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PETROLEUM RESERVOIR ENGINEERING Physical Properties

McGraw-Hill Classic Textbook Reissue Series AMYX, BASS and WHITING: Petroleum Reservoir Engineering: Physical Properties CHOW: Open-Channel Hydraulics DAVENPORT: Probability Random Process: An Introduction for Applied Scientists and Engineers DRAKE: Fundamentals of Applied Probability Theory GOODMAN: Introduction to Fourier Optics HARRINGTON: Time-Harmonic Electromagnetic Fields HINZE: Turbulence KAYS and CRAWFORD: Convective Heat and Mass Transfer KRYNINE and JUDD: Principles of Engineering Geology and Geotechnics MEIROVITCH: Methods of Analytical Dynamics MELSA: Linear Control Systems MICKLEY: Applied Mathematics in Chemical Engineering PAPOULIS: The Fourier Integral and Its Applications PHELAN: Fundamentals of Mechanical Design SCHLICHTING: Boundary Layer Theory SCHWARTZ and SHAW: Signal Processing: Discrete Spectral Analysis, Detection, and Estimation TIMOSHENKO: Theory of Plates and Shells TIMOSHENKO and GOODIER: Theory of Elasticity TIMOSHENKO and GERE: Theory of Elastic Stability TREYBAL: Mass-Transfer Operations TRUXAL: Introductory Systems Engineering WARNER and McNEARY: Applied Descriptive Geometry WELLMAN: Technical Descriptive Geometry

PETROLEUM RESERVOIR ENGINEERING Physical Properties JAMES W. AMYX DANIEL M. BASS, JR. ROBERT L. WHITING The Agricultural and Mechanical College of Texas

efill'>'APITtn

McGRAW-HILL

CLASSIC

TEXTB+2

c ..~ and C,.H2n-' C.If,,._, C,.H2n--' C.H2n--" C..H:n-a C..H:m-tt CJI:m-12 and C..H:z..-11

C,.ffi,.-t C,.H,,..., C,.H2n....s and C,.H2n-u CJitn-a and C..H2-12 C,.H2n-8 and CnH:i-u

C,.H:z,,.-1a

CJI:z..._14

C..H:..-20

of series identified in petroleum. Of these series, the most commonly encountered are the paraffins, the olefines, the polymethylenes, the acetylenes, turpenes, and benzenes. Natural gas is composed predominantly of the lower-molecular weight hydrocarbons of the paraffin series. Hydrocarbons can be classified into essentially four categories depending on the structural formula. Two of the categories refer to the structural arrangement of the carbon atoms in the molecule. These are (1) open chain and (2) ring or cyclic compounds. The remaining two categories refer to the bonds between the carbon atoms. These are (1) saturated or single bond and (2) unsaturated or multiple-bond compounds. The names of the various individual hydrocarbon molecules are derived in a systematic fashion from rules established by the International Union of Chemistry. The established names of the individual hydrocarbons of the paraffin series are utilized for compounds having the same number of

Kerogen Bituminous shale

{

Petroliferous

Mineral wax (ozocerite)

Cereous

ists in unsaturated hydrocarbons, the ending is modified to indicate the number of double bonds; thus, two double bonds are designated by "diene," three double bonds by "triene," etc. Ring or cyclic compounds are designated by adding the prefix "cyclo" to the name of the compound as derived from the above rules. However, the cyclic aromatic hydrocarbons, benzenes, retain the customary names except that the ending "ene" is used rather than the older form~, benzol, etc. The structural formulas of various hydrocarbons that have SIX carbon atoms are shown below. The group name and group formula of each series are designated Paraffin (alkane),

c..H211+2

H H H H H H

I

I

I

I I

I

!

I

I

I

I

H-C-C-C-C-C-C-H

I

H H H H H H Normal Hexane, CJI14

Olefin (alkene), C.H,,.

H H H H H H

I

I

I

I

I

I

I

I

I

I

H-C-C-C-C-C~

H H H H Normal Rexene, CJI1:r

I

H

-----

4

-------

INTRODUCTION

PEI'ROLEUM RE.SERVOm ENGINEERING

Polymethylene (cycloalkane), C,.Hin

H

H

b

~

H-0

I

/I

H/

~~

H/

"/ H 0

~ /"

H

0

"

I

H

H

Cyclohexane, C6H 12

Benzene, CaH6

Alkadiene, C,.H211-:

H H

I

!

