Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02534746 2006-01-26
DRILL CUTTINGS TREATMENT SYSTEM
BACKGROUND OF THE INVENTION
01 This invention relates to a method for separating hydrocarbons from drill
cuttings
produced during drilling operations.
02 For drilling of oil and/or gas wells, a drill bit at the end of a drill
string produces rock
cuttings as it cuts through subsurface rock. Drilling mud circulated from the
surface to the drill
bit and back to the surface carries these cuttings to the surface. These
cuttings are often
contaminated with hydrocarbons either from the formations being cut by the
drill bit, or by fluids
in the drilling mud. At the surface, the drilling mud and cuttings are treated
to separate the
cuttings from the mud with mechanical treatment, for example by use of shale
shakers,
desanders, desilters, hydrocyclones and centrifuges. Drilling muds may be
water based, oil
based and may be mixtures of the two (emulsions). Invert drilling muds are in
common use
where the oil is the continuous phase, and water or brine is emulsified within
the oil as the
dispersed phase. Removing hydrocarbons from drilling cuttings carried by
invert drilling muds
is a particularly difficult task. A mixture of drill cuttings and invert
drilling mud will be referred
to as invert mud drill cuttings.
03 United States patent no. 6,838,485, discloses a method that moves away from
mechanical
treatment of the drill cuttings and uses a chemical treatment to separate
hydrocarbons from drill
cuttings carried by an invert drilling mud. In this patent, it is stated that
"drilled cuttings may be
treated using any suitable system of equipment. After separation from the
drilling mud, the
contaminated cuttings typically pass through a holding bin into an inlet
hopper. The cuttings
preferably are treated directly in a batch mixer equipped with an appropriate
inlet for the relevant
solutions and an apparatus for low shear mixing, such as a paddle mixer. In a
preferred
embodiment, the cuttings are sprayed with an emulsifying solution effective to
transform the free
hydrocarbons in the cuttings into an emulsion. The emulsion thereafter is
treated with an
encapsulating material to encapsulate the emulsified hydrocarbons, and the
mixture of drill
cuttings and encapsulated free hydrocarbons is released into marine waters
where it disperses."
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The emulsifiers are specified to be a combination of non-ionic emulsifiers
with anionic
emulsifiers.
04 The invention described here is intended to provide enhanced recovery of
hydrocarbons
from invert drill cuttings by mechanical action, without the necessity of
using emulsifiers.
SUMMARY OF INVENTION
05 A process for the separation of hydrocarbons from drill cuttings in an
invert mud is
disclosed. Invert mud drill cuttings are supplied to a mixing chamber of a jet
pump. The invert
mud drill cuttings are agitated within the jet pump and then the hydrocarbons
and solids are
separated in a centrifuge. .
06 The process distinguishes itself from others in that it uses a jet pump to
effect a matrix
transformation of the solid and hydrocarbon emulsion matrix in the invert mud
drill cuttings
prior to centrifuging. Solid-liquid separation occurs within the centrifuge.
07 An apparatus according to an aspect of the invention comprises hopper,
motive fluid
supply, jet pump, pipeline and centrifuge. The hopper is designed to receive
the raw material and
can be shaped as a cone bottom vessel or alternatively equipped with a
mechanical auger
designed to convey material to the inlet of the jet pump. The motive fluid
supply is designed to
supply the high pressure fluid necessary to operate the jet pump which by use
of a nozzle within
the jet pump the fluid is converted into a high velocity jet to produce a
vacuum within the mixing
chamber of the jet pump to suction the invert drill cuttings into the inlet of
the jet pump. Further
aspects of the invention are described in the detailed description that
follows.
BRIEF DESCRIPTION OF THE DRAWINGS
08 An exemplary embodiment is now described in detail with reference to the
drawings, in
which:
Fig. 1 is a flow chart of a process for the treatment of invert mud drill
cuttings; and
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Fig. 2 is a detailed schematic of a jet pump for use in a method according to
the
invention.
DETAILED DESCRIPTION OF THE DRAWINGS
09 With reference to Fig. 1, an overview of a process for the separation and
recovery of
hydrocarbons from invert mud drill cuttings. Invert mud drill cuttings are a
matrix of
hydrocarbons, water, and mineral material. The hydrocarbons consist of various
hydrocarbons,
such as diesel, which form a continuous phase in which is carried other
components of the invert
mud drill cuttings. The mineral material consists of rock, sand, silt and
clay.
As shown in Fig. 1, invert mud drill cuttings are fed into a receiving hopper
10 via
suitable means such as a pipe from a mud tank or from the well. At this input
end of the process,
the unprocessed invert mud drill cuttings have undergone little or no
processing, and no phase
separation. The receiving hopper 10 may be supplied with an auger 12 and has
its discharge 30
coupled to a jet transfer pump 14. The auger 12 is also readily available in
the industry. The jet
pump 14 is also readily available in the industry, such as those manufactured
by Genflo Pumps,
but some care must be taken in choosing the jet pump, and it is preferred to
use the jet pump
shown in Fig. 2. The jet pump 14 should operate at a high Reynolds number,
above 250,000,
and preferably in the order of 650,000 to 750,000. Such a Reynolds number may
be obtained by
a combination of high pressure, for example 80 psi or more, and a sufficiently
long mixing
chamber, as for example shown in Fig. 2 to effect a matrix transformation in
the mixing
chamber.
