Oil & Natural Gas Projects
Exploration and Production Technologies
Calibration and Testing of Sonic Stimulation Technologies
This project was funded through solicitation DE-PS26-01NT41048, Round 2, Area
10. This section of the solicitation addressed the use of sonic stimulation
to enhance oil recovery.
The goal of this project was to design a set of standards to be met by field
demonstrations of sonic stimulation, to design and conduct field experiments
to determine the far-field characteristics of the various sonic sources in use
today, and to provide the fundamental observations to advance theoretical understanding
of the sonication process.
Michigan Technological University
Sonic Production Systems
Wave Energy Resources Inc.
Baker Atlas Wireline Services
Iowa State University
In conjunction with Baker Atlas Inc., Michigan Tech devised a system capable
of recording the earth motion and pressure due to downhole and surface seismic
sources. Four seismic sources were tested at Michigan Tech's Reservoir Characterization
Test Site to determine the distance the seismic waves would travel.
A second focus of the study was to gain an understanding of the fundamental
physical mechanisms of the effect of sonic stimulation on oil mobilization.
A theory has been developed to account for the behavior of oil drops (ganglia)
trapped in pore throats and their ultimate release through the additional incremental
pressure associated with sonic stimulation.
Based on the capillary mechanisms determined for oil mobilization, the following
criteria were outlined for successful seismic stimulation.
- The shallower the reservoir, the stronger the effect.
- Waterflooded reservoirs with water saturation greater than 90%.
- The lower the oil viscosity, the better the result.
- Optimal (resonant) frequencies should be selected (frequencies above a certain
threshold may be inefficient).
This work provides a physically based theoretical model that can be used to
improve the performance, reliability, and predictability of new or improved
sonic sources. The permanent test well and the downhole sonde will provide a
test site so that other sonic sources can be developed and tested. Criteria
for reservoirs most likely to benefit from sonic stimulation were delineated.
This project's success could pave the way to supporting the application of
a low-cost method to enhance oil recovery, which could revitalize many oilfields
across the Nation and add domestic reserves and production.
Sonic stimulation technology has the potential to provide a low-cost procedure
for enhancing oil recovery in depleted fields and making it economically feasible
to return some abandoned wells to production. Tests of the technology indicate
that sonic stimulation technology potential is greatest in fields with a high
water cut and large amounts of immobile oil, making the technology suitable
for mature domestic oil fields. Field tests with different seismic sources,
however, have yielded promising but mixed or inconclusive results for enhancing
oil production. In some cases seismic stimulation was reported to increase production
rates by 50%, but in other cases production was unchanged or actually declined.
The theoretical foundation for sonic stimulation is currently not well-constrained
by observational data from field experiments. While some laboratory experiments
have been conducted, their applicability to field conditions is not clear.
The purpose of this project was to establish the place, procedures, and hardware
necessary for rigorous far-field measurement of seismic signals (elastic waves).
The essential elements of the Baker Atlas-Michigan Tech system are 1) a borehole
test site that will remain unchanged and is available to test sonic sources;
2) a downhole sonde that will itself remain in place and, because of its downhole
digitization features, does not require the wireline or surface recording components
to remain constant; and 3) a set of procedures that ensures that the amplitude
and frequency parameters of a wide range of sources can be compared with confidence.
Four seismic sources were deployed at Michigan Tech's Reservoir Characterization
Test Site to record and measure the signal strength of a single activation of
the sources. To make source-to-source comparisons, every parameter of the tests
was kept constant except for the source. Three of the sources tested were downhole
sources, and one was a surface source. The downhole sources included one piezo-electric
vibrator and two oscillating water-jet types of tools. The surface source was
a small hydraulic vibrator.
The sources were recorded by a downhole receiver containing calibrated three-component
geophones and hydrophones. The seismic traces were analyzed in the time domain
and in the frequency domain. The three downhole sources could not be detected
above the ambient noise levels of the site in the time domain, but the surface
source was easily observed, making it the best source tested for sonic stimulation.
The surface source, the downhole piezo-electric vibrator, and one of the downhole
water-jet sources could be observed in the frequency domain. The frequency band
of the sources varied from a low of 18 Hz (the low end of the surface vibrator)
to a high of 1,600 Hz (the high end of the downhole piezo-electric source).
The mechanism proposed for sonic stimulation is capillary entrapment of oil.
Residual oil is trapped in a pore because of the resisting capillary forces
that prevent free motion of a non-wetting fluid. A finite, external-pressure
gradient, exceeding the "capillary-barrier" threshold, needs to be
applied to carry the ganglia through the pore throat. The application of vibrations
is equivalent to the addition of an oscillatory force to the constant pressure
gradient within the rock pore system. When this extra force acts along the gradient
and the threshold is exceeded, instant "unplugging" occurs, and the
oil blob may move through the pore throat.
The criteria of a ganglion's mobilization involve the parameters of both the
medium (pore geometry, interfacial tension and wetting properties, and fluid
viscosity) and the oscillatory field (amplitude and frequency). The medium parameters
vary widely under natural conditions. It follows that an elastic wave with a
given amplitude and frequency will always mobilize a certain subpopulation of
ganglia while leaving others intact; in this sense, the vibratory field always
will produce a certain mobilization effect. The exact macroscopic effect nonetheless
will be hard to predict, as it will represent a cumulative response of the populations
of ganglia with unknown parameter distributions. Variability of reservoir response
to vibratory stimulation thus should be expected.
Current Status (October 2005)
The project has been completed.
Project Start: October 1, 2001
Project End: December 31, 2004
DOE Contribution: $999,995
Performer Contribution: $250,514 (20% of total)
NETL - Jim Barnes (firstname.lastname@example.org or 918-699-2076)
Michigan Tech - (email@example.com or 906-487-2531)
Turpening, Roger, and Pennington, Wayne, Calibration and Testing of Sonic Stimulation
Technologies, Final Project Report FC26-01BC15165, March 2005. This report can
be accessed at www.osti.gov.
Beresnev. I.A., Pennington, W.D., and Turpening, R.M., Capillary Physics Mechanism
of Elastic-Wave Mobilization of Residual Oil, Geophysics, in press.
Finite-difference calculations of the seismic radiation from a source at 0.02
seconds (left) and when it reaches the receiver at 0.10 seconds (right).
The velocity structure used in the numerical modeling of seismic wave propagation
expected from downhole sources at the Michigan Technological University's Reservoir
Characterization Test Site. The gyroscope surveys shown place the boreholes
1,875 feet apart at a depth of 1,485 feet.