H

I

H H H

I

I

Degrees

API

0

~

0-H

I" H

0

0-H

I

H-0

~ /H

·H" /

/H

I

I I H H

I H

Hexadiene-1,5, CJI1n

Physical Properties of Hydrocarbons The detailed analysis of a crude oil is virtually impossible to obtain. Therefore, crude oils are classified according to their physical properties. Among the physical properties commonly considered in various classifications are color, refractive index, odor, density, boiling point, freezing point, flash point, and viscosity. Of these, the most important physical properties from a classification standpoint are the density (specific gravity) and the viscosity of the liquid petroleum. The specific gravity of liquids is defined as the ratio of the density of the liquid to the density of water, both at specified conditions of pressure and temperature. The specific gravity of crude oils ranges from about 0.75 to 1.01. Since crude oils are generally lighter tban water, a Baum&.type scale is used in the petroleum industry. This scale is referred to as the API or (American Petroleum Institute) scale for crude petroleum and relates the specific gravity through a modulus to an expression of density called API gravity. Expressed mathematically 141.5 'Y = 131.5 + 0 API

OAP! = 141.5 - 131.5

or

'Y

where

'Y

is the specific gravity and 0 API is the API gravity. It may be

Degrees Weight of of specific gallon, lb gravity

SPECIFIC GRAVITY, A.ND WEIGHT .

