Estimating Permeability in Carbonates Using the Rock-Fabric

Estimating Permeability in Carbonates Using the Rock-Fabric Method

F. Jerry Lucia
Bureau of Economic Geology

Design Objectives

Exercise: Estimating Permeability in Carbonates Using the Rock-Fabric Method

Before beginning the exercise, carefully read the instructions to understand both the exercise process and interface. Begin by examining the exercise interface below.

THE EXERCISE INTERFACE:

DESCRIPTION OF THE INTERFACE TOOLS

	Click to step back or forward through each step in the exercise.
	Click the – button to zoom out or the + button to zoom in.
	Click this button to use the point-counting tool to determine Svug porosity. It is strongly recommended that you use this tool in the full-screen mode. This tool places a grid of green points over the sample image. Clicking on a dot once changes it's color to red and adds it to the SVug porosity tally; clicking the same dot again turns it back to green and subtracts it from the tally. Red dots are automatically counted and used to calculate the Svug porosity value as indicated by the cursor. The final Svug Porosity value is automatically transposed to the answer field of Step 5 upon returning to the normal interface mode. Rules for using the point-counting tool.
	The crystal reference tools represent crystals of 100 microns and 20 microns respectively (automatically scaled to each sample) and are used to categorize grains as fine, medium, or large.
	The full-screen mode button allows you to enlarge the sample window to the full size of the exercise interface for greater detail.
	The info buttons allow you to page through available screens of information, and to select the permeability estimation exercise chart. The info window will automatically present instructions for each step. Additional relevant info is available by hitting eitehr arrow button.
	The help button opens this help section

THE EXERCISE PROCESS

This exercise is organized as a series of 8 steps. Using the information presented earlier in this module, you should be able to work through each of the steps for each sample.

The first 3 steps require simply entering the basic information given at the bottom of each sample image into the answer field.

STEP 1: note whether the sample is Limestone or Dolostone. Click the appropriate radio button then click the

button to enter your value in the answer chart and proceed to the next step.

STEP 2: note the Total Porosity indicated on the sample image. Enter the value in the answer field, then click the

button to enter your value in the answer chart and proceed to the next step.

STEP 3: note the Scale in microns as indicated on the sample image. Enter the value in the answer field, then click the

button to proceed to the next step.

STEP 4: By examining the sample image, identify the grains to determine both the Rock Fabric Description and the Petrophysical Class. Use the information provided in the info window to assist in your classification. Click on the

buttons to scroll through the available pages of information. Enter the values in the appropriate fields, then click the

button to enter your values in the answer chart and proceed to the next step.

STEP 5: Look within the grains to determine the Separate Vug (Svug) porosity. This process will vary depending on whether the sample is limestone or dolostone. If limestone, use the point-counting tool to help determine the observed Svug porosity (more). Enter the value in the answer field, then click the

button to enter your value in the answer chart and proceed to the next step. The Interparticle Porosity will also be automatically calculated and enetered into the answer chart.

STEP 6: In the answer chart, note the interparticle porosity automatically calculated in the last step. Then, use that value to to derive a Permeability Estimate. Use the permeability estimation chart in the information window (see graphic above) by placing the cursor cross-hair at the intersection of the correct interpartical porosity value on the X-axis and the corresponding Petrophysical Class transform (as entered in Step 4). Read the permeability estimate in millidarcies on the Y-axis. Enter the value in the answer field, then click the

button to enter your value in the answer chart and proceed to the next step.

STEP 7: click on the Validate button to apply the appropriate numerical class transform in order to validate the permeability estimate from the previous step. Read the value in the "calculated permeability" column of the answer chart. This step demonstrates the second of two appoaches to arriving at a permeability estimate. then click the button to proceed to the next step.

STEP 8: Click the Compare button to compare your values with the answers provided by the author. Review the similarities and differences. Then, click the

button to repeat the process for each of the remaining samples in the exercise.

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