Dr. Sergey Bondarenko,Dr. Sergey Bondarenko,Sergey.Bondarenko@gmail.comSergey.Bondarenko@gmail.com

Innovative Solutions for Logging While Drilling

Project Initialization ReasonsProject Initialization Reasons

2

Barrel per day Number of directional drill-holes

Bakken Shale, USA

Current State and Prospects of the Directional Drilling Service Market

Till now the main energy resources in the world continue to be oil and gas. However, depletion of large natural reservoirs considering their limited quantities has determined tendency to a complex profile directional drilling, especially in the field of shale oil and gas extraction. At the same time, nowadays only a few companies in the world provide appropriate service in the field of logging-while-drilling (LWD) such as Schlumberger, Halliburton, Baker Hughes. Nevertheless, unlike traditional vertical drilling, existing methods have some principal problems for borehole trajectory navigation and can’t provide maximal oil recovery extraction factor.

Main Geonavigation Goals Main Geonavigation Goals

3

Top of reservoir

Borehole trajectory Bottom of reservoir

Clay

Sandstone

Decision point of borehole trajectory real-time correction

Directional drilling into predefined boundaries (1 – 5 m) requires “targeting”, or “navigational logging” and drilling correction in a real time that guarantees maximal oil recovery extraction factor of horizontal borehole

The main tasks of LWD are remote measurements of soil parameters, their interpretation, contrast dismemberment of soil sections and reliable distance-to-boundary definition.

Project MotivationProject Motivation

4

Principal Problems of Existing Methods and DevicesPrincipal Problems of Existing Methods and Devices

Potential Opportunities of Georadars Potential Opportunities of Georadars 1. Radar sensor responds on the parameter difference of testing formations only, not their absolute values. This allows avoidance of threshold optimization and provides a high boundary contrast

2. Sounding depth doesn’t depend on antenna diversity spacing and practically alwaysα >1, that results in equipment compactness

3. Relatively small sensor size doesn’t restrict the rate of climb of drilling angle, but decreases operating problem and outside border drilling

Nowadays commercial LWD radar technologies are absent !

1. Optimal Threshold and Boundary Contrast Problems (Extensively usedinductive methods don’t provide a high contrast because they “don’t see” the

boundaryprincipally, and estimate only some proximity to it by comparison to a threshold)

2. Overall Dimensions Problem (Sounding depth, R, is proportional to transceiverantenna diversity spacing, L, : R = α ∙ L , where α < 1)

3. “Dead Zone” Problem (Diversity spacing moves away “a measurement point”)

4. Operating Problem and Outside Border Drilling (Inflexibility of tubes with a largetransceiver antenna spacing decreases the rate of climb of drilling angle)

L

R

Project GoalsProject Goals

5

Strategic goal is a complex technology for LWD and correct navigation of deep directional drilling

Final technical goal is development of industrial underground georadar (UGR) based on the standard drilling equipment for metrological support of drilling in a real time

Current technical goal is development of parametric prototype and field testing

Research goal is radio wave propagation and reflection in layered absorbing medium in the near field of antennas for their optimal design

The main principal problem is efficient radiation and reception of sounding signals in ultra wide band (UWB) under very hard operating conditions

The main design and technological problem is implementation of “completely buried active antenna sensor” with a low leakage for a minimal antenna diversity spacing

The main technical problem is joint optimization of transceiver , measurement, recording and processing equipment, data communication and power supply

The main metrological problem is discovery of adaptive processing method of a large array of measurements in a real time, correction of synthesized pulses and interpretation of the data, parametric mapping.

Project ProblemsProject Problems

Main ChallengesMain Challenges

6

There is an essential differ between the assigned problems and “classical radar problems” as well as more close problems of ground penetrating radars (GPR) despite their external similarity

The main challenges are caused by unique operating environment of underground (borehole) georadars

Principal distinctive feature is complete sinking antennas in layered absorbing medium with its significant parameter variation and essential dispersive attenuation factor of radio wave propagation

Crucial factor is presence of “a good conductor” in the downhole space -a drilling fluid that is undesirable for efficient radio wave transmission and reception especially for high-voltage sources

Size of any constructive unit is a very hard limited by required cross-section area for the drilling fluid circulation in both directions and a borehole diameter but slightly limited along the borehole

Limited design degree of freedom results in essential leakage between antennas decreasing dynamic range and sounding depth.

