U.S. patent application number 16/825342 was filed with the patent office on 2020-07-09 for optimizing drilling mud shearing.
This patent application is currently assigned to Highland Fluid Technology, Inc.. The applicant listed for this patent is Highland Fluid Technology, Inc.. Invention is credited to Kevin W. SMITH.
Application Number | 20200215505 16/825342 |
Document ID | / |
Family ID | 59897324 |
Filed Date | 2020-07-09 |
United States Patent
Application |
20200215505 |
Kind Code |
A1 |
SMITH; Kevin W. |
July 9, 2020 |
Optimizing Drilling Mud Shearing
Abstract
Viscosity and other properties are determined at desired
temperatures in drilling mud and other fluids by using a versatile
cavitation device which, operating in the cavitation mode, mixes
and heats the fluid to a specified temperature, and, operating in
the shear mode, acts as a spindle for application of Couette
principles to determine viscosity as a function of shear stress and
shear rate. The invention obviates the practice of adjusting
rheology of a drilling fluid by passing it through the drill bit.
Drilling fluid may be managed by a "straight-through" method to the
well, or by placing the cavitation device in a loop which isolates
an aliquot of known volume and circulating the fluid through the
loop including the cavitation device. A controller may be
programmed to manage the viscosity and other properties at various
temperatures by controlling the power input and angular rotation of
the "spindle" (which has cavities on its cylindrical surface), and
feeding viscosity-adjusting agents and other additives to the
fluid. Data may be collected from the loop and used in the
"straight-through" mode until it is determined that conditions
require a new set of data, or the loop may be used continuously.
The system may be used with a supplemental viscometer, density
meter, and other instruments.
Inventors: |
SMITH; Kevin W.; (Bellaire,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Highland Fluid Technology, Inc. |
Houston |
TX |
US |
|
|
Assignee: |
Highland Fluid Technology,
Inc.
Houston
TX
|
Family ID: |
59897324 |
Appl. No.: |
16/825342 |
Filed: |
March 20, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15467315 |
Mar 23, 2017 |
|
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16825342 |
|
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62312807 |
Mar 24, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 21/08 20130101;
B01F 15/00246 20130101; G01N 11/00 20130101; B01F 5/102 20130101;
E21B 21/062 20130101; B01F 11/0208 20130101; B01F 15/067 20130101;
B01F 7/00816 20130101; B01F 15/00389 20130101; B01F 2215/0081
20130101; E21B 41/00 20130101; B01F 3/1221 20130101; E21B 49/003
20130101; E21B 41/0092 20130101; B01F 2015/062 20130101 |
International
Class: |
B01F 11/02 20060101
B01F011/02; B01F 7/00 20060101 B01F007/00; B01F 15/00 20060101
B01F015/00; B01F 3/12 20060101 B01F003/12; G01N 11/00 20060101
G01N011/00; E21B 41/00 20060101 E21B041/00; E21B 21/08 20060101
E21B021/08; E21B 21/06 20060101 E21B021/06; B01F 15/06 20060101
B01F015/06; B01F 5/10 20060101 B01F005/10 |
Claims
1-8. (canceled)
9. A cavitation mixer comprising (a) a cylindrical rotor having a
plurality of cavities on its cylindrical surface (b) a housing for
said cylindrical rotor, said housing having a fluid inlet and a
fluid outlet and defining an interior space including a cylindrical
interior surface substantially concentric to said rotor's
cylindrical surface, (c) a shaft for rotating said rotor, and (d)
at least one of (i) a transducer for generating a signal
representing torque on said shaft, and (ii) a transducer for
generating a signal representing angular velocity of said
shaft.
10. The cavitation mixer of claim 9 including a processor for
generating a signal as a function of at least one of said torque
and said angular velocity.
11. The cavitation mixer of claim 10 including a remote receiver
for receiving said at least one signal generated by said processor
and for regulating rotation of said rotor.
12. The cavitation mixer of claim 9 including a flow director on
said rotor.
13. Apparatus for controlling the preparation of drilling fluid for
drilling a well comprising a drilling fluid flow loop including a
cavitation mixer, said cavitation mixer having transducers for
generating signals representing torque and angular velocity in said
cavitation mixer.
14. Apparatus of claim 13 wherein said cavitation mixer is a
flow-directed cavitation mixer.
15. Apparatus of claim 13 including a process controller for
receiving said signals representing torque and angular velocity,
computing viscosity of said fluid as a function of said signals,
and controlling the adjustment of viscosity in said fluid in
response to said computed viscosity.
16. Apparatus of claim 13 wherein said loop includes a density
meter.
17. Apparatus of claim 13 wherein said loop includes an in-line
viscometer.
18. Apparatus of claim 13 wherein said loop includes one or more
sensors for at least one of flow, pH, percent solids, water cut or
oil/water ratio, electrical stability, particle size, and
temperature of said fluid in said loop.
19. Apparatus for shearing and adjusting properties of drilling mud
comprising (a) a drilling mud flow loop including valves capable of
isolating an aliquot of said mud in said flow loop, (b) a
cavitation mixer in said loop, and (c) a process controller for
controlling angular velocity and power input to said cavitation
mixer in response to intermittent or continuous viscosity
measurements of said mud.
