Posts Tagged ‘Horizontal Drilling’

Before 2000, many successful natural gas wells had been completed in the Marcellus. The yields of these wells were often unimpressive upon completion. However, many of these older wells in the Marcellus have a sustained production that decreases slowly over time. Many of them continued to produce gas for decades. A patient investor might make a profit from these low yield wells with slowly declining production rates.

For new wells drilled with the new horizontal drilling and hydraulic fracturing technologies the initial production can be much higher than what was seen in the old wells. Early production rates from some of the new wells has been over one million cubic feet of natural gas per day. The technology is so new that long term production data is not available. As with most gas wells, production rates will decline over time, however, a second hydraulic fracturing treatment could restimulate production.
Copyright: Geology.com

Horizontal Drilling to Penetrate More Fractures

The fractures (also known as “joints”) in the Marcellus Shale are vertical. So, a vertical borehole would be expected to intersect very few of them. However, a horizontal well, drilled perpendicular to the most common fracture orientation should intersect a maximum number of fractures.

High yield wells in the Marcellus Shale have been built using the horizontal drilling technique. Some horizontal wells in the Marcellus Shale have initial flows that suggest that they are capable of yielding millions of cubic feet of gas per day, making them some of the most productive gas wells in the eastern United States. Although some experts are very optimistic on the long-term production rates of these wells, it is too early to determine their productive life or long-term yield.

A second method is used to increase the productivity of a well. That is to increase the number of fractures in a well using a technique known as “hydraulic fracturing” or “hydrofracing”. This method uses high-pressure water or a gel to induce fractures in the rock surrounding the well bore.

Hydrofracing is done by sealing off a portion of the well and injecting water or gel under very high pressure into the isolated portion of the hole. The high pressure fractures the rock and pushes the fractures open.

To prevent the fractures from closing when the pressure is reduced several tons of sand or other “propant” is pumped down the well and into the pressurized portion of the hole. When the fracturing occurs millions of sand grains are forced into the fractures. If enough sand grains are trapped in the fracture it will be propped partially open when the pressure is reduced. This provides an improved permeability for the flow of gas to the well.

Copyright: Geology.com