Geologic Aspects of Horizontal Drilling in Self-Sourcing Reservoirs

ILLICH, HAROLD A., Oryx Energy Company, Dallas, TX

Horizontal drilling techniques provide a way to exploit hydrocarbon reserves that are either noneconomic or only marginally economic using vertical drilling techniques. A significant fraction of these reserves is contained in reservoirs that are self-sourcing or in reservoirs that are closely associated with their sources. Most formations drilled as horizontal targets are self-sourcing. The Austin Chalk, Niobrara, Mesaverde, and Bakken are examples of horizontally drilled, self-sourcing reservoir systems.

In formations like the Bakken or Austin Chalk, the close relationship between reservoir and source makes risks associated with migration and accumulation less important. Reservoirs of this kind can contain oil or gas and often have little or no associated water. They can be matrix-dominated reservoirs, dual-porosity reservoirs (Mesaverde), or fractured reservoirs (Austin Chalk, Bakken, and Niobrara). Fractured, self-sourcing reservoirs also can possess matrix characteristics that contribute increased recovery efficiency. Most reservoirs drilled horizontally possess highly heterogeneous reservoir systems.

Characterization of the style of reservoir heterogeneity in self-sourcing systems is important if the favorable properties of horizontally oriented bore holes are to be realized. Production data and rock mechanics considerations are important in horizontal drilling ventures. Examples of the use of these data for the purpose of defining reservoir characteristics are discussed. Knowledge of lateral changes in reservoir properties is essential if we are to recover known reserves efficiently.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)