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Mechanisms
of Increased Recovery
DOE-Funded
R&D in Acoustic Stimulation Technology Development
Los
Alamos National Laboratory and Lawrence Berkeley National Laboratory
Laboratory
Experiments
Modeling
Field Tests
Field Testing in
the Osage Reservation, Oklahoma
Other U.S. Work by
Producers
Future Research
Directions
Commercially
Available Acoustic Stimulation Tools
Applied Seismic
Research, Plano, TX
PerfClean,
Midland, TX
Prism Production
Technologies, Edmonton, Alberta, Canada
Sonic Production
Systems, Aimes, IA
References |
Advances in Seismic Stimulation
Technologies
by Susan Jackson, RMC, Inc.
for DOE's National Petroleum Technology Office, Peter Roberts, Los Alamos
National Laboratory, Ernie Majer, Lawrence Berkeley National
Laboratory
Excerpts in PTTC
Network News, 2nd Quarter 2001
Seismic wave stimulation technology has the
potential for being a relatively low-cost procedure for enhancing oil
recovery in depleted fields, or returning some shut-in wells to
production. Tests indicate that potential is greatest in fields with high
water-cut and large amounts of immobile oil, making mature domestic
reservoirs a prime target. Field tests of the technology, however, have
yielded promising but mixed or inconclusive results.
Interest in seismic stimulation started in the
1950s with observed correlations between water well level and seismic
excitation produced from railroad trains and earthquakes. It was noticed
that a rise in well fluid levels and an increase in fluid (pore) pressures
were associated with earthquakes and cultural seismic noise. Similar
effects were observed in producing oil fields where distant earthquakes
caused increases in production, and wells close to operating machinery,
highways or railroads appeared to produce more oil than wells in quieter
areas. These anecdotal observations motivated Russian researchers to
perform surface Vibroseis stimulation tests in several producing oil
fields. The results of these early field tests were mixed. In some fields,
production increased after Vibroseis stimulation, but in others the
production actually declined. It became clear that a better understanding
of the stimulation phenomenon was needed before it could be exploited
reliably. This led to numerous research efforts beginning in the early
1970s and continuing today. Beresnev and Johnson (1994) provide a
comprehensive review of over 100 Russian and U.S. technical articles and
patents on the effects of seismic and acoustic stimulation on fluid flow
in porous media, including laboratory investigations, theoretical studies
and field tests. Documented work covers the use of a wide range of
stimulation wave types and energy coupling modes, with frequencies
spanning the range of one Hz to five MHz.
Another potential application that is being
investigated is using seismic stimulation for enhancing environmental
remediation efforts, particularly at oil refineries where large spills of
petroleum products are threatening groundwater quality. Numerous oil
companies and seismic source providers have expressed interest in pursuing
this application. Recent research has indicated that seismic waves could
enhance the extraction rate of groundwater contaminants by as much as a
factor of 20 under ideal conditions (Roberts et al., 2001). However, the
technology has been even less well tested in the field for environmental
remediation than it has for oil production enhancement
This article summarizes recent research efforts and
describes several existing field stimulation technologies. During the last
ten years industry interest in seismic stimulation technologies has grown
enormously. Along with this increased interest, our understanding and
validation of the phenomenon are also beginning to improve. Industry and
government supported research efforts are largely responsible for this.
The science and technology are at a critical stage of development now,
where continued research and applications testing efforts have an
excellent chance of answering many of the important questions that have
been raised regarding when, where and how seismic stimulation can be used
reliably.
Mechanisms of
Increased Recovery
Mechanisms responsible for improved recovery are
not well understood and remain the subject for further research. The
following mechanisms have been proposed to explain the changes in fluid
flow characteristics resulting from seismic stimulation.
·
Changes in Wettability.
Some laboratory work indicates that the wettability of a core saturated
with oil can be made more water wet, resulting in increased oil recovery
rate by waterflooding in conjunction with seismic stimulation.
·
Coalescence and/or
dispersion of oil drops. This school of thought speculates that
attractive forces acting between oscillating droplets of one liquid in
another (Bjerknes forces) induce the coalescence of oil drops, enabling
continuous streams of oil to flow.
·
Reduced viscosity.
Laboratory work has indicated that, immediately after a 30- to 60-minute
long exposure to an acoustic field, oil viscosity dropped by 20-25%, then
gradually returned to pretreatment level over a 120-hr period. Similar
viscosity reductions of 18-22% have been noted with polymers exposed to an
acoustic field. One researcher suggests that heat generated by ultrasound
absorption contributes to viscosity reduction.
·
Surface tension.
Under some theories, it is suggested that the fundamental source of the
increased permeability is the reduction in surface tension caused by the
differential velocity between the rock matrix and the pore fluid.
·
Increased permeability.
It has been speculated that seismic waves can disrupt immobile fluid
boundary layers on pore walls, which would increase the effective cross
section of pores. In early laboratory work, the permeability of a core
sample saturated with fresh water increased 82-fold after being exposed to
an acoustic field, returning to its original value within minutes after
removal of the sound field. It has also been demonstrated that stress
cycling of core samples at 50 Hz can mobilize in-situ particulates that
are plugging pore throats. The pore throats are unplugged and the rock's
permeability increases.
DOE-Funded R&D in
Acoustic Stimulation Technology Development
Two projects have been funded by DOE’s National
Petroleum Technology Office in Tulsa, one with Los Alamos and Lawrence
Berkeley National Laboratories involving laboratory, modeling, and field
experiments and a second with Oil & Gas Consultants International,
Inc. (OGCI) involving field testing of a vibration stimulation device in
Osage County, Oklahoma.
Los Alamos National Laboratory
and Lawrence Berkeley National Laboratory
Los Alamos National Laboratories (LANL) is
partnering with Lawrence Berkeley National Laboratories (LBNL), University
of California at Berkeley (UCB), AERA Energy LLC, Applied Seismic Research
Corp., Chevron, Conoco, Fluidic Technologies, Halliburton, Marathon, Oil
& Gas Consultants International, Inc., PerfClean Intl., Phillips,
Piezo Sona-Tool, and Texaco to study seismic stimulation.
The research objectives of this project are to
investigate the physical conditions or mechanisms by which low-frequency
(1-500 Hz) stress (seismic or acoustic) waves enhance oil production rates
in marginal reservoirs. Anecdotal evidence and limited field testing have
indicated that seismic stimulation can increase oil production rates by
50% or more, but it is currently difficult to predict how, when or where
to apply the technique successfully. Research is focused in three main
areas: (1) laboratory fluid flow and production enhancement experiments on
cores, (2) numerical and theoretical modeling of wave stimulation effects
on 2-phase fluid flow in porous media, and (3) full-scale experimental
field stimulation testing, source characterization, and production
monitoring.
Both steady-state constant flow and
non-steady-state displacement tests were performed in Berea Sandstone
using oil/brine and decane/brine systems. During steady-state experiments,
the drop in pressure increased in the oil/brine system, while it decreased
with the decane/brine system. Two possible explanations for the pressure
increase in the oil/brine system are 1) additional oil and/or brine became
trapped or 2) additional oil began flowing through a fraction of the pore
space previously occupied by mobile brine. The pressure decrease observed
during decane/brine flow could be explained by 1) previously trapped
decane and/or brine becoming mobilized or 2) decane with its lower
viscosity replaces flowing brine.
Non-steady-state displacement (flooding) tests
using both oil/brine and decane/brine systems indicated that stress
stimulation enhances brine production during drainage (oil flood) and
decreases the oil displaced during imbibition (brine flood). These
observations could be explained by the fluid-trapping mechanism mentioned
above. Stimulation may cause the highly water-wet Berea sandstone to
become temporarily more oil wet, causing oil to become trapped during
stimulation. With the decane/brine system, stimulation had little or no
effect on net fluid production during either drainage or imbibition.
