The process of drilling and completing a single horizontal oil or gas well takes about 70 to 100 days, after which the well can be in production for 20 to 40 years. That typically includes four to eight weeks to prepare the site for drilling, four or five weeks of rig work including drilling, casing and cementing, and moving all associated auxiliary equipment off the well site before fracturing operations commence, and two to five days for the multi-stage fracturing operation. Technological advances in horizontal drilling and hydraulic fracturing continue to advance the development of the oil and gas trapped within tight shale formations thousands of feet underground.
Once completed, the production site is about the size of a two-car garage, with the rest of the site restored to its original condition. Local impacts, such as noise, dust, and land disturbance, are largely confined to the initial phase of development.
But what really happens underground? Horizontal drilling and hydraulic fracturing (often called “fracking”) have been around for 50+ years. What pioneers of modern shale fracturing developed in the Barnett shale around Fort Worth, Texas in the 1990s was the technique of combining these two technologies with innovative proppants – fine sand and ceramic beads – to “prop” the cracks open so that oil and gas could be released to the drill hole. It took a lot of trial and error to figure out the exact combination of these techniques that would work, but the resulting developments have revolutionized the U.S. oil and gas future.
Geologists have always known that the shales and similar rock formations were the sources for the oil and gas that percolated upward over millions of years into the conventional reservoirs that have been tapped for more than a century. Knowing it was there did producers no good because the oil and gas in the rock is unable to flow very far due to the low permeability formations. They could drill a traditional vertical well into the shale, but very little oil or gas would flow into the well bore.
Horizontal drilling involves drilling down vertically to a desired depth and then making a 90 degree turn to continue drilling laterally through the shale seam away from the vertical well bore. This technique allows the production company to “mine” a seam of oil or gas bearing shale by drilling laterals that penetrate the oil or gas bearing shale layer horizontally. Lateral lengths can range from 1000 ft. to more than 10,000 ft. The long lateral creates a large surface area in contact with the rock and the potential for a lot more oil or gas flowing into the well bore.
Typically, steel pipe known as surface casing is cemented into place at the uppermost portion of a well for the explicit purpose of protecting the groundwater. The depth of the surface casing is determined based on groundwater protection and other factors. As the well is drilled deeper, additional casing is installed to isolate the formation(s) from which oil or natural gas is to be produced, which further protects groundwater from the producing formations in the well.
Casing and cementing are critical parts of the well construction that not only protect any water zones, but are also important to successful oil or natural gas production from hydrocarbon bearing zones. After the well is drilled and completed, the lateral section of the well pipe is perforated. Then a fluid mixture that is about 80 percent water, 19.5 percent sand and 0.5 percent various lubricants and chemicals, is pumped down the well at very high pressure. This so called hydraulic fracturing process is a high- pressure stimulation process used to create small cracks in the tight shale rock that allows fluids and natural gas trapped in the formation to flow more easily into the well pipe and up to the surface. When the pressure is released, the fractures attempt to close, but the sand contained in the fluid keeps the fractures open, making an easy path for oil and gas to flow into the well. Fracking opens up hundreds of little conduits for oil and gas to flow through (or actually around) the rock to get to the well bore deep underground. The proppants hold those little conduits open so they don’t close up right away.
Hydraulic fracturing and horizontal drilling have considerably increased the efficiency of oil and gas recovery for three reasons. First, there is lower geological risk - because producers know where the shale is, there are no dry holes. Second, many laterals can be drilled in several directions from one drilling pad. The same horizontal drilling rig can be moved slightly to extend a new lateral instead of packing up and moving to a new location to drill a new vertical well. And third, there are high initial production rates. Relative to vertical wells, shale wells are expensive to develop because of the high cost of long laterals and fracturing treatments. However, as a result of the efficiencies and greater production volumes described above, the per-unit cost of production is lower. In addition, because the initial production rate is high, producers recover their investment faster.
Pictures are worth a thousand words, and an excellent video of the process can be found at http://marcelluscoalition.org/2009/01/drilling-process-video/.
W. Norm Shade is the president of ACI Services Inc., headquartered in Cambridge, OH. ACI is a leader in the manufacture of custom engineered gas compressor products used throughout the world.