PA L E O N T O L O G I C A L R E S E A R C H I N S T I T U T I O N
T H E S C I E N C E B E N E AT H T H E S U R FA C E
M A R C E L L U S
S H A L E
•
I S S U E
N U M B E R
6
Understanding Drilling
Technology
•
J A N U A R Y
2 0 1 2
A discussion of the technologies associated with unconventional natural
gas drilling and how it compares to more familiar conventional drilling
techniques.
Introduction
The Marcellus Shale is an unconventional natural gas resource found
beneath the surface of Pennsylvania,
Ohio, West Virginia, and New York.
The natural gas found in the Marcellus Shale is requires unconventional
methods of extraction, in this case
high-volume, horizontal hydraulic
fracturing, because of the way the
natural gas is trapped in the formation. Until fairly recently, it was not
economically feasible to extract the
natural trapped in a tight shale like
the Marcellus. In recent years, however, a new combination of existing
drilling technologies – horizontal
drilling and hydraulic fracturing –
has emerged that makes this possible.
Conventional Natural Gas
Extraction
Unconventional natural gas
extraction is new to New York
State, but gas has been produced
by conventional drilling methods
in New York since the 1800’s. A
conventional gas resource is usually one in which the gas forms in
a specific rock unit, called a source
rock (the Marcellus is a source rock),
but migrates out of this rock unit
toward areas of lower pressure. It is
eventually trapped by an impermeable rock unit, called a reservoir or
reserve. Sometimes the reservoir is
a void created when a layer of rock
has broken and moved beneath the
surface; sometimes the reservoir is
created when gas collects in the pore
spaces in rock layers that have formed
subterranean ‘hills’ Conventional
drilling techniques require geologists
to find reservoirs of natural gas, and
then drill down into them to extract
the gas.
Sometimes it is difficult or impossible to set up drilling operations directly above a natural gas reservoir. If
the oil or gas deposit is located under
an urban area, for instance, surface
conditions would not allow drilling
there. To get around this problem,
conventional oil and gas wells can be
drilled at various angles underground
in a process called directional drilling.
One version of directional drilling, horizontal drilling, starts with
a vertical well bore (the hole the well
makes under the surface) which is
then angled until it is oriented horizontally. From there, the well can be
drilled horizontally underground for
MUSEUM OF THE EARTH
AT THE PALEONTOLOGICAL RESEARCH INSTITUTION
1259 Trumansburg Road
Ithaca, New York 14850
www.museumoftheearth.org/marcellusshale
Marcellus Shale • Issue Number 6 • January 2012
/ 1
thousands of feet. Horizontal drilling
provides access to reservoirs that are
too thin or compacted to be accessed
with conventional vertical wells.
Some directional wells have even
been angled beyond horizontal, and
have hooked back upward in order to
access particularly difficult-to-reach
oil or gas pockets. This is called fish
hook drilling. Horizontal drilling is
the type of directional drilling that
is currently being used to access the
natural gas in the Marcellus Shale in
Pennsylvania, and that will be used
to access the Marcellus Shale in New
York if Marcellus wells are drilled.
If a source rock does not have
abundant natural pore space or
fractures, the oil or gas may not be
able to migrate from its source rock
into a reservoir rock from which it
can be easily extracted. To get around
this problem, such tight source rocks
are artificially cracked or fractured,
by any of a variety of techniques,
in order to stimulate well production. Fracturing source rock in order
to increase gas well production in
conventional resources has a long
history in New York State. Beginning
in the 1860’s, the explosive nitroglycerin was used, sometimes illegally, to
crack rocks in shallow wells. Since
then, and throughout the United
States, various fracturing fluids
have been used to fracture rocks by
hydrostatic pressure. These fracturing fluids, when under high pressure,
either create or expand fractures in
the rock, creating hydraulic fractures.
The Marcellus Shale is one such tight
source rock, so hydraulic fracturing is
used to extract the natural gas from
it.