During imbibition, however, the rock reached residual decane saturation
faster. Altered wettability cannot account for this observation.
Modeling work strives to describe how each
individual component of oil and water should respond to a pressure pulse
in a porous medium. During the past year, the exact equations for mass and
momentum balance among all three components in an elastic porous medium
containing two immiscible fluids has been derived in the linear limit.
These equations lead to diffusion equations for pressure/stress and for
porosity (or total fluid mass) in the long-wavelength limit. The work will
allow a more exact calculation and understanding of the coupling of
different seismic and pressure effects. This work is being extended to the
long-wavelength limit by developing coupled partial differential equations
for wave propagation and solving them under boundary conditions
appropriate for fluid pressure-pulsing experiments. The ultimate goal is
to model performance in different geologies and formations as a function
of porosity, and fluid and matrix properties.
LBNL
and industry partners have conducted several field tests to monitor the
seismic energy in the formation resulting from stimulation activities. The
tests consist of careful measurements of the pattern of effects of the
stimulation correlated with the measurement of seismic energy at various
distances from the seismic source.
The
tests have been conducted by lowering a three-component geophone and
hydrophone array into wells at distances varying from 200 feet to 2300
feet during the stimulation period to record the seismic energy. With
these data, the level and bandwidth of energy produced in the reservoir
can be observed. The data collected are also correlated with production
increases in the wells to deduce the relationship to other factors, such
as differences in geology.
To
date, three different sources in three different formations have been
tested. The tests have been in the sandstone formation of the oil fields
just north of Loveland, Colorado, the diatomite in Central California and
a shale formation also in Central California. Bandwidth ranged from 2 to
2,000 Hz. In all of these tests, no seismic energy above background was
observed. It is thought that monitoring equipment was too far away. Future
tests will place sensors much closer (within 100 feet). In addition, the
pulse in the source will be monitored by placing a wide bandwidth and
large range pressure transducer in the perforated sections of the source
well.
For
additional information, visit
http://www.ees4.lanl.gov/stimulation
or contact Peter Roberts, Los Alamos National Laboratory, phone:
505-667-1199, email:
proberts@lanl.gov
or Ernie Majer, Lawrence Berkeley National Laboratory, phone:
510-486-6709, email:
elmajer@lbnl.gov.
Field Testing in the Osage
Reservation, Oklahoma
Oil & Gas Consultants International, Inc. (OGCI)
is partnering with the Osage Tribe, Calumet Oil Company, the field
operator, and Phillips Petroleum Company (Phillips) to test vibration
stimulation in the North Burbank Unit, a mature waterflood field located
on Osage tribal lands. Discovered in the 1920s, the North Burbank Unit
still has more than 200 million barrels of movable oil in place, but
currently produces only 1200 bbls/day at 99% WOR. The Burbank sand is at
about 2800 ft with permeability ranging from 50 md to one Darcy. Seismic
Recovery LLC, a subsidiary of OGCI, has designed and built, and will test,
a new version of a downhole vibration tool based on their patented
whirling orbital vibrator. The tool developed by OGCI uses a backward
whirling motion to create both compression and shear seismic waves from 5
to more than 500 hertz, and is capable of generating controllable force
levels up to many tens of thousands of pounds. Two sets of mechanical
slips are used to transmit the vibration energy from the backward whirling
mass into the producing formation. A schematic of the tool is shown in
Figure 1.
The direct mechanical contact with the formation
allows the device to be used in reservoirs with a gas cap—a situation
that would dampen a fluid pressure pulse technique. The tool can be used
to mitigate the effects of near wellbore condensate dropout and for
groundwater remediation, and functions equally well in producing and
injection wells.
Figure 1. Schematic of Seismic Recovery
LLC’s 7-inch downhole vibration tool.
