A DEMONSTRATION MODEL OF HYDRAULIC FRACTURING: HANDS-ON ANALOG TO FRACTURING SHALE

The Michigan Geological Survey and the Department of Geosciences at Western Michigan University has developed a physical analog model for hydraulic fracturing in a vertical well. Hydraulic fracturing has become a controversial issue over the past decade, even though it has been in use as a standard well-completion technique for over 60 years. The development of high-volume hydraulic fracturing and the increase in utilization of hydrocarbons from unconventional reservoirs has made this technique much more common. Because direct experience of hydraulic fracturing is not possible in most teaching contexts, we developed a hands-on model that illustrates this process. The model serves as one component of a module from the WMU CoreKids program for K-12 demonstration. It is also used in a laboratory lesson on hydraulic fracturing in a college earth science content course for future elementary teachers.

We use an artificial stratigraphy to illustrate the layered nature of sedimentary rocks in a basin similar to the Michigan Basin. One of the layers is composed of agar gelatin, whereas the other layers consist of either impermeable, cemented sand, or of plastic and foam. Agar gelatin sets at room temperature and is sufficiently transparent to observe the fractures that develop. A mixture of glycerin and colored sand is an analog to the hydraulic fracturing fluid. The glycerin acts as the injectant and carries the proppant (sand) into the agar layer. The hydraulic fracturing fluid is injected under pressure into a pre-set well-bore. The hydraulic fracturing process develops wing-shaped fractures in the agar. These fractures form this morphology as the well-bore is designed to only allow the hydraulic fracturing fluid out into the agar through a vertically aligned perforation in the well casing.

One of the more interesting properties of the agar is that it can be removed from the model readily as a discrete block. After removal, the students can slice the agar along the fracture planes. The students can observe that the sand (proppant) lines the surface of the fracture. In using the model in the classroom, we have found that children and adult students alike enjoy the (somewhat messy) hands-on aspect and gain an appreciation of the mechanics of hydraulic fracturing.