Key Borehole Radar RequirementsKey Borehole Radar Requirements

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High accuracy around boundaries (decrease of probability of drilling outside the boundaries) Radiation linearity over the entire frequency range (more options for efficient post-detection processing) Radiation in a one hemisphere (because of difficulty to make "needle“ UWB antenna patterns ,"top-down"

difference can be achieved by near-omnidirectional antenna combination) Space-time stability of antenna parameters (unpredicted dependence on soil parameters results in uncorrected

pulse shape deformation) Minimal antenna diversity spacing ( besides constructive advantages a total path length of radio wave is

decreased and, as a result, attenuation factor is decreased too) Efficient leakage suppression (the leakage must be less or equal to the level of reflected signals) Azimuthal localization of a long border (unlike the case of radio wave reflections from “point” target we need to

deform antenna patterns and/or transmission/reception conditions) Estimation of radio wave propagation velocity (this requires known propagation path geometry causing

different signal delays at the same distance to the boundary) Frequency independent or ultra wideband antenna combination (efficient leakage compensation is achieved

by differential reception with two equidistant symmetrical antennas) Good repeatability and manufacturability.

Innovative Approach: Innovative Approach: Creation of Controlled ConditionsCreation of Controlled Conditions

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For decrease an impact of random factors caused by absorbing medium and improvement of sounding signal stability some dominant controlled conditions is needed

Conditions provided by constructive methods: Displacement of a drilling fluid from antenna aperture Smoothing of conductive surfaces and their use for "antenna grounding" “Frequency dependent antenna shortening" by immersing its in special medium and unique shaping Antenna damping by special spaced loading Symmetric placement along drilling tube two identical receiving antennas offset by ± 450 related to the

symmetry plane of transmitting antenna pattern

Conditions provided by combined methods: Sounding field symmetry on the receiving antenna inputs independently on frequency and censor

orientation related to the tested stratum Reflected field asymmetry on the receiving antenna inputs and its dependence on censor orientation

related to the tested stratum Presence only a one harmonic process into any non-overlapped time intervals in any point of equipment

and tested space.

Resonance Solution – SFCW MethodResonance Solution – SFCW Method

9

High resolution at a small distance of the boundary (0.15 -3 m) requires UWB sounding methods (0.05–3GHz) Because of a huge underground medium attenuation very high radar dynamic range is needed (>140 dB)

which can be achieved only by sounding energy accumulation either at the transmitter side or at the receiver side Energy accumulation at the transmitter using high voltage sources (up to tens kV) for ultra short pulse

generation is quite reasonable for GPR due to a good air isolation but problematic for well being drilled Energy accumulation at the receiver, contra, doesn’t require high voltage sources and special methods

for their isolation in exchange for sounding time increase However a low rate of penetration (~1.5 cm per sec) and relatively small speed of drill string (~1 turnover per

sec) shift frequency method into category of resonance solution characterized by sharp efficiency increase, namely, in such “stationary" operating conditions

Then instead of wideband procedures and ultra short pulses in time domain, narrowband stationary procedures are possible in frequency domain

Essence of the method is replacement of powerful ultra short sounding pulse by the set its low power spectral components sequentially extended in time domain like stepped frequency continuous waves (SFCW) followed by synthesis of virtual impulse response

This alternative has significant implementation advance due to monochromic all signals on any non-overlapped time intervals in any space locations that allows essentially increase of georadar dynamic range and, as a result, improve its resolution.

