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 1

Unconventional Reservoirs Require Unconventional Analysis

Techniques

David Anderson

Society of Petroleum Engineers

Distinguished Lecturer Program www.spe.org/dl

2

3

This Presentation…

Introduction to rate transient analysis (RTA)

The challenge of analyzing unconventionals

Current methodologies – how has the technology

evolved?

The future of production analysis and modeling

Probabilistic approach

Field examples

4

Rate Transient Analysis (RTA) is the science (and art) of extracting useful information about the reservoir, completion and/or surface operations based on the interpretation, analysis and modeling of continuous measurements of production volumes and flowing pressures from a single well.

5

Concept of Rate Transient Analysis

W ell 01

Company: On Stream: 03/28/2013Field: Current Status: Flowing

Gp: 1775 MMscfNp: 0.000 MstbWp: 0.000 MstbQcond: 0.000 Mstb

3600

-1200

-800

-400

0

400

800

1200

1600

2000

2400

2800

3200

Op

Gas R

ate

(M

scfd

)

5200

0

400

800

1200

1600

2000

2400

2800

3200

3600

4000

4400

4800

Ru

n D

ep

th P

ressu

re (p

si(a

))

480 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46

Normalized Time (month)

- Production occurs under

changing constraints

- Reservoir “signal” may be in

rates or pressures (or both)

q (

Mscfd

) pw

f (psia

)

Time (days)

6

Concept of Rate Transient Analysis

Comparison View

10 -5

10 -4

10 -3

9 . 10 -3

2

3

4

6

2

3

4

6

2

3

4

6

No

rma

lize

d G

as

Ra

te (

MM

sc

fd/p

si)

160 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

MBT

160 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

Normalized Time (month)

Legend Normalized Gas Rate vs. Normalized Time

Normalized Gas Rate vs. MBT (2)

Instantaneous normalization

Superposition (Material Balance Time)

q/D

p (

Mscfd

/psi)

Time, Material Balance Time (months)

7

Type Curve Analysis – Characterize Reservoir

Comparison View

10-5

10-4

10-3

10-2

10-1

1.0

2 . 100

5 . 10-6

2

4

2

4

2

4

2

4

2

4

No

rmalized

Gas R

ate

(M

Mscfd

/psi)

10-4

10-3

10-2

10-1

1.0

4 . 100

2 . 10-5

3

5

2

4

2

4

2

4

2

4

2

q/D

(M

Mscfd

/(10

6p

si2

/cP

))

10-3 10-2 10-1 1.0 101 102 103 104 7 . 1043 . 10-4 5 6 2 3 4 5 6 2 3 4 5 6 2 3 4 5 6 7 2 3 4 5 6 2 3 4 5 6 2 3 4 5 6 2 3 4 5 6 2 3

MBT

10-2 10-1 1.0 101 102 103 104 105 8 . 1052 3 4 5 6 7 2 3 4 5 6 2 3 4 5 6 2 3 4 5 6 2 3 4 5 6 2 3 4 5 6 7 2 3 4 5 6 2 3 4

tca (d)

Legendq/D - TC

Normalized Gas Rate vs. MBTLog-Log Plot

- Identify flow regimes

Transient Flow

(permeability, skin)

Boundary Dominated Flow

(connected HCPV)

q/D

p (

Mscfd

/psi)

Material Balance Time (days)

Adapted from Palacio and Blasingame: “Decline-Curve

Analysis Using Type Curves” (SPE 25909) 1993

8

Flowing Material Balance – Estimate HCPV

Example 1

Company: On Stream: 10/01/2002Field: ApolloCurrent Status: Unknown

Gp: 3409 MMscfNp: 224.268 MstbWp: 16.566 MstbQcond: 0.000 Mstb

7000

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

Pre

ssu

re (

psi(

a))

30

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

Op

era

ted

Gas R

ate

(M

Mscfd

)

10.500.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 8.00 8.50 9.00 9.50 10.00

Cumulative Gas Production (Bscf)

LegendGas Rate

Flowing Pressure

Measured

flowing

pressure

Measured rate

Pro

duction R

ate

(M

scfd

)

pw

f (p

sia

)

Cumulative Production (bcf)

9

Flowing Material Balance – Estimate HCPV

Example 1

Company: On Stream: 10/01/2002Field: ApolloCurrent Status: Unknown

Gp: 3409 MMscfNp: 224.268 MstbWp: 16.566 MstbQcond: 0.000 Mstb

7000

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

Pre

ssu

re, p

/Z** (

psi(

a))