Hydraulic fracturing not used
solely to increase connectivity of pore
spaces in the rock to the well bore. It
is also used to decrease the hydraulic
pressure in the areas nearest a vertical well in order to minimize drilling
complications. It can also be used to
increase the gas flow rate of vertical wells damaged by the buildup of
scale (the accumulation of minerals
in pipes and other equipment) or
other materials.1
Unconventional natural gas drilling is considered “unconventional”
because the natural gas has not
migrated from the source rock into a
reservoir, but remains trapped within
the source rock. Extracting this natural gas requires
1) additional surface area contact between the well bore to the
source rock, which is provided by
drilling horizontal wells, and
2) the creation of pathways
for the natural gas to flow out of
the source rock and into the well,
which is provided by hydraulic
fracturing.
It is the combination of tight source
rock with the application of unconventional drilling technology (just
hydraulic fracturing, just horizontal
drilling, or a combination of both)
that makes a resource unconventional. Either the gas resource itself or the
technologies used to extract the gas
can be referred to as unconventional.
The remainder of this discussion will
consider the unconventional natural
gas drilling being used in the Marcellus Shale, which requires both horizontal drilling and hydraulic fracturing of a geologically unique reservoir
rock to be economically viable.
Unconventional and Conventional
Well Drilling – A Matter of Scale
Vertical well operations differ
from horizontal well drilling operations in scale. A vertical well pad
(the area at the surface, surrounding
the well bore that is used to conduct
the drilling and hydraulic fracture
activities) is smaller than a horizontal
well pad – a fraction of an acre to
about 3 acres for a vertical pad and 3
2 / Marcellus Shale • Issue Number 6 • January 2012
to 6 acres for a horizontal well pad.
The size of the well pad in both horizontal and vertical drilling operations
increases as on-site storage needs
increase for equipment and fluid. The
amount of water and chemicals used
in a horizontal well that is hydraulically fractured is greatly increased
(by up to 100-fold) over vertical
wells that are hydraulically fractured.
Vertical wells typically use 20,000 –
80,000 gallons of water for hydraulic
fracturing, and New York State regulations state that any well fractured
with more than 300,000 gallons of
water is considered a “high-volume”
well.2 Horizontal wells, however, use
between 2 and 9 million gallons of
water; 4.3 million gallons of water is
the average in a Marcellus well in the
Susquehanna River Basin of Pennsylvania.3
Hydraulic fracturing operations
in both vertical and horizontal wells
incorporate a variety of chemicals to
enhance recovery of oil or gas. Just
like the drilling process itself, the
chemicals used have changed over
time, largely through trial and error
experimentation, but also through
regulation. In the past, they have
included acid, water and acid combined, squeeze-cement, napalm and
gasoline, and a variety of gelled fossil
fuels.4
Modern methods of hydraulic
fracturing evolved in the 1960’s with
the advent of water-based gels that
were used to carry proppant into
fractures. Proppants are natural or
manufactured (e.g., ceramic beads)
sand grains that are used to hold
open the fractures created during
hydraulic fracturing. Adding proppants to the fracture fluid led to
further experimentation with fluid
viscosity. Surfactants and crosslinkers
(chemical additives) were added to
adjust the viscosity of the fluid in an
attempt to optimize the amount of
1: A Comparison between Conventional and Unconventional Drilling
Table
Well type
Well pad footprint
Road Construction
Footprint
Water required
Chemicals required
Time to drill well
Hydraulic fracturing
required
Source rock
Conventional Drilling
vertical
>1 acre to 3 acres
Similar to unconventional drilling
20,000 to 80,000
gallons
Unconventional Drilling
horizontal
3 to 6 acres
5.7 acres
~ 1 month
sometimes
~ 3 months
almost always
large pocket of resource; easy to extract
resource scattered
throughout rock, hard
to extract
proppant carried into the fractures
and the speed at which they were
transported. For information on the
chemicals used in Marcellus Shale
hydraulic fracturing operations,
please see Marcellus Shale Issue 7:
Water – Into the Wells. Eventually, the
combination of these different methods created what is called high volume, slickwater, horizontal hydraulic
fracturing, which is currently used in
the Marcellus Shale and other tight
shale gas plays (the area in under development by natural gas operators).
