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Relationship Between Wireline Log Response and Quantitative Pore Geometry Data in Shannon Sandstone, Hartzog Draw Field, Wyoming

C. M. Ross, Robert Ehrlich, Joseph A. Gellici, Brian O. Richardson

Log response of six wells and thin-section character of the Upper Cretaceous Shannon Sandstone in Hartzog Draw field, Wyoming, were compared and related quantitatively. Pore size, shape, and connectivity measured in thin section are sufficient to estimate all wireline logs save the caliper log. Shannon production in Hartzog Draw is from sandstone lenses with intercalated siltstones and shales. The sand fraction consists predominantly of quartz with subordinate amounts of glauconite. Carbonate exists as patches of intergranular cement. Successful estimation of gamma-ray logs from pore data demonstrates that porosity contains significant compositional information. For example, large proportions of microporosity ranging from 1.97 to 7.88 µ are associated with relatively high glauconite and clay content with corresponding high natural gamma-ray log values. Equations linking medium and deep induction logs and formation density with pore geometry all contain the same two variables (the proportion of pore area per unit perimeter and pore areas with a smallest dimension of 39.41 to 157.60 µ). Using values for resistivity of mud filtrate and formation water, these equations provide insights concerning the replacement of oil by mud filtrate and preferential flushing of certain pore types. Objective classification algorithms indicate that the Shannon Sandstone contains several classes of pore types that occur in various proportions from sample to sample. Each pore type can be associated with logs and facies classification. This study, therefore, links conventional petrography and depositional models to petrophysics.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.