U.S. patent application number 14/203710 was filed with the patent office on 2014-09-18 for methods for fraccing oil and gas wells.
The applicant listed for this patent is Rustam H. Sethna, Eugene Wexler. Invention is credited to Rustam H. Sethna, Eugene Wexler.
Application Number | 20140262285 14/203710 |
Document ID | / |
Family ID | 51522299 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140262285 |
Kind Code |
A1 |
Sethna; Rustam H. ; et
al. |
September 18, 2014 |
METHODS FOR FRACCING OIL AND GAS WELLS
Abstract
A method for stimulating or fraccing an oil or a natural gas
well by adding a liquefied hydrocarbon such as liquid petroleum gas
and liquefied natural gas, a proppant and a diluent such as carbon
dioxide, nitrogen or mixtures thereof to the well. The order of
addition is typically liquefied hydrocarbon then diluent but this
order can be reversed and in other circumstances the liquefied
hydrocarbon and diluent can be mixed together and fed to the well
as a mixture.
Inventors: |
Sethna; Rustam H.; (Clinton,
NJ) ; Wexler; Eugene; (Summit, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sethna; Rustam H.
Wexler; Eugene |
Clinton
Summit |
NJ
NJ |
US
US |
|
|
Family ID: |
51522299 |
Appl. No.: |
14/203710 |
Filed: |
March 11, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61776956 |
Mar 12, 2013 |
|
|
|
Current U.S.
Class: |
166/305.1 |
Current CPC
Class: |
E21B 43/267
20130101 |
Class at
Publication: |
166/305.1 |
International
Class: |
E21B 43/25 20060101
E21B043/25 |
Claims
1. A method for stimulating an oil or a natural gas well comprising
adding to the well a combination comprising a liquefied hydrocarbon
selected from the group consisting of liquid petroleum gas and
liquefied natural gas, a proppant and a diluent selected from the
group consisting of carbon dioxide, nitrogen and a mixture of
carbon dioxide and nitrogen.
2. The method as claimed in claim 1 wherein the oil or natural gas
well is in a shale gas formation.
3. The method as claimed in claim 1 wherein natural gas and natural
gas liquids are recovered from the oil or natural gas well.
4. The method as claimed in claim 1 wherein the well is a
horizontal well.
5. The method as claimed in claim 1 wherein the combination is
added to the well sequentially.
6. The method as claimed in claim 1 wherein the liquefied
hydrocarbon is added to the well first, followed by the
diluent.
7. The method as claimed in claim 1 further comprising adding water
to the well along with the liquefied hydrocarbon.
8. The method as claimed in claim 1 wherein the water and liquefied
petroleum gas is first added to the well, followed by natural gas,
followed by nitrogen.
9. The method as claimed in claim 1 wherein sufficient time is
allowed for between feeding the liquefied hydrocarbon to the well
before feeding the diluent to the well.
10. The method as claimed in claim 1 wherein the liquefied
hydrocarbon and the diluent are fed to the well together.
11. The method as claimed in claim 1 wherein the diluent is added
to the well before the liquefied hydrocarbon.
12. The method as claimed in claim 1 wherein the liquefied
hydrocarbon is fed to the well at a pressure of 5000 to 10,000
psig.
13. The method as claimed in claim 1 wherein the liquefied
hydrocarbons are fed to the well at a first pressure and increased
in pressure by the addition of a higher pressure diluent.
14. The method as claimed in claim 1 wherein the liquefied
hydrocarbon is in gel form.
15. The method as claimed in claim 1 wherein the proppant is
selected from the group consisting of silica sand, resin-coated
sand and man-made ceramics.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority from provisional
patent application Ser. No. 61/776,956 filed Mar. 12, 2013.
BACKGROUND OF THE INVENTION
[0002] In the production of natural gas from shale or other
"tight-gas" formations, hydraulic fracturing (or "frac" or
"fraccing") is used to break up the rock around the well bore and
reduce the resistance to gas flow. The frac technique generally
requires injecting into the well large amounts of fluids that are
compressible like nitrogen or carbon dioxide or incompressible such
as water or liquefied petroleum gas. The fluids are pumped to high
pressure to create large compressive forces around the well bore.
