How can you interpret and analyze well logs?

1 Choose the right logs

The first step in well log interpretation and analysis is to select the appropriate logs for your objectives and data availability. There are many types of well logs, such as gamma ray, resistivity, porosity, sonic, density, neutron, and nuclear magnetic resonance, each with its own advantages and limitations. Depending on the formation characteristics, you may need to use a combination of logs to obtain a comprehensive picture of the subsurface. For example, gamma ray logs can help you identify shale content and lithology, resistivity logs can indicate fluid type and saturation, and porosity logs can estimate the pore space and hydrocarbon volume.

2 Apply quality control and corrections

The next step is to check the quality and accuracy of the well logs, and apply any necessary corrections or adjustments. You should look for any anomalies, outliers, or inconsistencies in the log data, and compare them with other sources of information, such as core samples, drill cuttings, or mud logs. You should also correct the log readings for any environmental effects, such as borehole size, mud invasion, tool eccentricity, or temperature. Some of these corrections can be done automatically by the logging software, while others may require manual calculations or adjustments.

3 Identify zones of interest

The third step is to identify the zones of interest in the well logs, based on your evaluation criteria and goals. You should look for changes in the log responses that indicate the presence of hydrocarbons, such as resistivity contrast, crossover between density and neutron porosity, or gas effect on sonic velocity. You should also mark the boundaries of different formations or layers, based on the variations in the gamma ray or other lithology indicators. You can use log patterns, crossplots, or overlays to help you distinguish between different rock types and fluids.

4 Calculate petrophysical properties

The fourth step is to calculate the petrophysical properties of the zones of interest, such as porosity, water saturation, hydrocarbon saturation, permeability, and net pay. These properties are essential for estimating the reservoir quality and performance, and designing the optimal production strategy. You can use empirical formulas, charts, or models to derive these properties from the well log measurements, depending on the complexity and uncertainty of the situation. You should also consider the effects of clay, shale, or gas on the log responses, and apply appropriate corrections or adjustments.

5 Validate and calibrate the results

The fifth step is to validate and calibrate the results of your well log interpretation and analysis, by comparing them with other independent sources of data, such as core analysis, well testing, or production history. You should look for any discrepancies or deviations between the well log and the other data, and try to explain or resolve them. You may need to revise your assumptions, parameters, or models, and repeat the previous steps until you achieve a satisfactory match. You should also assess the uncertainty and sensitivity of your results, and report them with confidence intervals or ranges.

6 Integrate and visualize the data

The final step is to integrate and visualize the well log data with other geophysical, geological, and engineering data, to create a holistic and coherent picture of the reservoir. You can use software tools, such as petrophysical analysis, mapping, or 3D modeling, to combine and display the data in various formats and scales. You can also use the integrated data to perform further analysis, such as reservoir simulation, reserve estimation, or well placement optimization. You should always keep in mind the objectives and limitations of your well log interpretation and analysis, and communicate your findings and recommendations clearly and effectively.

7 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?