SFCW Method (illustration)SFCW Method (illustration)

10

t

ufu

t

Δf

Δt

Directional Synthesis

Synthesis by Weighted Processing

Basic Concept: Fundamental PrincipalsBasic Concept: Fundamental Principals

11

Generation of sounding signals at the transmitter as well as reference signals at the receiver are performed by two identical synchronous direct digital synthesizers (DDS AD9915) in the band 100 – 1000 MHz

One stage down conversion by mixer ADL5801 with a very low IF is used at the receiver followed by digital IQ demodulation with 24-bit Σ-Δ ADC (AD7764) and microcontroller unit (MCU STM32f4) in preprocessing unit

The receiver contains two channels one is the main (informative) and the second is reference for calibration and automatic signal correction

The reference signals are generated with use of the received signals which contain information about convolution of the sounding signal with the impulse response of receiving-transmitting tract

Digital signal processing is based on different algorithm combination in both frequency and time domains with mutual correction results for final resolution improvement

Required leakage level between antennas is achieved by multi-stage constructive and algorithmic suppression methods taking into account typical soil parameters

Active radar sensor is performed in the standard size of stabilizer-calibrator as a hard unit with the antennas placed inside the blades using outside metal surface and a drilling fluid as radio wave absorber for a one hemisphere radiation and “top-down” differentiation

Required antenna characteristics in given frequency band and operating conditions are provided by numerical computer simulation and optimization

Decrease of antenna characteristic sensitivity to variation of soil parameters is provided by displacement of a drilling fluid from the antenna aperture, replacing it with special "corrective" coating.

Basic Concept: Prototype FlowchartBasic Concept: Prototype Flowchart

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S2

S1

Digital Signal Processing

USB,Bluetooth

Antenna UnitPh. Shifter (P499.101.000)

Σ- Δ

Power Amplifier(ZHL-20w-

13)

Active Directional Coupler

24-bit ADC(AD7764)

24-bit ADC(AD7764)

MCU(STM32f4)

Preprocessing Unit

Signal Generator

LO

DDS(AD9915)«Master»

DDS(AD9915)«Slave»

LPF LPF

IF Amplifier IF Amplifier

Mix ADL5801

Main ChannelMix

ADL5801

Reference Channel

Ph. Shifter (R499.101.000)

Receiver

ADL5565ADL5565

Transmitter

Prototype: General DescriptionPrototype: General Description

13

The antenna unit is crucial element that defines final radar characteristics in general. In particular, increase of sounding depth by increase of transmitter radiation power with limited receiver maximal input power is possible only with leakage suppression

Traditional method of leakage suppression with antenna diversity spacing becomes no efficient in a high absorbing medium at the distance comparable to the length of the path of the reflected signal that essentially increase its attenuation simultaneously with the leakage suppression

In addition, increase of the antenna diversity spacing eliminates the main georadar advantage, namely, a short measuring sensor

Developed antennas are based on folded dipole with a complex profile and placed in the notch of the stabilizer blades providing the leakage suppression in typical soil up to 45 - 55 дБ for collinear antenna arrangement without gap

The antenna unit contains the transmitting antenna and symmetrically placed along drilling tube two identical receiving antennas angling by ± 450 related to the symmetry plane of the transmitting antenna pattern

The antenna apertures have specific corrective coating for linearization and stabilization of antenna characteristics

Cross transformation (Σ–Δ) of the receiving antenna output signals is performed by transformer-resistive circuit and differential amplifiers (ADL5565)

Precision tuning of the receiving antennas output signals parameters is carried out with mechanical coaxial phase corrector either PTS-A3A8-18-15f or R499.101.000

Developed build-in amplifier with power 1W is equal to 100W with using 100 harmonic signals, and external amplifier (ZHL-20W-13) with power 20W, respectively, is equal to 2 kW in pulse.

Prototype: General View Prototype: General View

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Antenna Unit: Constructive DetailsAntenna Unit: Constructive Details

15

97 мм 68 мм 120,6 мм38 мм

0.7 м

Substrate Coating

Antenna Unit: Main AdvantagesAntenna Unit: Main Advantages

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The antenna unit construction achieves six goals simultaneously: 1) displacement of a drilling fluid from the antenna aperture and increase of the antenna section size; 2) increase discrimination characteristic steepness in cross drilling plane;

3) residual leakage compensation; 4) evaluation of georadar instrumental function including medium transfer function; 5) estimation of radio wave propagation velocity; 6) active sensor compactness;

Proposed construction provides different reception conditions for leakage and echoes with two antennasThe receiving antenna signal difference causing by boundary reflection achieves a maximal value when a one

antenna is oriented perpendicularly to the stratum and the other along the stratum that can be classified as mode for reliable definition of a minimal distance to the stratum boundary

Wherein, there is a one angle only when the signal difference achieves a minimal value. This is exactly perpendicular orientation of the transmitting antenna to the stratum boundary that can be used for lock of the angle position of the antenna unit related to the stratum and for calibration too

At the same time, the leakage difference on the same outputs practically doesn’t depend on the antenna unit space orientation related to the stratum boundary and closed to zero

In contrast, the sum of the reflected signals also being weakly depended on the antenna unit space orientation is significant quantity due to strong leakage domination. This fact can be used for medium transfer function and radio wave propagation velocity estimation in the unit neighborhood thanks to unique design providing the fixed distance between antenna phase centers over the entire frequency range

However, a leakage compensation degree is strongly depended on the receiving channel identity achievement.

Antenna Unit: Parametric StabilityAntenna Unit: Parametric Stability

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The antenna unit construction provides very high stability of the main antenna characteristics over the entire frequency range due to the same radiation phase center

f=1000 МГц f=100 МГц

Antenna Unit: Space Signal AnisotropyAntenna Unit: Space Signal Anisotropy

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0.7 м

Oil Reservoir (εr =5; σ=0.05 S/m)Symmetric Receive Antennas Orientation

Difference Antenna Signal Δ → Zero

Aquifer : Clay (εr =20; σ=0.1 S/m)

Oil Reservoir (εr =5; σ=0.05 S/m)Asymmetric Receive Antennas Orientation

Difference Antenna Signal Δ → Max

90о90о

Aquifer : Clay (εr =20; σ=0.1 S/m)

Azimuthal ScanAzimuthal Scan

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Even with a low residual leakage compensation degree of current prototype (11 -13 дБ) the difference reception with two receiving antennas offset to one another by ± 450 in azimuthal plane provides resolution equal to a few angles. In addition, a very good coincidence of experimental and simulation curves evidences of adequate model.

SimulationField Testing

Mag

nitu

de,

dB

Angle, degree

45о

180о

315о

Border DetectionBorder Detection

20

Direct pulse synthesis

Spectrum reconstruction

Windowing

Spectrum reconstruction and windowing

Leakage selection zone

Border at the distance 0.5 m

Many different efficient processing methods are available either separately ones or together depending on goals and conditions.

Residual Leakage CompensationResidual Leakage Compensation

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Only residual leakage compensation is one of the goals that strongly depends on the receiving channel identity

Theoretical analysis and numerical simulations (taking into account the achievements of relevant technologies) indicate the possibility to provide tolerance for different destabilizing factors and to achieve residual leakage compensation to 40 - 50 dB at homogeneous soil in the borehole neighborhood

Numerical simulations of soil asymmetric irregularities in the borehole neighborhood to estimate impact on residual leakage compensation degree indicates pronounced threshold effect due to a large area of the field averaging for weakly directional antennas with a small diversity spacing

According to simulations and analytical estimations the deterioration of residual leakage compensation due to different irregularities of the near-field antennas can reach 15 - 20 dB

So, residual leakage compensation by 25 – 35 dB is realistic enough.

46Rr

Tr

Р дБР

Antenna Damping and “Shortening” Antenna Damping and “Shortening”

22

Frequency-phase characteristics linearity of UWB antenna is usually provided with selected lumped elements soldered in certain places along antenna profiles for damping unwanted resonances and reflections, that does not provide a good repeatability.

Proposed solution is Spaced Loading which consists in the field displacement from the notch in the blade and itsconcentration on the outer antenna surface with special coating that provides:

- desired damping level;- high antenna identity;- antenna characteristic stability for soil parameter variations (Fig. 1, 2).

The corrective coating additionally to damping provides “frequency dependent antenna shortening mode”, so that theantenna effectively radiates over the entire frequency range (Fig. 3). After multivariable numerical computeroptimizations developed antenna length is equal to 32 см.

