Abstract- It is well-known that the exploration of

hydrocarbons (oil and gas) has been playing a major role in the

world economy. Excessive exploration activities have pushed the

reservoirs of oil and gas either into hard terrains such as thrush,

folds, basalts and sub-basalts or several kilometers deep into the

surface of the earth. Traditional seismic methods and equipment

are not sufficient to ensure the exploration of hydrocarbons

around the world due to their low sensitivity in low frequency

bands and low signal to noise ratio (SNR). Features of Micro-

Electro-Mechanical System (MEMS) accelerometers show the

capabilities of replacing traditional equipment. In addition,

exploration of hydrocarbon can be more significant by using

passive seismic acquisition. This paper proposes a MEMS

accelerometer utilizing capacitive sensing designed in standard

SOI MUMPs technology. The proposed accelerometer will be

used for exploration of oil and gas using passive seismic

acquisitions.

Keywords: MEMS accelerometer, passive seismic, geophone,

sensitivity.

I. INTRODUCTION

Energy needs across the world are growing

continuously and an increase of upto 60% in its demand is

estimated over the next coming 25 years. Technological and

industrial advancement in the developed countries is also

seriously dependant on readily available energy. Fossil fuels

have been gaining attention since the early 1970s as a source

of energy production. It is well known that domestic oil and

gas, a fossil fuel energy source recovery can play a vital role

in this regard. Hence, it is suggested that the production rate of

domestic hydrocarbon could be increased by employing state-

of-the-art technology. Since the introduction of the systematic

exploration for oil in 1912 [1], modern technology and

engineering has been incorporated with the fundamental

process of exploration of oil to improve performance and

production. Drilling a wildcat exploration well or a well

within a known oil field are risky and tentative [2]; however

advances in seismic surveying techniques have reduced the

drilling risk by indicating direct hydrocarbons.

Active seismic imaging is the most commonly used

exploration technology to image reservoirs of oil and gas,

where explosives or vibroseis trucks are used to generate

seismic energy. The generated energy, which contains

information about existing potential oil and gas traps, is

received by a network of several seismic sensors spread over

the ground. The sensor data is then used to construct a 3D map

of the underlying strata to identify the location of hydrocarbon

deposits. Moreover, the increased demand for the supply of oil

and gas has compelled the industry to setup the exploration

activities in geologically complex areas as well, such as thrust

belts, folds and even seeking for good seismic images in high

impedance areas such as basalts [3]. Exploration in such areas

is very demanding and challenging as well as expensive. The

rock pores, containing oil and gas affect the physical

properties of the rock and the energy received from it; using

the conventional technique cannot provide reliable

information. Passive seismic is a new revolutionary technique

that utilizes naturally occurring seismic signals such as earth-

quakes, microtremors and ocean waves to image subsurface

structures. It monitors lower frequency waves that can travel

long s crust without attenuation

whereas the conventional technique utilizes the frequency

range from 10 to 300Hz. Passive seismic has applications in

the areas of reservoir monitoring (permanent/temporary) [4],

CO2

appropriation, mining, geothermal and geotechnical,

hazard safety monitoring [5], and microseismic recording

using a natural frequency for the exploration of oil and gas.

Passive seismic is developing attention after recognition that

the very low end of the seismic spectrum, i.e. less than 10 Hz,

contains more valuable information about the location of

hydrocarbon reservoirs [6], [7]. Different types of sensors are

required for passive seismic sensing as the existing devices are

not facilitated to record a frequency spectrum below 10 Hz.

Excessive exploration activities have pushed the reservoirs of

oil and gas either into hard terrains such as thrush, folds,

basalts and sub-basalts or several kilometers deep into the

surface of the earth. Traditional seismic methods and

equipment are not sufficient to ensure the exploration of

hydrocarbons around the world due to their low sensitivity in

low frequency bands and low signal to noise ratio (SNR).

Features of Micro-Electro-Mechanical System (MEMS)

accelerometers show the capabilities of replacing traditional

equipment. Table I shows the sensitivity of MEMS

accelerometers used in the field of everyday life [8]. Keeping

these views in mind, an analog MEMS accelerometer is

proposed that is based on capacitive-sensing. The proposed

accelerometer can be applied for enhanced oil recovery (EOR)

using passive seismic acquisitions.

