Program www.spe.org/dl
Klaus Potsch
Consultant, EC&C
Society of Petroleum Engineers
Distinguished Lecturer Program www.spe.org/dl
Understanding and Checking the
Validity of PVT- reports
3
PVT report – an old hat?
Yes
Decades of experiments
and reports
But with new feathers:
Improved equipment
Improved reporting
Needs new quality control
People forgot how to wear it
General ignorance about
how fluid properties are
determined and reported
4
Sampling
Black Oil systems
Gas Condensate systems
Flow assurance
Summary
Outline
5
Motivation
To know the fluid properties
from the reservoir
to the facilities
to the refinery Drilling mud invasion
Bottom hole sampling
Gas coning
Water coning
Condensate banking
Formation of a gas cap
Condensate dropout
Fluid – Fluid Interaction -> EOR
= Enhanced Oil Recovery
6
What are the data good for?
Reservoir engineer:
simulation (black oil or compositional),
well models
Facility engineer:
designs surface installations (simulation with process SW),
design of transportation routes
Economics:
reserves;
commodities (quality = price) stock tank oil, NGL,
condensate, gas
7
Starting point = reservoir fluid samples
Goal: information about the composition and quality
Essential, whether bottom hole sample (BHS) or
surface sample (SS):
Reservoir conditions (p,T,depth) experiments
Sampling conditions (p,T,V=rates) experiments
Sample only single phase streams
Sample only a conditioned well = clean and stable flow
Sample as early as possible
Laboratory work starts with good, representative samples.
Impossible to get good results from non representative
samples (garbage in, garbage out).
8
Bottom hole sampling
Danger: OBM mixed with reservoir fluid decontamination
Tracers help!
Artificial mud Diesel
0 10 20 30 40
single carbon number
mo
l%
0 10 20 30 40
single carbon number
co
ncen
trati
on
1.01
OBM
clean
9
Separator sampling
What is the flow rate and the retention time (size of the
separator)?
Is carry-over or carry-under significant?
Are the rates stable?
How high is the pressure?
How many phases are recorded?
inlet
oil + carry under
water
gas + carry over
10
Separator sampling, cont‘d.
Where is the reservoir in the phase diagram?
Gas phase is at a dew point
Liquid phase is at a bubble point
sat
vapor
sat
liquidpp
temperature
ab
so
lute
pre
ss
ure
res fluid
sep gas
sep liquid
separator
condition
11
Separator samples
reservoir
fluid
pres,Tres,zk
Reservoir Surface separator Laboratory
separator gas
psep,Tsep,yk
separator liquid
psep,Tsep,xk
gas 1
pamb,Tamb,yyk
liquid 1
pamb,=Tamb,yxk
GLR 1
Kyk=yyk/yxk
gas 2
pamb,Tamb,xyk
liquid 2
pamb,Tamb,xxk
GLRsep,Kk=yk/xk
GLR 2
Kxk=xyk/xxk
BHS SS
12
Samples (SS), validity checks
Was a valve leaking?
Liquid: Determinig psat at ambient condition and recalculating
to sampling condition.
Gas: p.V/T should be the same at ambient and sampling
conditions
13
Samples (SS), analyses
Analyses by gas and liquid
chromatography
earlier times now
scn Component scn Component
H2 0 Hydrogen 6 Benzene
H2S 0 Hydrogen
Sulphide 6 Cyclohexane
CO2 0 Carbon Dioxide C7 7 Heptanes
N2 0 Nitrogen 7 Methyl-Cyclo-
Hexane
C1 1 Methane 7 Toluene
C2 2 Ethane C8 8 Octanes
C3 3 Propane 8 Ethyl Benzene
iC4 4 iso Butane 8 Meta/Para-Xylene
nC4 4 normal Butane 8 Ortho-Xylene
neo
C5 5 neo-Pentane C9 9 Nonanes
iC5 5 iso Pentane 9 1,2,4-Tri-Methyl-
Benzene
nC5 5 normal Pentane C10 10 Decanes
C6 6 Hexanes …..
6 Methyl-Cyclo-
Pentane
C36
+
Hexatriacontanes
Plus
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Quality check of sample compositions
via equilibrium- or K-values (Wilson, Hoffman, etc) versus
characterization factor, e.g.
