Abstract: Chemical Fingerprinting of Stratigraphic Surfaces to Refine Reservoir Architecture and Differentiate Fluid Flow Regimes

Richard A. Eisenberg, Paul M. Harris

The variable development of depositional cycles within hydrocarbon reservoirs, especially reservoirs contained within platform carbonates, can have a profound influence on fluid flow. These cycles can be recognized in core and logs and should form the basis of subsurface geologic models. When placed into a sequence stratigraphic framework, cycle variability can be predicted. We herein investigate the use of chemostratigraphy to refine a reservoir-scale stratigraphic framework and demonstrate the influence of this framework on fluid flow.

Using cores and outcrops of the Permian San Andres Formation in the Guadalupe Mountains of southeastern New Mexico, permeability distribution and waterflood response was modeled for a small-scale carbonate sequence (105 m thick) containing variably developed depositional cycles that formed in a carbonate ramp setting. Cross-sectional fractal permeability fields, used in simulated waterfloods, demonstrate sensitivities of oil recovery and overall injection rate to the stratigraphic framework.

Major, minor and trace element variation, measured on 44 interval composites from core using a combination of techniques including inductively coupled plasma (ICP) and mass spectrometry, characterize and fingerprint important stratigraphic surfaces (sequence boundaries, cycle boundaries, and flooding surfaces). Multivariate analysis of the geochemical data yielded factors we relate to depositional/diagenetic processes and use to evaluate the stratigraphic surfaces.

Concentration of organic carbon and associated base metals coincides with a flooding surface and a transition from outer ramp to cyclic ramp-crest deposits. This geochemically distinct flooding surface separates layers with different fluid flow characteristics and is therefore a critical boundary within our outcrop analog reservoir architecture. Less distinct cycles below this surface are characterized by compartmentalized flow and poor vertical sweep efficiency, whereas well-developed cycles above are characterized in our analog by a potential for early water breakthrough and relatively high vertical sweep efficiencies.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France