The downhole tool and surface power source will be
tested in a newly drilled well that will be cored, logged and completed
with 7-inch production casing. Phillips will conduct laboratory tests using their proprietary sonic core apparatus to determine fluid
flow response to a range of vibration frequencies. Results will guide
final adjustments to the frequency generation mechanisms of the downhole
vibration tool. Drilling is planned during July 2001. Once baseline data
are gathered, vibration stimulation will begin.
One or more offset wells, adjacent to the vibration
test well, will be equipped with downhole geophones to determine strength
of signal and if the producing formation has a dominant frequency
response. Surface geophones will also be set out and arranged to pick up
the signal generated by the downhole vibration tool. The results of the
data collection will be a matrix of varying vibration stimulation
conditions corresponding to changes in production fluid rates and seismic
responses.
The results of the downhole vibration stimulation
test will be made available though Society of Petroleum Engineers papers
and workshops. A technical session on vibration stimulation will be
offered at the SPE/DOE Thirteenth Symposium on Improved Oil Recovery in
Tulsa, April 2002, bringing together the world’s experts in this
emerging technology.
Seismic Recovery LLC is actively seeking other
opportunities to field test its tool for vibration-enhanced recovery,
ground water remediation, and condensate dropout mitigation. For more information contact: Bob Westermark, Seismic Recovery LLC,
Phone: 918-828-2543, Email:
bwestermark@ogci.com.
Other U.S. Work by
Producers
BP is looking into the use of pressure pulsing for EOR,
well-bore cleanup, pipeline problems and drilling. In preparing for field
trials, they have screened reservoirs looking for onshore, low gas
content, and “softer” rocks to allow fluid-rock coupling. Five
candidate reservoirs have been selected from about 300 reservoirs.
Chevron is currently applying in-situ seismic stimulation
technology in their Lost Hills Field to lower their stimulation costs.
Results of the stimulation are being monitored through observation wells
and will be published.
AERA Energy has tried seismic stimulation (in cooperation with
LANL) in their Lost Hills, San Ardo, and Belridge fields. Two or three
additional field tests are planned. Lost Hills and Belridge fields, among
others, are being considered for the test.
Marathon conducted a test in the Tensleep in
Wyoming, a high viscosity oil reservoir. Tool failure and lack of
resources prevented completion of the test. The formation was hard and
fractured, resulting in water cycling problems. The resulting reduction in
injectivity was attributed to mobilization of high viscosity oil. Marathon
is considering another test of the technology.
Future Research
Directions
Although tests and applications of seismic
stimulation technology have been generally successful, further work is
required to improve the reliability of the technology. Some of the areas
that need further work include:
·
Increased understanding of fundamental science and physical
mechanisms governing the phenomenon
·
Well-controlled field tests of vibration technologies
·
Application of the technology to enhance other recovery
methods, such as thermal recovery and chemical flooding
·
Use of acoustic, elastic wave stimulation to obtain
reservoir imaging information along with reservoir stimulation
Commercially
Available Acoustic Stimulation Tools
Service companies with commercially available
acoustic stimulation tools were invited to describe their tools, and four
–Applied Seismic Research, PerfClean, Prism Production Technologies Inc,
and Sonic Production Systems --responded. Some other known suppliers were
not able to respond.
Applied Seismic
Research, Plano, TX
Applied Seismic Research (ASR) uses in-situ seismic
stimulation (ISS) to mobilize immobile oil through creation of high-energy
(up to 10 million watts of power) low-frequency shockwaves that enhance
oil mobility. The ISS Tool has increased oil recovery and production by as
much as 30% and has improved recovery in wells as far away as 1½ miles
from the tool.
The ISS Tool consists of two modified tubing pumps
separated by several sections of tubing (Figure 2). A conventional pumping
unit powers the ISS Tool. On each cycle of the pumping unit, the tool
releases highly compressed wellbore fluids creating seismic (hydrodynamic)
shockwaves. In an oil-bearing reservoir, the shockwaves transform into
localized, high-frequency wave fields that act to dislodge oil droplets
and/or coalesce thin oil films into mobile oil droplets.
