SPE-171706-MS

Review of Downhole Wireless Communication Techniques

Muhammad Arsalan, Talha J. Ahmad, and Mohamed N. Noui-Mehidi, Saudi Aramco

Copyright 2014, Society of Petroleum Engineers

This paper was prepared for presentation at the Abu Dhabi International Petroleum Exhibition and Conference held in Abu Dhabi, UAE, 1013 November 2014.

This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contentsof the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflectany position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the writtenconsent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations maynot be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.

Abstract

Real-time permanent monitoring and control is essential to maximize production from oil and gas wells.An interdisciplinary approach is needed for any cost-effective solution that can perform and be sustainedin the harsh downhole environment. For open hole horizontal wells, providing power and data through anumbilical is very challenging. Wireless communication is the essential component of any downholemonitoring and control solution in this situation. A wireless solution can also significantly reduce thecomplexity and cost associated with the wired solutions. In this paper various wireless communicationtechniques are classified and an extensive review of state-of-the-art downhole applications is presented.Advantages and limitations of each technique are discussed and recommendations are made of possiblesolutions.

IntroductionLong-term reservoir monitoring remains one of the critical requirements for the effective development andoptimization of oil and gas reservoirs (Brinsden 2005). Frequent monitoring and control is equallyimportant for both new and mature fields. Many new well completions now include sophisticatedpermanent monitoring systems that can transmit data to the surface via an electrical or fiber optic cable,associated with other downhole tools, such as clamps, wellhead and packer penetrations, surface powersupply, and surface data acquisition and transmission systems (Al-Nahdi 2011; Brinsden 2005; Harper2003). These systems require significant capital expenditures (CAPEX) in both components and rig time;and are prone to premature failure. A downhole wireless communication system can help resolve manyof the problems associated with wired well monitoring and control solutions by avoiding the difficulties,cost and maintenance associated with the wired infrastructure. A wireless system can potentially beretrofitted on-demand to avoid upfront CAPEX, and operational expenses (OPEX) associated withtraditional wired advanced completion monitoring and control systems. Any downhole wireless system,however, will require a power source or needs to generate its own power, which may limit its usabilityas well as the usable operational life.

This paper is focused on comparing wide range of wireless communication techniques for downholeenvironment and exploring the possibilities and limitations of using those techniques in restrictive openhole well configurations with no infrastructure, including umbilical for power, control and communicationand production tubing and liners, Fig. 1.

Classification of WirelessCommunication TechniquesTraditionally, in the literature, wireless communi-cation is almost always used for electromagnetic(EM) wave-based communication in both space(vacuum) and air. In a downhole environment, anycommunication in absence of electrical wires andoptical fibers is considered wireless. This includescommunication through production tubing and thereservoir formation. Keeping this in mind, the po-tential downhole communication techniques can beclassified either based on the communication me-dium (solid, liquid, gas or vacuum) or the mode oftransport, i.e., wave or particle, Fig. 2.

In the first case (medium), the communicationcan either be through a physical medium that can be in any form of matter, i.e., solid, liquid and gas, ormedium-less, i.e., through vacuum. The transfer of energy through fluids (liquid and gas) required forcommunication is mainly governed by the convection process where the particles of the mediumphysically travel from one position to the other carrying the information or energy. While in solids, themain phenomena that governs the energy transfer is conduction, in which the particles (atoms ormolecules) of the solid do not travel but only vibrates or oscillates around a mean position to transfer theenergy from and to the adjacent particles. Liquids also exhibit convection to a little extant. Communi-cation without medium, i.e., through vacuum is only possible though EM radiation, which can further beclassified as near and far field EM.

In mode-based classification, the energy transfer required for communication can either be throughparticle motion or wave motion. Moving particles from one location to the other requires an energygradient, such as a difference in pressure, temperature, or voltage. The waves can either be mechanical orEM. Mechanical waves require a physical medium to travel. The examples are vibrations, sound andpressure waves. EM waves, however, can travel through both physical mediums and vacuum. Examplesof EM waves are visible light, radio waves and X-rays among the others. Communication mode basedclassification is used in the following section comparing different techniques for downhole applicationsin an open hole environment.

Comparison of Communication TechniquesSeveral wireless communication solutions for downhole environment are available commercially (Al-Nahdi 2011; Brinsden 2005; Harper 2003), as well as, are proposed in the literature (Ring 2013). Thesesolutions have one or more shortcomings, which make them unsuitable for some applications andenvironmental and operational conditions. To make it easy to understand the possibilities and limitationsof each technique, a qualitative comparison of the available techniques is presented. The comparison isbased on important and meaningful application requirements, including range, power consumption, datarate, architectural complexity, safety, bidirectional communication ability, and long-term sustenancecapability in the restrictive harsh downhole environment. As shown in Table 1, the techniques are ratedas feasible (), not feasible , or may be (-) for each parameter.Communication Mode: ParticleIn this mode, physical particles travel from transmitter to the receiver or detector carrying information thatcan be in the form of shape, size, color, chemical, physical identity (ID), electronic ID, and radioactiveID, among others. An example of this kind of communication is the digital chemical telemetry system

Figure 1Simplified representation of open hole or bare hole horizontalwell environment having no production tubing or liner and umbilical inthe laterals (L1 and L2) and the motherbore (L0).

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(Ring 2013) in which different chemicals are stored in downhole containers that are released in apredefined pattern at certain conditions. The chemicals are decoded at wellhead using a detection system.The advantages of this system are its simplicity, long range, low complexity and operational safety. Onthe other hand, this kind of communication is very slow, requires flow of the medium, half duplex, andis limited to the amount of the particles that can be stored downhole. Although feasible for downholeapplications, the shortcomings seriously limit the possibilities of using this kind of telemetry for long-termreliable communication solution.

Communication Mode: WaveAs described in Table 1, the waves can either be mechanical or EM. The detail of both kinds ofcommunication using waves as a carrier follows.

Mechanical Waves Acoustic waves are mechanical waves that are widely utilized in downhole com-munication solutions (Harper 2003). Based on human audible frequency range they are further dividedinto infrasonic ( 20 Hz), audible (20 Hz 20 K Hz) and ultrasonic ( 20 KHz) waves.

Infrasonic These are very low frequency and long wavelength mechanical waves that are known totravel thousands of miles through the ocean without losing much power. They are commonly used inapplications, such as earthquake monitoring and charting rock and petroleum formations below the earthssurface. Due to very low frequency, infrasonic waves are very slow and have very low bandwidth.Infrasonic transceivers are generally expensive and very large in size, which limits their usage indownhole applications. Novel miniaturization techniques may help reduce the physical size and associatedpower consumption of infrasonic transceivers to make them feasible for downhole applications.

Figure 2Classification of downhole wireless (without electrical wires and optical fibers) communication techniques based on communication: a)medium, i.e., solid, liquid, gas or vacuum, or b) mode, i.e., particle or wave.

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Audible and Ultrasonic These waves are widely used in small to medium range underwater anddownhole communication systems (Harper 2003). Low absorption in both oil and water, long range,moderate power consumption and support for modern digital communication schemes to achieve highdata rates makes them a good candidate for bidirectional downhole communication. The limitations arethe large size of the transducers at relatively low frequencies, strong reflections and attenuation in thepresence of air and gas, and sensitivity to the turbidity, ambient noise, salinity, and pressure gradients. If

Table 1Comparison of Wireless Communication Techniques for Downhole Applications

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these difficulties can be compensated, ultrasonic waves are ideal for long range downhole wirelesscommunication.

EM Waves Traditionally, wireless communication is based on EM waves. The spectrum of EM waveshas been extensively explored and utilized in wireless communication systems. Based on the magneticdipole interaction of transmitter and receiver, which is a function of the distance between them, EMcommunication can principally be divided into near field and far field, Fig. 3.

Near Field Capacitive and inductive coupling are two useful methods of wireless communication whenthe transmitter and receiver plates of a capacitor or coils of a pair of inductors are placed relatively closeto each other. Near field communication is very energy efficient as it keeps all the energy at source if notcoupled with the other portion. Very high data rates can be achieved in near field communication. Recentadvancements in this concept has helped extend the communication range from a few centimeters to a fewmeters (Kesler 2013), which is still not suitable for desired long range communication in a downholeenvironment.

Far Field In far field, the EM spectrum from less than an Hz to THz and beyond can roughly be dividedinto radio, optical and radioactive waves. Each of the class is further divided into well-defined frequencydomains with their distinct properties and behaviors, Fig. 3.

Radio As the name suggest, radio waves are the primary and most widely used medium for wirelesscommunication. Going from low to high frequency, they are further classified into analog, RF, and micro() waves. RF and waves are ideal for high performance, high data rate, and miniaturized wirelesscommunication applications; however, in a downhole environment, tight power budget and high attenu-ation limits the use of the high frequency EM waves for long range wireless communication. On the otherhand, low frequency analog waves (100 Hz) are the prime focus of the downhole wireless applications(Brinsden 2005). The low frequency, however, seriously limits the available bandwidth and increases thesize of communication antenna to make it difficult to fit in tight downhole dimensions. Recent advance-ments in antenna miniaturization techniques (Arsalan 2013; Shamim 2008) coupled with new techniquesin wireless sensor networks may enable low frequency EM to be used as a prime candidate for challengingand compact downhole wireless applications.