20. Apparatus of claim 19 including a meter in said flow loop for
measuring density of said mud in said loop and reporting it to said
process controller.
21. Apparatus of claim 19 wherein said process controller is
programmed to receive readings of conditions in a well and adjust
properties of said mud in said loop as programmed.
22. Apparatus of claim 19 wherein said flow loop is located on a
conduit leading from sources of one or more drilling mud
ingredients to a well.
23. Apparatus of claim 19 wherein said process controller is
programmed to control said cavitation mixer to (a) heat, by
cavitation, said drilling mud in said loop to a first predetermined
temperature, (b) shear said drilling mud at said first
predetermined temperature, without cavitation, (c) further heat, by
cavitation, said drilling mud in said loop to a second
predetermined temperature, and (d) shear said drilling mud at said
second predetermined temperature.
24. Apparatus of claim 23 wherein said process controller is
programmed to heat, by cavitation, said drilling mud to at least
one additional predetermined temperature and to shear, without
cavitation, said drilling mud at said at least one additional
predetermined temperature.
25-44. (canceled)
45. Apparatus of claim 19 wherein said loop includes at least one
meter for viscosity, flow, pH, percent solids, water cut or
oil/water ratio, electrical stability, particle size, or
temperature of said fluid in said loop.
46. Apparatus of claim 19 wherein said process controller is
programmed to receive readings of conditions in a well and adjust
properties of said mud in said loop as programmed.
47-55. (canceled)
Description
FIELD OF THE INVENTION
[0001] This invention relates to the preparation and maintenance of
drilling mud properties, especially rheology, viscosity, shear,
density, solids, and water/oil ratio, either at a mud plant where
drilling fluids are mixed and stored for delivery or during the
ongoing drilling process in the recovery of hydrocarbons from the
earth. The invention utilizes a cavitation mixer placed in a loop
capable of isolating an aliquot of drilling mud from either the
conduit leading to the well or a tank used to make up new mud or to
store mud. The cavitation mixer imitates the shear and heating
generated when pumping the drilling mud through the drilling bit at
various temperatures. The rheology and other properties of the
drilling mud are maintained at desired values by regulating, in the
loop, the addition of viscosity-adjusting agents, other additives,
the flow rate, and the speed of the mixer to obtain a desired
shearing effect in the mixer in real time without the need for lab
tests. The cavitation mixer not only heats and shear mixes, but is
able to function as a viscometer, reinforcing optional separate
viscometer readings. Other properties can be monitored and
regulated in the loop.
BACKGROUND OF THE INVENTION
[0002] Drilling muds are complex, typically non-Newtonian fluids
that serve multiple, critical functions in drilling wells for oil
and gas extraction. The fluid is used to remove formation drill
cuttings from the wellbore, and the fluid adds hydrostatic mass to
help prevent uncontrolled flow of hydrocarbons from the well. The
fluid also enables buoyancy to counteract the weight of the drill
pipe so that one can drill deeper wells. The fluid also lubricates
the bit and stabilizes the wellbore as drilling continues deeper.
Limiting the loss of fluid to the recently drilled formation is
another important function, and limiting fluid loss typically means
the use of bridging agents that are sized particles. It is
essential to know the properties of the fluids so they can perform
their many functions efficiently.
[0003] Some fluid properties are relatively easy to determine in
line as the fluid is being used. For example, a Coriolis Meter can
accurately determine the flow rate and density of the fluid, but
determining rheology of a complex drilling fluid is more
complicated; it is commonly done by a manual mud check according to
API 13B. Accurate knowledge of a fluid's rheology is required to
calculate a Yield Point and plastic viscosity. If the mud is too
thick, the mud pump cannot pump it. If the fluid is too thin, it
may not suspend the solids that have to be removed from the
wellbore as one continues drilling deeper. To continue drilling
deeper, drill pipe has to be added to the string. During additions
to the string, the mud is no longer being pumped, and Yield Point,
which is part of the rheology, determines the pressure needed to
move the fluid again after it has been static in the wellbore. If
Yield Point (YP) is too high, the pump cannot begin to move the
flow of mud.
[0004] Prior to the present invention, it has been common not to
attempt to shear mix a drilling mud before it is sent down the well
to the drill bit, but rather to utilize the drill bit itself to
shear mix the drilling mud. This means the rheological properties
of the drilling mud are not the most desirable when the mud arrives
at the point of drilling, and often can be far from optimum.
Moreover, the drilling process adds drill cuttings and other solids
and fluids to the drilling fluid, which continuously change
significantly the physical properties of the fluid. The prior
method, relying on the drill bit for shear mixing, injects
considerable uncertainty into the overall process.
[0005] One reason the art has relied on the drill bit for shear
mixing is that there had not been available a practical way to
shear mix the ponderous drilling mud components in a continuous
recycling mode.
[0006] It takes time to run the "mud checks" specified by the
American Petroleum Institute (API) 13B. Mud checks require a
skilled operator to successfully run and to report the mud
properties. Without shearing the mud, however, the chemistry is not
fully activated and the desired rheology is not achieved. In the
laboratory either a Hamilton Beach blender or a Silverson mixer is
used to imitate the shear developed by a trip through the drilling
bit. There is disagreement about which device to use and the amount
of time required to mix the mud before running a mud check. Both
the Hamilton Beach blender and the Silverson have commercial units
that replicate their laboratory units, but they are not typically
used for large batches at a drill site for a number of reasons. One
problem is simply time. Typically in the laboratory it is common to
make 350 ml portions to represent one barrel of fluid. If you shear
a one barrel equivalent drilling fluid sample in the laboratory for
5 minutes, then to "scale up" the shear process at the wellsite, it
takes the same 5 minutes per actual barrel. Unfortunately it takes
too much time. If a rig has 1,000 bbls of drilling fluid, it would
take 5,000 minutes or 3.5 days of processing to equal 5 minutes of
shear used in the laboratory for the 1 bbl equivalent volume.
[0007] Volumes of drilling mud can range from 500 bbls to over
10,000 bbls on location that is stored in pits or tanks, and the
mud can stratify based on the density of the additives. When
relying on samples for API 13B, it is critical that they are
representative of the drilling fluid to be used in the well, but
all too often, imperfect sampling practice introduces errors into
the API 13B procedure.
[0008] Rheology of drilling muds is measured using a Fann 35 or
equivalent rotational viscometer that directly reads viscosity on a
dial at different rpm. The dial reading is based on the deflection
of a bob inside of a rotating cylinder, and the instrument must be
calibrated regularly to be accurate. Temperature changes mud
rheology, and to determine an accurate downhole rheology means the
mud must be heated before measuring its viscosity. By definition, a
mud check is done "offline" which takes valuable time and can delay
critical decisions about well control. Rig time is often lost while
the fluid is circulated in the hole to adjust drilling fluid for
the proper rheology after a time delay and before continuing to
drill.
[0009] A better way to conduct the shear mixing and the rheology
measurement process is needed. Ideally a realtime, inline
measurement of the mud properties is desired, but there are several
challenges to its achievement. One challenge is simply the shear
that happens at the bit needs to be replicated at the surface.
There are high-pressure mixing devices that accomplish this shear,
but they are expensive to build and operate; moreover,
high-pressure is an HSE (health, safety and environmental) issue.
The rheology measuring device is another challenge. Rheology
measurement is used in numerous industries and there are a number
of devices adapted for oil field use that include, but are not
limited to, the Brookfield TT-100, Grace M3900, and Chandler 3300.
The advantage of these types of devices is that they can be
calibrated to replicate the Fann 35, and Fann 35 readings have
become a de facto standard and it is not uncommon for mud engineers
to quote viscosity at various Fann 35 speeds, or add chemistry
based on a particular Fann 35 reading. A Fann 35 is a Couette style
viscometer as are these three devices, and while they can be
correlated to Fann 35 readings, they have intricate internal parts
and small flow lines that can easily plug when fluid loss additives
are in the drilling fluid. There are numerous other viscometers
used in other industries that presumably would also work; however,
a viscosity measurement is taken at a single shear rate or at shear
rates that are harder to relate to a Fann 35 viscosity reading.
[0010] Rheology requires a shear rate vs shear stress curve to
accurately calculate plastic viscosity and yield point. A pipe
rheometer can be used to measure viscosity by accurately measuring
the pressure drop across a known length of pipe of a known internal
dimension while measuring an accurate flow rate. Pipe rheometers
are commercially available from Chandler Engineering, Stim-Lab,
Inc, or Khrone but they are relatively simple devices that can
easily be built assuming an understanding of flow and viscosity
calculations that are widely published. An example of the
calculation required has been published by Petroleum Department of
The New Mexico Institute of Mining and Technology as a class
exercise available on the Internet as "L5_PipeViscometer.pdf".
[0011] An ideal device to measure flow in a pipe rheometer is a
Coriolis meter which has a full opening pipe internal diameter such
that it is not easily plugged. A Coriolis meter also gives an
accurate mass flow, not just a volume flow rate. Coriolis meters
such as the E+H Promass 83I can also measure viscosity. Given the
critical performance required of drilling muds to ultimately
prevent uncontrolled well events, using a combination of rheology
measurement devices based on different principles would make sense.
For example, a pipe rheometer requires accurate flow rate. Using
the E+H Promass 83I for accurate flow rate could also validate the
viscosity being reported by pressure drop. Whereas the pipe
rheometer calculations are based on flow and pressure drop, the
Promass 83I viscosity is a function of a vibration frequency.
[0012] Even with otherwise proper rheology measurement techniques,
heat is an additional challenge. The fluid rheology should be
measured at more than one temperature. Therefore the ideal device
would shear the mud to replicate the shear imparted by the drill
bit, heat the fluid to the proper temperature and report rheology
at different predetermined temperatures.
[0013] Another challenge is where to take a sample. Drilling fluid
often stratifies in a tank. A sample taken at the top of the tank,
or at any single level, will not be representative of the
composition in the entire tank.
SUMMARY OF THE INVENTION
[0014] Drilling mud is monitored and adjusted with immediate
response to requirements by placing a cavitation mixer in a loop on
the conduit leading from the source of mud ingredients to the well.
The loop can isolate an aliquot of the mud to be used so that its
rheology, viscosity, density and other properties can be determined
at known flow rates and at temperatures present around the drill
bit, and adjusted accordingly. Lab tests are not needed.
[0015] A cavitation mixer is a cavitation device used for mixing
and heating fluids; in the present invention, it is also used to
determine rheology of the drilling mud.
[0016] The phenomenon of cavitation, as it sometimes happens in
pumps, is generally undesirable, as it can cause choking of the
pump and sometimes considerable damage not only to the pump but
also auxiliary equipment. However, cavitation, more narrowly
defined because it is deliberately created, has been put to use as
a source of energy that can be imparted to liquids. Certain devices
employ cavities machined into a rotor turning within a cylindrical
housing leaving a restricted space for fluid to pass. A motor or
other source of turning power is required. The phenomenon of
cavitation is caused by the passage of the fluid over the rapidly
turning cavities, which creates a vacuum in them, tending to
vaporize the liquid; the vacuum is immediately filled again by the
fluid and very soon recreated by the centrifugal movement of the
liquid, causing extreme turbulence in the cavities, further causing
heat energy to be imparted into the liquid. Liquids can be
simultaneously heated and mixed efficiently with such a device.
Also, although the cavitation technique is locally violent, the
process is low-impact compared to centrifugal pumps and pumps
employing impellers, and therefore as a mixing technique is far
less likely to cause damage to sensitive polymers used in oilfield
fluids. Good mixing is especially important in mixing drilling
muds.
[0017] Examples of cavitation devices are described in U.S. Pat.
Nos. 5,385,298, 5,957,122, 6,627,784 and particularly U.S. Pat. No.
5,188,090, all of which are hereby specifically incorporated herein
by reference in their entireties. These patents may be referred to
below as the HDI patents.
[0018] The basic design of the cavitation devices described in the
HDI patents comprises a cylindrical rotor having a plurality of
cavities bored or otherwise placed on its cylindrical surface. The
rotor turns within a closely proximate cylindrical housing,
permitting a specified, relatively small, space or gap between the
rotor and the housing. Fluid usually enters at the face or end of
the rotor, flows toward the outer surface, and enters the space
between the concentric cylindrical surfaces of the rotor and the
housing. While the rotor is turning, the fluid continues to flow
within its confined space toward the exit at the other side of the
rotor, but it encounters the cavities as it goes. Flowing fluid
tends to fill the cavities, but is immediately expelled from them
by the centrifugal force of the spinning rotor. This creates a
small volume of very low pressure within the cavities, again
drawing the fluid into them, to implode or cavitate. This
controlled, semi-violent action of micro cavitation brings about a
desired conversion of kinetic and mechanical energy to thermal
energy, elevating the temperature of the fluid without the use of a
conventional heat transfer surface.
[0019] I refer to the cavitation device I use as a cavitation mixer
because it is sometimes, in my invention, used as a shearing device
instead of heating by cavitation, as will be explained below. The
loop in which the cavitation mixer is placed will also be described
and explained below.
[0020] The ingredients for a drilling mud are placed in a mud tank
or other container and may be roughly mixed together in any
conventional manner. As they are withdrawn to be sent down the
well, they encounter a cavitation mixer, preferably a
flow-controlled cavitation mixer, referred to herein as a FCCM. The
preferred FCCM is a TrueMud.TM. mixer. The FCCM has variable mixing
rates based on the speed of the disc (rotor) and the rate that
fluid is pumped through the device, is able to take in additives at
controlled rates or dosages, assures a uniform and turbulent entry,
preheats the fluid before beginning the cavitation process, and
includes means for setting the gap in the entryway as a function of
the viscosity of the fluid. The drilling mud passes continuously
through the FCCM to the well, where it is destined for the drilling
bit. On its way to the well, a rheology meter or viscosity meter
reads its rheology or viscosity directly in the conduit, or from
samples taken from it, or on a bypass line.
[0021] A cavitation device comprises a cavitation rotor within a
housing. The cylindrical surface of cavitation rotor has a large
number of cavities in it. Its housing has a cylindrical internal
surface substantially concentric with the cavitation rotor. The
cavitation rotor is mounted on a shaft turned by a motor. Fluid
entering through an inlet spreads to the space between the cavities
and the conforming cylindrical internal surface of the housing and
is subjected to cavitation--that is, it tends to fall into the
cavities but is immediately ejected from them by centrifugal force,
which causes a partial vacuum in the cavities; the vacuum is
immediately filled, accompanied by the generation of heat and
violent motion in and around the cavities. This highly turbulent
action in the cavitation zone between the two cylindrical surfaces
of the cavitation device thoroughly mixes and heats the materials
before the mixture passes through an outlet. While any cavitation
device as just described may perform satisfactorily in my
invention, I prefer to use a "flow-controlled" cavitation device,
which has a generally conical surface positioned centrally on the
rotor to face the incoming fluid and to assist the flow of the
fluid to the perimeter of the rotor.
[0022] The rheology or viscosity meter combined with the FCCM mixer
eliminates the need for routine mud checks by continuously
reporting rheology using a process control loop. Mud checks
primarily report rheology by measuring shear rate and shear stress
at predetermined temperatures. In the prior art, typically a sample
of the fluid is heated to 100.degree. F. where viscosity
measurements are taken with a Fann 35 or equivalent rotor and bob
viscometer and then the measurements are repeated at 150.degree. F.
