Timothy A. Cross1, Brice Caldes2, Andrés Fajardo3, Yohan Kusumanegara4, Juan Carlos Ramon5
(1) Colorado School of Mines, Golden, CO
(2) Marathon Oil Co, Cody, WY
(3) Ecopetrol-ICP, Bucaramanga, Colombia
(4) TotalFinaElf, Jakarta, Indonesia
(5) Hocol, Bogota, Colombia
ABSTRACT: Illustrations of Stratigraphic Controls on Reservoir Attributes
For a constant depositional environment, numerous petrophysical, sedimentologic and stratigraphic attributes important for reservoir characterization change systematically and predictably as a function of the accommodation:sediment supply (A/S) regime. These systematic changes in attributes of multiple scales and types are coherent, such that measurements of one attribute may be used to predict values of other attributes. As a consequence, reservoir characterization and analog studies conducted from the perspective of facies models or depositional environments are less accurate and more ambiguous than those conducted from a stratigraphic perspective sensitive to accommodation and sediment supply.
Coherent relations among porosity, permeability, trough cross-stratification set thickness, facies diversity, geometry, dimension, continuity and connectivity are illustrated from several surface and subsurface examples. Systematic changes of these attributes are products of changes in degree of preservation of geomorphic elements and accommodation controls on the types and dimensions of geomorphic elements that occupy an environment; both of which are related to the A/S regime.
Porosity and permeability are highest, and the range in values is lowest, in the most amalgamated fluvial channel sandstones that accumulated in low A/S conditions. These petrophysical attributes are associated with thin trough cross-stratification sets, low facies diversity, homogeneity, good connectivity and continuity. A linear relation between trough cross-stratification set thickness and channel belt sandstone dimension was measured in one study. These relations reflect variations in degree of preservation. Alluvial ridge height and crevasse splay thickness increase with increasing A/S conditions, and splays become sandier and have steeper clinoforms. These relations reflect stratigraphic control on geomorphic elements. Shoreface sandstones are heterogeneous and contain substantial mud drapes and partings when deposited in low A/S conditions. Their counterparts in high A/S conditions are sandy, homogeneous and have narrower facies tract widths. These relations reflect variations in storage capacity in continental environments as a function of A/S regime.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado