Abstract

In looking for log examples of “OLD” [Pre-1958] E – Logs an interesting Permian Basin Carbonate example was found Schlumberger’s Document #8. The log suite consists of the following: SP, 10” Short Normal (SN10), 18’8” Lateral (LAT18), 32” Limestone Lateral (LsLat), and a Microlog (ML). It was decided to do a log analysis of the “A” Zone (6660 ft to 6700 ft) pre 1970 using service company charts (no calculator/computer) to first determine formation Temperature (Tf) and correct the mud resistivities (Rm & Rmf) to Tf. Then formation water resistivity (Rw) was determined from the SP log using appropriate charts. Next the SN10 and LAT18 were borehole corrected using Schlum-berger Departure Curves. SN10, ML, and LsLat porosities were also determined using appropriate logging company charts. These three porosities were compared to average core porosity (PHIcore), and it was determined that PHILsLat was the best measure for log derived porosity (PHIcore = 15%; and PHILsLAT = 13% to 17%) . Last an Archie Water Saturation (Sw) Nomograph Chart (F = 1/PHI^2) was used to determine an Archie Water Saturation (Swarchie) of 18.5%. The well’s initial production was 700bopd and No Water.

The log data was then converted to a digital file at depth intervals of 2.5 feet from 6660ft to 6700ft. Based on either known equations or curves fitted to the logging company charts the digital data was used to calculate Tf, correct Rm and Rmf to Tf, and formation water resistivity (Rw). Then PHIsn, PHIml, and PHILsLat plus Sw(archie) were calculated. Assuming 80acre spacing and a BOI of 1.2 resulted in an OOIPstb of 2.1mmbo

Next, Moveable Hydrocarbon Index (Sw/Si) and Ratio Water Saturation (Swratio) were determined. Using these data along with a DEW Plot (Rt/Rw versus SN/Rz) the “A” Zone in this Permian Carbonate appears to be a vuggy water-wet carbonate.

The last step was to calculate a value for Mobile OOIPstb using Maximum Producible Oil Index Method (Tixier, 1956):

Mobile OOIPstb = (7758*Y*Area*h)/BOI

Y (Maximum Producible Oil Index) = (Rz/SN)

^0.5 – (Rw/Rt)^0.5

Mobile OOIPstb = 742,000bo

This poster was designed to illustrate that quanitative log analysis is possible with our older well logging suites. In addition, this poster illustrates what log analysis was like pre-1970’s.