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Acoustic Stimulation
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Acoustic Well Stimulation
Presented by
Apisit Kumpangtong 5530629621
Pavin Pirom 5530344721
Setthakrit Towiwat 5530613521
Tanipon Wattana-A-Sakit 5530246921
Varat Ruangvanichayakul 5530505421
Section 7
Instructed By
Prof. Supanee Chinnawongs
(FIRST DRAFT) Acoustic Well Stimulation
Abstract
Over a certain period of time, oil wells are depleted or damaged by
fine solid particles which are occasionally co-produced with the production of the
hydrocarbon. Caused by the precipitation of the solid, damage lessen the flow cross-
sectional area of the oil and gas and hence compromises the hydrocarbon production
rate. Various studies have done on a number of well stimulation, or well cleaning,
techniques to alleviate the problem. Herein a novel and non-conventional technique of
stimulation known by different names, namely acoustic wave stimulation, elastic wave
stimulation, seismic wave stimulation etc., is mentioned. The technique gained interest
by engineers when improvement in oil production rate was observed after earthquakes.
Although it has been around for over 50 years, a clear laboratory research about the
efficiency of which has not been published. In this paper, we examine the effect of
sonic wave in rock permeability improvement which implies the cleaning efficiency of
the method. Normally, the stimulation practice is executed in fields, usually thousands
of feet below the surface, hence a microscopic research of which is impossible under
the condition. In order to do so, laboratory procedures were designed herein to
simulate a specific reservoir stimulating condition. They involved the use of dirty
rock core samples, sonic device generating unit, and a pressurised chamber. The core
samples with known permeabilities were tested with a 12kW sonic generating unit in
the pressurised chamber using different durations. Permeability improvements were
then be analysed and plotted versus time durations. It was found that permeabilities
improved greatly with time duration until it reached the duration of 20 minutes where
their improvement was critically lessen. The results point out the appropriate duration
for 12kW wave stimulation and also emphasise the effectiveness of this technique.
Page 2 of 9
(FIRST DRAFT) Acoustic Well Stimulation
Introduction
When producing hydrocarbon, we seek for the highest possible
production rate to subsidise the operation cost each day. However, oil wells are
depleted or damaged when produced for a certain period of time resulting in the
production rate being compromised. The depletion is inherent and “unfixable.”
However, the damage which is the blockage of solid particles in the rock pores can
be alleviated. Efforts are made to recover the production rate of depleting reservoirs
right from the secondary recovery stage such as water flooding. Also, numerous
stimulation techniques have been developed to improve damaged formations by either
removing or bypassing the damaged zone, each with its own unique principle.
There are many well stimulation techniques available these days. One of
these is acoustic wave stimulation which is also known as elastic wave or seismic
wave. This method was studied in the 1950s when changes in oil production rate
were noticed after earthquakes. Some observations were made in oil fields of
California and Northern Caucasus[1] in the influence of earthquakes on oil & gas
production. It was found that the production rates somehow were improved. By using
an acoustic wave, it creates vibrations in the same nature in which earthquakes do
and stimulates a well by “letting loose” small sand particles in the rock pore to
create wider fluid pathways, hence increasing the flowability[2]. The available field
data have demonstrated that it is a very promising method to regain the production
rate in most wells.[3][4] Unfortunately, very few laboratory studies have been done on
the technique, especially its cleaning efficiency.
In the present paper, we design and conduct a laboratory experiment on
the effect of the acoustic well stimulation in the permeability improvement of rock
samples which represents the cleanliness of the rocks. The objective of this paper is
to study the cleaning mechanism of the wave to initiate a better understanding on the
cleaning effect using the commonly utilised 12 kW wave at different testing
durations. The study can emphasise the effectiveness of the technique in improving
permeabilities, as well as present the best operational duration for the 12kW wave.
Page 3 of 9
(FIRST DRAFT) Acoustic Well Stimulation
Field Operation
In operations, an acoustic-source-generating tool is used to execute the
stimulation. Being able to withstand high temperatures and pressures downhole, the
tool is constructed with the C-60 high-strength steel[5]. Its generating power is very
high, approximately up to 30 kW[6]. In addition, the depth of treatment is around 10-
15 cm measuring from the borehole wall[7].
A stimulation session starts with charging the tool with a power source
which can be either connected directly to a 380V/AC power outlet or from series of
batteries[8]. Then, the tool is conveyed downhole through tubing. During the trip, it
can be attached with a regular electrical wireline or a coiled tubing. Reaching a
desirable depth, the tool will be stopped and the stimulation will be performed
selectively at the depth. The wave will emit a sonic wave of a certain power,
commonly 12 kW. The vibration will be propagated to the formation rock and let
loose any impurity particles attached with the pore surface of the rock. Therefore, the
flow path area will be recovered resulting in the recovery of oil production rates.
