Environment of Deposition Models Developed Using Borehole Images: Examples from Low Permeability Reservoirs, Rocky Mountain Region, U.S.A.

Michael C. Puchalski
Fronterra Integrated Geosciences, LLC, Houston, TX

Over the last decade, the use of borehole micro-resistivity images has become more common as a tool for reservoir description and characterization. When full diameter core is not available, these data provide important information concerning bedding geometry, sedimentary structures and fabrics, and depositional lithofacies not available through other wireline logging methods.

The potential of low permeability sandstone reservoirs of the western United States as targets for exploration and development has lead to an increasing need for better characterization of this unconventional reservoir type. The internal stratigraphy and architecture of these reservoir types is often variable and complex. In order to fully understand the reservoir complexity and architecture in the context of the petroleum system as well as, to reduce exploration risk, the development of depositional models is warranted.

Using a suite of conventional open hole wireline logs and image data from multiple wells along with full diameter core as a calibration tool, a depositional model was developed for Cretaceous strata of a southwestern Colorado basin. The model for this vertical succession documents a regressive depositional sequence. This regressive cycle is defined by a vertical transition from shallow-water, marine, sandstone, through coastal plain and transitional marine sediments, and ultimately to terrestrial, alluvial reservoirs. This paper will outline the methods involved in the creation of this type of depositional model using borehole image data as well as, present representative examples of the lithofacies types and sedimentary textures and structures observed.