Note: Descriptions are shown in the official language in which they were submitted.
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WATER BASED DRILLING FLUID FOR SHALLOW WELLS
BACKGROUND OF THE INVENTION
01 Conventional shallow wells are drilled with water under the surface shoe.
The drilling
mud is made thicker at a point known as the mud-up to protect the production
zone and
facilitate running electric logs and running casing. Usually this point occurs
at a few
hundred meters before the total depth of the well is reached. A typical
shallow well is drilled
within 48 hrs. Inefficient mixing and time do not permit attaining an
efficient mix or the cost-
effective optimization of properties.
02 To make the mud thicker a bentonite product such as Wyoming Bentonite, is
added
to the water. Other chemicals added may include a fluid loss reducer such as a
starch or
polyanionic cellulose such as Drispac, pH control such as caustic or citric
acid and mud ring
control such as sodium pyrophosphate. Due to time constraints in drilling the
well and
inefficient mixing, the chemicals added rarely have enough time to properly
yield. This
means that to obtain the desired properties of the mud system, over treatment
of the
chemicals into the drilling fluid system is often the norm.
SUMMARY OF THE INVENTION
03 This invention combines a number of chemical products into one package and
allows
for rapid delivery of the chemicals to the drilling system, improving chemical
performance
and reducing waste.
04 A blend of solids and liquids are suspended in oil, which may be any type
of
environmentally friendly mineral oil, for rapid dispersion when added to
water. This blend
includes viscosifiers, a fluid loss reducer, surfactants to remove the oil
from the solid
particles, clay, pH control and "mud-ring" additives. The blended fluid of
solids and liquids is
mixed together to form a suspension of solids in oil before addition to a
water tank. The
blended suspension of solids in oil is mixed in a mixing plant and stored in
pails. It is then
transported to the well site where it is added to the water in the tank at the
drilling rig to
make "drilling mud". Simple agitation in the water tank produces a drilling
fluid.
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05 Further summary of the invention is found in the claims, particularly
referring to
specific ranges of components of the blended fluid.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
06 In this patent document, the word comprising is used in its inclusive
sense, and does
not exclude other steps or product components being present. The indefinite
article before
a product component, eg viscosifier, does not exclude more than one type of
that product
component being present. In this patent document, a shallow well is a well
drilled to a depth
of less than 1500 meters. A blend or blended fluid in this patent document is
a suspension
of solids in oil, and may include a fraction of other liquid.
07 A blend of solids and liquids are suspended in oil for rapid dispersion
when added to
water. This blend includes viscosfiers, a fluid loss reducer, surfactants to
remove the oil
from the solid particles, clay, pH control and a "mud-ring" additive. The
blended fluid of
solids and liquids is mixed together to form a suspension of solids in oil
before addition to a
water tank (suction tank) at a well site. The fluid may be blended and stored
in a pail before
adding to the suction tank to produce a drilling fluid. Agitation of the fluid
in the tank causes
rapid dispersion of the solid component in the water. The components added to
the blend at
a well site may be selected to match the requirements of the well. The system
may be
hauled to the next drilling location and used to drill surtace hole. In this
case, the alkalinity
may be adjusted to make the system thick again, or otherwise adjusted as
required.
08 The blend of solids and liquids are suspended in a mineral oil or any
environmentally
friendly oil such as HT40NTM or HT30NT""from Petro-Canada of Calgary, Alberta,
Canada,
AmodrilT"" (from Amoco), EnvirodrilTM (from Shell), DriIIsoIT"" (from
Enerchem), SyndrilT""
(from SynOil Fluids), BiodieselT"" (from Bio-diesel Canada), Methyl canolate,
BayoIT"",
ExxsoIT"" (from Exxson), SheIIsoITM (from Shell), glycols, or vegetable oils
such as canola oil
or soya oil. The oil may be present in the range of 35% to 50% by weight of
the total
blended fluid, for example 37% by weight. All weight percents are expressed as
percentage
of the total blended fluid. An environmentally friendly oil is an oil with a
high flash point,
readily biodegradable in the environment and safe to use from a human hygiene
perspective
(i.e. reduced amounts or contains zero concentrations of aromatic chemical
components).
