PETE 310 - Petroleum Engineering at Texas A&M University

PETE 310

Lectures #22 & #23

Chapter 11: Pages 317‐19, 321‐22, 326‐333

Liquid Density

Calculated using ideal solution principles (i.e. additive volumes & masses)

∑

∑

=

==ρ Nc

ii

Nc

ii

V

m

1

1

Evaluation Methods

Composition of saturated liquid known (iterative procedure)

Composition of saturated liquid known (correlations)

Solution Gas‐Oil, Gas Composition, and Stock‐Tank oil gravity known

Solution Gas‐Oil, Gas Specific Gravity, and Stock‐Tank oil gravity known

Less information

Problems

C1 & C2 are not liquids at atmospheric conditionsA liquid mixture at reservoir conditions will partially vaporize at standard conditionSolution

Create a fictitious pseudo density for C1 and C2 and for the liquid

Pseudo‐densities of C1 & C2

C1

C2

Mixture Density (stc)

Apparent liquid densities of C1 and C2

Page 302 (figure 11.2)

Equations from Appendix B (starting page 509)

poC,a

poC,a

..

..

ρρ

ρρ

31670315

45003120

2

1

+=

+=

Pressure Correction

( ) )(),(, RscscatRsc PPTPT ρρρ Δ+=

47.4 = 45 + 2.4

Temperature Correction

( ) )(),(, RRscRR TPTPT ρρρ Δ−=

47.4 = 45 + 2.4

From previous plot

43.4 = 47.4 ‐ 4

Now follow examples in Excel files provided in our WEB site

Correction using W1, W2

Correction for H2S

42.1 = 43.4 – 1.3

Apparent Liquid Densities of Gases

Consolidate Oil Reservoir Density Calculations

Methods DiscussedGiven composition of saturated liquid‐ iterative procedure (guess contribution of C1 & C2) –Excel file & Ex. 11‐4Given composition of saturated liquid‐correlation ‐ using W1 & W2 – Excel file & Ex. 11‐5Given solution gas‐oil‐ratio, gas composition and stock tank oil gravity (or API) – Excel file & Ex. 11‐6


Methods Discussed (cont.)All these methods evaluate oil density in stagesa) Pseudo‐oil at Tsc, Psc

b) Correct oil density in (a) 1st for reservoir pressure

c) Correct density in (b) for reservoir temperature

JCPT paper method & Example 11‐7 of text book


JCPT paper method & Example 11‐7 of text bookBoth require solution gas‐oil‐ratio, separator gas gravity, API gravity of stok tank, pressure, and temperatureJCPT includes a more current correlationBoth calculate pseudoliquid density at standard conditions and adjust for reservoir pressure and temperature using same equations as in the other methods.Compare densities from both methods

Oil density is at or below pb


Example 11‐7 highlights…Given data: API, Rs, T, p, γgs Find molecular weight of gas as

Find mass of gas dissolved in one STB of oil as

Find mass of oil in 1 STB as… (your turn!)

[ ]molelblb

SCFmolelb

STBSCFM

VR

wgidM

s

−×

−×=×

29M gswg ×γ=


Example 11‐7 highlights… (more)Pretend that the oil components are two: stock tank oil & surface gas

Figure 11.8


Compare the densities obtained by JCPT procedure with that from Example 11‐7

Discuss results

Different evaluation methods will result in different values of Bo


The oil formation volume factor is evaluated at or below pb

How do we evaluate Bo above the bubble point?

OR

gssSTOo

R01357.0B

ργ×+ρ

=

For Pressures Above pb

The Oil Density Above Pb

Coefficient of Isothermal Compressibility of Oil (Co)

Why??

Correlations for Co

Above bubblepoint pressure (undersaturated)

Below bubblepoint pressure (saturated)

Co for pressures higher than pb

Co for pressures above pb (Appendix B –page 522)

Co for pressures below pb

Oil volume will change because ofPressure

Gas in solution

⎥⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

−⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

=

⎥⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

−⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

−=

−

−

s

og

s1oo

1o

sg

s

s

oo

RBB

pRBC

Bp

RBp

RRBC

1o

sg

oo B

pRB

pBC −

⎥⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

−⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

−=

Co for pressures below pb

You can evaluate Co using the methods of JCPT paper…

Need to have Bg

⎥⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

−⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

=

⎥⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

−⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

⎟⎟⎠

⎞⎜⎜⎝

⎛∂∂

−=

−

−

s

og

s1oo

1o

sg

s

s

oo

RBB

pRBC

Bp

RBp

RRBC

Co for p < pb

Co for pressures below pb (Appendix B)

Bo for pressures below pb

These ancient plots are useful to…

Establish ranges of applicability (API, Rs, p…)Determine trends for the physical properties as a function of p, T, API, etc.

Does Bo increase with Rs?Does Bo increase with API?

Provide quick estimates (sometimes)Exercise our visual skills

Total Formation Volume Factor

Oil Viscosity

Viscosity is a measure of the resistance to flow exerted by a fluid

This is called dynamic viscosity and has units ofcentipoise = g mass / 100 sec cm

Kinematic viscosity is viscosity / density, units are in centistokes = centipoise /g/cc

Needs of Crude Oil Viscosity

Calculation of two‐phase flow

Gas‐lift and pipeline design

Calculate oil recovery either from natural depletion or from recovery techniques such as waterflooding and gas‐injection processes

Variation of Oil Viscosity O

il Vi

scos

ity

T = constant

Pb

Single Phase FlowTwo Phase Flow

Gas Out of Solution

Evaluation of Oil Viscosity

Evaluate dead oil viscosity (no gas in solution) given oil API and reservoir temperature (Figure 11‐13)

Correct for pressure by “adding gas in solution” (Fig 11‐14)

Most of the oil viscosity correlations are oil dependent (large errors)

Dead Oil Viscosity

Dead Oil Viscosity (Appendix B)

Saturated Oil Viscosity (add gas)

Saturated Oil Viscosity (Appendix B)

Oil Viscosities above pb

Oil Viscosity Above Pb

No correction for p =pbLarger corrections for higher pressures

pbp> pb

Viscosity of Undersaturated Black Oils

Viscosity Correlations

Judge These Oil Viscosity Correlations

Judging Correlations…

Judging Viscosity Correlations…

Judging Bubble Point Correlations

1600

1800

2000

2200

2400

2600

2800

3000

Bub

ble

Poin

t, ps

ia

0 5 10 15 20Correlation

Bubble PointCorrelation Comparison

Untitled

Reg: CPTC PSS - Chevron Oil Corporation

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Viscosity References

Oil Viscosity References

PETE 310 - Petroleum Engineering at Texas A&M University

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