Figure 3Classification of electromagnetic waves based communication.

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Optical These waves are widely used in modern telecommunication systems. Extremely high data ratescan be achieved with optical based wireless systems. For wireless communication, visible waves are nota suitable due to the abundant optical noise in the form of other visible light sources. Both visible andinfrared (IR) laser-based systems can achieve very high data rates in line of sight communications, whichrequires transparent clear medium in a straight line between the transmitter and the receiver; that is notthe case in most downhole applications. Certain IR and ultraviolet wavelengths can be used for very shortcentimeter range wireless communication inside oil and water, but is not usable for long range applica-tions. A major hurdle in optical communication is the accumulation of the solids over optical source anddetection window that limits their usability and lifetime and makes them not feasible for restrictivedownhole applications.

Radioactive In principle, the radioactive waves, including X-rays and -rays, can be used as carrier wavein wireless communication systems. Recently, some systems have been reported using X-rays for wirelesscommunication applications (Gendreau 2007). Radioactive waves can be useful for short range downholecommunication due to their capability to penetrate through mediums, including metal casing. This avoidsthe issue associated with optical window maintenance. Subsequently, due to restrictive downholeenvironments, very short range of the radioactive waves and operational safety requirements restrict theuse of radioactive sources for any downhole wireless communication applications.

Summary and ConclusionCommunication techniques without electrical wires and optical fibers are explained and classified in thispaper. Different methods in a variety of physical domains are presented with an explanation of theadvantages, limitations and possible downhole applications. The techniques are compared based on theenvironment, communication range, data rate, power requirements, and other factors. Recommendationsare made for the best solutions in specific scenarios. This paper may serve as a valuable reference andresource for exploring and evaluating design choices for a wireless monitoring and control solution fordownhole applications.

ReferencesAl-Nahdi, A. A., Saleh, R. F., Omidiya, A.-R. B. et alet al. 2011. Deploying a Wireless Downhole

Testing System Enabling Real Time Interpretation and Tool Control. Presented at the SPE Middle EastOil and Gas Show and Conference, Manama, Bahrain, 25-28 September. SPE-142669-MS. http://dx.doi.org/10.2118/142669-MS.

Arsalan, M., Ouda, M.H., Marnat, L. et alet al. 2013. A 5.2 GHz, 0.5 mW RF Powered WirelessSensor with Dual On-chip Antennas for Implantable Intraocular Pressure Monitoring. Presented at theIEEE MTT-S International Microwave Symposium (IMS), Seattle, USA, 2-7 June. http://dx.doi.org/10.1109/MWSYM.2013.6697639

Brinsden, M. S. 2005. A New Wireless Solution to Real Time Reservoir Surveillance. Presented at theSPE Middle East Oil and Gas Show and Conference, Manama, Bahrain, 12-15 March. SPE-93512-MS.http://dx.doi.org/10.2118/93512-MS

Gendreau, K. 2007. Next-Generation Communications. NASA, http://gsfctechnology.gsfc.nasa.gov/TechSheets/XRAY_Goddard_Final.pdf (eaccessed 7 September 2014)

Harper, G., Almanza, E., Foss, A. et alet al.. 2003. Advanced Acoustic Telemetry System ProvidesReal-time Data Acquisition that Increases Efficiency in Well Testing Operations. Presented at theOffshore Technology Conference, Houston, Texas, 5 May 2003. OTC-15324-MS. http://dx.doi.org/10.4043/15324-MS

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Kesler, M. 2013. Highly Resonant Wireless Power Transfer: Safe, Efficient, and Over Distance.Witricity. http://www.witricity.com/assets/highly-resonant-power-transfer-kesler-witricity-2013.pdf (ac-cessed 7 September 2014)

Ring, L., LEMBCKE, J.J., LEHNER, D.T. et alet al. 2013. Method and Apparatus for Monitoring aDownhole Tool. US Patent Application No.2013/036839; International (PCT) Patent Application No.WO2013158682 A3.

Shamim, A, Arsalan, M., and Roy, L. 2008. Wireless Interconnect Between On-chip and LTCCAntennas for System-in-Package Applications. Presented at the European Conference on WirelessTechnology, Amsterdam, Netherlands, 27-31 October. 2008. http://ieeexplore.ieee.org/stamp/stamp.jsp?tp&arnumber4753797&isnumber4753760

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Review of Downhole Wireless Communication TechniquesIntroductionClassification of Wireless Communication TechniquesComparison of Communication TechniquesCommunication Mode: ParticleCommunication Mode: WaveMechanical WavesInfrasonicAudible and UltrasonicEM WavesNear FieldFar FieldRadioOpticalRadioactive

Summary and Conclusion

References