High-volume, horizontal hydraulic
fracturing is so named because it
differs from other drilling methods
in a few important ways. In this
technology, a vertical well is drilled
with a horizontal leg (or lateral)
that runs parallel to the rock being
drilled. Wells that travel horizontally
through a gas-bearing layer require a
higher volume of water to fracture, or
crack, the rock than wells that only
bore vertically; about 4.5 million
versus 80 thousand gallons, respectively. The term slickwater refers to
the combination of chemicals added
to the fracturing fluid to modify its
2 to 9 million gallons;
average 4 million gallons
viscosity, thus increasing the speed at
which it travels in the well.
Drilling a Well
Drilling a well to extract natural gas from the ground may sound
simple but it is not. Vertical or
horizontal, hydraulically fractured
or not, all gas well drilling requires a
long series of usually complex steps.
Before any drilling takes place, the
well pad must be established, and
be large enough to support all of the
equipment needed to drill and hydraulically fracture a well. In the case
of horizontal wells, a special drill bit
is used to turn the drill at an angle at
a predetermined depth, referred to
as the “kickoff point.” To turn a well
fully horizontal takes around 1000
vertical feet of drilling.
As the well is being drilled, it is
lined with steel casing in order to
prevent collapse of the hole. Casings
also prevent drilling fluids and gas
from escaping through the sides of
the well. Steel casing is inserted into
the drilled hole, cemented in place,
and then the well is drilled deeper
with a slightly smaller drill bit. Then
another, slimmer casing is hung in
the deeper well hole and cemented in
place.4 Guiding shoes on the ends of
the casing help the lengths of casing move down the well safely, and a
spring-like centralizer positions the
casing in the center of the well hole.
Eight types of cement are classified by the American Petroleum
Institute (API) for use in well casings. This classification system was
designed to address quality concerns
such as poor raw ingredients, and the
cement chosen is commonly mixed
with cement additives that modify its
setting time and density. The cement
is pumped down the well inside the
casing. When it reaches the bottom
of the hole, it flows out and back
up the space between the casing and
the drilled well, the area called the
annulus. To ensure that the cement
in the casing is pushed fully into the
annulus, a wiper plug is inserted
behind the wet cement to force the
cement out of the well bore, clean
the inside walls of the casing, and
separate the cement from additional
drilling muds. After the wiper plug is
inserted, drilling muds (substances
that lubricate the drill bit and make
drilling easier and faster)are pumped
into the well to continue to force the
cement into lining the outside of the
casing wall.5
Marcellus wells are drilled and
cased in multiple stages. This process
is called a casing program. The first
piece of casing, called the conductor pipe, has the largest diameter. Its
primary job is to prevent the collapse
of the top of the well. It also prevents exchange of fluids between the
well and nearby shallow water and
gas reserves and provides a path for
drilling muds. Blowout preventers
(valves that help regulate erratic pressure changes that can be found while
drilling) are attached to this level of
casing.5
Marcellus Shale • Issue Number 6 • January 2012
/ 3
Surface casing is the next level
of casing, and is commonly around
13 ¾ inches in diameter. Its job is
similar to the conductor pipe; it prevents contamination of groundwater
by drilling muds and keeps sediment
from caving into the well. Intermediate casing, which is typically 8
5/8 inches in diameter, is added to
mitigate potential problems at greater
depths, like areas of unusually high
pressure (due to shallow gas pockets).
The last casing to be inserted into the
well is thinnest in diameter (between
2-4 inches) and is called the production casing. It is run through the
length of the well that will be producing natural gas.
Because casing lines the entirety of the well, it must have
holes punctured into it in order for
natural gas to have a pathway into
the well. These holes are created by
perforation guns (perf guns) that
are positioned in the lateral part of
the well with a wire line or drill pipe
and guiding wheels. There are many
varieties of perf guns, but they all
function in a similar way. Once in
position, the perf gun shoots small
projectiles (called shaped charges),
which are essentially armor-piercing
bullets, directly into the casing. These
charges punch through the steel casing and cement-filled annulus.
