146434 - digital oil field at deep ocean

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Faculty of Engineering

Department of Chemical and Environmental

Engineering

EEE3100

Electric and Electronic Technology

Assignment:

Case StudyDigital Oil Field at Deep Ocean

Name : Muhammad Faizol Bin Mohammad

Matrix No. : 146434

Date of submission : 8 December 2011Lecturer : Dr. Maryam Bt Mohd. Isa


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Case Study EEE3100 Digital Oil Field at Deep Ocean

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Introduction

At present, the worlds oil field at deep ocean produces only at average of one third of

their total potential production rate. This is happening due to physical difficulties in deep ocean

oil rig operation and its expensive cost for exploration, production operation and maintenance.

Thus, the production efficiency could not be performed at its optimum and profitable condition.

The technological innovation in development of enhancing the hydrocarbon production

system nowadays had comes to the extent of Digital Oil Field conception. The goal of

performing digital oil field concept is to achieve the total asset awareness in future development

of deep ocean oil rigs. By allowing the offshore oil production companies to operate their assets

at the technical limit of efficiency, recovery and cost, they could maximize the oil rig production

performance. The digital oil field concept for future deep ocean hydrocarbon production is

replacing and/or utilizes the existing technology, electrical feed-through systems with the new

classes and formats of sensors installed into the production process to generate more accurate

real time data monitoring on certain key parameters.

The newly innovative technology operating this kind of system is known as optical feed-

through system and had been classified as one of the advance in-well optical fiber sensing

technology. Digital oil field with combined advance modeling, control system and actuators will

demonstrate a significant parameters improvement, such as reservoir condition and flow rates in

term of its efficiency of oil and gas recovery of the deep ocean well.

The first step in enhancing the hydrocarbon production system in any oil field is to

improve the extraction rate of oil from the reservoir. In modern hydrocarbon production method,multi-feed through of production wells on surface of deep sea is a major extraction concern,

rather than a single vertical well. Comprehending the condition and dynamics of the oil fields

and individual well in such a complex system and to manage the well system in order to optimize

the production is far more challenging.


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Scope of Work

The digital oil field works with concept of using optical fiber as a medium to provide a

real time monitoring basis from the extraction process at the surface of deep sea. There are a lot

of sensor types available in the market for such measure requirement in monitoring reservoir

condition and status, but the harsh in-well environment deep under the sea is prohibits the use of

off-shelf devices.

Figure 1: Subsea hydrocarbon production system overview

The operational environment for in-well sensors includes temperature up to 300oC and

pressure up to 15,000 psi with variety of production fluids, often loaded with abrasive sand and

rock fragments as shown in Figure 1, above. The current development electronic device only

provides limited information due to its limitation in the working environment issue especially, at

elevated temperature condition. This has caused a communication problem as the current

technology for feed-through system is using electrical feed-through system with wire based

system and the properties of data transport material itself has a limitation due to the in-well

environment.


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The optical fiber communication and sensor system are much more suitable with the

downhole environment under the deep sea and attract great interest and significant investment

from oil and gas industry, recently. The glasses material used for constructing the optical feed-

through system are promising and lengthen the lifetime of the equipment use to extract oil from

oil field up to 25 years without maintenance, because of its properties that stand the in-well harsh

environment. Moreover, it provides excellent real time data monitoring compared to wiring

based system. The used of this new invention has provides the oil extraction operation with all

necessary information with advantage of increasing their extraction rate and efficiency of oil

recovery.

The optical feed-through system for in-well optical fiber sensing is embedded to the

Christmas tree, shown in Figure 2(a). From Figure 2(b), the schematic diagram shows where the

optical is and electrical feed-through system is located and functioning. The production fluid will

enter the tubing hanger and the optical and electrical sensing will determine the flowrate of the

extract fluid.

(a) (b)Figure 2: (a) Christmas tree system, (b) Schematic of tubing hanger assembly and EH5 connector.

(Adapted from Journal of Physics: Conference Series 76 (2007) 012066)


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In operation, the electrical and optical feed-through system is capable to be function at

high temperature and high pressure of in-well environment. They also act as pressure barrier to

prevent the in-well fluids leaking to the sea.

Figure 3: Schematic diagram of Christmas tree Optical fiber feed-through system

From Figure 3, the EH5 connector and tube hanger assembly was designed to be suit for

the Christmas tree system. The feed-through is also design to be easily mate and de-mate. The

optical feed-through is capable to do multiple services and re-mating without degradation of its

performance. The overall system shown in Figure 3, includes a downhole gauge dry mate optical

connector, a tubing hanger wet mate optical connector, a stem wet mate optical connector located

in the OEH5 and a stem dry mate optical connector. Each of the connector components has

appropriate pressure barriers built-in. The optical jumper used to transport real time data from

the Christmas tree.