The oil and gas industry has been supercharged in the

21st century via innovations and utilization of new

technologies [9]. Progression in technology has significantly

changed the exploration, development and production of oil

and gas reservoirs. Land Seismic is the classical geophysical

method used for the exploration of oil and gas based on the

principle of reflection. In this process acoustic waves are made

incident to enter into the sub-surface of earth with the help of

energy sources such as an air gun, dynamite and vibroseis;

some of these incident acoustic waves when struck with the

subsurface of the earth or rocks, reflect back to the surface of

An Unconventional Method for Exploration of Oil and Gas

M.T. Jan1, Abid Iqbal

2, M. Shoaib

3

1Department of Physics, Kohat University of Science & Technology, KPK, Kohat, 26000. Pakistan

2Department of Electrical Engineering, C.I.I.T Abbottattabad, Pakistan

3MERC, University of the Punjab, Pakistan

m.tariq.jan@kust.edu.pk, engr_abi85@yahoo.com, shoaib-shafi@hotmail.com

978-1-4673-4451-7/12/$31.00 ©2012 IEEE

the earth.. These reflected waves are detected by a number of

sensors, mainly Geophones. Geophysicists then interface the

travel time of the seismic waves and the reflected waves and

buildup images of the sub-surface of the earth; these images

can be simple or multi dimensional [10]. When seismic

technology comes under discussion, the significance of the

Geophone cannot be underestimated. It has been the main

pillar in the exploration of oil and gas on the surface of earth

or under the water and for the detection of ground motion in

the form of earth quakes and landslides. To determine

microearthquake location patterns, a borehole geophone can

provide high quality data but this can be expensive as special

observation wells should be drilled for microseismic studies.

Due to the day to day increase in the consumption of oil and

gas, conventional geophones are insufficient to get the desired

outcomes due to their low bandwidth and low sensitivity. New

technologies such as Microelectromechanical System

(MEMS), optical sensors and gyroscopes are step-in to

overcome these limitations, are stepped-in to overcome these

limitations. Natural earthquake phenomena have opened the

gateways of obtaining sufficient knowledge about the structure

of the earth and its crust [11]. Passive seismic techniques have

been adopted for the characterization of reservoirs in terms of

fault and fracture location and orientation. Researchers have

also diverted their attention towards passive seismic as a new

tool for oil and gas exploration. Passive seismic is a promising

technique which can be a major contributor in exploration

industries. Recovery of oil and gas without any harm to

Mother Nature has been the main advantage of passive seismic

over the land seismic methods. It is performed for the

detection of movements of the earth (both P and S wave

velocities) at natural frequencies (0 to 10 Hz) and for the

location detection of oil and gas reservoirs under the ground.

Such topographic imaging methods are particularly attractive

since they provide both the structural information as

conventional 3-D reflection surveys and lithological (rock

formation) [12]. Furthermore the information collected during

the passive surveys for the exploration of hydrocarbons

around the world can be applied to a specific area with minor

modifications depending upon the location and geology of the

area [13]. Mapping complex regions (subbasalts, shallow

carbonates, over thrust belts) are relatively easy in passive

seismic as the energy source (microearthquake) comes from

below the target [14].

The passive seismic has the main advantage that it does not

require application of an active source and thus can be

performed without mobilizing a synthetic source or waiting

for major earthquake events. Observations regarding data

collection can be carried out in several hours or can be

extended to several days depending on the location of the site

[13].

In the past passive equipments were specifically designed

for particular tasks which were costly and were not considered

compatible for other seismic operations. Recently universal

equipments are available in the electronics industry and can be

utilized for almost all passive and active seismic operations

[15].

TABLE I

APPLICATIONS OF MEMS ACCELEROMETERS USED IN EVERY DAY LIFE.

II. PROPOSED MEMS ACCELEROMETER

The main objective of this present research is to model a new

MEMS accelerometer using standard SOI MUMPs

technology, which is sensitive enough to detect minuscule

moments so that it can be used in geologically complex areas

for exploration of oil and gas. The MEMS accelerometer

presented in [16] relate to this proposed research work in

terms of its applications in seismology. Unfortunately, it

carries a higher value of 2g and cannot be employed for the

detection of oil and gas using passive seismic techniques due

to its lower sensitivity and high noise level. The authors in

[12] presented a comparison between the modern geophones

and MEMS accelerometers for improved reflected seismic

images and rays for detection of oil and gas. The sensitivity

and frequency range of the accelerometer used are much

higher than the proposed accelerometer. In addition, the

method used for detection of oil and gas was land seismic,

whereas, the proposed research focuses on passive seismic.

