Use of Outcrop Analogs to Assess the Impact of Lateral Petrophysical Cyclicity on Static Connectivity and Fluid Flow within Dolomite Reservoirs

Matthew J. Pranter and Zulfiquar A. Reza
University of Colorado, Boulder, CO

Multiple scales of lateral petrophysical variability exist within dolomite rock fabrics of the Mississippian Madison Formation at Sheep Canyon and Lysite Mountain, Wyoming. Distinct cyclic patterns with varying magnitudes are present in porosity and permeability laterally within a single dolomite unit. This is significant because reservoir models that incorporate these scales of heterogeneity are shown to impact fluid flow within a reservoir.

Of interest, the cyclic patterns are also present in geochemical parameters (e.g. trace elements) which could be attributed to a self-organization process during dolomitization. At Sheep Canyon, a 481-ft lateral transect was acquired within a dolo-wackestone within transgressive systems tract of sequence 1. At Lysite Mountain, a 495-ft lateral transect was acquired within a dolo-grainstone within the highstand systems tract of sequence 2. Periodicities for porosity and permeability are both approximately 28 ft for the dolo-wackestone. The dolo-grainstone has approximately 40-ft periodicities for both porosity and permeability.

3D geostatistical reservoir models and multi-phase fluid-flow simulations are used to evaluate the effects of these periodicities in petrophysical properties on reservoir dynamics. The modeling approach entails stochastic simulation of porosity and permeability to capture the multiple scales of variability including the lateral periodic trend. Cosimulation of permeability using previously simulated porosity is used to preserve the correlation between the two parameters. Both static (connectivity) and dynamic measures (break-through time, water breakthrough, and fingering) are affected by the varying degrees of heterogeneity and cyclicity. To properly characterize and model these scales of variability within a petroleum reservoir, outcrop analogs are essential to provide accurate quantitative descriptions of lateral variability within dolomite rock fabrics.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005