Classification of Fractured

Reservoirs

Delineates the reservoir parameters most

important in quantifying the reservoir

(highgrades data acquisition)

Potential production & evaluation problems

can be anticipated

The style of reservoir simulation necessary

can be constrained

Type I: Fractures provide the essential storage capacity and

permeability in a reservoir. The matrix has little porosity or

permeability.

Type II: Rock matrix provides the essential storage capacity and

fractures provide the essential permeability in a reservoir. The

rock matrix has low permeability, but may have low, moderate, or

even high porosity.

Type III: Fractures provide a permeability assist in an already

economically producible reservoir that has good matrix porosity and

permeability.

Type IV: Fractures do not provide significant additional storage

capacity or permeability in an already producible reservoir, but

instead create anisotropy. (Barriers to Flow)

Nelson (1999)

Fractured Reservoir Classification

I II

III

IV

All

Fractures

All

Matrix

% of Total Porosity

% o

f To

tal

Perm

eab

ilit

y

100 % k f

100% k m

100% f m 100% f f

Increasing Effect of Fractures

Decreasing Effect of Matrix

Schematic Distribution of

Fractured Reservoir Types

Nelson (1999)

M

Evaluation Characteristics by

Fractured Reservoir Type

Type 1 (Fractures provide essential por. & perm.)

Fracture characteristics define reserves

Static description is critical

Production highly variable in 4-D

Few wells required to deplete

Evaluation Characteristics by

Fractured Reservoir Type

Type 2 (Fractures provide essential perm.)

Cross flow and rate control are critical

Fractures define rate

Water influx must be monitored & intervention

planned

If overpressured, fracture closure must be

controlled

Evaluation Characteristics by

Fractured Reservoir Type

Type 3 (Fractures provide a perm. assist)

Fractures define anisotropy

Highly customized flood patterns needed

Rates & drainage areas better than predicted

from matrix alone

Evaluation Characteristics by

Fractured Reservoir Type

Type 4 (Fractures create perm. reduction)

Fractures create baffles, barriers and

compartments (flow & saturation)

Fracture descriptions made generally by core

only

Inefficient drainage & sweep

Rates & reserves lower than predicted from

matrix alone

Examples Of Fields In Which

Fractures Provide The Essential Porosity

And Permeability To The Reservoir

Reservoir Type 1

_____________________________________________________

Field Location Reserves

I . Amal Libya 1700 mmbbl

2. (5)Ellenburger Fields Texas 107.8 (1957)

3. Edison California 42

4. Wolf Springs Montana 5.4

5. (8) PC Fields Kansas 3.8

6. Big Sandy Kent./W.V 3 Tcf

Reservoir Type 1 Fields

Examples of Contrasting History

__________________________________________________

Reservoir Type 1:

Fractures Provide the Essential Porosity

and Permeability

Edison (California) Poor HistoryTectonic Fractures

Big Sandy (Kentucky/W. Virginia) Good HistoryRegional Fractures

The Difference is Primarily One of Drainage

Area and Fracture Type.

Contrasting History

Examples Of Fields In Which

Fractures Provide The Essential

Permeability To The Reservoir

Reservoir Type 2

Field Location Reserves

1 . Agha Jari Iran 9500 mmbbI

2. Haft Kel Iran 2660

3. Rangely Colorado 600

4. Spraberry Texas 447

5. Altamont- Utah 250

Bluebell

6. Sooner Trend Oklahoma 70

7. La Paz/Mara Venezuela 800

Reservoir Type 2 Examples

Examples of Contrasting History

Reservoir Type 2:

Fractures Provide the Essential Permeability

Spraberry (Texas) Poor HistoryUnderpressured

Altamont-Blue Bell (Utah) Good HistoryOverpressured

The Difference is One of Reservoir Energy.

Contrasting History

Fractures Provide A Permeability

Assist To The Reservoir

Reservoir Type 3:

Field Location Reserves

1 . Kirkuk Iraq 15000 mmbbi

2. Gachsaran Iran 8000

3. Hassi Messaoud Algeria 6000

4. Dukhan Qatar 4570

5. Cottonwood Creek Wyoming 182

6. Lacq France 8.8 TCF

Reservoir Type 3 Examples

Reservoir Type 3:

Fractures Provide a Permeability Assist

Cottonwood Creek (Wyoming) Poor HistoryLate Recognition of Fractures

Kirkuk (Iraq) Good HistoryEarly Recognition of Fractures

One Difference is When the Fracture Systems

Were Recognized in Production Procedures.

Contrasting History

Reservoir Type 3

Fractures Provide a Permeability Assist

1. Reserves dominated by matrix properties

2. Reserve distribution fairly homogeneous

3. High sustained well rates

4. Great reservoir continuity

Reservoir Type 1.

Fractures Provide Essential Porosity and Permeability

1. Drainage areas per well are large.

2. Few wells needed in development

(in-fill for rate acceleration only)

3. Good correlation between well rates and well

4. Best wells are often early

5. Generally high IPs 6. Can produce from non-standard and non-reservoir

Reservoir Type 2.

Fractures Provide Essential Permeability

1. Can develop low permeability rocks

2. Often higher than anticipated well rates

3. Hydrocarbon charge often fostered by fractures

Attributes of

Reservoir Types

100% 0%

0%

100%

%Porosity in Fractures

%P

erm

eab

ilit

y i

n F

ract

ure

s

Matrix

All

All Fractures

Valhall

Hod

Blackburn

West Rozel

Pineview

Ryckman Creek

Lost Soldier

Tensleep

Lost Soldier

Madison

Opon

Hugoton

Anschutz Ranch East,High

Anschutz Ranch East, Low

Beaver River/

Pointed Mountain

Beaver Creek

Sabria/

El Franig

Middle Ground Shoals/

Granite Point

Pearsall Sajaa/

Kahaif

Pressure, Wellbore Stability & Rate control

Reserve

Calculation &

Rate Decline

Inappropriate

Floods & Non-Recognition

Development Patterns

& Well Paths

Whitney Canyon

Liuhua

Wamsutter

Critical Exploration & Development Issues by Fractured Reservoir Type

Darius

Rijn Cedar Rim

R.A.Nelson, 1999