This is a time-consuming procedure which delays reports, often
resulting in their misapplication. The TrueMud.TM. mixer used in
the present invention is a heating device that not only shears the
mud, but heats it by converting shaft horsepower into heat. By
adding temperature controls to the device, the heat can be adjusted
with the speed (RPM, or angular velocity) of the disk and the flow
through the device. By adding a pump and a bypass line, a process
control loop with a known volume can be circulated in the present
invention to shear the mud at a given flow rate and to heat the mud
to report accurate, temperature dependent rheology of the fluid
actually headed to the well.
[0023] There are several devices that can measure viscosity of
drilling mud including, but not limited to a Brookfield TT-100 that
measures viscosity at different reciprocal seconds of shear to
provide real time rheology. Other devices such as an Endress+Hauser
Promass 83i measures viscosity based on vibration feedback
correlated to different reciprocal seconds. Since drilling muds
contain solids, a pipe rheometer also works well, also enabling the
calculation of a friction factor at different flow rates. A pipe
rheometer calculates rheology based on flow rate and pressure drop
across a known length of pipe. Once steady-state is reached in the
process control loop, fluid can be added and removed from the same
loop by controlling the valves that allow fluid into and out of the
process control loop. The flow into and out of the loop can be
automatically adjusted by simple temperature, desired process
flowrate or by viscosity/rheology measurement. Using all digital
sensors, the process control loop can be automated by a process
logic controller, and/or a computer and then easily reported
remotely using the Internet. Such a device including the process
control loop is scalable. A 1 inch device may be used simply as a
method to do automated mud checks or as a laboratory device,
whereas a 2 inch or 3 inch device can fully process the fluid being
used at the well.
[0024] The combined shearing device and rheology process control
loop acts on a realtime aliquot of the drilling fluid in the well
or in a tank. The realtime aliquot solves the problem of sampling
in a stratified tank, or running mud checks in a dynamic system
where the mud is changing for any number of reasons including water
influx. The known volume of fluid in the loop is actually used in
the well, unlike a sample tested in a laboratory. The aliquot may
be isolated and the method of the invention performed while
drilling is stopped (for example when a pipe is added to the drill
string) and the mud is not flowing to the well, or while drilling
is progressing.
[0025] The process control loop can contain (contains) mixing
equipment such that the realtime aliquot of the larger volume of
drilling mud can be adjusted and rheology, density, pH, electrical
stability, and other properties measured immediately to check
potential mud treatments before mixing the full volume of drilling
fluid. In the laboratory such adjustments are done on a "barrel
equivalent" of mud which consists of 350 ml of fluid and 1 gram
equals 1 pound per barrel. In the field you have to adjust the full
mud volume and wait to run mud checks after the mud has circulated
through the drill bit. That process often takes more than one
circulation and more than one mud check to get the desired mud
properties. There is a known volume of mud in the process control
loop of the present invention and a known flow rate. Small volumes
of chemistry can be mixed into the mud either by isolating the
process control loop or by proportioning the chemical concentration
based on flow in the process control loop to immediately know the
mud properties before adding the chemistry (chemicals) to the full
volume of mud.
[0026] Furthermore, the meter can send readings continuously or
intermittently to a controller which controls the addition of mud
thinner, polymers to add viscosity, and other additives. The
controller also controls the speed of the mixer and/or flow through
the mixer. The thus prepared drilling mud proceeds to the drill bit
where it already has the desired attributes.
[0027] In the vicinity of the drill bit, the drilling mud picks up
drill cuttings and other solids; the drilling mud is designed to do
so efficiently and carry the solids back to the surface where the
bulk cuttings are removed with surface separation equipment such as
hydrocyclones, screens and centrifuges. The separation process is
designed to be efficient, but some of the mud is lost in this
process and low gravity solids below 10 micron in size are
generally not removed. New mud is mixed in a mud tank where the
used mud including low gravity solids that could not be removed is
mixed with new drilling mud ingredients, thus changing the
properties of the material in the tank. The invention continues to
adjust the properties of the drilling mud by monitoring and
maintaining viscosity or rheology by regulating the energy input to
the FCCD and the amount of additives replenished or added to the
drilling mud. Furthermore information generated in the present
invention can be used to remotely monitor the drilling mud such
that a skilled mud engineer is not required to do continual mud
checks at the rig site and can therefore manage more rigs.
[0028] The TrueMud.TM. (FCCD) mixer configuration allows for
viscosity measurements since it is essentially a Couette style
device with a rotor. The calculations are widely reported in the
literature and can be found on Page 21 of "More Solutions to Sticky
Problems" published by Brookfield Engineering Labs, Inc.
[0029] The FCCD is a spinning disk inside of a cylinder and can be
set up to measure rheology. Rheology is shear stress measured at
different shear rates. Shear rate is represented by the speed of
the spinning disk. Shear stress is the torque required to spin the
disk. Both can be accurately measured and the calculations are
known to convert the speed of the disk and torque into a viscosity.