30

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

Op

era

ted

Gas R

ate

(M

Mscfd

)

10.500.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 8.00 8.50 9.00 9.50 10.00

Cumulative Gas Production (Bscf)

LegendFlowing p/Z**

Gas Rate

Flowing Pressure

Original Gas-In-Place

Calculated p/z

pss

wf

qbz

p

z

p

- Mattar L., Anderson, D., Dynamic Material Balance – Oil or Gas

In Place Without Shut-ins - 2, CIPC 2005-113

Pro

duction R

ate

(M

scfd

)

pw

f and p

/z (

psia

)

Cumulative Production (bcf)

Modeling – Validate and Forecast

Results

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

5.50

6.00

6.50

7.00

7.50

8.00

8.50

9.00

Cal G

as R

ate

(M

Mscfd

)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

7000

7500

8000

8500

9000

9500

10000

10500

11000

11500

Gas C

um

(M

Mscf)

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

7000

7500

8000

8500

9000

9500

10000

Pre

ssu

re (p

si(a

))

2002 2003 2004 2005 2006

Pressure match

Production Forecast

Benefits of RTA

Evaluation of reserves

Reliable early evaluation- choked wells

Scientific support for reserves auditors

Dynamic reservoir characterization

Estimate permeability and in-place hydrocarbons

Estimate completion effectiveness

Calibrate reservoir simulation models

Reservoir surveillance

Distinguish productivity fall-off from depletion

Identify optimization candidates

The Challenge of Analyzing Unconventionals…

Unconventional reservoirs are more complex

Complex, non-uniform fracture networks

Reservoir properties are significantly altered by

completion

Low permeability – long term transient flow

Drainage area continually expands

Difficult to distinguish clear drainage boundaries

Flow Characterization – Conventional vs.

Unconventional

Radial Flow - Conventional Linear Flow - Unconventional

Fluid flows to the sandface

Pressure drawdown localized

at sandface

Fluid flows to the fracture(s)

Pressure drawdown throughout

fracture(s)

High Permeability

Low Contact Area

Low Permeability

High Contact Area

Unconventional Analysis Methods…

Square Root Time Plot- Linear Flow

q

pD

t

A = 4 nf xf h

2 xf

h

Skin btm

q

p

D

kA

fAAComplex

Simple

Boundaries and Drainage – Conventional vs.

Unconventional

a) Conventional Reservoir b) Unconventional Reservoir

Geological features Well interference

Parallel Fractures

Parallel and Orthogonal

Fractures

15

Fracture

interference Stimulated

Reservoir Volume

(SRV)

Vertical Wells Horizontal Wells

Unconventional Analysis Methods…

Flowing Material Balance

wf

z

p

Stimulated Reservoir Volume

2 xf

h

In-place

hydrocarbons

(SRV)

Cumulative Productioni

Le

Unconventional Analysis Methods…

Simplified Approach-

A√k

skin

tetf = SRV

SRV

Assume – uniform fractures

Calculated- xf, k, skin, SRV

Anderson et al 2010, Analysis of Production

Data from Fractured Shale Gas Wells – SPE

131787

W ell 02

Company: On Stream: 25/06/2013Field: Current Status: Flowing

Gp: 705 MMscfNp: 0.000 MstbWp: 0.000 MstbQcond: 0.000 Mstb

103

104

3 . 104

2

3

4

5

6

7

8

9

2

Op

Gas R

ate

(M

scfd

)

540

0

20

40

60

80

100

120

140

160

180

200

220

240

260

280

300

320

340

360

380

400

420

440

460

480

500

520

Ru

n D

ep

th P

ressu

re (p

si(a

))

June July August September October November December

2013

Illustrating the Challenge of Analyzing

Unconventionals

- Non-uniform frac length,

spacing and conductivity

- Ultra low matrix permeability

- Six months production,

constant pwf

Simulation of flow into a complex fracture network in a gas shale

q (

MM

scfd

) pw

f (psia

)

Simplified Approach – Bulk Reservoir Properties

A√k

skin

tetf = SRV

Contacted

HCPV

SRV =

0.75 bcf

Contacted

HCPV = 1.1 bcf

Dp

/q (

psi/M

Mscfd

)

Square Root Time

q/D

p (

MM

scfd

/psi)

Time (d)

q/D

p (

MM

scfd

/psi)

Gpa/ceDp (bcf)

