Chapter 7
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Start of production
Artificial lift
Well workover
Improved oil recovery
Gas production management overview
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Once drilling is complete, focus is turned to well
management to achieve cost effective, safe and
environmentally sensitive extraction of crude oil
and gas.
This chapter focuses on actions that optimize
production from oil and gas wells, including
maintenance, repair, and improved-recovery
programs that help achieve this goal while
extending the productive life of wells.
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For production operation of a well
the top of the wellbore is usually
outfitted with a collection of valves
and other components called a
Christmas tree. It regulates
pressure, flow and connects to
pipeline for distribution.
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If reservoir pressure remains high,
the Christmas tree is sufficient for
well production. If well pressure
decreases, artificial lift methods
can be employed to maintain
economic production.
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Following initial production, two
things happen: water (which is
heavier than oil and much heavier
than gas) begins to encroach into
the formation; and reservoir
pressure increases as the reservoir
depletes. If no action is taken,
then flow from the well will
eventually stop.
1. The most common approach is
to remove the Christmas tree and
install a surface pump. The
motor-driven sucker-rod pump
(also called a pumpjack) is by far
the most common.
2. Gas lift- a compressed gas is injected into the annulus
between the casing and the tubing where it dissolves in
the produced gas/water liquid and also forms bubbles. The
dissolved gas and bubbles force the liquid up the tubing
string, where the gas can be captured and recycled.
3.Installing a powered pump electric or hydraulic—at the
bottom of the well tubing
4. pump hydraulic fluid down into the tubing string
itself,allowing the produced gas and water to flow upward
through he tubing/casing annulus to the surface.
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Well workover-remedial action needed to
maintain production from a well after
months/years of production.
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Prior to work-over, a well is shut in to stop
production. Flow is killed by pumping brine,
drilling mud, oil, or some other fluid down into
the annulus, between the casing and the tubing,
and back up the tubing string.
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A BOP is usually installed while the tubing string
and other downhole equipment are removed.
Removal of water or drilling mud (swabbing), done
either right after a well is completed or later.
 Repair or replacement of downhole pumps, valves,
and packers
 Installation of smaller-diameter tubing to boost
flow rates
 Removal of scale (salts, e.g., calcium sulfate) or
paraffin from tubing
 Cleanout of loose sand from the bottom of wells
drilled in sandstones
 Repair of damaged tubing or casing or of the
cement around the casing
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A sidetrack well is drilled (if the original casing is
damaged) using special drill tools—such as a
whipstock, bent housing, or bent sub —are used to
drill outward at an angle from the original well. The
new wellbore is completed in the conventional
manner, and drilling continues after a liner is set.
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Recompletion- Done if operators determine that a
particular pay zone is depleted. It is the completion of
other pay zones below or above the original zone.
Cement is used to seal off the original producing zone.
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Use of a remotely
operated vehicle (ROV) is
often a better option.
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Primary production- Oil produced
by the original pressure in a
formation usually yields only about
30%–35% of the oil in place. (For
gas wells, primary production
generally yields about 80% of the
gas in place, so less attention is
given to improved recovery.)
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A common technique often used
first by operators to extract
additional oil is called water flood,
which can recover 5%-50% of the
remaining oil. They introduce
treated water through several
injection wells placed in specific
patterns around a producing well.
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Enhanced oil recovery- Involve the
introduction of substances not naturally
found in a reservoir (gases, chemicals, or
thermal energy) to boost reservoir pressure
and sweep hydrocarbons from various parts
of the reservoir towards the wellbores.
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Gas injection- CO2, N2 or LPG is sent into the reservoir
(gases that dissolve in the oil). The gas then pushes the fluid
oil through the pores and cracks in the rock toward producing
wells. This approach can often recover 35% of remaining oil.
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Chemical injection method injects a slug of detergent
(reduces surface tension of oil) into a depleted sandstone
reservoir in separate batches, or slugs. The next slug—water
thickened with polymers—pushes the micro-emulsion toward
the producing wells.
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Thermal recovery: used to make heavy oil remaining in a
reservoir flow more easily. It includes methods like cyclic
steam injection, Steamflood or steam drive and Steamassisted gravity drainage, Fireflood or in situ combustion
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Steamflood or steam-drive
technique is a thermal recovery
method that pumps superheated
steam into injection well to heat
up oil to reduce its viscosity
(resistance to flow). Recovers
25% to 65% of oil in place.
