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EERC Research Scientist Blaise Mibeck is experimenting with optical microscope image analysis techniques such as extended depth of field (EDF) and image segmentation to enhance the analysis of rock samples in order to study the porosity, or open space between grains of the rock, and permeability, a measure of the ease with which a fluid can move through a porous rock.

EDF allows the EERC to make high-resolution 2-D and 3-D images of core samples from oil and gas reservoirs and saline formations that can show detailed structure and composition of the rock and its porosity. Image segmentation simplifies digital images to make them easier to analyze quantitatively. Mibeck calls these techniques “more tools in the toolbox” for delivering information to improve oil and gas recovery and CO2storage in environmentally safe ways.

Mibeck develops experimental apparatus and analytical techniques in the EERC’s Natural Materials Analytical Research Laboratory. His work also involves quantitative phase analysis, powder x-ray diffraction, optical microscopy, and other material science techniques for the analysis of geologic samples.

“The microscopic structure of the rock is responsible for the macroscopic behavior of the formation,” said Mibeck. “Knowing what the pores look like and what is coating the grains, the size distribution of the pores and fractures, as well as how they connect to each other can provide information to help predict how a formation is going to behave when something is pumped into it or out of it, as in enhanced oil recovery or CO2storage.

“I am always interested in getting as much useful information out of an analytical technique as possible,” said Mibeck.

Optical microscopy is a common and relatively inexpensive means of analyzing rock samples. Unfortunately, at high magnifications it has a limited depth of field, making it difficult to image the entire thickness of a sample in focus. However, with the EDF technique, Mibeck is able to make high-resolution 2-D images or even 3-D images from a series of narrow-focus 2-D images. The EDF technique produces a higher-resolution image, allowing researchers to see smaller features. It provides a third dimension that is useful in clarifying the surface of pore walls, grain boundaries, and intergrain structure.

In the animated images shown below, the blue areas indicate pore space, or porosity, in the rock.

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“There is no easy way to observe fluid flowing through individual pores,” said Mibeck, “but we can use image analysis to get important information like how tortuous (twisty) the pores are in a sample, what the distribution of pore size is. This information is useful for understanding the history of the formation and may also allow predictions of how the formation will behave.

“Understanding the rock structure is critical to understanding how injections of water, CO2, or H2S will enhance oil production,” said Mibeck. “By determining the surface area of different minerals on the pore wall, we can predict how changing fluid conditions (such as pH) will change porosity,” he said.

For more information on EDF, image segmentation, or other optical microscope laboratory techniques, contact Blaise Mibeck at bmibeck@undeerc.org. For more information on the Natural Materials Analytical Research Laboratory, contact Beth Kurz at (701) 777-5050 or at bkurz@undeerc.org, or find information on the EERC Web site at www.undeerc.org/Facilities/Labs/Materials.aspx.