After the well has been completed, the gas company runs a series of
pressure tests, commonly called “shut
ins,” on the well. These tests, which
usually last 72 hours, assess whether
the newly drilled well was drilled and
cased correctly. After these tests, a
device known as a Christmas Tree is
placed on the top of the well at the
surface. This device allows gas to be
pumped into production pipelines. It
also monitors production and holds
the regulating blowout valve that is
designed to control erratic pressures
in the well and to seal the well in an
emergency.
greater than for vertical wells.
The direction and length of the
Unconventional Natural Gas
lateral (horizontal part of the well)
Extraction
depends on the local geology, the
Fossil fuel extraction by convenamount of land available to the
tional means is very costly. Fewer
driller, and the available technolthan 50% of oil and gas wells ever
ogy. Laterals in shale gas wells have
drilled in the U.S. have become com- commonly been around 4,000 to
mercially successful. This is because
5,000 feet in length, but companies
many turn out to have little or no oil are expected to increase the length of
or gas that can be extracted economi- laterals in the Marcellus as the limits
cally. Some of them are truly ‘dry
of the technology are more widely
holes’ while others have oil or gas,
tested. The directions in which the
but the source rock was damaged
laterals extend from the vertical part
during drilling, lowering permeabilof the well bore are determined as
ity near the well, or were otherwise
a result of analysis of the current
less prolific than originally thought.
underground stresses and the preNew drilling techniques were
dicted effects of existing and stimuoriginally developed in an effort to
lated fractures. In the Marcellus, gas
extract more resources from those
companies are directionally drilling
conventional wells in a second or
laterals in the north-northwest and
third drilling attempt. These techsouth-southeast directions.6 For
niques, known as secondary or
more information on why laterals
tertiary recovery, received the first
are drilled in this direction, please
hydraulic fracturing treatments.
refer to our pamphlet Marcellus Shale
Later, the technology, combined with Issue 5: Jointing and Fracturing in the
horizontal drilling, became useful for Marcellus Shale.
recovering fossil fuels in impermeable, unconventional reservoirs.
The Hydraulic Fracturing Process
Hydraulic fracturing, specifically
The Horizontal Drilling Process
the high volume, slickwater, horizonHorizontal drilling in and of itself tal fracturing used in the Marcellus
is not highly controversial. Because
Shale, is the process of forcing liquid
horizontal wells are so much longer,
into the gas-bearing rock unit under
however, they are drilled by larger
high pressure to fracture the rock
pieces of equipment, take more time adjacent to the well. These fractures
to drill, and require more hydraulic
form pathways for the natural gas
fracturing fluid to be stimulated
trapped in the rock to escape via the
successfully. During this process, a
well bore. Hydraulically fracturing a
far greater amount of rock must be
horizontal well in the Marcellus Shale
drilled through, which generates
requires about 4.5 million gallons of
more cuttings (a mixture of coarse
water, which is mixed with a variety
chips and finer particles of rock that
of chemicals and sand. The chemicals
are produced as the well is drilled)
the fracture process by doing things
that must be disposed of from a
like keeping the fractures free of
horizontal well compared to a vertibacteria and transporting the sand
cal well. And the length of time a
grains. Various-sized sand grains,
horizontal well is in the development called proppant hold open the fracphase – and therefore the total local
tures created by this process. To learn
impact of drilling – can be much
more about the chemicals required
4 / Marcellus Shale • Issue Number 6 • January 2012
Figure 1: Drilling and Casing a Well
Drill
Casing
Centralizer
Cement
Casing
Annulus
Drill
Hole
1
Drilling
Muds
Cement
Wiper
Plug
4
Guide
Shoe
2
3
Empty
Well
Hole
Cement
5
New Drill
Hole
6
First
Casing
Cemented Casings
Second
Casing
Third
Casing
Production Casing
7
The process of drilling and casing vertical and horizontal wells is the same in the initial drilling depths. 1) The drill initially bores into the ground.