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09 The blended suspension includes viscosifiers. The viscosifier is present in
the range
of 20% to 50% by weight, as for example 35% guar by weight. If Xanthan is
used, the
xanthan may be present in the amount of 1 % to 10% by weight, for example 2%
by weight,
in addition to one or more other viscosifiers, such as guar. The guar may be
unmodified or
modified guar and the xanthan may be Xanvis'n" both available from numerous
suppliers.
Oil suspended guar systems in themselves are well known in the art, such as in
US patent #
5969012. The viscosifier may be a water dispersible or soluble hydrophilic
polysaccharide
such as xanthan or guar gum previously mentioned or gellan gum, algin, locust
bean gum,
derivatized locust bean gum, carrageenan, derivatized guar gum, cellulosics
such as
carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose and
polyanionic cellulose,
succinoglucans, polyacrylamides, starch and starch derivatives or mixtures of
any of these
components.
A fluid loss reducer such as DrispacT"" available from chemical suppliers such
as
Canamara United in Calgary, Alberta, Canada is added to the blended fluid in
an amount
ranging from about 5 to 15% by weight, for example 11 % by weight. Surfactants
such as
nonylethoxy phenol (for example, NEP-9T"') available from Canadian Colors of
Edmonton,
Alberta, Canada to remove the oil from the solid particles, are added to the
blended fluid in
the amount of 2% to 5% by weight. The surfactants that work well in this
application are
specifically surfactants that emulsify oil in water; they are used to take the
oil off the solids
present in the mixture when the total mixture is added to water. Soda ash,
which is
commonly available, may be added to improve the hydratability of the guar by
controlling the
pH of the blend. pH controllers are primarily added to help the biopolymers
viscosify faster
in water. pH control of drilling fluid is well known in the art and need not
be further
described here.
11 A mud-ring agent such as Dril Kan MRPTM available from Millennium
Technologies
should be added to the blended fluid in the amount of 1 to 15% by weight, for
example, 8%
by weight, to inhibit the formation of mud deposits on the drill pipe. Various
mud ring agents
may be used that are effective in dispersing or inhibiting a mud ring. Typical
mud-ring
agents are surfactant based molecules and can be classified as soaps. They
disperse or
inhibit a mud ring by coating the individual clay particles, which stops them
from joining
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together. Mud ring agents also include drilling detergent, LIQUISPERSET"',
DriIconT"" from
suppliers such as Millenium and Canamara.
12 Clay may be added as required, such as a bentonite, as for example SD-1 T""
available from Elementis, for example in the amount of between 1 and 4% of the
total weight
of the blended fluid, for example 2% by weight. The organophilic clay is used
to suspend
solids in oil based products, that is to stop settling of the solids when
sitting in a packaged
form. Another supplier is Southern Clay. The order in which the solids are
added to the oil
is preferably first the clay, then all the rest of the solids and liquids.
13 Additional viscosity can be achieved by using viscosifiers that can be
crosslinked.
Crosslinked bio-polymers can impart very high viscosities in short time
periods. Suitable
cross-linked bio-polymers are found in US patent # 6642185, 6177385, 4579942.
14 Benefits to the liquid suspension include reduced mixing times. The system
requires
no mixing equipment (pumps and hoppers). The product is added directly to the
suction
tank, above the agitator. Thus less equipment is required to mix products.
Components
disperse efficiently eliminating the "fish eye" and "clay ball" problem
associated with
conventional systems. Conventional clay based systems do not have time to
hydrate and
yield efficiently when drilling shallow wells, whereas in the present
invention, components
yield efficiently. All components are in one package, as for example a pail.
For systems
formulated with the product, it is possible to adjust properties for logging
or circulating
casing much more readily than with conventional systems. It also reduces the
number of
products to be managed (inventory and mixing) on the drilling location. Damage
to
inventory and inventory shrinkage of products will not occur to products in
pails.
15 The system costs as much as a conventional gel / chem system. The savings
are be
realized in trucking and logistics. Enough product will fit in a van to drill
8 - 10 wells
compared to 2 - 3 with conventional drilling fluid products. Immaterial
modifications may be
made to the composition and method disclosed here without departing from the
invention.
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