There are some unknowns such as critical velocity. To measure
rheology, the fluid should be in laminar flow below the critical
velocity. To overcome any unknowns, the FCCD can be calibrated
either by using a calibration fluid such as 100 centistoke silicone
oil that is also used to calibrate laboratory rheometers, or the
viscosity can be normalized to one known viscosity point using
pressure drop across a known length of pipe or a device that
measures viscosity at one shear rate. Furthermore, the viscosity
can be compared to a manual Fann 35 reading done in the field and
in all cases software can be used to adjust the viscosity to match
the Fann 35 viscosity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a diagram of the prior art method using the drill
bit to shear the fluid.
[0031] FIG. 2 is a diagram of the invention method.
[0032] FIG. 3 is a partly sectional view of the flow controlled
cavitation mixer.
[0033] FIG. 4 shows a basic process loop including a cavitation
mixer.
DETAILED DESCRIPTION OF THE INVENTION
[0034] FIG. 1 illustrates diagrammatically the prior art method of
relying on the drill bit to shear mix the mud ingredients. The
parts are not shown in relative proportion. Mud tank 1 contains the
ingredients for a drilling mud. It may have a rough mixing
capability, not shown. As drilling commences and proceeds, the mud
in tank 1 is sent in conduit 2 to the well 3 below rig 6, following
the path indicated by the downwardly oriented arrows to the bottom
of the well 3 and the drill bit 4. The fluid may be directed
through nozzles or ports on the drill bit, causing shearing. As the
drill bit 4 does its work, drill cuttings are created, and these
are picked up by the drilling mud and removed as indicated by the
upwardly oriented arrows. From the top of the well 3, the
solids-laden used drilling fluid is returned through conduit 5 to
the tank 1 where it mingles with the mud ingredients already there.
The effects of shearing through or around the drill bit are
difficult to relate to the properties of the fluid in the tank.
Moreover, the fluid is not sheared prior to entering the well, as
is desirable. In addition, the prior art method, and modifications
of it, rely on time-consuming and error-prone sampling and
laboratory tests.
[0035] Referring to the simplified diagram of the invention in FIG.
2, mud tank 11 contains the ingredients for a drilling mud. It
normally will have a rough mixing capability, not shown. As
drilling commences and proceeds, the mud in tank 11 is sent in
conduit 12 to the flow-controlled cavitation mixer 17, where it is
shear mixed, and then through conduit 18 to viscometer 19, which
measures its viscosity. It then continues in conduit 18 to well 13
associated with rig 16, following the path indicated by the
downwardly oriented arrows to the bottom of the well 13 and the
drill bit 14. As the drill bit 14 does its work, drill cuttings are
created, and these are picked up by the drilling mud and removed as
indicated by the upwardly oriented arrows. From the top of the well
13, the solids-laden used drilling fluid is returned to the tank 11
where it mingles with the mud ingredients already there.
[0036] Viscometer 19 generates a signal sent through line 20 which
is used to control the speed or energy input of flow-controlled
cavitation mixer 17 as a function of viscosity. Viscometer 19 also
generates a signal sent through line 21 which is used to control
the introduction of viscosity-modifying agent from source 22. A
process controller, not shown, can manage the viscosity inputs and
regulate the mixer and the viscosity-modifying agents according to
programmed instructions.
[0037] It is thus not necessary to rely on the drill bit to perform
the highly desirable function of shear mixing. And, the drilling
mud is at all times at the desired viscosity. The shear mixing
action of the cavitation mixer 17 will be further explained with
respect to FIG. 3.
[0038] FIG. 3 is a partly sectional view of a flow-controlled
cavitation mixer, or FCCM. The FCCM comprises a substantially
cylindrical rotor 31 within a housing having an inlet end 41, an
outlet end 39, and encasement 33 defining a cylindrical internal
surface substantially concentric with that of rotor 31. Rotor 31 is
mounted on shaft 32 which is turned by a motor not shown. Shaft 32
is set on bearings 45 and 46 in extension 38, and its position may
be adjusted horizontally (as depicted) to vary the spaces between
rotor 31 and housing ends 41 and 39 as indicated by arrow 47. Rotor
31 has cavities around its cylindrical surface; the cavities are
illustrated as sections 34a and as openings 34b. Rotor 31 also has
a flow director 37 on its inlet side. While rotor 31 rotates, fluid
from a source not shown enters through inlet 35 and encounters flow
director 37 which spreads it to the periphery of rotor 31 as
indicated by the arrows. The fluid then passes through cavitation
zone 40, a restricted space where cavitation is induced if the
rotor is rotating fast enough, as explained elsewhere herein.
Cavitation can be controlled to increase the temperature of the
fluid to a desired value by controlling the speed of rotation of
the rotor. Conversely, energy input to the FCCM can be controlled
by direct measurement of rotation speed, a very useful datum to
have for fluids of varying viscosity and rheology such as drilling
mud.
