Classification of Fractured Classification of Fractured ReservoirsReservoirs

• 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 ClassificationFractured Reservoir Classification

III

III

IV

AllFractures

AllMatrix

% of Total Porosity% of Total Porosity

% o

f T

ota

l %

of

To

tal

Per

mea

bil

ity

Per

mea

bil

ity

100 % k f100 % k f

100% k m100% k m

100% 100% m m 100% 100% ff

Increasing Effect of Fractures

Decreasing Effect of Matrix

Schematic Distribution of Schematic Distribution of Fractured Reservoir TypesFractured Reservoir Types

Nelson (1999)

M

Evaluation Characteristics byEvaluation Characteristics byFractured Reservoir TypeFractured 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 byEvaluation Characteristics byFractured Reservoir TypeFractured 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 byEvaluation Characteristics byFractured Reservoir TypeFractured 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 byEvaluation Characteristics byFractured Reservoir TypeFractured 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

Reservoir Type 1 FieldsReservoir Type 1 Fields

Contrasting HistoryContrasting 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 ExamplesReservoir 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 HistoryContrasting 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 ExamplesReservoir 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 HistoryContrasting History

Attributes of Attributes of Reservoir TypesReservoir Types

100%0%

0%

100%

%Porosity in Fractures

%P

erm

eab

ilit

y in

Fra

ctu

res

MatrixAll

All Fractures

Valhall

Hod

Blackburn

West Rozel

Pineview

Ryckman Creek

Lost SoldierTensleep

Lost SoldierMadison

Opon

Hugoton

Anschutz Ranch East,High

Anschutz Ranch East, Low

Beaver River/Pointed Mountain

Beaver Creek

Sabria/El Franig

Middle Ground Shoals/Granite Point

PearsallSajaa/Kahaif

Pressure, Wellbore Stability & Rate control

Reserve Calculation &Rate Decline

InappropriateFloods & Non-Recognition

Development Patterns & Well Paths

Whitney Canyon

Liuhua

Wamsutter

Critical Exploration & Development Issues by Fractured Reservoir TypeCritical Exploration & Development Issues by Fractured Reservoir Type

Darius

Rijn Cedar Rim

R.A.Nelson, 1999