Figure 2. The Applied Seismic Research In-situ
Seismic Stimulation Tool.
ISS has been proven effective in sandstone,
dolomite, and diatomite reservoirs with permeability ranging from 0.0001
to 1 Darcy, API gravity ranging from 17 to 38 degrees, and on both
fractured and non-fractured systems. Typically, ISS is most effective in
reservoirs having a relatively low (field-wide) gas-oil ratio, less than
2000 scf/stb, API gravities greater than 20-22 degrees, and heterogeneous
reservoirs containing areas of by-passed or trapped oil. Reservoir rock
type, depth, and wettability do not significantly affect performance.
Requirements for technology implementation are a
pumping unit of 120 or 144” stroke length having 6 to 7 strokes per
minute, tubing, and rods. ASR provides the tool and on-site consulting for
installation. The tool can be installed in active injection wells that
remain active during ISS and in production wells provided the tool can be
set at or below the bottom set of perforations.
A recent field test conducted in conjunction with
Lawrence Berkeley National Laboratory, Los Alamos National Laboratory, and
Chevron in Chevron’s Lost Hills field illustrated the ability of the ASR
ISS tool to enhance oil production and recovery. The ISS tool was placed
in an active injection well at a depth of approximately 800 feet. It was
run continuously at seven strokes/minute using a 120-inch conventional
pumping unit. The seismic waves created every 8.5 seconds by the slimhole
version of the tool had an average power of 1.5 megawatts (million watts).
The seismic shockwaves traveled down the wellbore to connect hydraulically
with the formation through the perforations at 2,200 to 3,600 feet.
A continuous 12-day stimulation test conducted
during July 2000 increased oil cut with no overall increase in fluids. A
longer 38-day test performed during October-November 2000 in a group of 60
wells increased oil cut and oil production by 11% and 17%, respectively.
Because many of the 60 wells had undergone various types of workovers and
fracture stimulation, a control group of 26 wells that had not been
disturbed by stimulation procedures was also monitored. By the end of the
second stimulation treatment, oil cut from the 26 control wells had
increased 29% and oil production had increased by 26% (see Figure 3).
Increases in oil production and oil cut attributed
to a series of earthquakes occurring in September and October of 1999; the
epicenters of which were located approximately 230 miles from the Lost
Hills field, are also evident in Figure 3. The earthquake and ISS events
are statistically significant as each event has pre- and post-event
trendlines. Since oil production and oil cut curves both return to
original trendlines, continuous application of ISS in the Lost Hills
reservoir is required.
Figure 3. Oil production and
oil cut data from a controlled subset of 26 producing wells from the Lost
Hills field, California. Historic production data show a clear response to
a magnitude 7.1 earthquake in October 1999 and to downhole stimulation
treatments performed during July - November 2000.
For
further information about the ISS Tool, contact Bill Wooden, phone:
972-381-4236, email:
wow@zowi.to
Although the PerfClean© Tool System is used
primarily for near wellbore clean up, a field test to demonstrate
applicability for enhancing recovery is planned in a South Texas field.
The system uses a patented fluidic oscillator that creates pulsating
pressure waves within the wellbore and formation fluids. These pressure
waves break up any type of near wellbore damage, restore, and enhance the
permeability of the perforations and near wellbore area. The PerfClean©
Tool System is run into the well via coiled tubing, conventional tubing,
wash pipe or drill pipe. The desired treatment fluid (acid, water,
seawater, diesel, nitrified fluids, etc.) is pumped down the tubing
through the PerfClean© Tool.
