8/17/2019 PETSOC-97-80

1/7

8/17/2019 PETSOC-97-80

2/7

TH P TROL UM SO I TY

 coustic Dew Point and ubble

Point Detector for   s Condensates

and Reservoir Fluids

A. Sivaraman

Y

Hu EB. Thomas

D.B. Bennion A.K.M. Jamaluddin

Hycal nergy Research Laboratories Ltd

PAPER 97-80

This paper is to be presented al the 48th Annual Technical Meeting of The Petroleum Society in Calgary Alberta Canada June 8 - 11

1997. Discussion of this paper is invited and may be presented at the meeting if fi led in writing with the technical program chairman prior

to the conclusion of the meeting. This paper and any discussion filed will be considered for publication in CIM journals. Publication rights

are reserved. This is a pre-print and is subject

to

correclion.

ABSTRACT

A novelacoustic dewpoint and bubblepoint detector

may be a valuable devicefor natural gas processing

industries. The device is

free

from mercury andcan be

appliedto a broadrange

of

phase transitions. Even in

very

lean gas systems or opaque heavy oils, this

technique has application when high accuracy and

automation are required In the new stateof the art

AcousticResonance Technology ART) system at Hycal

Energy Research Laboratories Ltd two acoustic

transducers are used, one to stimulate

and

the other to

detect normal mode vibrations ofreservoirfluids in a

small cylindrical resonator. The acoustic spectra,

along with temperature, pressure and volume

measurements, are recorded at close inten als

throughout the phase em-elope. The time domain data

collectedare processedto obtain the specific condition

oJphase transition.

TIle

high pressure  RTsystem is

capable

of

operation from -40°C to 150°C -40°F to

300°F) and pressures up to a maximum of 7 MPa

  10.000 psia). The system is capable oJoperation in

an isothermal mode with variable volume or in a

constant volume mode with variable temperatures.

The accurate determination

of

bubblepoint and

dev.pointpressures

 

reservoirtemperaturearecrucial

fo r natural gas processing. transportation and

metering. Results oJ two systems a binary mixture

and live reservoir fluid) are presented

TIle

onset

of

bubblepointanddev.point are easily obtainedfrom the

processeddata. Since thefrequency response

of

sonic

speed is influencedby density, micro-andmacroscopic

structural features, at the phase boundaries, the

acoustic response shows a sharp abrupt change. The

interpretation

of

results can be free from operator

subjectivity. Comparisonofthe   RTresults with those

obtained using visual methods

and

equation

oJ

state

calculations show excellent agreement. These results

will be presented in this paper.

INTRODU TION

 n reservoir engineering detailed knowledge   the

phase

behaviour   reservoir fluids

is

very important

in

planning managing operations involving production

transporting processing

and

utilization  

fluids

lthough visual techniques have been used commonly

in the petroleum industry

when it

comes to very lean

gas

mixtures and very dark fluids detection

 

phase

8/17/2019 PETSOC-97-80

3/7

change can be a serious problem.

The recent AR technique is a highly accurate,

independentmethod and can

be

complementary to, or

a substitute for, visual method.

It

is

fast

and

additional information can be obtained in one

measurement. AR exploits the advancement

in

PC

technology for data collection and control

of

measurements. The evolution

of

the resonance

response of reservoir fluids as a function of changing

conditions of pressure, volume and temperature is

measured in

 R

in real time.

The results yield accurate information related to

reservoir fluid phasebehaviour bubblepoint, dey point,

etc.). It has been shown in earlier work that some

useful information about fluids can be inferred reliably

from the acoustic signature.   2 3

This paper illustrates the use

of

a versatile acoustic

system in determining accurately the dewpoint or

bubblepoint of gas condensates and reservoir fluids.

 XP RIM NT L

Material

The samples employed were a binary

mv tUre

and

a recombined live oil whose compositions were

analyzed by an HP 5890 Series   gas chromatograph.

Tables I and 2 list the composition

of

the samples

analyzed.

Description of EqUipment and Procedures

The system consists

of

a cylindrical resonator,

of

0.25 inches

in

diameter, made

in

Hastelloy material to

resist corrosion from reservoir fluids. There are two

piezoelectric transducers, one at the top

of

the

resonator throughwhichacoustic stimulation is applied

in

the fluid by an applied voltage and the other at the

bottom of the resonator to receive the response from

the stimulated vibrations through the fluids. At certain

applied stimulation frequencies, standingwaveswill be

set up

in

the contents

of

the resonator. The acoustic

signature depends on the geometry

of

the cavity, the

nature

of

fluids and their state. Since the cylindrical

cavity is oriented vertically, the signature will depend

on the geometry

of

any of the multiple phases present

as well as on the nature of their interface. The

cylindrical resonator is provided with two pistons

 0.25 diameter); one at the bottom, a stationary one

and the other at the top, which is a dynamic precision

variable one whose movements are controlled by a

worm gear assembly and a Strepper motor, interfaced

to a control computer. This makes it possible for the

system to have density and pressure sweeps

of

the

contents.

 

The computer also controls the temperature of a

well-insulatedair bath in which the resonatorassembly

is housed. The system can be operated n both

isothermal and sweep modes. The air bath is provided

with liquid nitrogen, control heater and a liquid

nitrogen servo valve interfaced to the computer for

better low temperature control down to -40°C. The

system can be operated at pressures up to 10,000 psia

in

the temperature rage of 150°C to -40°C. Both

transducers were shielded within the pistons to keep it

free from corrosive reservoir fluids at these extreme

conditions.

The maintenanceand sweep control of pressure

 P),

volume

 V

and temperature  T) is supplied by precise

and stable sensors high precision strain gauge

transducer for P, an LVDT for V and a calibrated

platinum resistance thermometer for T) read by

precisionKiethley digital voltmeters, each interfacedto

a control computer. The control program uses a

 il l

type algorithm. The result

of

any tuning changes for

each control variable can be seen and updated in real

time on the computer screen through a graphic

interface. Through the control computer, one can

program pressure sweeps, volume sweeps, or

temperature sweeps. One can also maintain both

temperature and pressure constant and acquire data.

A second computer oversees the acoustic excitation

of

the resonator and acquires the spectrum.  n

interfaced function generator supplies the signal

necessary to excite the transducer. The acoustic signal

through the fluids at the receiver

is

processed through

a low noise amplifier and then through a fast, high

precision analog to digital converter ADC). Acoustic

sampling is done at the rate

of

100 kHz by the ADC,

synchronized to the function generator, which

generates a trigger signal when to acquire data. The

acquisition computer is interfaced to the control

computer in a network configuration. Raw time

domain data is stored along with P, T and V data.

during sweeps. Control of all system functions

including those

of

the acquisition computer is directed

by the control computer. The acquisition computer

displays the frequency domain spectrum in real time

through a graphic interface.

In

a typical Acoustic Resonance experiment, the

clean evacuated resonator is charged with the

homogeneous fluid to predetermined temperature and

pressure conditions. Subsequently, one

of

the

following three procedures is conducted to determine

either a dewpoint or a bubblepoint temperature:

• Maintain a constant volume and vary the

temperature and record the acoustic spectrum

8/17/2019 PETSOC-97-80

4/7

8/17/2019 PETSOC-97-80

5/7

8/17/2019 PETSOC-97-80

6/7

8/17/2019 PETSOC-97-80

7/7