Robert G. Loucks,1 David Entzminger,2 and Shinichi Sakurai3
Depositional and diagenetic processes at the scale of high-resolution sequence stratigraphy (parasequence level) have the strongest effect on carbonate-reservoir flow units and their petrophysical properties. The layering of the reservoir should therefore be done at a scale that reflects high-frequency cycles or parasequences. At this level, flow units and petrophysical properties become meaningful to reservoir modeling.
This concept can be illustrated by examining the hierarchy of factors that control reservoir dimensions and petrophysical properties. Regional depositional setting is the basis for understanding general, large-scale facies distribution, but it is not fine-scaled enough to explain or predict flow-unit properties. It is at the scale of high-resolution, sequence stratigraphic systems tracts analysis that effects of depositional environment and resulting texture and fabric are made clear. Depositional environment generally controls dimensions of a reservoir, and texture/fabric controls petrophysical properties.
The Upper Clear Fork through Lower San Andres section in North Cowden field shows a strong correlation between parasequence-level stratigraphy and resulting reservoir continuity, pore types, porosity, permeability, and capillary pressure. Parasequences deposited during different stands of relative sea level show consistent, but not necessarily homogeneous, petrophysical properties. The boundaries of the flow units generally match parasequence boundaries except where a parasequence boundary and a sequence boundary coincide. The most meaningful approach to picking flow units in this carbonate reservoir is first to construct the high-resolution sequence stratigraphic architecture of the reservoir and then to relate the petrophysical parameters to this architectural framework.
1Bureau of Economic Geology, The University of Texas at Austin, University Station Box X, Austin, Texas 78713; e-mail: firstname.lastname@example.org.
2Dave Entzminger, BP Amoco p.l.c., 200 Westlake Park Blvd., WL4, Rm. 239, Houston, Texas 77079; e-mail: email@example.com.
3Bureau of Economic Geology, The University of Texas at Austin, University Station Box X, Austin, Texas 78713; e-mail: firstname.lastname@example.org.