Geologists have known for years that substantial deposits of oil and natural
gas are trapped in deep shale formations. These "shale reservoirs" were
created tens of millions of years ago. Around the world today, with modern
horizontal drilling techniques and hydraulic fracturing, the trapped oil and
natural gas in these shale reservoirs is being safely and efficiently produced,
gathered, and distributed to customers.
Let's look at the drilling and completion process
of a typical oil and natural gas well.
Shale reservoirs are usually one mile or more below the surface, well below any
underground source of drinking water which is typically no more than three
hundred to one thousand feet below the surface. Additionally, steel pipes, called
casing cemented in place provide a multilayered barrier to protect
During the past sixty years, the oil and gas industry has conducted fracture
stimulation in over one million wells worldwide.
The initial steps are the same as for any conventional well. A hole is
drilled straight down using fresh water based fluids, which cools the drill bit,
carries the rock cuttings back to the surface,
and stabilizes the wall of the wellbore.
Once the hole extends below the deepest freshwater aquifer,
the drill pipe is removed and replaced with steel pipe, called surface casing.
Next, cement is pumped down the casing.
When it reaches the bottom, it is pumped down and then back up between the casing
and the borehole wall,
creating an impermeable, additional protective barrier between the wellbore
and any fresh water sources.
In some cases,
depending on the geology of the area and the depth of the well,
additional casing sections may be run and like surface casing,
are then cemented in place to ensure no movement of fluids or gas
between those layers and the ground water sources.
What makes drilling for hydrocarbons in a shale formation unique is the
necessity to drill horizontally.
Vertical drilling continues to a depth called the kickoff point. This is where
the wellbore begins curving to become horizontal.
One of the advantages of horizontal drilling
is that it's possible to drill several wells from only one drilling pad,
minimizing the impact to the surface environment. When the targeted distance
is reached, the drill pipe is removed, and additional steel casing is inserted
through the full length of the wellbore.
Once again, the casing is cemented in place.
For some horizontal developments, new technology in the form of sliding
sleeves and mechanical isolation devices
replace cement in the creation of isolation along the wellbore.
Once the drilling is finished and the final casing has been installed,
the drilling rig is removed
and preparations are made for the next steps - well completion. The first step in
completing a well
is the creation of a connection between the final casing and the resevoir
This consists of lowering a specialized tool called a perforating gun which is
equipped with shaped explosives charges down to the rock layer containing oil or
natural gas. This perforating gun is then fired,
which creates holes through the casing, cement, and into the target rock.
These perforating holes connect the reservoir and the wellbore.
Since these perforations are only a few inches long and are performed more than a
mile underground, the entire process is imperceptible on the surface. The
perforation gun is then removed
in preparation for the next step - hydraulic fracturing.
The process consists of pumping a mixture of mostly water and sand, plus
a few chemicals, under controlled conditions into deep underground
The chemicals are generally for lubrication, to keep bacteria from forming
and help carry the sand.
These chemicals typically range in concentrations from 0.1 to
0.5 percent by volume,
and help to improve the performance of the stimulation.
This stimulation fluid is sent to trucks that pump fluid into the wellbore
and out through the perforations that were noted earlier.
This process creates fractures in the oil and gas reservoir rock. The sand
in the frac fluid remains in these fractures in the rock, and and keeps them
open when the pump pressure is relieved.
This allows the previously trapped oil or natural gas
to flow to the wellbore more easily.
This initial stimulation segment
is then isolated with a specially-designed plug
and the perforating guns are used to perforate the next stage.
This stage is then hydraulically fractured in the same manner.
This process is repeated along the entire horizontal section of the well,
which can extend several miles.
Once the stimulation is complete, the isolation plugs are drilled out and
Initially water, and then natural gas or oil, flows into the horizontal casing
and up the wellbore.
In the course of initial production of the well, approximately fifteen to
fifty percent of the fracturing fluid is recovered.
This fluid is either recycled to be used on other fracturing operations or safely
disposed of according to government regulations.
The whole process of developing a well typically takes from three to five
a few weeks to prepare the site, four to six weeks to drill the well, and then one
to three months of completion activities, which includes one to seven
days of stimulation.
But this three to five month investment can result in a well that will produce
oil or natural gas for twenty to forty years or more.
When all of the oil or natural gas that can be recovered economically from a
reservoir has been produced, work begins to return to land to the way it was
before the drilling operations commenced.
Wells will be filled with cement
and pipes cut off three to six feet below ground level. All surface equipment
will be removed and all pads will be filled in with dirt or replanted.
The land can then be used again by the landowner for other activities, and there
will be virtually no visual signs that a well was once there. Today,
hydraulic fracturing has become an increasingly important technique for
producing oil and natural gas in places where the hydrocarbons were previously
Technology will continue to be developed to improve the safe and economic
development of oil and gas resources.