III. MODELING OF THE ACCELEROMETER

The analytical modeling of the proposed MEMS

accelerometer is given below, based on the specification yield

from this will be use to model the Novel MEMS

accelerometer. The differential equation for the mass-spring-

damper accelerometer shown in Fig 1 can be given as equation

1. Where the displacement x is a function of external

acceleration:

extext maFkxt

xB

t

xm 2

(1)

Where k is the spring stiffness, B is the damping coefficient,

m is the effective mass, extF is the external force and exta is

the external acceleration.

Field Sensitivity Power

Consumption

Frequency

Range

Medical ± 16 g >= 19 mA 2.4 MHz IEEE standard

Implantable ±2g, ±4g, ±8g,

±16g

25 uA 2.4 MHz

IEEE standard

Automobile ±35g, ±50g, ±70g.

>= 1.3 mA 2.50 GHz

Defense Up ±70 g 2.0 A, 20 V 650 KHz to

1.5 MHz

Communication ±20 to ±70g Varies with applications

2.7 to 10 GHz

Seismology >= ±2g Varies with

applications

>= 1 KHz

Figure 1. Mechanical model of an accelerometer

i. Sensitivity

The sensitivity of the accelerometer can be defined as the

ratio of the output over the input acceleration in terms of g.

CS

a(2)

Where S is the sensitivity, is the sense capacitance and a

is the input acceleration. Output may be in terms of

capacitance or voltage. Sensitivity is determined for the

proposed design in terms of its output capacitance w.r.t. input

g.

ii. Minimum Detectable Acceleration

Minimum detectable acceleration can be determined by the

total noise referred back to the accelerometer input. We

assume Brownian noise; hence the Brownian equivalent

acceleration noise as minimum detectable acceleration can be

given as:

mQ

Twk

m

TBkA oBB 44

min (3)

Where Bk the Boltzmann is constant, T is the temperature, B

is the damping factor and Q is the quality factor. From the

above equations, it can be seen that sensitivity of the model

increases with an increase in the proof mass.

iii. Maximum detectable acceleration

The maximum detectable acceleration is given by:

maxmax

Kda

m (4)

The spring constant K directly affects the resonant

frequency, bandwidth, sensitivity and also the pull-in voltage.

Whereas, in the real design, the spring constant is related

directly to the beam characteristics, which are the length (L),

the thickness (t), the width (W) and the elasticity of material

coefficient (Young modulus (E)).

Figure 2. Resonance frequency Vs proof mass

iv. Noise Analysis

Noise is defined as the output signal there is no

acceleration applied to the sensor. The mechanical noise is

calculated in terms of for the designed accelerometer.

The thermo mechanical noise equivalent acceleration can be

written as .

28/ secB n

TM

K TwA m Hz

M (5)

where KB is Boltzmann constant, T is the temperature in

Kelvin, wn is the resonant frequency, is the damping factor

and M is the proof mass of the accelerometer. The value of the

mechanical noise is given in table II.

v. Spring Constant

The folded spring structure is used for the designed

accelerometer. The fixed-guided beams are allocated

symmetrically around the proof mass not to disturb the

parallelism of the free and fixed end of the beams. The spring

constant changes in a beam due to the tensile and compressive

stresses. However, it is assumed that there is no variation in

spring constant and the following equation can be applied for

each beam.

3

3

4L

EWtK (6)

vi. Sense Capacitance

The lateral differential capacitance scheme is used for

sensing the capacitance. The analytical calculation for the

capacitance is given below :

1 '

[ ( )]. ot l d

C N nd

(7)

2 '

[ ( )]. ot l d

C N nd

(8)

1 2C C C (9)

The external acceleration causes the seismic mass to

move from its rest position, which results in the change in

overlap length of the sensing fingers. The change in

capacitance with change in overlap length of the sensing

fingers can be found by using Equations (7) and (8), showing

a linear change in capacitance with respect to the change in

acceleration. Where N is the number of comb drives, n is the

number of fingers in each comb drive, t is the thickness of the

electrode finger in a comb; l is the initial overlapping length

of the fingers and do is the change in overlapping distance

between two fingers. The total change in differential

capacitance is equal to the sum of the capacitances in the two

combs, as given in Equations (9).

