Monday, January 25, 2010

Meet Marcellus Up Close & Personal

Pick up a chunk of Marcellus shale and you immediately understand why energy companies are interested in it: it’s dark, like coal, and leaves a greasy smear on your hand. Like all sedimentary rock, the Marcellus shale was created by compressing layers of mud together for a long, long time. 

If you could slice through the earth here in upstate NY, you’d notice that the rocks stacked up like layers of a birthday cake  –  11,000 feet of sandstones, limestones and shales. And Marcellus shale is only one of the gas-bearing layers; Oriskany sandstone, located just below Marcellus, and Trenton-Black River, another four to five thousand feet down, also produce gas in this area.

Unlike sandstone, Marcellus shale is composed of fine-grained clay particles so tightly packed that there are very tiny spaces – pores – between the particles. Those tiny spaces are where the natural gas is trapped - and that's what makes getting the gas out so difficult. Not only that, the pores are not connected to each other which means that gas can’t travel from one pore to the next. The only way to extract gas from a stone with such low porosity and low permeability is to break it apart using a process called hydraulic fracturing.

Hydraulic fracturing may seem like a new-fangled invention, but according to Tony Ingraffea. Ingraffea, a civil engineering professor at Cornell, the technique could have been used for hundreds of years. He believes the Romans introduced water into cracks to aid in breaking rock. Hydro-fracking is all about physics, Ingraffea says. A rock is strong when you push on it, but weak when you pull on it, or put tension on it. Engineers use water pressure to put tension on rock, taking advantage of the rock's weakness.

Initially hydro-fracking of oil and gas wells was used to open existing cracks - to "stimulate" the flow of oil or gas by making existing fractures bigger.  "As long as the pores in the rock are interconnected, you can get oil to flow," Ingraffea says. But in shale the pores are not interconnected, which makes the rock impermeable to water. "That's good from a fracking point of view," Ingraffea says, "because the water will create fractures without going into the rock." And the way shale is made - with thin layers of mud compressed together - means the rock will fracture more easily on those planes, going further than, say, a crack trying to travel through a crystalline formation.

But fracking is just one small piece of the picture, Ingraffea says. People don't understand just how industrialized the process of extracting gas from shale is, and the number of wells that will be required to make extraction economically viable for the energy companies.According to new research from Terry Engelder at Pennsylvania State University, we'll be eventually looking at multiple wells on 80-acre units. As others have already said, gas drilling will be the most profound land use issue to face this region.

1 comment:

  1. Fracing is torture, to land, people, wildlife,
    air and water. Thanks Sue for such a vivid