Abstract: Computerized Old E-Log Analysis of the Pennsylvanian Strawn (Cross Cut/Morris) Sandstone, TWP and Busher Fields, Runnels County, Texas
George B. Asquith, Steve K. Henderson
In the area of the TWP and Busher fields approximately 15 percent of the wells were logged with old electric logs (SP-LATERAL-LN-SN-ML). In order to be able to determine net pay thicknesses and to calculate volumetric oil reserves for the Strawn pay in these two fields log analysis of the wells with Old E-Logs should be included.
The Old E-Logs were first digitized and then loaded into a computer program called Old E-Log Advisor (OEA). In the program the electrode spacings of the Lateral (LAT), Long Normal (LN), and Short Normal (SN) logs were required as input because corrections for bed thickness and the method of Rt determination are a function of tool spacing. Porosities were calculated from both the microlog (ML) and the Short Normal log, and the volume of clay was determined from the SP. Before the calculation of net pay and hydrocarbon pore-feet thicknesses, the log was displayed like a modern log with the SP in track #1, the SN-LN-Rt in track #2 (logarithmic scale), and the Porosity in track #3. The reasons for re-displaying the old log data like a modern log was to first observe and compare the old lo data with nearby modern logs and to be able to observe resistivity invasion profiles (SN-LN-Rt). When the porosity and Rt values determined from the old log data were comparable to the modern log data, net pay and hydrocarbon pore-feet thicknesses were determined.
In the example presented there are two thin (<10 feet) Cross Cut/Morris sandstones both of which contain hydrocarbons. However, using net pay cut-offs of Vcl < 15%, Porosity > 8%, and Sw < 50% only the upper sand contained net pay, because the lower sand is too shaly and has low permeability.
AAPG Search and Discovery Article #90960©1995 AAPG Southwest Section Meeting, Dallas, Texas