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Electrical Concept Applied

The basic fiber optical interface can be illustrated as shown in Figure 4, below. A fiber

optic interface generally consists of five major functions as shown in Figure 4. Pre-equalizer acts

as transmitter, the circuit process the input signal in order to drive the electro-optical converter.

The converter can be LED or a laser diode, will generates the signal dependent on light intensity

modulation and its mechanical case eases transmission of the signal into the fiber. At the fiber

end, pin diode coverts the optical signal back into a low electrical current. The function of

transimpedance is to converts the current signal into voltage and amplifies it into an acceptable

level. Photodiode used for the input signal can vary in amplitude, thus an AGC amplifier is used

to adjust the peak-to-peak signal level and restore the DC level for no signal (0V).

Figure 4: Block diagram of fiber optic transmission


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Figure 5: Bias Control

Figure 6: Transmitter Block Flow Diagram

Figure 5 shows the schematic of discreet circuit to adjust the LED bias point. R QC can be

calculated by the equation shown in equation (1). Current source has high impedance and to

avoid current distribution, the output impedance should be much higher than the load impedance.

The transmitter diode has 2 to 4 load adjusted to the correct bias point. The high output

impedance of 10 k for the current source prevents any distribution.


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Pre-equalizer compensate for the nonlinearity of the diode and the driver circuit converts

the input signal into an output current, which generates the optical signal when flowing through

the LED as shown in Figure 6.

Figure 7: Voltage to Current converter

Figure 7 shows the resistor RE is the only element that has to be selected in order todefine the conversion factor between input voltage and output current according to equation (2).

To modulate the diode current, the OTA operates as a voltage controlled current source and

converts the input voltage into output current. REis the output impedance of the OTAs emitter

output.


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Figure 8: Transmitter Circuit

Figure 8 shows the complete transmitter circuit and Figure 9 shows the complete receiver

circuit. The transmitter section is the one that being embedded to the tubing hanger that being

connected to the Christmas tree and placed at deep sea surface. While, the receiver section is the

one that installed in the control system room high above the sea surface and using fiber optic to

interconnect both section. The voltage output of the receiver in Figure 9 is illustrated in term of

signal output using oscilloscope and/or digital data reader. The voltage output of transimpedance

amplifier in Figure 10 can be calculated using equation 3.


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Figure 9: Receiver Circuit

The voltage output of the transimpedance amplifier is a stabilize signal after being

amplified from weak and unstable signal due to length of transmitting the optical power.

Figure 10: Transimpedance amplifier


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From all figure discussed in this section, it is observed that the highly advance electronic

system are made base on simple basic electrical components and concepts. Hence, it is

importance to understand the fundamental knowledge of basic electrical component before

develop the high technology control system especially this optical feed-through system for in-

well monitoring.

Conclusion

The development of new technology of using glass fiber optic for applying digital oil

field concept is promising in order to enhance the extraction and production rate of oil from deep

oil field. The application still new and just started in 1990s, but the development progress has a

significant result and has become industrial demand in the oil and gas industry. Digital oil field

can perform better extraction efficiency compared to single extraction well and also cut down

operation and maintenance cost. The recovery rate of current loss during extraction of oil at deep

sea could also be increase. The probability of failure for all permanent monitoring technology is

highest at installation where most adverse condition and external factor exist. However, once

installed, the optical system will outperform other technologies. The technology is still under

great development and evaluation, in short the optical feed-through system is a brand new

solution for the advance oil and gas exploration and refinery industry.


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Reference

Optical Sensing System (2006) - Brochure 4136.00. Weatherford. Houston, Texas. Shiach. G, Nolan. A, McAvoy. S, McStay. D, Prel. C, Smith. D, (2007). Advance Feed-

through System for In-well Optical Fiber Sensing. In Journal of Physics: Conference

Series 76 (2007) 012066. IOP Publishing Ltd.

David. S, Designing Fiber Optical System. Christian. H, (2000). Fiber Optic Transmission. In Application Bulletin. Tuscan, AZ.

Texas Instruments Incorporated.

Baharch. G, and Hooman. N, (2008). Fiber Optic Sensors. In World Academy of Science,Engineering and Technology 42 2008.

Nick. M, (2000). Fiber Optic Telecommunication. In Fundamentals of Photonics.Springfield Technical Community College. Springfield, Massachusetts.

146434 - digital oil field at deep ocean

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