At this point the drill is lubricated with...and the drill hole is empty. 2) After the initial hole is drilled, a steel casing is inserted into the hole, guided
by a springlike ‘guiding shoe’ that positions the casing in the center of the hole. The space between the casing and the rock on the outside of the hole
is called the ‘annulus.’ 3) Cement is poured into the casing from the surface. It flows to the bottom of the hole and begins to infill the annulus. 4)
When enough cement has been poured into the well to line the casing, wiper plugs are inserted into the casing to wipe the inside clean of wet cement.
The plugs are pushed down by drilling muds, which are later used to lubricate the drill bit. The cement is allowed to dry. 5 & 6)The new well hole is
now the only void space in the well. A drill is re-inserted into the well where it drills through a layer of cement and into deeper rock. 7) The process
of drilling, casing, and cementing the casing is repeated with thinner and thinner casings that are intended to prevent any exchange between fluid
flowing through the well and surrounding groundwater sources. The production casing lines the length of the well and is intended to be porous in the
region where natural gas is to be extracted (in this diagram, the horizontal portion will undergo small blasts to puncture the steel and allow fracture
fluid out and natural gas in).
Marcellus Shale • Issue Number 6 • January 2012
/ 5
in high volume, slickwater hydraulic
fracturing, see our pamphlet Marcellus Shale Issue 7: Water: Into the Wells.
Because the horizontal portion
of a Marcellus well is typically 4,000
to 5,000 feet in length, the well is
hydraulically fractured section by
section, a process called multi-stage
hydraulic fracturing. The section
farthest away from the vertical part
of the well is fractured first, and then
closed off from the remainder of the
well. Then the process is repeated
with the next section, and so on until
the full lateral length of the well has
been fractured. It has been common
for a multi-stage fracture to have
three or four sections of fracturing,
but as lateral lengths of the wells
increase, so could the number of
stages in the full hydraulic fracture of
a well.
The actual process of fracturing
occurs in three phases. First fracturing fluid, consisting of water and
chemicals, is injected into the well,
creating fractures near the well bore,
although sometimes acidic or basic
fluid precedes the fracturing fluid to
break down natural cements in the
rock or to mitigate buildup of mineral deposits.7 Second, more fracturing
fluid is mixed with proppants and
injected into the well. During this
phase, the initial fractures are elongated and the proppants are forced
into the fractures to hold them open
after the pressure from hydraulic
fracturing is released. Finally, the well
is flushed out to remove the excess
fracturing fluid from the well.5 In the
Marcellus Shale, only around 9-35%
of the fracturing fluids return to the
surface.2
While the fate of the fracturing
fluid that remains underground after
the Marcellus Shale is fractured is
not yet fully understood, geologists
and engineers hypothesize that the
remaining 70-90% of fracturing fluid
is trapped in the multiple, tiny fractures due to a combination of capillary action and the swelling of clays.
In very small spaces the molecular attraction between water molecules and
the molecules in the shale fractures
can be stronger than other pressures
acting on the water. This holds the
fracturing fluid in the fractures and
is referred to as capillary action. Clay
can also “trap” the fracturing fluids
because clay grains can absorb water,
swell, and decrease permeability.
