**4. Poly-harmonic characterization of SMBS and SRS gain and FBG reflection spectra as the base of software defined down-hole telemetric systems**

#### **4.1. State-of-the-art in modern down-hole telemetric systems**

In the last decade, fiber optic technologies (FOT) more intensively penetrate the oil and gas industry, especially in those interrelated topics in this industry as seismic, drilling, geophysical surveys in wells and oil and gas extraction. Different measuring system were developed based on FOT, which were characterized by high accuracy and better than electronic devices for the same purpose in terms of mechanical and thermal stability. Measuring elements (fiber or FBG) of such systems are not affected by magnetic and electric fields and are resistant to vibration and shock. Moreover, the measurements produced by the fiber optic wire line systems are not part of the wellbore which requires a power supply and operates only with the light sources.

Despite the fact that the installation of the pilot monitoring systems and production of oil wells, using FOT, began in 1980 and proved to be a number of positive factors, fiber telemetry means (FTM) installed today only in a small part of the hundreds of thousands of oil wells. On the one hand, this is due to the policy of preferential production of "easy" oil, on the other-a frequent haze fiber during hydrogen penetration into the ground and operating at high temperatures and pressures typical of oil production, and finally, the third one is the number of disadvantages of FTM structures themselves. Since stocks of "easy" oil is not unlimited, and emerging technologies allow to create a protected sealed fiber with the ability to work in the fields of temperatures up to 700 °C, the eyes of developers and operational organizations turned again to the possibility of installing FTM in wells by presenting to them the requirements to improve the metrological, feasibility, perform‐ ance, which resulted in the appearance of the need for the optimization and upgrading of the structural construction of complexes of the specified class. This shows the relevance of the theme of alleged applied research.

frequency method with two different average and difference frequencies, discussed in section 2.5. The advantage of both methods is the absence of the need to measure the phase charac‐ teristics of the tested contours. The results of its practical realization proved the results of

74 Advances in Optical Fiber Technology: Fundamental Optical Phenomena and Applications

We call the first as "the method of difference frequency variation" analogically to the methods of frequency and capacity variations for Q-factor measuring. This method can be widely used in different systems for Q-factor measuring as in optical, so in microwave range. For example, in [49] we applied this method to monitoring of cure processes in composite materials. In optical range it can be applied to the measuring of Q-factor of transmitting window of CFBG with phase shift, for example presented in [23,50], which isn't effected to shift of central wavelength. The second method with it simple realization can be widely used in precise sensor monitoring loops in laboratory conditions and special circuits for temperature control in the

**4. Poly-harmonic characterization of SMBS and SRS gain and FBG reflection spectra as the base of software defined down-hole telemetric**

In the last decade, fiber optic technologies (FOT) more intensively penetrate the oil and gas industry, especially in those interrelated topics in this industry as seismic, drilling, geophysical surveys in wells and oil and gas extraction. Different measuring system were developed based on FOT, which were characterized by high accuracy and better than electronic devices for the same purpose in terms of mechanical and thermal stability. Measuring elements (fiber or FBG) of such systems are not affected by magnetic and electric fields and are resistant to vibration and shock. Moreover, the measurements produced by the fiber optic wire line systems are not part of the wellbore which requires a power supply

Despite the fact that the installation of the pilot monitoring systems and production of oil wells, using FOT, began in 1980 and proved to be a number of positive factors, fiber telemetry means (FTM) installed today only in a small part of the hundreds of thousands of oil wells. On the one hand, this is due to the policy of preferential production of "easy" oil, on the other-a frequent haze fiber during hydrogen penetration into the ground and operating at high temperatures and pressures typical of oil production, and finally, the third one is the number of disadvantages of FTM structures themselves. Since stocks of "easy" oil is not unlimited, and emerging technologies allow to create a protected sealed fiber with the ability to work in the fields of temperatures up to 700 °C, the eyes of developers and operational organizations turned again to the possibility of installing FTM in wells by presenting to them the requirements to improve the metrological, feasibility, perform‐ ance, which resulted in the appearance of the need for the optimization and upgrading of

mathematical modelling.

**systems**

range of 5-10 °C with accuracy 0,01°C [11,51].

and operates only with the light sources.

**4.1. State-of-the-art in modern down-hole telemetric systems**

The fiber-optic distributed temperature sensor DTS based on SRS is the most common and is used in almost the entire world's oil companies. However, a number of shortcomings associ‐ ated with the complexity of instrumentation, instability of pulse parameters, the need for complex calibration procedures, highlights the use of its concurrent methods based on SMBS and the methods used pure system on FBG. If the methods based on SMBS can achieve a spatial resolution of 0.1 m, the ones using FBG – 0.01 m.

Another important factor is the cost of FTM installing, which is for SRS equal to 50-100, SBS – 100-150, and FBG – 15-25 thousand of US dollars. It would seem the choice is clear, however, for the complexes at SRS and SMBS simply fiber as sensor is need, but for complexes on FBG it is necessary to "write" gratings in fiber and then to "pack" each of them in order to bring the properties of sensors for temperature, strain, pressure, acoustic noise measuring flow parameters. The FBG requires a significant investment in the pipeline sensor cable and makes it significant costs during the operational phase.

FTM based on FBG are widely used for the construction of point sensors, such as temperature control of the submersible pump and quazi-distributed temperature sensors. It is known their use in wells with temperatures up to 374 °C and pressures up to 220 bar, when cable length is up to 10 km and the error of measurement of pressure – up to 1%. FTM based on SMBS with the analysis in the time domain allow you to measure the temperature and pressure at the same time. The possibility of measuring the pressure reached with an accuracy of 2 , the temperature with an accuracy of 0.1 °C with a spatial resolution of 0,1 m, which is comparable with the characteristics of a wide class of FMT on FBG (1, 0,2 °C) at discrete installation respectively. Discrete setting of FBG is determined by the presence of inter-grating distortion when you install more than 5 arrays in series or a significant appreciation of the interrogator with an increase in the number of gratings.

In recent years, SRS FTM with the analysis in the frequency domain of the company LIOS Technology, GMBH are appeared on the market. These systems are the main competitors of the systems developed by the authors since 2004. The main advantages of said system are lower cost as compared with systems with time analysis, using a more stable cwlaser compared to pulse, the application of heterodyning circuitry for increasing the sensitivity of measurements and thereby improve the metrological characteristics. Howev‐ er, the work of these systems is provided only up to a temperature of 90 °C, at what rate, made by heterodyning, is realized in the secondary electron receiver, so the noise of the photo-detector continue to play a significant role in reducing the metrological characteris‐ tics of this FTM type. Transfer of the heterodyning in the optical range is accompanied by significant cost of the system through the use of additional Mach-Zehnder modulators (up to \$ 1,000 per channel).

#### **4.2. Background of software defined down-hole telemetric systems**

Following conclusions about combined methods were made on the base of Weatherford, Schlumberger, Halliburton companies patent and development analysis:


In addition, it should be noted kinds of systems combined in pairs – Raman and Mandelstam-Brillouin, Raman and Rayleigh. We did not find projects that would take advantage of all three types of measurement procedures simultaneously. Modern technology, including patent solutions of our research group lead to the formation of parallel procedures in the fiber response of different nature (Raman, Mandelstam-Brillouin, Rayleigh and reflection from FBG) on the temperature and pressure in the well and make a universal procedure of polyharmonic sensing responses, given their similar quasi-resonance character. These factors determine the urgency of developing a fiber optic down-hole telemetry system based on a combined non-linear reflectometry.

Scientific novelty of the research is to create a scientifically based methodological basis for the construction and implementation of technical and algorithmic solutions for down-hole fiber optic telemetry systems based on a combined nonlinear reflectometry, including methods and means for:


### **4.3. Planned research directions**

**4.2. Background of software defined down-hole telemetric systems**

76 Advances in Optical Fiber Technology: Fundamental Optical Phenomena and Applications

obtained for 7 years before such Schlumberger one.

readings, such as, FBG;

Brillouin scattering;

combined non-linear reflectometry.

of temperatures and pressures;

and pressure profiles;

means for:

Schlumberger, Halliburton companies patent and development analysis:

Following conclusions about combined methods were made on the base of Weatherford,

**•** Halliburton use the system of wells monitoring on SMBS, the benefits of which are based on modern technological solutions in the field of measurement and application of the reference temperature sensors or pressure to separate multiplicative Brillouin sensor

**•** Schlumberger has patents with the use of FBG, which relate only to point measurements. Particularly noteworthy is the patent for an integrated system of down-hole thermometry that uses backscattered signal of one/any of the species: Rayleigh, Raman, Mandelstam-

**•** the patent portfolio of Weatherford differs from a similar Schlumberger one by presence of a large number of FBG patents, which are using to some extent of complementary Raman and Mandelstam-Brillouin reflectometry, and are also used as point sensors. Particularly noteworthy is the patent for an integrated system of down-hole thermometry that uses backscattered signal of one /any of the species: Rayleigh, Raman, Mandelstam-Brillouin

In addition, it should be noted kinds of systems combined in pairs – Raman and Mandelstam-Brillouin, Raman and Rayleigh. We did not find projects that would take advantage of all three types of measurement procedures simultaneously. Modern technology, including patent solutions of our research group lead to the formation of parallel procedures in the fiber response of different nature (Raman, Mandelstam-Brillouin, Rayleigh and reflection from FBG) on the temperature and pressure in the well and make a universal procedure of polyharmonic sensing responses, given their similar quasi-resonance character. These factors determine the urgency of developing a fiber optic down-hole telemetry system based on a

Scientific novelty of the research is to create a scientifically based methodological basis for the construction and implementation of technical and algorithmic solutions for down-hole fiber optic telemetry systems based on a combined nonlinear reflectometry, including methods and

**•** formation of quasi-resonant nonlinear response (Raman scattering, Mandelstam-Brillouin scattering and reflection from FBG) in the fiber, carrying information about the distribution

**•** probing of Raman, Mandelstam-Brillouin and Bragg structures based on poly-harmonic radiation and quasi-coherent Rayleigh scattering poly-harmonic registration of temperature

**•** design of algorithms and software procedures for measuring the temperature and pressure, and flow rate of the liquid component composition, including the presence of occluded gas,

based on the information obtained from the distributed and point sensors.

Planned methods and approaches of down-hole fiber optic telemetry development based on the software-defined combined nonlinear reflectometry based on unity structures formed feedback from optical fiber to an external influence – temperature, pressure, flow parame‐ ters of the liquid (crude oil). If Mandelstam-Brillouin and Raman scatterings are carrying distributed information of the measured parameters (temperature, pressure), the FBG allows to receive its point localization and flow velocity data. For more information OTDR with Rayleigh scattering can be used and characterized to the Mandelstam-Brillouin ones by Landau-Plyachek relation. So way it seems reasonable to use a single radiation source for getting fiber-forming response to external stimuli, forming its special signal shape or spectra, optimized for recording spectrally separated responses from various nonlinear effects and reflections, and monitoring their bound to the central wavelength of the radiation. Some pair wise effects of such an implementation are known. Comprehensive option to gener‐ ate and use of responses from the three types of scattering and reflection from the Bragg gratings not yet been studied. Its implementation could put information redundancy in the process of measuring, the use of which would improve the metrological characteristics systems being developed.

The second approach is based on the poly-harmonic probing and resonance response obtain‐ ing. In recent years, significant progress in terms of accuracy and resolution of measurements, as well as practicality, was registered in the use of narrowband poly-harmonic technology for characterization of contour spectrums that makes them competitive for the above mentioned methods in metrological characteristics, ease and cost of implementation. Their main advant‐ age is that no measurements in the resonance region of spectral characteristics are necessary, that allows eliminating the influence of power instability of probing laser radiation and to detect information on the difference inter-harmonic frequency in the region with small noise level of photo-detector. The above-mentioned circumstances determine the relevance of the topic and the scientific and technological objectives to develop poly-harmonic methods and tools for the analysis of the spectral characteristics intended for separate registration of physical fields of different nature (temperature, pressure, flow parameters of the three-phase) and the construction on the basis of their optoelectronic down-hole telemetry using complex effects of nonlinear reflectometry in their software-defined domain.

The third approach concerns the structure of the construction of down-hole flow-meter. Over the past five years, down-hole monitoring systems installations are significantly increased. More than 90% are deep and complex branched wells. Traditionally, continu‐ ous monitoring is primarily used to control the pressure and temperature in the bore‐ hole. Thanks to the development and establishment of fiber optic down-hole flow-meters it became possible to measure the productivity of wells in its branches. Sophisticated flow structure defines the requirements for the construction of the flow-meter, however, note that its primary purpose is the definition of a flow within the wellbore, and not on the surface. To construct the flow set point is used temperature and acoustic pressure sen‐ sors. We have proposed to use for such purposes FBG-PS, FBG with a phase shift, which is characterized by high resolution and the ability to check-in without a shift of the center wavelength, as shown in several studies [11,25,48,50].

#### **4.4. Discussion of results**

FOT systems and FTM for down-hole telemetry – a developing area of science and technology in Russia, which would create a competition international manufacturers of similar systems for the oil and gas industry and solve the problem of import substitution, significantly reduce the cost of the components used, displace traditional systems on electronic components. Based on the analysis of advanced domestic and foreign developments at the level of patents in the field of fiber optic systems of down-hole telemetry shows the relevance and scientific novelty of research areas, which determines the need to develop an integrated fiber optic down-hole telemetry system which is used to record the measured parameters for all kinds of scatterings assessments and distributed FBG – for point and the quasi ratings, including to resolve the multiplicative response to temperature and deformation (pressure) for FBG and Brillouin systems and error analysis in Raman systems. The studies will be established scientifically based methodological basis for building and technical and algorithmic solutions for the downhole fiber optic telemetry systems based on a comprehensive nonlinear reflectometry and universal poly-harmonic probing of generated responses. These results allow to significantly improve the metrological characteristics of systems, including the reproducibility of results, because it will be used the measurement results with high redundancy on the basis of three or four feedback mechanisms of different nature of the optical fiber at the same environmental exposure. Scientific and methodological foundations and principles of systems can be used to monitor not only the down-hole structures, but any extended engineering structures and natural systems.

Proposed by us for the first time the concept, approaches and methods for its implementation allow reasonably formulate and solve the problem of creation of scientific and technical basis for designing software-defined down-hole fiber optic telemetry systems based on the combi‐ nation of nonlinear reflectometry with improved metrological characteristics of poly-harmonic probing of sensing structures, including the removal of multiplicative and measurement errors caused by instability of the forming radiations in wide frequency range.