API

of

of

Degrees

API

specific

gallon,

gravity

lb

Weight of

Degrees

Degrees Weight Degrees

of specific gravity

gallon,

lb

8.962 8.895 8.828 8.762 8.698 8.634

36 37 38 39 40

0.8448 0.8398 0.8348 0.8299 0.8251

7.034 6.993 6.951 6.910 6.870

71 72 73 74 75

0.6988 0.6953 0.6919 0.6886 0.6852

5.817 5.788 5.759 5.731 5.703

1.0000

8.571 8.509 8.448 8.388 8.328

41 42 43 44 45

0.8203 0.8155 0.8109 0.8063 0.8017

6.830 6.790 6.752 6.713 6.675

76 77 78 79 80

0.6819 0.6787 0.6754 0.6722 0.6690

5.676 5.649 5.622 5.595 5.568

11 12 13 14 15

0.9930 0.9861 0.9792 0.9725 0.9659

8.270 8.212 8.155 8.099 8.044

46 47 48 49 50

0.7972 0.7927 0.7883 0.7839 0.7796

6.637 6.600 6.563 6.526 6.490

81 82 83 84

85

0.6659 0.6628 0.6597 0.6566 0.6536

5.542 5.516 5.491 5.465 5.440

16 17 18 19 20

0.9593 0.9529 0.9465 0.9402 0.9340

7.989 7.935 7.882 7.830 7.778

51 52 53 54 55

0.7753 0.7711 0.7669 0.7628 0.7587

6.455 6.420 6.38/i 6.350 6.316

86 87 88 89 90

0.6506 0.6476 0.6446 0.6417 0.6388

5.415 5.390 5.365 5.341 5.316

21 22 23 24 25

0.9279 0.9218 0.9159 0.9100 0.9042

7.727 7.676 7.627 7.578 7.529

56 57 58 59 60

0.7547 0.7507 0.7467 0.7428 0.7389

6.283 6.249 6.216 6.184 6.151

91 92 93 94 95

0.6360 0.6331 0.6303 0.6275 0.6247

5.293 5.269 5.246 5= 5.199

26

27 28 29 30

0.8984 0.8927 0.8871 0.8816 0.8762

7.481 7.434 7.387 7.341 7.296

61 62 63 64 65

0.7351 0.7313 0.7275 0.7238 0.7201

6.119 6.087 6.056 6.025 5.994

96 97 98 99 100

0.6220 0.6193 0.6166 0.6139 0.6112

5.176 5.154 5.131 5.109 5.086

31 32 33 34 35

0.8708 0.8654 0.8602 0.8550 0.8498

7.251 7.206 7.163 7.119 7.076

66 67 68 69 70

0.7165 0.7128 0.7093 0.7057 0.7022

5.964 5.934 5.904 5.874 5.845

0 1 2 3 4 5

1.076 1.068 1.060 1.052

6 7 8 9 10

1.029 1.022 1.014 1.007

C=C-0-0-0=0

I H

AP!,

PER GALLON OF CRUDE On}

H

"cf H" /

TABLE 1-3. RELATION OF

Benzene (aromatic), C..H!n-1

1.044

1.037

I

I

-- ---

----

----------

--------

INTRODUCTION TABLE 1-4. VALUES FOR CONVERTING KINEMATIC VISCOSITY TO

noted that the API gravity yields numbers greater than 10 for all materials having specific gravities less than 1. Since the density of a liquid is a func-

SAYBOLT UNIVERSAL Vrscos1TY2

Equivalent Saybolt Universal viscosity, sec

Equivalent Saybolt Universal viscosity, sec Kinematic viscosity, cs

At 100°F (basic values, see Note)

At 130°F

At 210°F

2.0 2.5 3.0 3.5· 4.0

32.6 34.4 36.0 37.6 39.1

32.7 34.5 36.1 37.7 39.2

32.8 34.6 36.3 37.9 39.4

4.55.0

40.7 42.3

40.8 42.4

41.0 42.6

6.0 7.0 8.0 9.0 10.0

45.5 48.7 52.0 55.4 58.8

45.6 48.8 52.1 55.5 58.9

45.8 49.0 52.4 55.8 59.2

11.0 12.0 13.0 14.0 15.0

62.3 65.9 69.6 73.4 77.2

62.4 66.0 69.7 73.5 77.3

16.0 17.0 18.0 19.0 20.0

81.1 85.1 89.2 93.3 97.5

21.0 22.0 23.0 24.0 25.0 26.0 27.0 28.0 29.0 30.0

Kinematic viscosity, cs

31 32 33 34 35

_..\.t 100°F (basic values, see Note) 145.3 149.7 154.2 158.7 163.2

130°F

At 210°F

145.6 150.0 154.5 159.0 163.5

146.3 150.7 155.3 159.8 164.3

At

7

tion of temperature and pressure, it is necessary to designate standard

conditions for reporting specific grayity and API gravity. The petroleum industry has adopted as standards a temperature of 60°F and atmospheric pressure. Table 1-3 lists the refationship between API gravity and other commonly used expressions of the density of petroleum liquids. The viscosity of crude oil ranges from about 0.3 centipoise for a g'd.Ssaturated oil at reservoir conditions to about 1,000 centipoises for a gasfree crude oil at atmospheric pressure and 100°F. Viscosities of crude-oil and liquid-petroleum products are frequently reported in terms of the time

of efflux, in seconds, of a known volume of liquid through a standardized orifice. The times reported depend on the instrument employed such as Saybolt Universal, Saybolt Furol, Engler, or other similar device. The time of efflux from such instruments has a complex functional relationship

39 40

167.7 172.2 176.7 181.2 185.7

168.0 172.5 177.0 181.5 186.l

168.9 173.4 177.9 182.5 187.0

62.7 66.4 70.l 73.9 77.7

41 42 43 44 45

190.2 194.7 199.2 203.8 208.4

190.6 195.1 199.6 . 204.2 208.8

191.5 196.1 200.6 205.2 209.9

81.3 85.3 89.4 93.5 97.7

81.7 85.7 89.8 94.0 98.2

46 47 48 49 50

213.0 217.6 222.2 226.8 231.4

213.4 218.0 222.6 227.2 231.8

214.5 219.1 223.8 228.4 233.0

101.7 106.0 lI0.3 l14.6 l18.9

101.9 106.2 110.5 114.8 119.1

102.4 106.7 lII.l l15.4 l19.7

55 60 65 70

254.4 277.4 300.4 323.4

254.9 277.9 301.0 324.0

256.2 279.3 302.5 325.7

123.3 127.7 132.1 136.5 140.9

123.5 127.9 132.4 136.8 141.2

124.2 128.6 133.0 137.5 141.9

Over 70

Saybolt

Saybolt see = cs x 4.629

36 37 38

I

sec =cs x 4.620

Saybolt = cs x 4.652

sec

NOTE: To obtain the Saybolt Universal viscosity eauivalent to a kinematic viscosity determined at t°F, multiply the equivalent Saybolt ~Universal viscosity at 100°F by I + (t - 100)0J)00064; for example, 10 cs at 210°F is equivalent to 58.8 X 1.0070 or 59.2 Sa.ybolt Universal seconds at 2I0°F. 6