These forces break the rock and create tiny fissures for gas
flow.
[0003] The stimulation of natural gas containing formations, such
as shale gas has been the subject of intensive study. Several
methods of fracturing these deposits are known and incompressible
fluids such as water with other chemicals and solids; e.g., mineral
acids and proppants are employed on the order of 1 to 2% by volume
to the injected fluid. The use of water results in the generation
of a large amount of waste that is laden with chemicals and creates
an expensive disposal issue. Thousands of tons of fluid may be
injected during each frac job and much of this fluid is returned to
the surface when the flow is reversed (hereafter called "produced
fluids") and natural gas is produced from the well. Alternatively,
high pressure frac fluid sources including carbon dioxide and
nitrogen help overcome the liquid waste disposal cost associated
with hydraulic fracturing. However, the frac gas generated upon
drilling has a high initial content of carbon dioxide and nitrogen.
This mixture can be difficult and expensive to separate and
inevitably leads to natural gas losses and even venting of the
initial diluted natural gas to the atmosphere because it cannot be
readily flared.
[0004] Recently GASFRAC has tested the use of liquid petroleum gas
(LPG) which has high propane content and lowers the amount of frac
fluid necessary as well as being easier to separate from the gas
that results from drilling. The LPG is readily recoverable and can
be reused at later stages in the overall process. However,
injection of LPG at high pressures carries some risk involving
explosions. The use of other liquid hydrocarbons such as gelled
hydrocarbons is also possible and would facilitate the complete use
of the resulting well gas; however flammability concerns could
limit its use.
[0005] Hydraulic fracturing is used to produce gas and oil from low
permeability formations, such as for example, unconventional
natural gas reservoirs. Most fracturing treatments use water and
polymers with a gelling agent as a fracturing fluid.
[0006] A hydraulic fracturing process can be energized by the
addition of a compressible, sometimes soluble, gas phase into the
treatment fluid. When the well is produced, the energized fluid
expands and gas comes out of solution. Energizing the fluid creates
high gas saturation in the invaded zone, thereby facilitating gas
flowback.
[0007] During a flowback period, a mixture of gas is used as the
energized solution (e.g., N.sub.2 and/or CO.sub.2) and natural gas
comes out. Before selling the natural gas to a pipeline operator,
the concentration of energizing gas needs to be dropped to
acceptable levels dictated by the pipeline operator (usually 2 to
3%). Although the concentration of energizing gas decreases quite
rapidly in the beginning of the process, achieving the required
levels may take considerable time (up to 30 to 45 days).
[0008] In order to address the issue of environmental pollution
from flaring during a flowback period, various techniques have to
be employed to facilitate natural gas clean-up by separating it
from the energizing gas. Such techniques may include N.sub.2 and/or
CO.sub.2 separation by using membrane and/or adsorbent (PSA/VSA)
technologies, which involves the deployment and operation of
relevant equipment, which in turn adds cost to the natural gas
production process.
[0009] Alternative technologies for shale gas development utilize,
for example, liquefied petroleum gas (LPG) in place of conventional
fracturing fluids, and specifically, in place of high volume, high
pressure slick water-based fracturing fluids. The unique properties
of the LPG fracturing process result in significant savings on
material expenses, increased well productivity and fracture as well
as flow-back mixture clean up.
[0010] The gelled LPG used in the fracturing process has the
ability to generate the necessary fracture system, carry the
proppant through the wellbore and place into the oil and gas
reservoir being stimulated. The LPG used in the process is highly
soluble in well formation hydrocarbons. As a result, the LPG
process results in less damage to formations than conventional
hydraulic fracturing processes. Unlike conventional treatments
where as much as 50% of the carrier remains in the reservoir and
hinders well performance, virtually 100% of the LPG can be
recovered, The obvious advantage of LPG fracturing is that gelled
propane would replace the use of water, thereby reducing the amount
of fresh water used and the associated environmental concerns. In
addition, propane that is injected into the formation can be
recovered and reused, therefore eliminating the need to treat or
dispose of large volumes of wastewater that may have high
concentrations of naturally occurring salts, metals, radionuclides
and other constituents commonly found in shale reservoirs.
