The Marcellus Shale Gas Play: Part 2

The following is continued from the article prepared by Penn State University and explains the Marcellus Shale Gas Play.

Peter

The Marcellus Shale
The Marcellus shale is a deep layer of rock that
lies 5,000 to 9,000 feet underground and runs from
the southern tier of New York through the western
portion of Pennsylvania, into the eastern half of
Ohio, and through West Virginia. In Pennsylvania,
the formation extends from the Appalachian plateau
into the western valley and ridge. While this area has
produced natural gas for years, many gas production
companies are now interested in the Marcellus shale
because of higher energy prices and new drilling
technologies that could recover an estimated 50
trillion cubic feet of natural gas. Conservative
estimates state that the Marcellus shale contains 168
trillion cubic feet of natural gas; in reality, it could

contain as much as 516 trillion cubic
feet. The United States currently
produces roughly 30 trillion cubic feet
of gas a year and demand for this gas
is increasing steadily.

Typical drilling rig and pipe used to drill a deep and long horizontal well.

Where and How Does Drilling
Take Place?
Natural fractures in the Marcellus
shale are important to recovering large
amounts of gas. As heavily organic
sediments were deposited 380 million
years ago, the black shale that makes
up the Marcellus was formed. As the
organic material decayed, methane
and other components of natural gas
formed and are now trapped tightly
in the dense shale.

About 300 million
years ago the pressure of the gas
caused fractures in the formation.
These fractures run as slices from the
northeast to the southwest and are
fairly close together. While a vertical
well may cross one of these fractures and other
possibly less productive fractures, new technology
allows for horizontal drilling, which crosses a series of
fractures and may be more productive.

Gas wells are drilled in locations where a gas
company has obtained the right to explore for and
develop natural gas. Wells are spaced according
to mineral laws and regulations, with the goal of
extracting gas efficiently using as few wells as
possible.

Geologists and geophysicists working
for gas companies use seismic data to interpret the
formations of rock layers underground. If seismic data
suggest a reasonable possibility of efficient gas access,
a well will be drilled in a specific location using long
sections of drill pipe. Depending on the geology, the
drillers may drill vertically for several thousand feet
and then use special joints to turn the shaft 90 degrees
over the course of several hundred feet and continue
drilling horizontally for an additional distance of
up to 5,000 feet.

A steel casing is cemented in place
to stabilize the surface of the well bore and protect
groundwater resources. Horizontal drilling enables
companies to extract more gas in a cost-effective
manner. In many cases, multiple wells may be drilled
side by side on the same well pad, radiating out in
different directions.

Natural Gas Well Development
Development of an individual natural gas well site
typically follows this basic timeline, though it may
vary somewhat at any one site. The stages include:

1. Leasing activity, during which land is put under
contract and secured for natural gas exploration
and development. This stage normally lasts four
to six months.

2. Exploration and seismic testing, which is done to
find the areas that will offer the highest potential
natural gas yields. Exploration and seismic testing
typically last about four months.

3. Site preparation and drilling stage, including earth
moving, road grading, and well pad construction
as well as drilling and fracing. This stage lasts
from four to eight weeks. Pipeline is laid to
connect the well to feeder pipelines, allowing the
gas to reach market.

4. Site reclamation activities, during which stage
the active well site is stabilized and vegetation
is established. Site reclamation lasts about two
weeks.

5. Extraction and transport of natural gas from the
well, which can potentially last from five to thirty
years (depending on the productivity of that individual
well). Wells receive active maintenance
throughout their lifespan, which means ongoing
access is required. In addition, it is possible
that the well may be refraced at some later date,
temporarily bringing back much of the equipment.

6. Closure plan, a procedure that is influenced by
the landowner’s leasing terms, during which the
inactive well is closed and the site restored.
When their role on an individual site is completed,
the different crews typically move to a new well site
nearby to do site prep and drilling. Thus, within any
one community at any one time, there will be well
sites in different stages of development.

Why Marcellus Is Different from Shallow Wells
The gas produced from deep well drilling is under a
higher pressure than in shallow or traditional wells,
which necessitates different handling techniques and
equipment. Unlike shallow wells with natural gas
reserves, gas derived from the Marcellus shale is held
tightly within the shale so the method of extraction
is quite different.

Current technology uses significant
quantities of water under very high pressure to
fracture (frac) the shale. Due to the fact that wells are

horizontally drilled to access more shale, the amount
of water required for fracing these wells is significant,
between one and five million gallons or more per
well. This quantity of water required for fracing may
contribute to a significant number of issues in affected
communities.