to the kinematic viscosity, which is usually expressed in centistokes. The absolute viscosity in centipoises is obtained by multiplying the kinematic viscosity in centistokes by the density of the fluid in grams per cubic centimeter. Table 1-4 gives the relationship between the Saybolt Universal viscosity and centistokes. Viscosity is dependent on temperature. There-

fore, standard tests with the Saybolt viscosimeter are conducted at 100°F. Other physical properties of liquid petroleum are frequently correlated with API gravity and viscosity. In general, such correlations have rather limited application. Crude oils are frequently classified by "base." The earliest such classification system provided three classifications: 1. Paraffin-base, or oils containing predominantly paraffin series hydrocarbons 2. Asphalt-base, or oils containing predominantly polymethylene or olefin series hydrocarbons 3. Mixed-base, or oils containing large quantities of both paraffin and polymethylene series hydrocarbons

The U.S. Bureau of Mines' introduced a somewhat more elaborate system of classification which provides for nine possible classifications. This system is based on a modified Hempel distillation of the crude oil and upon the API gravity of certain fractions obtained upon distillation. The distillation is conducted in two phases: one at atmospheric pressure and one at an absolute pressure of 40 mm of mercury. The fraction boiling between 482 and 527°F at atmospheric pressure is key fraction 1. The fraction boiling between 527 and 572°F at 40 mm absolute is key fraction 2. The nine possible classifications of a crude oil are summarized in Table 1-5. The U.S. Bureau of Mines reported the average results of distillations of

8

PEI'ROLEUM RESERVOIR ENGINEERING

q

TABLE 1-5. U.S. BUREAU OF MINES CLASSIFICATION OF CRUDE 0ILs3

Key fraction 1, °F

Key fraction 2, °F

Paraffin

40 or lighter

Paraffin-intermediate Intermediate-paraffin Intermediate Intermediate-naphthene Naphthene-intermediate Naphthene

40 or lighter

30 or lighter 2()-30 30 or lighter 2()-30 20 or heavier 2()-30 20 or heavier 20 or heavier 30 or lighter

Oil

Para:ffin-naphthene N aphthene-paraffin

33-40 33-40 33-40 33 or heavier 33 or heavier 40 or lighter 33 or heavier

303 crude-oil samples from throughout the world. These results appear in Table 1-6. Analyses of this type are useful in evaluating crude oils for refining purposes. Note that of the 303 samples analyzed, 109 samples are classified as intermediate and 83 samples are naphthene base. Natural gas is composed largely of hydrocarbons of the paraffin series. Methane and ethane frequently comprise 80 to 90 per cent by volume of a natural gas. Other hydrocarbons, ranging in molecular weight from 44 (propane) to in excess of 142 (decane), together with impurities compose the remaining percentage. Carbon dioxide, nitrogen, and hydrogen sulfide are the more common impurities found in natural gas. Helium and other inert rare gases occasionally occur in small concentrationf? in natural gases. Gas gravity is widely used to characterize natural gases. Gas gravity is the ratio of the density of a gas at atmospheric pressure and temperature to the density of air at the same condition of pressure and temperature. Since at atmospheric pressure and temperature the densities of gases are directly proportional to the molecular weight, the gravity is the ratio of the molecular weight of the gas to the molecular weight of air. The molecular weight of methane is 16. Therefore, the gravity of pure methane is 0.55 or 16 + 29. Gas gravities for natural gases range from 0.6 to 1.1, depending on the relative concentration of the heavier hydrocarbons present in the gas. Compositional analyses of natural gases are readily obtained by lowtemperature distillation, chromatography, or mass spectrometry. Volume or mole percentages of the individual components present are ordinarily reported through heptanes plus. The heptanes-plus fraction includes heptane and all heavier hydrocarbons. Natural gases are also described as dry or wet gases depending on the amount of condensable hydrocarbons present in the mixture. Pentane and heavier components are considered to be condensable hydrocarbons, as at atmospheric pressure and temperature pure pentane exists as a liquid.

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