Because many of the inorganic sediments that make up the Marcellus
Shale are clay grains, geologists think
that some of the fracturing fluid is
absorbed by clay at depth. For these
reasons, only a small portion of the
fracturing fluid is returned to the surface during when the well is flushed
out to remove excess fluid. 7,8,9
The characteristics of the target
formation (the rock from which gas
is being extracted) determine what
specific techniques will be used to
extract gas. Data must be collected
for every new region and formation
that is developed for gas drilling. The
stresses on the rock at the depth of
gas extraction and the rock permeability help determine what fluid and
propping agent characteristics are
needed to fracture wells most effectively. More, larger fractures yield
more natural gas produced from the
unit, but are costlier to create. It
takes time to develop the information on each region, but eventually
the engineers in charge of each well
use the data to establish the optimum
fracture treatment for each well.1
The effectiveness of a hydraulic
fracture treatment can be measured
using a combination of microseismic
mapping in the field and measurements taken in the well (i.e. temperature, production, and video image
logging) to supply information on
fractures immediately near the well
6 / Marcellus Shale • Issue Number 6 • January 2012
bore, and modeling. These techniques can be very expensive, and
are usually used in research wells to
initially characterize a region being
drilled in order to design the fracturing process for that region.1
Hydraulically fracturing horizontal wells requires a large quantity of
water mixed with a variety of chemicals ranging from benign to toxic,
and a portion of this fracturing fluid
is returned to the surface. In addition
to the chemicals used by the drilling
industry, this flowback water can also
contain a variety of heavy metals,
salts, and naturally-occurring radioactive material found in the gas-bearing unit. Because of this, handling,
treating, and disposing of contaminated flowback fluids has become
an important issue in the Marcellus
Shale. Options for wastewater currently include: deep fluid injection
wells, where contaminated water is
injected into a deep, impermeable
formation and stored permanently;
disposing in a wastewater treatment
facility designed for flowback fluids;
or onsite water treatment and recycling for additional hydraulic fracturing jobs by the industry. To learn
more about wastewater treatment
options, see our pamphlet Marcellus
Shale Issue 8: Water: Out of the Wells.
It is currently unclear how many
times a well will be hydraulically
fractured in the Marcellus Shale. A
multi-staged hydraulic fracture of
a well is typically considered one
hydraulic fracturing event. Should
a portion of the well become damaged or if the well performs beneath
the expectations of the company,
a portion of the well or the whole
well may be hydraulically fractured
again. To what extent this will occur
is not yet known, as most wells in the
Marcellus region are less than a few
years old.
Natural Gas Extraction and
Transport: What happens when the
gas leaves the well
Once a Marcellus Shale natural gas well has been successfully
drilled, natural gas is extracted,
processed, and sold for profit. It is
estimated that Marcellus Shale wells
will produce economically valuable
quantities of natural gas for at least
30 years. It is hard to predict, at this
stage in Marcellus Shale gas development, the accuracy of that time
frame. All gas wells produce the highest flow rates of natural gas in the
first weeks of production, and this
rate declines over time as the pressure in the gas-bearing unit declines.
When a well is producing at rates so
low it is barely profitable, it is called a
stripper well. Because no wells in the
Marcellus Shale have been producing
for an extended period of time, it is
hard to estimate when they will no
longer be economically viable. However, with each month analysts gather
more data, and the predicted rate of
decline, frequently called the decline
curve, of Marcellus Shale gas wells
can be more accurately estimated.5
Some of the first Marcellus wells that
have been producing since 2004 in
West Virginia currently show decline
curves that suggest a given well will
be profitable for around 20-25 years.7
If the gas being extracted from
the Marcellus Shale is nearly free of
impurities, it can be immediately
sold by the gas industry to the pipeline industry, transported to a final
gas processing plant and placed on
the market. If there is a high level of
water or hydrocarbon liquids in the
gas, or if the gas contains corrosive
gases (like carbon dioxide or hydrogen sulfide), the gas must be processed in the field before being sold
to the pipeline industry.5
Once the gas is of a high enough
quality to be sold to the pipeline for
final processing and sale on the market, it is collected by gathering lines
which feed into compressor stations
and metering sites. These stations
connect to larger pipelines owned
by pipeline companies who distribute and sell natural gas to utilities.
Figure 2: Highlighted Major Pipeline Infrastructure in the U.S.
US LNG Terminals
Existing
Under Construction
Permitted
Note: pipeline systems in certain
regions omitted for clarity.
Variously-colored grey lines represent pipeline systems that transport natural gas to recipients. The majority of natural gas is transported to the Northeast region of the U.S. because of heating demands and high population densities. Note that pipelines can only transport natural gas in one direction,
and is usually transported from Texas and the Gulf of Mexico in the south, and from Canada in the north, with some LNG being imported in the
NE and the rest imported through the G
Marcellus Shale • Issue Number 6 • January 2012
/ 7
Interstate pipeline companies transporting natural gas are regulated by
the Federal Energy Regulatory Commission (FERC) with help from the
U.S. Department of Transportation’s
Pipeline and Hazardous Materials
Safety Administration (PHMSA).