IV. ACCELEROMETER LAYOUT

The proposed accelerometer is designed in standard

SOIMUMPs process. The layout of the proposed design is

shown in Fig 3. The lateral capacitive differential scheme is

used for sensing the magnitude of acceleration. Two comb

drives are attached with the proof mass to support the

differential capacitive sensing. The external acceleration

causes the proof mass to displace from its mean position. This

displacement is directly proportional to the magnitude of

displacement which results in the change in overlap length of

the sensing fingers. The change in capacitance with change in

overlap length of the sensing fingers can be found by using

Equations (7) and (8), showing a linear change in capacitance

with respect to the change in acceleration. The total change in

differential capacitance is equal to the sum of the capacitances

in the two combs, as given in Equations (9). The resonance

frequency of the designed accelerometer is 101Hz while the

frequency found by the Finite Element Analysis in COMSOL

is found as 102Hz as shown in Fig 4, which is in close

agreement with the analytical model. Total of four serpentine

springs are attached with the active mass which allow the

displacement in one direction only. When there is acceleration

along the y-axis, the proof mass will displace from its mean

position which will be proportional to the magnitude of

acceleration. The graph between the acceleration and

displacement, obtained analytically is shown in Fig 5. The

maximum displacement can be observed at 10µm while the

graph shows the linear behavior between acceleration and

displacement. The plot between the acceleration and change in

capacitance is shown in Fig 6. The plot shows the linear

increase in capacitance in the left comb and the linear decrease

in capacitance in the right comb when the acceleration is

applied along the negative y-axis. The total sense capacitance

is equal to the sum of the two differential capacitances, that is,

45 fF. The specification of the designed accelerometer is

shown in table II.

Figure 3. 2d Layout of the proposed Accelerometer

Figure 4. Finite Element Analysis of the proposed

accelerometer for the finding the eigen frequency

Figure 5. Relation between acceleration and displacement.

Figure 6. Relation between change in capacitance and

acceleration.

TABLE II

SPECIFICATIONS OF THE PROPOSED ACCELEROMETER.

S. No. Parameters

1 Mass (µgram) 2.0416

2 Spring Constant (N/m) 1.4746

3 Resonant Freq. (Hz) 101

4 Sense Capacitance (F) 45fF

6 Sensitivity (F/g) 19.594nF/g

7 17.7

V. DISCUSSION

Excessive exploration activities have pushed the reservoirs of

oil and gas either very deep into the earth or into the

geologically hard terrains. It is important to mention that only

30% of the reservoirs of oil and gas have been explored and

70% is still unexplored. To ensure the speedy and safe

exploration of the remaining 70% of the reservoirs of oil and

gas, there is a great need for adopting latest scientific methods

and equipment for the exploration of oil and gas. The

conventional geophones, utilizing land seismic approach, are

not sufficient to track the presence of oil and gas due to its

limited bandwidth and very low signal to noise ratio.

Moreover, heavy and bulky equipment, lengthy survey times

and areas, large number of crew members and creating

disturbances for seismic reflection using dynamites or heavy

vibrators are some of the disadvantages of this technique. The

proposed capacitive accelerometer is presented which can be

used for oil exploration in future. The bandwidth of the

designed accelerometer is 100Hz which is capable of sensing

the acceleration of the reservoirs under the ground. The FEA

analysis of the designed accelerometer is performed in Comsol

to verify the design of proposed accelerometer.

VI. CONCLUSION

A novel MEMS accelerometer using SOI MUMPs

technology is proposed in this paper for exploration of oil and

gas with sensing capabilities ranging up-to micro level gravity

and broad bandwidth of 100 Hz. The proof mass of the

proposed MEMS accelerometer is kept heavier while the

spring is made less stiffer in order to obtain equilibrium at

point where the designed accelerometer can detect the

minimum detectable acceleration at frequency range of 0 to

100 Hz. Broad bandwidth allows sensing of small

displacements caused due to micro-earthquakes for several

hundred meters below the earth surface. The FE analysis of

the designed accelerometer is performed in Comsol to verify

the design of the proposed accelerometer. The simulated result

shows a close agreement to the analytical calculation. The

passive seismic technique is used in this research which is

more environmental friendly over the land seismic.

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