Recognizing Influence of Burial History and Diagenesis on Reservoir Heterogeneity

Thomas L. Dunn, Ronald C. Surdam

The newly recognized need for dimensional data of reservoir heterogeneity related to depositional systems has generated renewed interest in outcrop studies. Data on macroscopic-scale features such as shale and sandstone lateral dimensions, bedding types, and overall depositional system geometries can be collected from the outcrop.

Sandstone diagenesis impacts reservoir heterogeneity on both the microscopic and macroscopic scales. These alterations are complexly related to the burial and thermal history of the sediments. Past petrologic and diagenetic studies have clearly indicated the common presence of extensive and widely ranging cementation and pore geometry alteration within buried sedimentary rocks. The permeability tensor within any portion of the reservoir evolves during burial and uplift. Cementation patterns developed within specific environments alter the dimensions of the macroscopic-scale features. Cementation horizons whose formation are controlled by large-scale chemical processes potentially form barriers to flow. More importantly, the burial history and diagenetic alteration of the subsurface re ervoir and the outcropping depositional analog may be significantly different. Also, certain depositional systems may evolve along different diagenetic pathways, suggesting that the changes in reservoir heterogeneity with burial may not be obvious. Examples from aeolian and fluvial depositional systems will be discussed.

It is suggested that workers in reservoir characterization include in their studies comparative analyses of the burial histories and diagenesis of both the to-be-modeled reservoirs and the outcropping depositional analogs.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.