Gathering lines that connect wells to
pipeline companies are not regulated
under FERC and PHMSA. Instead,
these are regulated locally by a state’s
Public Service Commission. See
Figure 2 fot existing US pipeline
infrastructure.
advantages to hydraulic fracturing
property rights belong only to one
with propane, including less truck
company. The initial cost of propane
traffic than is currently seen hauling
is also much higher than water. As
water, fewer chemical additives than a result, it may take years for wideis used in water hydraulic fracturspread industrial use of hydraulic
ing, and no hydraulic fracturing
fracturing with propane to occur.
wastewater issues. However, there
Certainly, as new technologies
are also drawbacks to using liquid
become available they bring with
propane. Compressing large quantithem the potential for more efficient
ties of propane on a regular basis
natural gas extraction, but they also
increases the potential for explosions bring forth a new set of environmenand fire. Propane, itself, is a fossil
tal and other concerns that need to
fuel that may need to be produced
be considered.
in larger quantities beyond existing
production if it is to be directed to
Summary
Looking Ahead: More Technological hydraulic fracturing. Finally, financial
The geological context of the
Advances in Hydraulic Fracturing
incentives may drive companies using Marcellus Shale plays an important
Even as the technology associated propane to hydraulically fracture a
role in the extraction of the unconwith unconventional gas drilling in
well to drill more finely spaced verti- ventional natural gas resource stored
the Marcellus Shale is being refined,
cal wells instead of horizontal wells,
within. The extraction, processing,
newer technologies are also being de- which could dramatically increase the and transportation of that natural
veloped and tested. A few companies amount of land altered by drilling in gas to its intended market is complex
are experimenting with the technolthe region.
and actively evolving. The techniques
ogy used to hydraulically fracture a
Currently, the process of hyrequired have environmental implicaformation with propane gas. Early
draulic fracturing with propane is
tions that are discussed in other patesting suggests that the quantity of
not widespread, and the intellectual
pers in this series and socio-political
gas extractable from an unconvenGlossary
tional unit using propane to hydrauAnnulus: The space between the casing and the drilled well.
lically fracture a well is considerably
Blowout preventer: A valve that helps regulate erratic pressure changes that
more than with water-based hydraucan be found while drilling.
lic fracturing technology.
Capillary action: In very small spaces the molecular attraction between water
In principle, the idea behind
molecules and the molecules in the shale fractures can be stronger than other
hydraulically fracturing a well with
pressures acting on the water. This holds the fracturing fluid in the fractures and
propane is based on the physical
is referred to as capillary action.
Centralizer: A spring-like centralizer positions the casing in the center of the
properties of the propane, itself. Surwell hole.
face tension is defined as the ability
Casing Program: The multiple stages used to drill and case a well are colof a liquid to resist an external force.
lectively
called a casing program.
Because propane has about ten times
Conductor Pipe: The first piece of casing inserted into the well with the
less surface tension than water, friclargest diameter.
tional forces associated with pushing
Conventional: A conventional gas resource is usually one in which the gas
propane through a well are far lower
forms in a specific rock unit, called a source rock, but migrates out of this rock
than when pushing water through a
unit toward areas of lower pressure.
Cuttings: A mixture of coarse chips and finer particles of rock that are prowell.8,10 Propane is also eight times
duced as the well is drilled.
less viscous than water. Viscosity is a
Directional drilling: A gas well that is not drilled vertically is drilled direcmeasure of a fluid’s internal friction
tionally.
(molasses has a high viscosity while
Drilling muds: Drilling muds lubricate the drill bit and make drilling easier
water has a low viscosity). Finally, liqand faster
uid propane is also a less dense liquid
Fish hook drilling: Wells that have been angled beyond horizontal, and have
than water.
hooked back upward in order to access particularly difficult-to-reach oil or gas
There are a number of predictable
8 / Marcellus Shale • Issue Number 6 • January 2012
implications that are actively being
studied by sociologists.
