the spe foundation through member donations and a ... · pvt report – an old hat? yes decades of...

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

14

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

19

BO: Differential liberation experiment (DLE)

Principle:

20


Gas in solution – Rs(p) determines the volumetric behavior

Test 1: Bo(Rs(p)) almost linear in Rs

Rs

Bo

21


Test 2:

Ct = Bo(patm)-1 =

= O (10-3) [K-1]

22


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


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


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

28

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.

34

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.

35

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