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Steam-assisted gravity drainage
(SAGD) has been used with great
success in the tar-sands
formations of Alberta. Steam is
injected into an upper horizontal
well to melt the tarlike bitumen,
which flows downward into a
lower horizontal well. The
bitumen is then pumped from
that lower well to the surface. By
some estimates, SAGD can
recover up to 60% of the oil in
place.
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relatively shallow
reservoirs, operators use a
gas burner or other
ignition source to set on
fire the subsurface oil in
one part of the formation.
Recovers up to 40%.
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Natural gas from a well that was drilled chiefly to
extract oil is called associated gas—that is, the gas is
associated with oil production.
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If a well is drilled specifically for natural gas and yields
little or no oil, then the gas produced is called nonassociated gas.
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Condensate wells contain natural gas, as well as a
liquid hydrocarbon mixture (condensate) that is often
separated from the natural gas either at the wellhead
or during later processing of the gas.
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About 75% of the raw natural gas in the
US comes from underground reservoirs
with little or no oil. This non-associated
gas is cleaner (and therefore easier to
process) than gas from wells that do
contain oil. But regardless of the source,
dirt, sand, and water vapor must be
removed from the raw gas to prevent
contamination and corrosion of
equipment and pipelines.
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A device called a wellhead separator
performs initial cleanup, removing water,
condensate and sediment. Dirt and sand
are removed with filters or traps. Water
vapor is typically removed by passing the
gas through a desiccant material, such as
silica gel or alumina (solid granules) or
glycol (a liquid).
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A network of small-diameter, low-pressure piping called
a gathering system routes the gas from multiple
(sometimes more than 100) wells to the gas plant.
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When only hydrogen sulfide is present, natural gas is
referred to as sour. Natural gas is described as sweet
after the removal of hydrogen sulfide.
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One common approach flows raw natural gas up
through a tower while a spray of water mixed with a
solvent is injected at the top. The solvent reacts with the
two gases (carbon dioxide and hydrogen sulfide), and
the solution is drained from the bottom of the tower for
further processing.
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A lattice structure of methane and water molecules,
hydrate can plug pipelines, pressure regulators, and
other equipment.
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As the gas comes in contact with the cold oil, the
heavier hydrocarbon gases condense into liquids and
are trapped in the oil. The lighter hydrocarbon gases,
such as methane and ethane, do not condense into
liquid and flow out the top of the tower. About 85% of
the propane, 40% of the ethane, and almost all of the
butane and heavier hydrocarbons can be extracted
using this absorption process.
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Nitrogen can reduce the heating value of natural gas (because
nitrogen does not burn).
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The collective removal of carbon dioxide, hydrogen sulfide,
and nitrogen is called upgrading, because the natural gas is
made cleaner and will consequently burn hotter.
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Natural gas is the main source of helium gas for industrial use
in the United States. Extraction of helium gas is done after the
nitrogen has been removed, using a complex distillation and
purification process to isolate the helium from other gases.
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water vapor-Besides affecting the heating value of the
natural gas and contributing to corrosion, water can become
part of a solid or slushlike compound, methane hydrate.
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Both gas and oil extraction bring significant
amounts of water to the surface and this
produced water must be treated and/or disposed
of in ways that minimize environmental impact.
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In Oil/Gas wells, Produced water typically
contains dissolved salts, as well as varying levels
of hydrocarbons (oil and grease), chemical
additives and propants, sediment, and even
something called NORM—naturally occurring
radioactive materials (e.g., radium-226 or -228).
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Methane is a potent greenhouse gas which
can trap heat 20 times more effectively than
carbon dioxide.
In 1993, the natural gas industry joined with
EPA to launch the Natural Gas STAR Program
to reduce methane emissions. Program data
from EPA indicate that emissions were
educed by more than 820 bcf from 1993 to
2008 (by 114 bcf in 2008 alone).
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After a well has been depleted to the point at
which further economic recovery of oil or gas is
not possible, it must be plugged and abandoned.
This action is required by law, to prevent briny
water from the well from polluting groundwater.
 -cut and extract the well casing for salvage purposes
 Install mechanical and cement plugs to eal off all
high-pressure and permeable producing zones in the
well.
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When an offshore platform is abandoned,
usually only the deck equipment is salvaged.The
legs that held up the deck can be cut off at
seabed level, and the entire rig can then be