Simplified Approach – Comparison of Analyzed

Reservoir Properties with Actual

Actual Hz fractures – 250 ft, FCD=50

Vert fractures – 500 ft, FCD = 100

k (matrix) = 0.0001 md

OGIP = 46 bcf (1 section)

As Analyzed Stimulated reservoir width = 120 ft

k (stimulated zone) = 0.011 md

k (matrix) = 0.0005 md

Contacted OGIP = 2 bcf

Actual SRV ~ 0.75 bcf

As Analyzed SRV = 0.75 bcf

Simplified Approach – Comparison of Analyzed

SRV with Actual

Comparison View

10-1

1.0

101

2 . 101

2

3

4

5

6

8

2

3

4

5

6

8

Cal G

as R

ate

(M

Mscfd

) / R

ate

Fo

recast

1 (

MM

scfd

)

0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80

Time (month)

2013 2014 2015 2016 2017 2018 2019

Gp = 1.8 bcf

Simplified Approach – Comparison of 5 year

Production Forecasts

Gp = 1.9 bcf

q (

MM

scfd

)

Time (years)

23

Field Example - Bakken Oil

Bakken

Bakken OilCompany: On Stream: 06/05/2008Field: Undefined FieldCurrent Status: Flowing

Gp: 72 MMscfNp: 98.451 MstbWp: 19.879 MstbQcond: 0.000 Mstb

1.0

101

102

103

2 . 103

2

3

4

5

7

2

3

4

5

7

2

3

4

5

7

Op

Oil R

ate

(stb

/d)

Op

Wate

r R

ate

(stb

/d)

1.0

101

102

103

2

3

4

5

7

2

3

4

5

7

2

3

4

5

7

Op

Gas R

ate

(M

scfd

)

5200

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

2600

2800

3000

3200

3400

3600

3800

4000

4200

4400

4600

4800

5000

Casin

g P

ressu

re (p

si(a

))

Calc

ula

ted

San

dfa

ce P

ressu

re (p

si(a

))

Ru

n D

ep

th P

ressu

re (p

si(a

))

Tu

bin

g P

ressu

re (p

si(a

))

04 05 06 07 08 09 10 11 12 01 02 03 04 05 06 07 08 09 10 11 12 01 02 03 04 05 06 07 08 09 10

2008 2009 2010

24

Field Example – RTA – Simplified

A√k

FCD’

tetf = SRV

Contacted HCPV = 2,800 Mstb

SRV = 850 Mstb

Dp

/q (

psi/stb

/d)

Square Root Time

q/D

p (

stb

/d/p

si)

Time (d)

q/D

p (

stb

/d/p

si)

Np/ceDp (Mstb)

Field Example – RTA - Modeling

High efficiency “short” fracs Low efficiency “long” fracs

Ozkan et al. 2009, “Tri-Linear Flow” Stalgorova et al, 2013, “Five Region

Model”

Provides a “bulk” reservoir interpretation

Reliable estimation of stimulated and total

connected HCPV

Identification of effective system permeability and

apparent skin damage

No unique interpretation of fracture properties

(orientation, distribution, density, length and

conductivity)

No unique interpretation of matrix permeability

Analytical models with different geometries are

available

Summary of Current Unconventional RTA

Technology

27

The Future of Unconventional RTA –

Probabilistic Approach

Data

q, pwf

Rate Transient Analysis:

Deterministic

Modeling – Realizations of RTA results:

Probabilistic

28

Probabilistic Well Performance Analysis

Define ranges or distributions of input parameters

Completion properties

Reservoir properties

Run the reservoir model probabilistically using Monte

Carlo simulation

Keep only history matches that meet a minimum

goodness of fit criteria

Report reservoir characteristics and production

forecasts as distributions, not single values

29

Probabilistic Well Performance Analysis –

Forecasts

Rate vs Time Rate vs Cumulative

Expected Ultimate Recovery Original Gas in Place

30

Conclusions

RTA provides “bulk” reservoir interpretation

Ideal for establishing connected HCPV

Assists in understanding recovery mechanism

Yields reliable production forecasts

Analyzing unconventional well production presents

significant challenges

Analysis and modeling technology has evolved

Unconventional plays are statistical in nature – many

wells must be analyzed to understand behavior

A probabilistic approach will help to manage and

communicate uncertainty

31

Thank-you…

Questions?

Society of Petroleum Engineers

Distinguished Lecturer Program www.spe.org/dl 32

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