Page 4 of 9
(FIRST DRAFT) Acoustic Well Stimulation
Materials and Methods
Although the wave stimulation technique is very useful in the industry,
the mechanism and efficiency of which cannot be thoroughly studied in a real
operation since all the procedures are done downhole, thousands of feet below. In
order to study the technique, we designed a practical laboratory method by simulating
a real downhole environment using the pressurized chamber manufactured by Formtec
Inc. To simulate the formation rock, five 12-inch-diameter low permeability core
samples were drilled out from a dirty formation at 1,500 ft in a well of PTT
Exploration and Production in Kamphaeng Phet, Thailand. Their original pemeabilities
were known to be 13 mD, equally. The cores’ lengths were between 10 and 15
inches. Also, to simulate the wave emitter, the actual downhole sonic tool was
disassembled and the wave generating unit of which was used in the experiment.
The experiment was carried out in the chamber at the typical formation
temperature and pressure settings which are estimated to be 170 °F and 1500 psia,
respectively[9]. Then, the wave generating unit was charged, set at the commonly used
power level of 12 kW, and placed in the chamber. After that, a core sample was
placed in the chamber and the wave generation cycle was initiated. Finally, after a
certain treatment time, the core sample was taken out and its permeability and fine-
solid content were measured. The above procedures were repeated for the four
remaining core samples varying the treatment durations and each result was recorded.
Page 5 of 9
(FIRST DRAFT) Acoustic Well Stimulation
Result
0 10 20 30 40 500
7.5
15
22.5
30
Treatment Duration (min)
Perm
eabi
lity
Im
prov
emen
t (m
D)
Plotted from the experimental result included in the appendix, the above
figure shows the permeability improvement of the core samples stimulated at different
time duration. The x-axis and y-axis represent the time durations in minutes and the
permeability improvement in milidarcies, respectively. It was found in the experiment
that the permeabilities improved with increasing time durations. However, at longer
durations starting from the 20th minute, the permeability showed less improvement
(the above graph slope exhibits significant reduction). Thus, it could be concluded
that the acoustic wave could help the permeability improvement, but certain wave
powers had their own optimal durations. In addition, the treatment duration of 20
minutes was the most optimal duration for the 12 kW sonic wave in which the best
cleaning to time ratio is achieved.
Page 6 of 9
(FIRST DRAFT) Acoustic Well Stimulation
Conclusion
The objective of the present paper is to study the effect of acoustic
wave stimulation in permeability improvement of the formation rock. From the
controlled experiment conducted, it was found that the wave helped in cleaning core
sample. In addition, for 12 kW wave, 20-minute duration yielded the best cleaning to
time ratio. The findings have a number of important implications for future practice.
First, it gives an additional proof to the effectiveness of the acoustic wave in rock
cleaning. Also, it derives the best treatment duration of 20 minutes for 12 kW sonic
wave for the use in real operation. However, a number of issues remain unclear,
especially the effect of varying wave powers and the rock properties of core samples.
Further experimental investigations are needed to obtain the most economical setting
and duration for certain type of reservoir.
Page 7 of 9
(FIRST DRAFT) Acoustic Well Stimulation
References
1. Igor A. Breznev & Paul A. Johnson, “Elastic-wave stimulation of oil production:
A review of methods and results”, Geophysics Vol 59, No. 6, (June 1994); page
1000-1017
2. Adinathan Venkitaraman, Peter M. Roberts, Mukul M. Sharma, “Ultrasonic
removal of near well bore damage caused by fines and mud solids”, SPE 27388
3. Peter M. Roberts, Adinathan Venkitaraman, Mukul M. Sharma, “Ultrasonic
removal in North Sea”, SPE 62046
4. Le Hui Zhang, Peter Ho, Yun Li, Shengning He, “Pilot Test of Acoustic Wave
Stimulation in Beijing”, SPE 51914
5. Enhanced Oil Recovery with Downhole Vibration Stimulation, R. V. Westermark
et. al. SPE 67303
6. Paul A. Johnson, “Seismic stimulation of oil production in depleted reservoirs:
Proposal Summary”
7. Susan Jackson, “Advances in Seismic Stimulation Technologies”
8. Peter M. Roberts, “An integrated approach to Seismic Stimulation of Oil
Reservoirs: Laboratory, Field and Theoretical Results from DOE / Industry
Collaborations”, LANL, 16th International Symposium on Nonlinear Acoustics,
Moscow, 2002
9. Mayank Rastogi, & A K Mishra, “Production Enhancement Through Stimulation
Techniques”, 19th Annual India Oil & Gas Review Summit & International
Exhibition
Page 8 of 9
(FIRST DRAFT) Acoustic Well Stimulation
Appendix
Core Sample 1st 2nd 3rd 4th 5th
Stimulation Duration (min)
10 20 30 40 50
Original Permeability (mD)
13 13 13 13 13
New Permeability
22 35 39 41 40
Permeability Improvement (mD)
9 22 26 28 27
Page 9 of 9