References
1. Department of Energy, Hydraulic
Fracturing Whitepaper, Appendix A,
June 2004
2. Department of Environmental
Conservation, Draft SGEIS on the Oil,
Gas and Solution Mining Regulatory
Program, September 2011
3. Susquehanna River Basin Commission, Frequently Asked Questions,
http://www.srbc.net/programs/natural_gas_development_faq.htm.
4. King, Robert F., Morehouse, David
F. “Drilling Sideways-- A Review of
Horizontal Well Technology and its
Domestic Application.” U.S. Department of Energy- Energy Information
Administration April 1993. 26 January
2011 Http://www.eia.doe.gov/pub/oil_
gas/natural_gas/analysis_publications/
drilling_sideways_well_technology/pdf/
tr0565.pdf
5. Hyne, Norman J. Nontechnical guide
to petroleum geology, exploration, drilling, and production. PennWell Books,
2001
6. Engelder, Terry, Gary G. Lash, and
Redescal S. Uzcategui, 2009 Joint sets
that enhance production from Middle
and Upper Devonian gas shales of the
Appalachian Basin, AAPG Bulletin; July
2009; v. 93; no. 7; p. 857-889
7. Conner O’Laughlin, Camp, Dresser,
and McKee. Personal communication,
pockets
Gas play: The area in under development by natural gas operators.
Horizontal drilling: A gas well that starts with a vertical well bore which is
then angled until it is oriented horizontally.
Intermediate Casing: This is typically 8 5/8 inches in diameter, and is
added to mitigate potential problems at greater depths.
Lateral: The horizontal portion of the well bore.
Multi-stage hydraulic fracturing: A process by which a well is hydraulically
fractured section by section.
Production Casing: This is run through the length of the well that will be
producing natural gas.
Proppant: Natural or manufactured (e.g., ceramic beads) sand grains that
are used to hold open the fractures created during hydraulic fracturing.
Reservoir: An area of low pressure underground where gas has collected,
trapped by a layer of rock the gas cannot penetrate.
Scale: The accumulation of minerals in pipes and other equipment.
Shoe: Guiding shoes on the ends of the casing help the lengths of casing
move down the well safely.
Source rock: A rock unit in which natural gas formed.
Surface Casing: The level of casing after the conductor pipe, commonly
around 13 ¾ inches in diameter.
Target formation: The rock from which gas is being extracted.
Tight: Source rock that does not have abundant natural pore space or
fractures is considered tight.
Unconventional: Refers to either the natural gas or the extraction process
to retrieve the gas when the gas has not migrated from its source rock and
requires a combination of drilling technologies to extract.
Well bore: The hole the well makes under the surface.
Well pad: The area at the surface, surrounding the well bore that is used to
conduct the drilling and hydraulic fracture activities.
Wiper plug: The wiper plug is inserted behind the wet cement to force the
cement out of the well bore, clean the inside walls of the casing, and separate
the cement from additional drilling muds.
July, 2011.
8. GasFrac Energy Services Inc., http://
www.gasfrac.com/
9. Al-Mhaidib, A. I. (1997) “Influence
of Loading Rate on Undrained Bearing Capacity of a Model Pile in Clay”
proceedings of the Fourth Regional
Conference on Geotechnical Engineering (GEOTROPIKA ‘97) , Johor Bahru,
Malaysia, pp. 357-370.
10. Dictionary.com, 2011, http://dictionary.reference.com/ (accessed 2011)
Partnering Organizations include
Funded by NSF GEO No.1016359.
Cornell Cooperative Extension (naturalgas.cce.
Any opinions, findings, and conclusions
cornell.edu)
or recommendations expressed in this
New York State Water Resources Institute (wri.cormaterial are those of the author(s) and
nell.edu), Cornell University Department of Earth
do not necessarily reflect the views of the
and Atmospheric Sciences, and Cornell University
National Science Foundation.
Agricultural Experiment Station.
Authored by Trisha A. Smrecak and the PRI Marcellus Shale Team
Illustrations by J. Houghton unless otherwise attributed.
Marcellus Shale • Issue Number 6 • January 2012
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