Classification of Fractured Reservoirs

1
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

2
Fractured Reservoir Classification
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)
3
Schematic Distribution of Fractured Reservoir
Types
All Fractures
100 k f
I
II
of Total Permeability
III
M
100 k m
IV
of Total Porosity
100 f f
100 f m
All Matrix
Nelson (1999)
4
Evaluation Characteristics byFractured 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

5
Evaluation Characteristics byFractured 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

6
Evaluation Characteristics byFractured 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

7
Evaluation Characteristics byFractured 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

8
Reservoir Type 1 Fields
9
Contrasting History
10
Reservoir Type 2 Examples
11
Contrasting History
12
Reservoir Type 3 Examples
13
Contrasting History
14
Attributes of Reservoir Types
15
Critical Exploration Development Issues by
Fractured Reservoir Type
All Fractures
Pressure, Wellbore Stability Rate control
100
Development Patterns Well Paths
Blackburn
Valhall
West Rozel
Beaver River/ Pointed Mountain
Hod
Sabria/ El Franig
Sajaa/ Kahaif
Pearsall
Anschutz Ranch East, Low
Opon
Whitney Canyon
Middle Ground Shoals/ Granite Point
Lost Soldier Madison
Reserve Calculation Rate Decline
Wamsutter
Permeability in Fractures
Lost Soldier Tensleep
Liuhua
Ryckman Creek
Darius
Anschutz Ranch East,High
Rijn
Cedar Rim
Pineview
Inappropriate Floods Non-Recognition
Beaver Creek
Hugoton
0
100
0
Porosity in Fractures
Matrix All
R.A.Nelson, 1999