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

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)

Schematic Distribution of Fractured Reservoir Types All Fractures 100 % k f I II Permeability % of Total III Decreasing Effect of Matrix Increasing Effect of Fractures M 100% k m IV % of Total Porosity 100% f f 100% f m All Matrix Nelson (1999)

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

Reservoir Type 1 Fields

Contrasting History

Reservoir Type 2 Examples

Contrasting History

Reservoir Type 3 Examples

Contrasting History

Attributes of Reservoir Types

%Permeability in Fractures Critical Exploration & Development Issues by Fractured Reservoir Type Pressure, Wellbore Stability & Rate control All Fractures 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 Beaver Creek Inappropriate Floods & Non-Recognition Hugoton 0% 100% Matrix All 0% %Porosity in Fractures R.A.Nelson, 1999