Your task is to Quality Control (QC) and plot the wireline log data for the South Pepper-1. You have been provided with the following data: digital well log file (*.las), and Adobe Acrobat (

Formation Evaluation Case Study

Part 1 – Log Display And QC Of South Pepper-

Your task is to Quality Control (QC) and plot the wireline log data for the South Pepper-1. You have been provided with the following data:

• digital well log file (*.las), and
• Adobe Acrobat (*.pdf) plot of the well log as a

The aim of this exercise is to make the appropriate corrections to the South Pepper- 1 raw data so that the good data can be displayed as a composite log. This should be a quick QC, with corrections that need to be made to these logs.

Hints

• Using Excel, check that all of the logs are on depth. If there are any logs off depth then shift the log by the appropriate depth and make a note of your changes (you may wish to keep a copy of the original log?)
• Check the condition of the hole quality by firstly using the caliper log. You can create a bad hole flag if required, using different cut-offs. Compare the cut-off flag to your log
• Check that the log readings have a sensible range, and correspond with one another on

Answer the following questions:

• What is the bit size over the logged interval?
• Is hole condition a problem in this well, and has it impacted on the log readings of any of the tools?

Note: You will be limited by your plotting capabilities in Excel, but try and replicate the log display given, to the best of your ability.

 

Part 2 – Volume Of Shale (V_shale) Calculation Gamma Ray Log

The Problem

Determine the volume of shale (V_sh), and sand to shale ratio from the gamma-ray log.

Step 1 – Sand / Shale Ratio

• Discriminate between sand and shale based on the gamma ray log, and calculate a sand to shale ratio for the complete section (well top to well bottom).

Step 2 – Volume of Shale Calculations

• Generate volume of shale curves using GR log

Step 3 – Volume of Shale Corrections (V_shc)

• Correct your volume of shale calculation, using the following IGR / V_shale corrections:

where: Vsh = shale content from GR, and V_shc = shale content corrected for non-linear effects (fractional).

Note: V_sh must be within the range of 0.0 to 1.0 before applying these formulae. Hence you may have to correct your V_sh calculations first.

Part 3 – Sonic, Density And Neutron

The aim of this part is become familiar with the use of the sonic, density and neutron logs for calculating porosity and to identify lithologies and fluid type.

Step 1 – Porosity Log Calculations

Calculate the sonic porosity, density porosity, neutron porosity and neutron-density total porosity.

Then calculate 2 different density porosity logs, assuming that the pore space is filled with a different fluid in each case. The two different fluids are:

• Oil
• Gas

Also calculate 2 different density porosity logs for, assuming a limestone (r_ma=2.71) and dolomite matrix (r_ma=2.87) saturated with salt water.

Step 2 – Calculate V_Shale from the Neutron Density Separation

Step 3 – Use the neutron and density logs in combination to discriminate between different lithologies and fluid types.

Answer the following Questions

• What effect does changing the fluid content have on your porosity calculations for the density log?
• What effect does changing the matrix have on your porosity calculations for the density log?
• How does the V_shale log compare with the GR V_shale log?
• Can you identify the presence of hydrocarbons?
• How shale and sandstone intervals are plotted on the FDC-CNL crossplot?
• Is there any gas effect on the FDC-CNL crossplot?

Part 4 – Full Log Interpretation For South Pepper No. 1

The aim of this part is to complete a log analysis task.

You have already calculated some petrophysical parameters including V_sh and total porosity for South Pepper No. 1.

In this part:

1. Calculate effective porosity (shale corrected porosity) from the Sonic Porosity, Density Porosity, Neutron Porosity
2. Compare total and effective porosity graphically
3. Calculate Rw from Archie method
4. Calculate water saturation from Archie method
5. Calculate water saturation from Simandoux method
6. Compare Archie and Simandoux water saturation
7. Estimate NTG ratio (cutoffs; Vsh<50%, f>4% and Sw<50%)
8. Calculate STOOIP for an area of 3 km² (RF=30% and FVF=1.2)

Note: Consider deep resistivity = Rt and a=1, m=2 and n=2