The kinetic energy of the pressure pulse travels
through the wellbore fluid with no appreciable energy loss. When the
pressure wave contacts the formation, the energy is "dumped" and
the process of removing the near wellbore damage is initiated. As the
damage is removed and the permeability is restored, these pressure waves
penetrate deeper and deeper into the formation. The pressure waves expand
in a spherical fashion from the point of origin, which ensures that
360-degree coverage is accomplished, while moving the tools through the
interval. The acoustic streaming induced by the oscillator focuses the
treatment fluid and tool energy and allows for treating specific
intervals.
The PerfClean© oscillators are true fluidic
oscillators. There are no moving parts. They do not rely on cavitation to
create pressure waves. There are no packer elements to fail. Unlike
mechanical tools, which suffer from high-energy losses, the PerfClean©
oscillator maximizes the energy potential of the pumped fluid.
PerfClean tools have been used to treat over 2,500
wells in 12 states and 7 international areas. The majority of these
treatments have taken place in the Permian Basin region of Texas and New
Mexico where PerfClean International Inc. is currently based. The tools
have been successfully used to treat and correct near wellbore damage in
wells ranging from 90' to 27,000' deep. The treatment design and execution
varies according to well conditions and the goals of the operator.
Applications of the technology are best in
formations that can support a full column of fluid. This allows for easy
manipulation of the wellbore pressures during the treatment. Theory and
experience show that incompressible fluids provide the best coupling of
the pressure pulse generated by the tool to the formation.
For
further information, contact David Facteau, phone: 915-686-7432, email: PerfClean@hotmail.com.
Prism
Production Technologies, Edmonton, Alberta, Canada
Prism Production Technologies provides Pressure
Pulse Technology (PPT), a technology that improves recovery through large
but elastic-range (reversible) excitation implemented through tailored
pressure impulses within the borehole. The method concentrates energy in
the right frequency range for porosity dilation wave generation, and
because the tool is at hole-bottom, energy losses that occur as a pressure
pulse travels down a wellbore are avoided.
PPT has been used to solve environmental problems.
Here, the types of problems are physically similar to those encountered in
the petroleum industry except for two major factors; the pressures are
much lower because of the shallow burial and there is often a phreatic
interface close to or within the aquifer.
PPT can be used to increase production of
conventional and heavy oils using primary, secondary, and tertiary
recovery methods as well as single well stimulations. The greatest
potential of PPT lies in the application of the technology to the field
scale where fluid flow rates to individual wells or groups of wells are
increased. In past applications, perforations were kept open and flowing
by continuous destabilization of perforation sand arches. In heavy oil
reservoirs, incidents of sudden massive sand influx into sand producing
wells, causing pump blockages were reduced. In low permeability
reservoirs, injectivity of liquid floods was increased.
The PPT increases flow rates, reduces mechanical
and capillary flow blockages, and improves sweep efficiency and resource
recovery ratios. To achieve these effects, dynamic energy at an
appropriate magnitude and frequency is introduced to the reservoir through
pressure pulsing. This must be applied correctly, in an optimum
configuration, as with any other type of enhanced oil recovery process. To
decide the optimum approach to PPT in a producing reservoir requires
knowledge of reservoir history, current reservoir conditions, and the
options available for continued development.
The presence, quantity, and distribution of free
interstitial gas affect the physical propagation of the porosity dilation
wave. Wave propagation is impeded by free gas in either a continuous phase
or a bubble phase. The gas compresses during the transit of a porosity
dilation wave and can lead to an increase in the attenuation rate of the
wave.
The area influenced by PPT depends on a number of
factors. In one case, flow enhancement propagated slowly outward for a
distance of 1000 m in a heavy oil (m
»
10,800 cP) reservoir after a period of 10 weeks. Because the porosity
dilation wave follows all the laws of physics associated with waves, it
attenuates because of geometric spreading. However, because there is a
pressure build-up effect associated with the porosity dilation wave,
pressure diffusion spreads out from the source at a rate controlled by the
permeability and the viscosity of the liquid phases. If the outward
propagating pressure front is intercepted by production wells (sinks),
they will arrest propagation of the effects. The spatial distribution of
the PPT impulse devices with respect to the existing or proposed well
locations must be optimized.