-8
-6
-4
-2
0
2
4
6
8
-6 -4 -2 0 2 4 6 8
ln K
characterization factor F
experimental data
Wilson's estimates
regression
15
Reservoir fluid: composition
BHS: mathematical recombination
SS: mathematical and physical recombination
Reservoir fluid: properties
Experiments, that mimic the flow process
Correlations for Black Oil (BO)
EOS
16
Experiments, mimicking the flow process
Black Oil (BO):
Gas gets out of solution, moves
upward, forms a gas cap
2phase flow into the well bore,
different mobilities, GLR
questionable
CCE
DLE
CCE
CVD
Gas Condensate (GC):
Formation of a condensate bank, in case of
lean condensate immobile well stream
composition reservoir composition
Rich condensate: 2-phase flow into the well
bore, different mobilities,
GLR questionable
17
Constant composition expansion (CCE)
p1 p3=pb p4 p5 p6 p7 p2
> > > > > >
BO:
p1 p3=pd p4 p5 p6 p7 p2
> > > > > >
GC:
Test: Y(p)=(p/psat-1)/(Vt /Vsat-1) linear in p
ln (
cell
vo
lum
e)
absolute pressure
pb
1ph
2ph
p.V
/Z1p
h
absolute pressure
18
Constant composition expansion (CCE)
GC
theory
pdew
1ph 2ph
experiment
BO
Determination of saturation pressure
dV/dp is discontinuous
saturation pressure pb
p>pb: compressibility Cp=O (10-3) [MPa-1]
d(pV/Z1ph)/dp is discontinuous
saturation pressure pd
Z1ph from overall-composition
SPE36919
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BO: Differential liberation experiment (DLE)
Principle:
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BO: Differential liberation experiment (DLE)
Gas in solution – Rs(p) determines the volumetric behavior
Test 1: Bo(Rs(p)) almost linear in Rs
Rs
Bo
21
BO: Differential liberation experiment (DLE)
Test 2:
Ct = Bo(patm)-1 =
= O (10-3) [K-1]
22
BO: Differential liberation experiment (DLE)
Test 3: Y-function, use Vg,lib(p) for Vt, (not in textbooks) and Zg
(check with REFPROP from NIST)
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
0.0 0.2 0.4 0.6 0.8 1.0
Y
pr
Y_CCE
Y_DLE
23
BO: Differential liberation experiment (DLE)
Test 4: ln(µo(patm)/µo(p)) similar shape as Bo(p), (not in textbooks)
Bo(p) -Bo(p_atm)
ln(µ
o(p
_a
tm/µ
o(p
))
24
BO: Differential liberation experiment (DLE)
Test 5: well stream composition, concentation of light components
(N2, C1, possibly CO2 and C2 are convex, the rest is concave)
abs.pressure
ln c
on
ce
ntr
ati
on
CO2 N2 C1 C2 C3
iC4 nC4 iC5 nC5 C6
Rsd
,Rsf
abs.pressure
Rsd
Rsfb
Rsd-Rsf
Rsf
Rsf_ lit
CCE
0
25
BO: Production process
Combination of DLE (reservoir) and CCE (tubing)
Flash (CCE) Bof,Rsf < diffferential (DLE) Bod,Rsd
.
:
constR
R
pp
sd
sf
b
Bo
d,B
of
abs.pressure
Bod
Bofb
Bof
Bof_lit
Bod-Bof
CCE
1
26
BO: Production process
.
:
constRR
BB
pp
sfsd
ofod
b
27
GC: Constant volume depletion (CVD)
Principle
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GC: Constant volume depletion (CVD)
Test 1: VlCCE(p) > Vl
CVD(p) …liquid drop out
0
5
10
15
20
25
0 100 200 300 400 500 600
p abs [bar]
Vl/
Vd
%
CCE
CVD
29
Constant volume depletion (CVD)
Test 2: Y-function, using 1+Vwell stream(p) slightly curved, close to YCCE,
(not in textbooks)
1.30
1.35
1.40
1.45
1.50
1.55
1.60
1.65
1.70
1.75
100 200 300 400
p abs [bar]
Yv
Yv_CVD
Yv_CCE
30
Correlations
Estimates for Black Oil – tables
General form:
pb = fb(Tres,rSTO,rSTG,Rs)
Bo = fB(Tres,rSTO,rSTG,Rs)
µo = fµ(Tres,rSTO,rSTG,Rs)
µg calculated from Gonzales, Eakin
Zg from REFPROP (developed by NIST)
31
Equations of State - EOS
input = composition
try to match the experiments
prerequisite: C6+ modeling
reveals the inconsistencies
mind the errors of the field measurments
best worst monophasic BHS 0% invalid separator GOR 5 % 25 % human or equipment failure 0 % invalid BHP 0.01 1 % 3 %
BHT 0.25 1 % 5 %
32
Flow Assurance
Gas hydrates: gas composition necessary
Paraffins
Saturates, aromates, resins, asphaltenes
SARA or PNA analysis
Heavy end liquid chromatography
Wax appearance temperature (WAT) cold finger test
Asphaltenes
SARA or PNA or IP44
Flow test with capillary
33
Summary
Starting point for determination of fluid properties:
quality-sampling
Tools exist to check the laboratory data
Estimates can be gained via correlations or EOS
Further reading
Ahmed, T.; Hydrocarbon Phase Behavior. Gulf Publishing Co,
1989.
Bon J., Sarma H., Rodrigues T., Bon J.; Reservoir-Fluid
Sampling Revisited – A Practical Perspective, SPE101037.
Danesh, A.; PVT and Phase Behaviour of Petroleum
Reservoir Fluids; Elsevier 2008.
Michelsen, M.L.; Mollerup, J.M.; Thermodynamic Models,
Fundamentals and Computational Aspects; Tie-Line
Publications, 2004.
Moffat B.J.; Williams J.M.; Identifying and Meeting the Key
Needs for Reservoir Fluid Properties. A Multidisciplinary
Approach, SPE49067.
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Further reading
Pedersen, K.S.; Fredenslund, A.; Thomassen, P.; Properties
of Oils and Natural Gases. Gulf Publishing Co, 1989.
Prausnitz, J.M.,Lichtenthaler, R.N.,Gomez de Azevedo, E;
Molecular Thermodynamics of Fluid Phase Equilibria.
2nd edition, Prentice Hall, 1985.
Riazi, M.R.;Characterization and Properties of Petroleum
Fractions, ASTM manual series MNL50; 2005
Whitson, C.H.; Brulé, M. R.; Phase Behavior;
SPE Monograph, volume 20, 2000.
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