[0039] The versatile FCCM is also able to act as a viscometer
because, when it is not causing cavitation, it acts as a
cylindrical spindle, a known form of viscometer employing Couette
principles. For the fluid materials relevant to the invention,
viscosity may be expressed as the ratio of shear stress to shear
rate, or
.mu. = .tau. .gamma. ##EQU00001##
where the shear stress .tau. is
.tau. = T 2 .pi. R s 2 L ##EQU00002##
and shear rate
.gamma. = 2 .omega. R c 2 R s 2 x 2 ( R c 2 - R s 2 ) ,
##EQU00003##
that is
2.omega.R.sub.c.sup.2R.sub.s.sup.2/x.sup.2(R.sub.c.sup.2-R.sub.s.-
sup.2), where R.sub.c is the radius of the cylinder, in this case
the internal width of inlet and outlet ends 41 and 39, R.sub.s is
the radius of the spindle, in this case the radius of rotor 31, T
is the torque of the rotor acting on the fluid, .omega. is the
angular velocity of the rotor, and x is the radial location at
which shear is being calculated. As indicated above, this formula
assumes there is no cavitation taking place around the rotor--that
is, that the action of the cavitation mixer is limited to
generating the shearing action that enables reading shear stress
and shear rate without the disruption that would be caused by
cavitation. I call this the "shear mode," and when the cavitation
mixer is causing cavitation, I call it the "cavitation mode." The
above described method of calculating viscosity, and similar
formulas in the literature using a spindle and cylinder, I call the
"spindle viscosity formula" or, sometimes, "Couette
principles."
[0040] Persons skilled in the art may observe that most
presentations of Couette principles or the cylindrical spindle
measurement of viscosity illustrate a spindle that is longer than
the diameter of the cylinder in which it resides, and that the
cavitation mixer of the present invention is illustrated as the
opposite--that is, the length of the "spindle" is the width of
rotor 31, which is depicted as shorter than its diameter, or even
its radius. This relationship of the cylinder and the housing
within which it resides does not fundamentally change the
calculation of
.tau. .gamma. ##EQU00004##
to obtain the viscosity .mu.. However, some reports on the spindle
viscosity formula are concerned with the effects of the space at
the end of the spindle, and various workers have calculated
additional formulas for them. In the present invention, not only
are relatively large surfaces present on both "ends" of the rotor
31, but also, the fluid continually flows through the cavitation
mixer while the calculations are made. Although the non-cylindrical
faces of rotor 31 (the "ends" of the "spindle") are relatively
large compared to the width of the rotor, their effects on the
calculation of viscosity are reduced by two features of the FCCM
construction: first, flow director 37 spreads the incoming mud
evenly over its surface so that when the mud enters cavitation zone
40 it will follow a helical path in substantially laminar flow over
the cylindrical surface of rotor 31. In the non-cavitation
mode--that is, when the rotor 31 is not rotating fast enough to
cause cavitation, the cavities 34a and 34b are nevertheless filled
with fluid which tends to remain in the cavities, providing
surfaces over which the fluid passes. As indicated in FIG. 3, the
profile of flow director 37 is a smooth curve tending to reduce
turbulence and encourage laminar flow. The smooth curve profile of
flow director 37 may be parabolic, elliptical, hyperbolic or a more
complex smooth curve, generally campanulate and asymptotic toward
the neck of rotor 31. Second, helical flow through cavitation zone
40, even in the absence of cavitation, is somewhat assisted by the
position of outlet 36 near the periphery of rotor 31, as the mud
passes quickly to outlet 36 from cavitation zone 40 without
establishing a significant flow pattern on the outlet side of rotor
31.
[0041] Viscosity of slurries has been successfully measured in a
helical flow instrument. See, for example, T. J. Akroyd and Q. D.
Nguyen, Continuous Rheometry for Industrial Slurries, 14.sup.th
Australasian Fluid Mechanics Conference, 10-14 Dec. 2001. The
authors recognized a tangential component to the shear stress as
well as an axial component, incorporated into their calculations.
See also Shackelford U.S. Pat. No. 5,209,108. Because laminar flow
is encouraged across the cavitation zone when measuring viscosity,
pressure drop across the cavitation mixer may be used, according to
the classical Poiseuille formula explained below, to modify the
calculation of viscosity.
[0042] In FIG. 4, a flow diagram is presented for a loop of the
invention. In this configuration, the cavitation mixer 53 performs
two separate functions. In one function, it is operated with power
input sufficient to cause cavitation in the fluid until a desired
temperature is attained in the fluid. In the cavitation mixer's
second function, the power input is reduced so that no cavitation
takes place and the cavitation mixer acts as a viscometer.
[0043] In the optional "straight-through" mode, which does not
employ the recycle loop, the drilling mud ingredients pass through
valve 51 on conduit 50 to pump 52, through valve 62, and then into
cavitation mixer 53, where they are heated and mixed, then through
conduit 54 to Coriolis meter 55 and viscosity meter 61 before
passing through valve 56 to a well, or to storage or other use not
shown. Coriolis meter 55 (which may be an E+H Coriolis meter) may
measure density in conduit 54. Viscosity meter 61, which may be a
Brookfield TT-100 viscometer, may be programmed to continually read
viscosity at all Fann 35 speeds.
