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 Programwww.spe.org/dl

Society of Petroleum Engineers

Distinguished Lecturer Programwww.spe.org/dl

2

Tao YangStatoil ASA

Estimation of Shale Gas and Oil Properties Based on Field Data

Outline

• Fluid properties (PVT) for conventional reservoirs

• Challenges to obtain shale gas and oil properties

• Can we estimate shale gas and oil properties based on

field data?

• Application examples

• Conclusions

3

4

Conventional vs. Shale asset life cycle

Wood Mackenzie, 2012

5

Fluid properties (PVT) for conventional reservoirs

• Empirical correlations

– Standing correlation from 1940s

• Standard/modern approach

– Sampling, laboratory measurement and Equation of

State (EOS) modeling

6

Surface Gas

Surface OilLive Oil

Challenges to obtain shale fluid properties

• Difficult to take in-situ

representative samples

• Very little published PVT

data available

• Uncertainty of geochemical

basin modeling

7

Cander, H., 2012

GOR - Gas oil ratio

Is PVT important for liquid rich

shale production?

8Kumar et al., 2013

Review of recent activities

• In-situ representative samples

– Pressure coring

– History matching of production data

• Impact of Nano-sized porous media on PVT properties

9

Can we estimate shale gas and oil properties

based on field data?

• Most productions have no PVT samples, no PVT

measurements, but there are some field data available.

• For shale play evaluation, drilling target and well

completion optimization, timely decision has to be made

before detailed fluid data are available.

10

A large PVT program for Eagle Ford Shale

• Designed for understanding fluid properties in shale play

• Highly undersaturated reservoir fluids range from dry gas, gas

condensate, volatile oil to black oil

• Surface recombined samples from early production

• 50+ wells covering large areas

• Fluid sampling and PVT laboratory measurement over two years

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12Yang et al., 2014

13Yang et al., 2014

14Yang et al., 2014

15Yang et al., 2014

16Yang et al., 2014

Unique findings for shale fluid properties

• Consistent PVT correlations field-wise even though the

reservoir fluids cover very wide range.

• Most fluid properties can be estimated from only one

parameter – GOR.

• What made shale reservoir fluid properties unique?

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18

Petroleum alteration for conventional reservoirs

Reservoir fluid gradient comparisons

19

?

Reservoir fluid gradient comparisons

20

Simplified petroleum alteration

process in shale reservoirs

• Extremely low permeability limits fluid communication

and migration.

• Reservoir fluid differences are dominantly determined by

thermal maturity.

• Reservoir fluid system in shale reservoir is a closed

system at chemical equilibrium.

21

New method for fluid property estimation

• Closed system in shale reservoir makes a simplification

of fluid property estimation possible.

• Reservoir fluid composition and PVT properties can be

estimated based on correlations with GOR.

• PVT correlations are fluid system (field/play) dependent.

• Supported by fluid property data and field operations

from many US shale plays.

22

How to obtain GOR?

• Before production

– Mud logging gas composition

• Production phase

– GOR data

– API gravity of surface oil/condensate (stock tank oil)

– Surface gas composition

23

24Yang et al., 2014

Flowchart for estimating shale gas

and oil properties

25

Automatically updated fluid

property correlations

GOR

API gravity

Surface gas ormud logging gascomposition

Reservoir fluid composition

Black oil properties

Natural gas liquids

One of the field data input

All outputs

Applications

• Simplification of fluid property estimation for shale

reservoirs is a small step but opens the possibility of

broad practical applications.

26

Drilling and completion Production

Mud logging gas composition

GORAPI gravitySurface gas composition

Example 1: Production optimization

• Surface gas analysis is available for all wells.

• Fluid properties from each well are required input for

production optimization (e.g. network modeling).

• Estimating PVT properties from surface gas composition is a

practical approach.

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28Surface gas Well stream

Mole%

N2 Nitrogen 0.06

CO2 Carbon Dioxide 1.81

C1 Methane 79.27

C2 Ethane 10.59

C3 Propane 3.60

iC4 i-Butane 0.98

nC4 n-Butane 1.07

iC5 i-Pentane 0.49

nC5 n-Pentane 0.28

C6 Hexane 0.95

C7+ Heptane Plus 0.90

Components

Surface Gas Composition Mole%

Molecular

Weight

(kg/kmol)

(Apparent)

Gravity

N2 Nitrogen 0.07 28.0 0.808

CO2 Carbon Dioxide 1.59 44.0 0.827

C1 Methane 74.20 16.0 0.300

C2 Ethane 10.97 30.1 0.356

C3 Propane 4.12 44.1 0.508

iC4 i-Butane 1.25 58.1 0.563

nC4 n-Butane 1.53 58.1 0.584

iC5 i-Pentane 0.83 72.2 0.625

nC5 n-Pentane 0.62 72.2 0.631

C6 Hexane 0.92 86.2 0.664

C7+ Heptane Plus 3.88 134.8 0.775

Components

Estimated Well Stream

Saturation Pressure (psia) 3848

Oil or Condensate Gravity (°API) 58.8

Gas Oil Ratio (scf/stb) 14640

Formation Volume Factor (rcf/scf) Wet 0.0031487

Dry 0.0033273

Estimated PVT Properties

Yang et al., 2014

Example 2: Completion optimization

• Fixed completion design often leads to low efficiency for

liquid rich shale production.

• Mud logging gas composition can be used to make real time

interpretation of in-situ reservoir fluid properties while

drilling.

• The timely PVT input provides important inputs to optimize

completion design.

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30Yang et al., 2014

Shale play evaluation

• For shale play evaluation, condensate gas ratio (liquid yield) is

most critical parameter.

• For most early phase evaluations, such data is not available.

• It is a robust approach to integrate geochemical prediction and

PVT estimation based on field data.

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• Low stock tank oil (STO) API gravity

• Basin modeling indicates both gas and oil in

the play.

• Geochemical arguments for gas or oil cases

are not conclusive for target area.

Gas or oil prospect?

Yang et al., 2014

Limitations of the new method

• Accuracy

• Complex geology

• Play dependence

33

Conclusions

• Thanks to low permeability in shale reservoir,

closed system makes a simplification of fluid

property estimation possible.

• Wide range of field data can be used to estimate

shale gas and oil properties with reasonable

accuracy.

34

Acknowledgements

• Statoil and Talisman (Repsol) management

• Colleagues from Statoil shale assets (USA) and technology central (Norway)

– Remy Basquet, Lisset Sousa

– Angel Callejon, Jan Joost Van Roosmalen, Bob Bartusiak

– Knut K. Meisingset, Timothy P. Isom, Svein Tollefsen, Inge Brandsæter

• Peers nominated and supported me for SPE distinguished lecturer program

– Karen S. Pedersen (Calsep), Julian Y. Zuo (Schlumberger)

• Special thanks for kind help to improve the presentaion

– Sunil Kokal (Saudi Aramco), Stephen Begg (University of Adelaide)

– Curtis H. Whitson (NTNU)

35

Society of Petroleum Engineers

Distinguished Lecturer Programwww.spe.org/dl

36

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