Stratigraphy and reservoir geology of the Carmopolis Oil Field, Brazil

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The Carmopolis Oil Field occupies a sequence of Neocomian and older sandstones and extends into an unconformably overlying wedge of Aptian conglomerates. The conglomerates are the subject of this study and are interpreted to have been deposited in an alluvial-fan environment under semi-arid climatic conditions. Systematic textural and compositional variations have been identified. Proximal to distal trends include decreasing clast size and composition, heavy mineral proportion and rock grain density. These changes provide the basis of a reservoir classification which begins with definition and mapping of lithologic units and establishment of regional changes of lithology and reservoir quality. Rock grain density varies systematically with grain size and permeability and new correlations provide a method of obtaining more accurate porosity estimates and, therefore, reservoir volume. Permeability can be estimated indirectly from bulk density derived from well logs where core is not available. Diagenetic modifications also are related to the composition of clasts and primary texture and regional trends of secondary porosity are predicted. The effects of diagenesis on enhanced oil recovery are of two types: those related to modification of original pore structure and those caused by pore blockage related to the presence of clay minerals. Reservoir heterogeneities are recognized on several scales from those related to major conglomerate units to pore scale heterogeneities formed by selective dissolution. Reservoir sweep and displacement efficiency is related to the types and extent of heterogeneity and regional mapping of types may be useful in estimating recovery factors and implementing new recovery schemes.
Bibliography: p. 103-107.
Candido, A. (1984). Stratigraphy and reservoir geology of the Carmopolis Oil Field, Brazil (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from doi:10.11575/PRISM/12600