[0011] Additionally the injection of a hydrocarbon into the shale
creates less "damage" due to "swelling" as compared to water, which
may impede hydrocarbon flow; therefore LPG fracturing has the
potential to increase well production. While there are a variety of
potential benefits to using LPG fracturing for shale energy
development, there may be some potential disadvantages, such as
increased costs for conducting the fracturing treatment, increased
explosion hazards, and limited capacity to utilize this technology
on a wide commercial basis. One advantage water-based fracturing
technologies have though is that water is virtually incompressible,
therefore the pressure is transferred more directly to fracture the
shale more effectively, whereas LPG may require more surface
pressure to exert the necessary downhole pressure.
[0012] LPG fracturing is a promising technology that may become
more common as advancements in its use occur and has the potential
to reduce water use and increase well yields.
[0013] The proposed invention offers safer and a potentially more
economical solution to conventional and/or energized hydraulic
fracturing by utilizing a combination of high-efficiency fracturing
fluids (e.g., water, LPG, etc.) with environmentally safe and inert
gases, like nitrogen.
[0014] These methods improve natural gas and natural gas liquids
recovery from fraccing operations; reduced flammability of the
overall combination makes for a safer operation; reduced use of
diluents such as carbon dioxide or nitrogen allows for better
natural gas recovery; cost reduction improvements over the use of
liquid petroleum gas by itself; and augmentation of the hydrocarbon
pressure by using nitrogen or carbon dioxide so that high pressure
equipment does not need to be employed.
SUMMARY OF THE INVENTION
[0015] A method for stimulating an oil or a natural gas well
comprising adding to the well a combination of a liquefied
hydrocarbon selected from the group consisting of liquid petroleum
gas and liquefied natural gas, a proppant and a diluent selected
from the group consisting of carbon dioxide, nitrogen and a mixture
of carbon dioxide and nitrogen.
[0016] The stimulating of the oil or natural gas well will lead to
a fracturing of the fissures in the well thereby leading to an
increased yield of oil or natural gas.
[0017] The invention may also be employed in fraccing operations of
shale gas formations. These methods allow for the recovery of
natural gas and natural gas liquids from frac gas. The well can
also be a horizontal well.
[0018] The methods of the invention will provide for the recovery
of natural gas and natural gas liquids from the oil or natural gas
well.
[0019] In the methods of the invention, the combination is added to
the well sequentially. The liquefied hydrocarbons are typically
added first followed by addition of the diluent to the well.
Sufficient time is typically allowed for between feeding the
liquefied hydrocarbon to the well before feeding the diluent to the
well. The liquefied hydrocarbons are fed to the well at a first
pressure and their pressure is increased by the addition of the
diluent at a higher pressure. In preferred embodiments, the
liquefied hydrocarbon is in gel form.
[0020] In an alternative embodiment, the diluent is fed to the well
before the liquefied hydrocarbon.
[0021] Water may be fed to the well along with the liquefied
hydrocarbons in certain circumstances. In one embodiment, the water
and liquefied petroleum gas is first added to the well, followed by
natural gas and then followed by a feed stream of nitrogen.
[0022] In a further alternative embodiment, the liquefied
hydrocarbon and the diluent are not fed to the well sequentially
but are mixed together before being fed to the well
simultaneously.
[0023] The liquefied hydrocarbons, whether liquefied petroleum gas
or liquefied natural gas are typically fed to the well at higher
pressures in the range of 5000 to 10,000 prig (345 to 690 bar).
[0024] The proppant when present is selected from the group
consisting of silica sand, resin-coated sand and man-made
ceramics.
[0025] The use of the diluents alters the flammability of the
hydrocarbon combination and will allow for easier separation from
the well gas that is derived from drilling operations as described
in FIGS. 1, 2 and 3. Carbon dioxide is preferably used because of
its higher density, higher heat capacity and easier separation from
methane and other hydrocarbons.
[0026] Liquefied hydrocarbons can be effectively used in the
stimulation of gas wells. Liquid petroleum gas which has higher
propane content can be employed advantageously because of its
higher density and higher temperature. Rich liquefied natural gas
which has a higher ethane and C3+ content and which is more readily
available and economical being derived from peak shavers will
remain a liquid at high pressures even at elevated temperatures as
noted in FIG. 4.
[0027] The proppants are typically selected from the group
consisting of silica sand, resin-coated sand and man-made
ceramics.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a graph showing the effect of carbon dioxide
concentration on methane flammability.
[0029] FIG. 2 is a graph showing the effect of carbon dioxide feed
concentration versus ignition response.
[0030] FIG. 3 is a graph showing carbon dioxide feed concentration
versus flame propagation.
[0031] FIG. 4 is a chart of vapor liquid equilibriums at various
temperatures and pressures for rich liquefied natural gas.
DETAILED DESCRIPTION OF THE INVENTION
[0032] The invention is applicable to horizontal wells utilized in
unconventional gas production and consists in the gradual
introduction of the fracturing fluid of choice into the well under
moderate pressure, followed by introduction of the inert gas under
high pressure, sufficient to increase the overall pressure of the
fracturing fluid to required levels.
[0033] The fluid introduced first could be water or a liquid
hydrocarbon, which are easy to separate. This step is followed by
the addition of a high pressure energized fluid like N.sub.2 and/or
CO.sub.2, or natural gas, or even LPG. It is also possible to have
multiple fracturing fluid combinations, for example: water/LPG,
followed by natural gas, followed by N.sub.2. The top fluid serves
to boost the pressure and ideally to provide a non-flammable
blanket. By changing the N.sub.2 and/or CO.sub.2 concentration
profile in the flowback mixture from exponential decay to a more
rapid, near-square shaped decay, this will allow for easier
separation of the fracturing fluid from the recovered hydrocarbons.
It should be noted that some diffusion/mixing of the fluids is
inevitable, which would prevent a user from obtaining a perfect
square-shaped drop in N.sub.2 and/or CO.sub.2 concentration
profile. The methods of the present invention will yield beneficial
results. The invention will improve flowback fluid cleanup. A
better recovery of fracturing fluids can be achieved. The inventive
methods are also advantageous in water sensitive formations that
suffer from water saturation and clay swelling issues. The
inventive methods will work to enhance production of oil in
low-permeability and low porosity well formations as well as
shallow formation and those nearly depleted gas reservoirs.
Additionally, in those geographical regions where water shortages
are prevalent or those with stricter water regulations, the present
invention will provide for enhanced gas or oil recovery without
using more water as well as limiting the amount of chemical
employed.
[0034] The reduced water consumption is beneficial when water is
the main fracturing fluid due to its replacement with inert gas
(e.g., nitrogen) in the vertical portion of the well.
[0035] The fracturing operation can be safer even when using more
risky but more formation friendly fracturing fluids (e.g., LPG) due
to the compression taking place below the ground under a blanket of
a more environmentally safe inert gas such as nitrogen. This may
also result in partial or almost complete elimination of gelling
agents, which otherwise must be added to LPG to reduce the chance
of explosion.
[0036] The invention further reduces the flowback period and
subsequent elimination of the need for natural gas clean-up due to
reduced content of CO.sub.2 and/or N.sub.2 in the flowback
mixture.
[0037] This latter benefit can be appreciated because the nitrogen
for example is only present in the portion of the well and is not
used in actually fracturing the rock formation. Although some
mixing and diffusion is unavoidable, the nitrogen is not mixed with
the natural gas when used as the energized solution. This means
that once the fracturing is complete and the flowback is started,
nitrogen gas will flow out first, relatively quickly and at a
relatively constant concentration as opposed to traditional
flowback scenario.
[0038] The invention is further explained by way of non-limiting
examples, provided below.
[0039] Using homogeneous energized fluid in the entire wellbore
(baseline--longest flowback period).
[0040] In this case, a fracturing fluid containing energizing
component(s), CO.sub.2 and/or N.sub.2, is prepared at the surface
and pumped down hole at a selected pressure that exceeds the
reservoir pressure. In the typical fracturing application, the
first and the last step of the process are done without proppant
(first is to pump-in the fracturing fluid without the proppant (pad
stage) to create fractures, and the last is to clean-up remaining
proppant from the wellbore (flush stage). During intermediate
stages, the proppant is introduced into the fracturing fluid and
its load is gradually increased. This results in quite a lengthy
flowback period, required to bring the concentration of the
energizing components down to the required level which is usually 2
to 3%.
[0041] Gradual introduction of the fracturing fluid components
(shortest flowback period).
[0042] In this case, the components of the fracturing fluid are
introduced gradually in stages. The first component (water or
liquid hydrocarbons) is followed by a high pressure energized fluid
like N.sub.2 and/or CO.sub.2 serving to boost the pressure and
ideally provide a non-flammable blanket. In this case, during
flowback, N.sub.2 and/or CO.sub.2 will flow out first and their
concentration in the flowback mixture will decrease much more
rapidly as schematically depicted below. It should be noted that
some diffusion/mixing of the fluids is inevitable, which would
prevent an operator from obtaining a perfect square-shaped drop in
N.sub.2 and/or CO.sub.2 concentration profile.
[0043] Using a mixture of hydrocarbon(s) and energizing components
to pump down hole (intermediate flowback period).
[0044] In this case, by using the energizing or diluent component
(N.sub.2 and/or CO.sub.2), it becomes possible to safely pump the
potentially flammable hydrocarbons (for example, natural gas) down
hole at required pressures due to diluting them below their
flammability limits. Although this will not result in the shortest
flowback period, it does still reduce the concentration of the
energizing component (N.sub.2 and/or CO.sub.2) and therefore,
minimizes the cleanup effort.
[0045] In general during the practice of the invention, the
liquefied hydrocarbon mixture is pumped up to pressures of about
5000 to 10,000 psig before their subsequent use for fraccing. In
the methods of the invention, gelled liquid petroleum gas or gelled
liquefied natural gas are the preferred hydrocarbons and can be
employed individually or as a mixture of the two. Proppants such as
silica sand, resin-coated sand and man-made ceramics are added to
the hydrocarbon mixture and will act in the oil or gas well
formation to keep fissures open and enhance gas recovery. A high
pressure intermediate gas which is typically carbon dioxide or
nitrogen can be added either simultaneously with the pressurized
hydrocarbon or separately and will serve as a blanket. The
resulting frac mixture becomes less flammable as a result.
[0046] Moreover, in a different embodiment, the liquefied
hydrocarbon can be pumped at a lower pressure for fraccing and its
pressure can be subsequently boosted with the addition of higher
pressure carbon dioxide or nitrogen. This pressure boosting by the
carbon dioxide and/or nitrogen diluent will provide benefits of
both using the liquefied natural gas or liquid petroleum gas in gel
form with the properties of the diluent in fraccing operations
while minimizing the risks associated with the high pressure
pumping of hydrocarbons.
[0047] Carbon dioxide or nitrogen when used alone in well
stimulation and fraccing operations can be effective. However,
separation of these components after a few days time after the well
has been drilled becomes more difficult. For example, carbon
dioxide fraccing may yield an initial gas content that is lean in
methane which can only be enriched via cleanup once the carbon
dioxide content is lowered to 50%. Nitrogen fraccing faces the same
limitation. The use of hydrocarbons with either of carbon dioxide
or nitrogen facilitates natural gas recovery by limiting the
initial amount of carbon dioxide or nitrogen introduced into the
well to a more manageable level.
[0048] While this invention has been described with respect to
particular embodiments thereof, it is apparent that numerous other
forms and modifications of the invention will be obvious to those
skilled in the art. The appended claims in this invention generally
should be construed to cover all such obvious forms and
modifications which are within the true spirit and scope of the
present invention.
* * * * *