ABSTRACT: Log Analysis of a Pennsylvanian Strawn Sand Reentry in Central Texas
The Pennsylvanian Strawn sands on the eastern shelf of the Midland basin in central Texas were deposited as fluvial-deltaic sands. In this area are numerous wells that penetrated these Strawn sands exploring for deeper zones. Many of these wells drilled from 1955 to 1962 and, therefore, porosity logs commonly are unavailable. However, using resistivity-derived porosities from both the short-normal and the microlog, together with computer-aided log analysis, detailed log evaluation is possible.
The Strawn sand used in this study consists of a thick, lower sand (28 ft) overlain by a thin, upper sand (7 ft). A series of logging crossplots indicates that the lower sand is wet and the upper sand should be productive. These crossplots include (1) Q-plot, (2) short-normal porosity versus microlog porosity, (3) deep induction porosity versus microlog porosity, (4) Pickett plot, (5) Archie water saturation versus ratio water saturation, and (6) Rt/Rw versus Rsn/Rz (dew) plot. Net pay summaries for the two Strawn sands used the following cutoffs: Vcl <20%, effective porosity >10%, and Sw (Archie) <50% indicate no net pay in the lower sand and 4 ft of net pay in the upper sand. When the well was reentered the upper sand had an initial production pumping of 25 BOPD and no wate .
AAPG Search and Discovery Article #90991©1993 AAPG Mid-Continent Section Meeting, Amarillo, Texas, October 10-12, 1993.