Here’s the link to the CGS page. Here’s the introduction:
The Niobrara strata in the Denver Basin are currently being developed for oil production using horizontal drilling and hydraulic fracturing. This development is moving into parts of the Denver Basin where many people depend on groundwater to meet their household needs. Citizens are concerned that this activity may adversely affect their water wells. This calculation tool was developed to help citizens or planners understand the geologic conditions that exist beneath their property.
The tool is designed to help people visualize the spatial relation of hydraulic fracturing in the Niobrara Formation to the important fresh-water aquifers. The tool will show the average depth to the Niobrara Formation at any selected point or address on the map. It will also show the minimum thickness of the shale barrier (Pierre Shale) that separates the Niobrara strata from fresh water aquifers. The tool also provides the depth of the deepest fresh water aquifer at any spot on the map.
The above cross section [ed. Click on the the thumbnail graphic above and to the right] represents what we would encounter if a giant, vertical slice were cut out of the Denver Basin so that we could observe the various layers of rock. Notice that the Niobrara strata are so deep that they are actually below sea level in some parts of the basin.The illustration shows how an oil company would drill a vertical well into the Niobrara strata and then turn the drill bit so that it would drill horizontally in the Niobrara limestone layers. After the horizontal part of the well is drilled (sometimes more than a mile in length), the company pumps liquid and sand out into the horizontal borehole. The pressure of this slurry fractures the limestone so that the oil flows into the well at much higher rates than it normally would without the artificial fracturing.
Controlling where fracturing occurs is important for two reasons. First, if fracturing were to extend into overlying freshwater aquifers it would create a potential pathway for contamination of water supplies. Second, oil production would decrease if fractures extended into non-oil bearing formations.
Fortunately, in the Denver Basin we have a stack of rocks (the Pierre Shale) that separates the Niobrara from shallower aquifers. The properties of the Pierre Shale are ideal for preventing upward migration of fractures or fluids. The Pierre Shale has extremely low permeability and it is very thick (varying from more than a half a mile thick to about a mile and a half thick). These two properties combine to make the possibility of fractures or fluids working their way up through it, essentially nil. The calculation tool will show you how thick this barrier is at any spot in the Denver Basin.
More coverage the Craig Daily Press:
Citizens around the state have been seeking a better understanding of how ground water supplies are protected amid energy development and the geologic conditions that separate ground water from the oil and natural gas deposits in the Niobrara.
The purpose of the tool is to answer the following questions: If a company were to hydraulically fracture the Niobrara formation under a house, how deep would this be occurring? How thick would the shale barrier be between the house’s water well and the Niobrara strata?