11 As the invert mud drill cuttings enter the receiving hopper 10 they may be
directed to the
hopper discharge 30 using an auger 12, and may be ground using the auger 12 to
produce
reduced sized particles, such as 50 mm in size or smaller. The jet transfer
pump 14 at the base
16 of the receiving hopper 10 mixes the ground invert mud drill cuttings with
a water stream
from power fluid supply 18 to produce a slurry mixture in line 20 which is
passed into settling
tank 22. Solids-oil matrix material settling to the bottom of the settling
tank 22 is pumped by
conventional slurry pump 24 through line 26 into centrifuge 28, such as a
basket or solid bowl
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centrifuge. Centrifugal forces within the centrifuge 28 separate a high
percentage of the solids
from the hydrocarbons and water mixture. Alternative mechanical dewatering
technology such
as inclined dewatering screws or belt filter presses can also be used. The
power fluid supply 18
may use a pump such as a conventional centrifugal pump (not shown).
12 Referring to Fig. 2, the operation of the jet pump 14 is described in
further detail. Unlike
other pumps, a jet pump has no moving parts. A typical jet pump consists of
the following: a jet
supply line 32, a nozzle 34, a suction chamber 36, a mixing chamber 38 and a
diffusor 401eading
to the discharge line 20. In a jet pump, pumping action is created as a fluid
(liquid, steam or gas)
passes at a high pressure and velocity through the nozzle 34 and into a
suction chamber 36 that
has both an inlet and outlet opening. Pressurised wash fluid is fed into the
jet pump 14 at jet
supply line 32. The wash fluid passes through inlet nozzle 34, where it meets
invert mud drill
cuttings gravity fed from hopper inlet 30 at the suction chamber 36. The high
pressure water
stream from the inlet 32, at approximately 120 psi, is converted within the
jet pump nozzle 34
into a high velocity water jet, referred to as the primary flow. The
substantial pressure drop
within the jet pump draws the slurry mixture from the hopper 30, referred to
as the secondary
flow, into the jet pump where it is mixed with the primary flow to achieve a
resultant percent
solids concentration of 25 % or less by volume. The resulting slurry is mixed
and agitated within
the mixing chamber 38 where it undergoes a matrix transformation of the solids-
oil matrix. This
matrix transformation permits effective oil and solid separation in the
centrifuge. The agitated
slurry slows in velocity in the diffuser 40. Thus, upon entry into the jet
pump 14, the invert mud
drill cuttings from hopper 10 are entrained and mixed with the wash fluid from
the nozzle 34,
which undergoes a substantial pressure drop across the jet pump 14 and causes
extreme mixing
of the slurry. The extreme mixing and pressure drop causes cavitation bubbles
to develop on the
inside of chamber 36, which implode on solid particles to enhance the
transformation of the
matrix of the oil and solids. The nature of the transformation is not known,
but is thought to
involve the conversion of the water in oil emulsion to an oil in water
emulsion, except that,
without the use of the jet pump, inefficient oil and solid separation occurs
in the centrifuge.
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13 The jet pump used with the present invention functions as an ejector or an
injector or an
eductor, distinct from a venturi pump and an airmover. A venturi has little in
common
conceptually with a jet pump. A venturi is a pipe that starts wide and
smoothly contracts in a
short distance to a throat and then gradually expands again. It is used to
provide a low pressure.
If the low pressure is used to induce a secondary flow it becomes a pump,
resulting in a loss of
pressure in the throat. If the secondary flow is substantial the loss will be
too great to have a
venturi operate like a pump. To operate like a pump it would have to be
redesigned as a jet
pump. Venturi pumps have limited capacity in applications like chemical dosing
where a small
amount of chemical is added to a large volume of fluid. A jet pump is a pump
that is used to
increase the pressure or the speed of a fluid. Energy is put into the fluid
and then taken out by a
different form. In a jet pump energy is added by way of a high speed jet fluid
called the primary
flow. In the design shown in Fig. 2, the primary flow is produced by jet
nozzle 34. Energy is
taken out mostly as increased pressure of a stream of fluid passing through.
In a jet pump this
stream is called the secondary flow and it is said to be entrained by the
primary flow. A jet pump
is designed to be energy efficient. A venturi pump does not have the capacity
to induce large
volumes of flow, where as a jet pump can and operate energy efficient. Unlike
a venturi pump, a
jet pump consists of a nozzle, mixing chamber and diffuser. In a jet pump
these components are
specifically engineered to have the pump operate energy efficient. A venturi
pump does not have
a defined nozzle, but instead a constriction in the pipe. It also does not
have a defined mixing
chamber.
14 The wash fluid supplied through power fluid supply 18 is preferably water
at a
temperature between 70C and 100C, preferably at about 90C. The continuous
supply of wash
fluid by the motive pump provides for the transport of the invert mud drill
cuttings carried in the
wash fluid stream to continue the matrix transformation of the oil and solids
in the invert mud
drill cuttings in the pipeline 20. Settling tank 22 and centrifuge 28 are used
to separate the oil and
water fraction from the solids fraction, with the solids fraction deposited
into a second hopper.
The settling tank 22 is used to ensure that an effective ratio of water and
solids is supplied to the
centrifuge 28. Depending on the type of centrifuge 28 or other separator used,
different ratios of
water and solids fraction allow the centrifuge 28 to operate most efficiently.
For example, an
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80% water 20% solid/oil mixture might be most efficient for the centrifuge 28.
As the matrix
transformed solids-oil mixture settles to the bottom of the settling tank 22,
water may be
removed from the tank 22 and supplied in a metered fashion to pump 24 to
obtain the correct
liquid-solid ratio for the centrifuge 28. Other methods for obtaing a suitable
water-solids ratio
may be used.
16 It has been found that, without the use of the jet pump in this process,
the separation of
solids and oil in the centrifuge is not efficient. Immaterial modifications
may be made to the
embodiments disclosed here without departing from the invention.
