How can you identify common well logging errors?

1 Checking the tool calibration

Before running any well logging tool, it is essential to check its calibration and performance. A poorly calibrated tool can produce inaccurate or inconsistent measurements, which can lead to erroneous interpretations of the reservoir properties. To check the tool calibration, petroleum engineers can compare the tool readings with known standards, such as calibration pits, reference logs, or laboratory tests. If the tool readings deviate significantly from the standards, the tool should be recalibrated or replaced.

2 Comparing different logs

Another way to identify well logging errors is to compare different logs from the same well or from nearby wells. For example, if the gamma ray log shows a different trend than the resistivity log, it may indicate a problem with one of the tools or the logging conditions. Similarly, if the porosity log shows a different value than the density or neutron log, it may suggest a calibration or interpretation error. By comparing different logs, petroleum engineers can spot any discrepancies or anomalies that may signal a well logging error.

3 Analyzing the borehole environment

The borehole environment can also affect the quality and accuracy of well logging data. Factors such as borehole size, shape, rugosity, mud type, temperature, pressure, and fluid invasion can influence the tool response and measurement. Therefore, petroleum engineers should analyze the borehole environment and adjust the logging parameters accordingly. For example, if the borehole is enlarged or eccentric, the tool may not be centered or in contact with the formation, which can cause errors in the log readings. In this case, petroleum engineers can use a centralizer or a caliper to correct the tool position and alignment.

4 Reviewing the log quality indicators

Most well logging tools have built-in log quality indicators (LQIs) that provide information about the tool status and performance during the logging operation. LQIs can include parameters such as tool voltage, current, temperature, tension, speed, depth, and signal strength. By reviewing the LQIs, petroleum engineers can identify any abnormal or erratic behavior of the tool that may indicate a malfunction or a failure. For example, if the tool voltage drops suddenly or the signal strength fluctuates wildly, it may mean that the tool is damaged or disconnected.

5 Applying correction methods

If petroleum engineers detect well logging errors, they should apply correction methods to reduce or eliminate the errors and improve the log quality. The type of correction method used depends on the source of the error. Environmental corrections are used to account for the effects of borehole environment on tool response and measurement, such as borehole size and shape corrections, mud and invasion corrections, temperature and pressure corrections, etc. Tool corrections take into consideration the effects of tool design and configuration on the tool response and measurement, for example, tool eccentricity and standoff corrections, tool normalization and calibration corrections, tool drift and noise corrections, etc. Interpretation corrections consider the effects of interpretation assumptions and models on the tool response and measurement, such as lithology and fluid corrections, formation factor and saturation corrections, shale and clay corrections, etc. By applying these correction methods, petroleum engineers can enhance the accuracy of well logging data and draw more reliable conclusions about reservoir properties and conditions.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?