Look at the Well Log and identifiy which geophysical logs are present.

Look at the Well Log and identifiy which geophysical logs are present. Fill in Table 1 on the Exercise 1 Data Sheet with the logs that are present, along with a short description of what the logs measure.

Use the Gamma Ray Log to identifiy the shales (high radioactivity). u have to be drawing a vertical line showing the “shale baseline” on your log. Generally, any reading above 120 API can be considered a shale in this exercise. Each vertical grid line is 20 API units on this log, so count out to 120, and draw a thick vertical line with a permanent marker for your shale baseline (anything to the right of this line will be considered a shale).

Using the Bulk Density Log (RHOB) (red line on the right column) in conjunction with the Gamma Ray Log, mark off the likely distribution of shale, sandstone, and limestone. The average densities of these rock types are given in the geophysical log section of your lab manual. Remember that limestone has a higher density than sandstone. In general, sandstones and limestones have a low level of radioactivity, and shales have a high level of radioactivity.

Note: Organic black shales have a very high radioactivity. The gamma ray log will show a line that reaches the far right end of the gamma ray column, and then wraps back around to the far left side again to continue adding API units. When this happens, the gamma ray log shows diagonal lines between the gamma ray curves.

Now, color in each of these lithologies (shale, sandstone, and limestone) on the central blank column that shows the footage of the well (these sections are numbered to help you identifiy the boundaries between rock units). Use the following colors: yellow = sandstone; blue = limestone; gray = shale; black = organic shale.

After you have identified all the lithologies on the Well Log, list them from the most radioactive to least radioactive on the Data Sheet.

Using the Neutron Porosity Log (the dashed line on the right column), roughly mark out any porous zones that you think might be important reservoir faces. Using the permanent marker, mark these zones with a star in the central column where you color-coded the rock units. Disregard any shale zones because these zones mark false porosity.

Take a picture of your Well Log and send it to your instructor. (Your instructor should have procedures in place for how to upload your picture.)


1. What causes shale zones to have false porosity?

2. What other factors might geologists take into account when assessing reservoir potential?


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