The PPT method is based on a rigorous theoretical
construct that successfully predicts a number of phenomena that have now
been observed and that follow the laws of physics. These include spatial
attenuation, pressure diffusion, and gravity segregation of fluids of
different density. For example, although PPT increases the rate of flow
through the application of additional energy in the optimum dynamic range,
the rate of flow is still controlled by viscosity, pressure drop, and
permeability. Therefore, the presence of permeability barriers is as
serious an impediment to successful PPT as it is to other methods that
depend on permeable connections. In addition, it is important to remember
that PPT suppresses the various viscosity-dominated instabilities such as
fingering, channeling, and coning. The suppression occurs because the
pulsing energy is applied in the right area to push forward protruding
fingers and increase sweep efficiency. Permeability barriers, disposition
of strata, permeability ratios, and similar factors all have an effect on
the fluid flow regime, even if flow rate is enhanced by PPT. These
factors, therefore, must be assessed before implementation.
Requirements for implementing the PPT include well
production history from the date of the last re-completion or significant
operational change that would affect the ability to produce fluid, as well
as the production history of the six-month period immediately preceding
the pulsing, irrespective of interventions. The instantaneous background
production rate and trend of each well immediately prior to pulsing
initiation can then be more or less rationally extrapolated from the
historical data. Since the reservoir production rate evolves dynamically
and tends to follow the natural (expected) trends, this background period
is considered sufficient, particularly since a number of offset production
wells will likely be used for project evaluation. This approach allows
project success to be evaluated rationally, despite difficulties in
developing clear well histories and standard concerns about data quality.
Production history details and intervention activity for the six to twelve
months prior to the proposed date of PPT implementation must be used to
develop base line trends that are used to evaluate program success.
For
further information, contact Brett Davidson, phone: 780-486-2222,
email:
brett@prismpt.com
Sonic
Production Systems, Aimes, IA
Sonic
Production Systems, a business unit of Etrema, offers the PowerWave
technology for enhancing production. The technology consists of two
magnetostrictive (an alloy that changes shape and produces a powerful
force in the presence of a magnetic field) actuators opposing an acoustic
element. The set up of the tool is similar to that of an electric
submersible pump. The PowerWave tool is a solid-state source with only
three moving parts-two output shafts and one acoustic element. This
provides for a long tool life. The tool runs at 250-400 Hz (cycles/second)
continuously. Produced pressure waves act to decrease surface tension
between oil and pore walls; destroy surface films that cover pore throats,
allowing the oil to move out of the pore; and coalesce oil droplets so
they can move to the wellbore.
Field tests are
ongoing, with applications in Alabama, Oklahoma, and Indonesia. A short
test was run in San Ardo field, California, where the tool operated for a
period of 6 days in a cyclical steam flood. Production before installation
was about 450 barrels of oil per day. Six days of stimulation resulted in
a production increase to about 885 barrels per day. Water cut was above
90% in both cases, and even when production nearly doubled, water
production did not increase.
Screening
criteria include high water cut, high flow, consolidated formations (the
harder the better), good production history, 5.5-inch or larger casing,
and 440-480 V 3-phase power available. Well temperature needs to be less
than 180 F. Formations at depths less than 5,000 feet are preferable.
For further
information, contact Tim Drake, phone: 816-246-0566, email:tim.drake@sonicproduction.com.
Beresnev, I.A. and P.A. Johnson, 1994,
"Elastic wave stimulation of oil production: A review of
methods and results," Geophysics, (June 1994) 59, No. 6, 1000.
Roberts, P.M., A. Sharma, V. Uddameri, M.
Monagle, D.E. Dale and L.K. Steck, 2001. Enhanced DNAPL Transport in a
Sand Core during Dynamic Stress Stimulation, Environ.
Eng. Sci., 18-2, 67-79.
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