acoustic stimulation

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.

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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.

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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.

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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.

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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.

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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.

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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

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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

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acoustic stimulation

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