[0044] But an important feature of the invention is that an aliquot
of fluid (drilling mud) can be isolated in the loop defined by
closing valves 51 and 56 and opening valves 58 and 59, thus flowing
an isolated, known quantity of fluid continuously in the loop
through cavitation mixer 53, conduit 54, conduit 57 and again
through conduit 54 to cavitation mixer 53. This may be referred to
as the "loop mode." In accordance with the invention, the
cavitation mixer is operated in the cavitation mode to quickly heat
the mud aliquot to a desired temperature (measured by a transducer
or other device not shown), and then it is operated in the
non-cavitation, or shear, mode so it can shear the aliquot and be
utilized as a viscometer. Acting on the same aliquot of drilling
mud as it circulates in the loop, the cavitation mixer 53 may be
programmed to heat the mud, by cavitation, to a second temperature
and then, without cavitation, to shear it. While shearing the mud,
the cavitation mixer may be utilized as a viscometer employing
Couette principles. The isolated aliquot may be further heated to a
third temperature and viscosity measurements obtained as described
elsewhere herein, as a function of torque on the mixer's shaft and
angular velocity of the rotor.
[0045] When viscosity-modifying agents or other chemicals are to be
added to the mud, valve 62 may be closed and valves 64 and 70
opened, causing mud to flow through additive conduit 65. Additive
conduit 65 passes through an eductor 67 which assists the feeding
of dry chemical (such as dry polymer) from hopper 66 if such a feed
is required by the controller. Conduit 65 also is associated with
liquid feeder 68, which can, on command, deliver doses of liquid
chemical (such as dissolved polymer) into additive conduit 65
through inlet 69. Additives introduced to the mud in additive
conduit 65 will be thoroughly mixed into the mud when it passes
into cavitation mixer 53.
[0046] Persons skilled in the art may recognize that additive
conduit 65 is not essential for liquid feeder 68, which could be
placed on conduit 50 anywhere upstream of cavitation mixer 53.
Eductor 67 for solid additives, however, is an in-line device and
accordingly is best used in a separate conduit such as additive
conduit 65.
[0047] A dashed-line rectangle bearing the reference number 63 on
conduit 57 in FIG. 4 is labeled "Mud Check Instruments." This
represents any or all of meters, probes, instruments and
transducers for detecting or measuring density, flow, viscosity,
pH, percent solids, water cut or oil/water ratio, electrical
stability, particle size, temperature and other properties of the
mud. Such devices are not limited to positioning in or on conduit
57. They may be anywhere in the system; for example, temperature
probe 71 and pressure probe 72 are illustrated in conduit 54.
Included in Mud Check Instruments 63 are (one or more) computers,
processors or controllers necessary or useful to monitor and modify
the properties of the mud in the loop. For example, computers,
processors, or controllers may be programmed to vary the power
input and/or angular velocity of the shaft of cavitation mixer 53,
or to open and close valves so that hopper 66 or liquid feeder 68
can deliver prescribed amounts of additives. Data about the mud and
the well's operation may be accumulated to provide increasingly
accurate refinements to be used possibly in the "straight-through"
mode. Additives are proportioned to the aliquot in the loop and
circulated to confirm the modifications made to its properties. The
"straight-through" mode may be modified to take the illustrated
detour through additive conduit 65 for continuous proportionate
injections of additive(s).
[0048] Viscosity may be measured by a viscometer, not shown, in
conduit 54 or conduit 57. Optionally, viscosity may be read by
pressure difference as is known in the art. The reduction in
pressure between points Pr1 and Pr2 may be ascertained by any
acceptable pressure reading devices and the difference used to
reinforce the calculations according to the spindle viscosity
formula described above and/or viscometer 61. Poiseuille's pressure
drop equation for viscosity .mu. for a fluid flowing in a tube
is:
.mu. = .pi. R 4 g c ( P 1 - P 2 ) C 8 L Q ##EQU00005##
where R is the radius of the tube, gc is the gravitational
constant, P.sub.1 is the measured upstream pressure in the tube,
P.sub.2 is the measured downstream pressure in the tube, C is a
constant conversion factor for expressing viscosity in poises, L is
the distance on the tube between P.sub.1 and P.sub.2, and Q is the
flow rate of the fluid in the tube. So, where the radius of the
tube is fixed and the flow is steady, and because everything else
is a constant except the measured pressures, the viscosity .mu. is
directly proportional to the pressure difference.
[0049] One of the advantages of my process is that data may quickly
be accumulated for more than one temperature for one or more
aliquots of the mud. The aliquot isolated in the loop is easily
ramped up from, for example, 100.degree. F. to 150.degree. F. to
175.degree. F. In this example, the aliquot is first heated by the
cavitation mixer in the cavitation mode to 100.degree. F., the
viscosity is measured either by Couette principles applied to the
cavitation mixer or by a separate viscometer, or both, then the mud
is heated to 150.degree. F. and the viscosity is again measured by
one or more devices, and the mud is further heated by the
cavitation mixer to, say, 175.degree. F., after which the viscosity
is again measured by at least one device, which may be the
cavitation mixer itself. Additional temperature levels may be
included, or not. As Couette principles require inputs of torque
and angular velocity of the rotor 53, these are monitored and sent
to the process controller along with the temperature and other
properties.
[0050] Thus, whether viscosity is measured in the loop at one
temperature or at more than one temperature, the viscosity
measurements can be stored (along with any other properties found
by other instruments) and then used in the straight-through mode to
heat the fluid and adjust the viscosity to the desired value until
it is determined that additional data are needed. Converting from
the loop mode to the straight through mode may be accomplished
either by the programmed controller or by a human operator.
* * * * *