PVT ANALYSIS

FIVE RESERVOIR FLUIDS

1. Black oil: GOR of 2000 scf/STB or less. stock tank oil gravity is usually below 45º API. stock tank oil is dark indicating of presence heavy

hydrocarbons. Color is often black or brown.

PHASE DIAGRAM OF BLACK OIL:

EXERCISE 1:

The reported production from the discovery well of the Nancy Field is given below. How would you classify this reservoir fluid?

PRODUCTION DATA

Date(month) API Oil ,STB Gas , Mscf

1 29 4276 1165

2 28 16108 5270

3 28 15232 4800

4 28 15585 4960

5 28 15226 4650

6 28 14147 2335

7 28 15720 4707

8 28 15885 4904

9 28 15434 4979

10 28 12862 4339

11 28 14879 4814

12 28 15192 4270

PRODUCTION DATA

Date(month)

API Oil ,STB Gas , Mscf

GOR

1 29 4276 1165 272

2 28 16108 5270 327

3 28 15232 4800 315

4 28 15585 4960 318

5 28 15226 4650 305

6 28 14147 2335 165

7 28 15720 4707 300

8 28 15885 4904 308

9 28 15434 4979 322

10 28 12862 4339 337

11 28 14879 4814 323

12 28 15192 4270 281

FIVE RESERVOIR FLUIDS

Volatile oil: Initial gas-oil ratios between 2000-3300 scf/STB. Stock-tank oil gravity is usually 40 ºAPI or more. Stock tank color is brown ,orange or green. Oil formation volume factor is usually greater than 2.0 res

bbl/STB.

Retrograde Gas:

Initial gas-oil ratio is more than 3300scf/STB up. Practically gas-oil ratios more than 50000 scf/STB are usually

treated as wet gases. Stock-tank oil gravity is between 40 ºAPI and 60 ºAPI. Liquid can be lightly colored, brown, orange greenish or water-

white.

PHASE DIAGRAM OF GAS CONDENSATE:

PHASE DIAGRAM OF VOLATILE OIL:

FIVE RESERVOIR FLUIDS

Wet gas: A wet gas exists solely as a gas in the reservoir throughout the reduction in reservoir pressure.

Produced stock tank liquid gravity is the same as retrograde gas however it doesn’t change during the life of the reservoir.

Dry Gas: is simply methane with some intermediates.

No liquid is formed at the surface.

PHASE DIAGRAM OF WET GAS:

PHASE DIAGRAM OF DRY GAS:

EXERCISE 2:

The annual production statistics for west Oakvale field are given. Classify the reservoir fluid.

Date API Oil STB Water STB

Gas Mscf

1982 46 4646 1484 463,265

1983 50 2608 1177 342075

1984 47 1350 1215 241048

1985 48 1430 932 221,020

1986 50 1662 1122 267,106

1987 51 1110 665 178,951

ANNUAL PRODUCTION

Date API Oil STB Water STB

Gas Mscf

GOR

1982 46 4646 1484 463,265 99712

1983 50 2608 1177 342075 131163

1984 47 1350 1215 241048 182612

1985 48 1430 932 221,020 154559

1986 50 1662 1122 267,106 160713

1987 51 1110 665 178,951 161217

PHASE DIAGRAMS:

EXERCISE 3: Laboratory analysis of a reservoir sample is given. The

sample was obtained from the reservoir at 184 F and 3463 psig.

Plot the formation volume factor and solution gas oil ratio.

OIL FORMATION VOLUME FACTOR:

SOLUTION GAS OIL RATIO:

COEFFICIENT OF ISOTHERMAL COMPRESSIBILITY

The coefficient of isothermal compressibility is defined as the fractional change of volume as pressure is changed at constant temperature.

1. Ideal gases:

2. Real gases: