Note: Descriptions are shown in the official language in which they were submitted.
CA 02602883 2007-09-14
METHODS OF FORMING AND USING AN IN SITU HEAVY HYDROCARBON
EMULSION
FIELD OF THE INVENTION
The present invention relates to methods of forming and using an in situ heavy
hydrocarbon emulsion produced during drilling operations from heavy oil and/or
crude
bitumen recovered through processes such as cyclic steam stimulation and steam
assisted
gravity drainage (SAGD). After optional upgrading at the surface, the emulsion
may be
used as a road construction material, fuel source or an asphalt emulsion flux.
BACKGROUND OF THE INVENTION
As is known, heavy oil and bitumen (collectively referred to herein as "heavy
hydrocarbons") have a high viscosity at formation temperature. As a result,
during
production of such heavy hydrocarbons, some form of heat or dilution of the
hydrocarbons is required to enable the heavy hydrocarbons to flow from the
formation to
a production well as the heavy hydrocarbons will not flow under the virgin
temperature
and pressure conditions of the formation.
Steam assisted gravity drainage (SAGD) is a well known enhanced recovery
technique to
recover heavy hydrocarbons from an oil field. Generally, SAGD techniques are
used to
recovery heavy hydrocarbons from a formation that would not otherwise be
released from
the formation without the use of steam to heat the formation. The introduction
of steam
heat to the formation will reduce the viscosity of the heavy hydrocarbons and
allow the
heavy hydrocarbons to flow to a recovery well.
SAGD operations are usually relatively large scale operations, often requiring
injection
and recovery wells of considerable length to effectively enable the recovery
of
hydrocarbons over a substantial horizontal distance. As a result, injection
and recovery
wells are drilled over these horizontal distances through the heavy
hydrocarbon zones of
a formation.
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In the drilling of SAGD injection and recovery wells, the disposal of drill
cuttings has
been a significant issue for drill site operators. For example, in a typical
drilled SAGD
operation, upwards of 100 m3 of drill cuttings may be produced from a single
injection or
recovery well. Typical drill cuttings contain a variety of contaminants
including the
heavy hydrocarbons, salts, metals, soaps and other agents that may have been
added to
the drilling fluid to assist in the drilling processes.
As a result of the contaminants, disposal of these materials is expensive.
Acceptable
methods of disposal of drill cuttings are usually dictated by various
jurisdictional
regulations and will usually require that the drill cuttings are properly
remediated into the
local soil or alternatively, removed to a landfill site. Either disposal
method may lead to
certain environmental contamination as the various contaminants may ultimately
leach
into the local groundwater. Moreover, the cost of transportation of drill
cuttings to a
landfill and/or the cost of soil remediation is significant.
For example, in a typical heavy oil or bitumen drilling process, recovered and
dried drill
cuttings may include approximately 15 % (w/w) heavy hydrocarbon contaminants.
Such
levels of heavy hydrocarbons represent a significant volume of hydrocarbons
and pose a
significant disposal problem.
As is known, road construction is subjected to specific environmental
regulations that
may or may not be similar to either a local drilling site or landfill. That
is, at a local drill
site, as a result of the relative concentration of contaminants within drill
cuttings,
regulations are usually relatively strict concerning acceptable levels of
contaminants that
may be contained within a particular area without proper remediation or
disposal. In
contrast, during the construction of a road, the same standards would
generally not apply.
That is, it is well known that government agencies and their contractors use
hydrocarbons
and/or chlorides mixed with gravel aggregates to provide dust suppression in
gravel or
dirt roads. At a drill site, acceptable levels of hydrocarbons present within
the soil would
be relatively low whereas in providing dust suppression to a gravel or dirt
road
significantly higher levels of hydrocarbons in the form of crude oil can be
laid down over
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large areas notwithstanding that it is known that certain quantities of the
hydrocarbons
will, over time dissipate from the road into the local environment.
As a result, there has been a need for effective disposal methods wherein
bitumen or
heavy hydrocarbon contaminated drill cuttings are disposed of in a manner that
meets
environmental regulations and that does not significantly increase or
otherwise adversely
affect the overall cost of disposing of such drilling cuttings. More
specifically, there has
been a need for a disposal method in which the bitumen contaminated drill
cuttings
provide a useful product and where in one method the bitumen is emulsified
during
drilling to produce a useful bitumen emulsion for use in roads or
alternatively as a fuel
source.
SUMMARY OF THE INVENTION
In accordance with the invention, there is provided a method of preparing a
viscous
heavy hydrocarbon/drilling solution emulsion comprising the step of preparing
a water-
based drilling solution containing an effective amount of a surfactant wherein
the drilling
solution is effective in emulsifying heavy hydrocarbon from a production zone
and
forming a viscous heavy hydrocarbon/drilling solution emulsion with suspended
drill
cuttings during drilling. The concentration of heavy hydrocarbon within the
viscous
heavy hydrocarbon/drilling solution emulsion and drill cuttings mixture is
preferably
60% (w/w) or higher.
The mixture may be used for different downstream uses including road
construction or a
fuel. In either use, the hydrocarbon fraction within the heavy
hydrocarbon/drilling
solution emulsion with suspended drill cuttings may be increased or adjusted
as
appropriate to create an asphalt emulsion suitable for road construction or to
create a fuel.
Suspended drill cuttings may be separated from the emulsion.
In another embodiment, the invention provides a water-based drilling fluid
produced
from downhole drilling comprising: a water phase; at least one surfactant for
dispersing/emulsifying downhole heavy hydrocarbons; emulsified heavy
hydrocarbon
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and, drill cuttings from the downhole drilling, wherein the water-based
drilling fluid is
characterized by having at least 60% (w/w) dispersed heavy hydrocarbon with
respect to
the water phase and associated drill cuttings.
In yet another embodiment, the invention provides a method of preparing a
drilling fluid
comprising the steps of: forming a water-based drilling fluid with an
emulsifier; drilling a
wellbore with the water-based drilling fluid wherein upon approaching a
planned drilling
distance through a production zone having heavy hydrocarbons, the viscosity of
the
drilling fluid is permitted to increase by increasing the concentration of
emulsified heavy
hydrocarbon within the drilling fluid; and, recovering the viscous drilling
fluid at the
surface.
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DETAILED DESCRIPTION
Methods of preparing and using a drilling solution emulsion that contains a
high
concentration of emulsified heavy hydrocarbons are described. The drilling
fluid
emulsion with or without suspended drill cuttings may be thereafter used as a
road
construction material or as fuel.
More specifically, and in accordance with the invention, a water-based
drilling fluid
containing suitable surfactants for dispersing/emulsifying downhole heavy
hydrocarbons
(preferably bitumen) are prepared such that the resulting heavy
hydrocarbon/drilling
fluid/drill cuttings mixture produced during drilling is an effective and
viscous blend of
emulsified hydrocarbons (preferably asphaltenes) and suspended drill cuttings
that are
suitable for road construction or as a fuel.
The method of the invention initially involves the creation of a water-based
drilling fluid
containing at least one heavy hydrocarbon (including asphalt/bitumen)
emulsifier.
Thereafter, using this drilling fluid, the drill operator will commence
drilling towards the
production zone of a formation in the known manner. That is, normal drilling
practices
would be observed including increasing the downhole drilling fluid volume and
adjusting the drilling fluid composition as drilling progresses.
Upon reaching the production zone, and particularly in the case of SAGD
production, the
drill operator may change the drilling direction to horizontally penetrate the
production
zone with the objective of thereafter advancing the horizontal section through
the
production zone to a planned distance.
As the production zone is drilled, and in accordance with the invention, the
drilling
operator will maintain the properties of the drilling fluid such that
effective drilling can
occur through the production zone. In the case of a bitumen production zone,
the drill bit
will be penetrating through bitumen and, as a result, the drill fluid will
increasingly
become contaminated with bitumen. As a result of the emulsifier within the
drilling fluid,
the bitumen will be emulsified within the water primary phase of the drilling
solution.
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Left unadjusted, the drilling solution will become progressively more viscous
as a result
of water loss to the formation through seepage and other factors. As a result,
the drill
operator will normally adjust the chemistry of the drilling fluid such that
the viscosity of
the fluid is maintained within acceptable parameters in order that drilling
can continue.
Under normal drilling, drill cuttings may be removed at the shaker.
In accordance with the invention and at an appropriate distance in advance of
the planned
drilling distance, the operator will adjust the properties of the drilling
fluid such that a
maximum quantity of heavy hydrocarbon is emulsified within the drill fluid
together with
suspended drill cuttings. In other words, the operator will allow the
viscosity of the
drilling fluid to rise such that a maximum amount of heavy hydrocarbon and
drill cuttings
are emulsified or suspended in the drilling fluid. Ideally, the drill operator
will allow the
viscosity of the drilling fluid to rise at an appropriate time prior to
reaching the planned
distance such that upon reaching the planned distance the drilling fluid
viscosity has
reached or is very close to the maximum viscosity to permit further drilling.
At the planned distance, drilling is stopped and the viscous drilling fluid
containing the
emulsified heavy hydrocarbons and suspended drill cuttings is pumped to the
surface by
displacing the viscous drilling fluid with a cleaning solution.
The viscous drilling fluid is collected at the surface and ideally will
contain greater than
60% (w/w) heavy hydrocarbon. This viscous drilling fluid may then be used for
other
applications.
Road Construction
As is known, a typical road construction includes a sub-grade of supporting
native rock,
soil, sand, clay or other material onto which a base course generally
comprising a depth
of crushed gravel or aggregate is placed and compacted with a surface course
of a smaller
gradation. The aggregate will usually range in depth from 12 inches to several
feet
depending on the engineering requirements of the road and may include various
additives
that provide dust suppression if the road is not to be sealed.
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In a sealed road, a surface course of a concrete (usually an asphalt concrete)
is applied
and compacted over the aggregate to seal and bind the upper surface of the
road. The
asphalt is a complex mixture of hydrocarbons primarily comprised of bitumen
which in
itself is generally comprised of asphaltenes as the dispersed phase and
maltenes as the
continuous phase. Mixed with various aggregates or mixtures of aggregates,
varying
blends of asphalt concrete can be produced depending on the desired qualities
for the
road surface.
In accordance with one embodiment of the invention, upon completion of the
drilling, the
recovered viscous heavy hydrocarbon/drill cuttings mixture is transported to
an asphalt
preparation facility where the mixture may be upgraded through the addition of
further
amounts of asphalt/bitumen and other materials that produce a product suitable
for use as
an asphalt emulsion. The resulting product may then be used in an appropriate
road
construction application as an asphalt cement or dust suppressant as described
above.
Fuel
In an alternate embodiment, the recovered heavy hydrocarbon/drill cuttings are
upgraded
for use as a fuel. In this embodiment, the drill cuttings may be separated
from the
recovered drilling fluid/drill cuttings on surface to an acceptable level
whereupon the
hydrocarbon content may be increased to a level suitable for using the mixture
as an
emulsion fuel. In another embodiment, if the hydrocarbon content is
sufficiently high,
the drilling fluid/drill cuttings mixture may be used directly as a fuel
without separation.
In this embodiment, the use of the heavy hydrocarbon/drill cuttings mixture as
a fuel may
be an effective way of decontaminating the drill cuttings such that the
"burnt" drill
cuttings have been cleansed of contaminants, thus enabling remediation of the
drill
cuttings to soil or use in another application.
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Surfactants
Surfactants may include those surfactants used in the road asphalting industry
including
anionic, cationic and non-surfactants such as fatty acids and sodium or
potassium-based
soaps and others as known to those skilled in the art.
The above-described embodiments of the invention are intended to be examples
only.
Alterations, modifications and variations may be effected to the particular
embodiments by those of skill in the art without departing from the scope of
the invention
which is defined by the following claims.
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