Usual dielectric medium

Special coating

λ / m

Frequency / MHz

Fig. 1 Fig. 2 Fig. 3

Soil permittivity variation Soil conductivity variation

Propagation Medium Parameter Estimations Propagation Medium Parameter Estimations

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Under perfect DDS synchronization all amplitude and phase disturbances are caused only antenna feeder circuits and propagation medium. The first ones are compensated with calibration. The second ones are information parameters and can be estimated with spectrum directly

The output antenna signals in frequency domain can be represented as

where S(ω) is known sounding signal spectrum, R(ω) is reflection coefficient, H(ω) is transfer function, “near” and “far” are near and far zone, "t" abd "r" are transmitter and receiver, respectively

Generally the sum and the difference signals are

there Wherein inverse Fourier transform from SΣ(ω) gives two characteristic bursts :

a) relatively strong leakage burst ,L(t), always located in the area of the smallest delays depending only on propagation medium parameters, antenna spacing, RL, and antenna isolation degree;

b) relatively weak signal reflected from border , S(t), always located in the area of the biggest delays depending on propagation medium parameters, distance to border, R1, and their properties

Inverse Fourier transform from SΔ(ω) also gives two characteristic bursts but leakage burst significantly suppressed with compensation circuit

Hence, knowing exactly sounding signal, we have:

1111 rfarneartt HHRHHSS 2222 rfarneartt HHRHHSS

1 1 1 2 2 22t r far r far rS K H R H H R H H

1 1 1 2 2 22t r far r far rS K H R H H R H H

1 2 1 2, 0.5 , 0.5t t t near r r r r r rK S H H H H H H H H

,

t t

НS

НS SS

Propagation Velocity EstimationPropagation Velocity Estimation

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Applying windowing processing to select leakage burst (Slide 20) we have spectral estimation through full path taking into account the borehole environment allowing to calculate soil parameters and wave propagation velocity due to known antenna spacing RL

Then, due to space anisotropy we receive

On the other hand, direct calibration with the sum (reference) channel gives

If ΔHr(ω) << Hr(ω) and Hr1(ω)≈ Hr2(ω)≈ Hr(ω), then wherein R2(ω) << R1(ω) due to space anisotropy we have

Taking into account that for actual distance range we obtain

2 2 expt r near L L

L

Lt near r L R

R

RL H H H H V

1 1 1

11 1 1 1,

1ˆ 0.5 exp2 r r r far r

rfar far rH H

r

S L HS R H

VR

LRH

H

1 1 1 2 2 2

1 1 1 2 2 2

22

r far r far r

r far r far r

H R H H R H HH R H H R H HS

S

1 1

1 1

/ 0.51 0.5

r r far

far

H H RS

HSR H

1 10.5 1farR H

1 1 1 1

0

10.5 0.5 expr

r

rfar far rH

r H

HR H R H

VHR

SS

System Dynamic Range System Dynamic Range ((SDR)SDR)

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Given calculation doesn’t take into account implementation losses which usually equal to 10 -15 dB. But even in this case SDR = 189 dB that provides projected sounding depth more than 3 m because for typical stratum average attenuation over the entire frequency range is about 30 dB/m.

Nmin = -172 dBm (B =1 Hz, T=150о С)

P, dBm

Nant = - 82 dBm

Gdif_amp = 12 dB

NFdif_amp = 9 dB

Dmixer = 81 dB

DADC = 126 dB

Gdig.filter = 25 dB

Gp = 20 dB

SNR = 10 dB

GIF-filter = 45 dB

Nr_out = -151 dBm

Pt = 43 dBm (20 W)

leakage = - 15 dBm

Pmixer_max = 20 dBm

Nmixer = - 61 dBm

SDR =204SDR =204 dBdB

Direct leakage suppression” ≥ 40 dBdue to antenna isolation

Gdif_amp = 12 dB

Additional two channel leakage compensation ≥ 30 dB

Ddif_amp = 102 dB

Output antenna noise power

NADC = - 106 dBm

Ndig_filter = - 131 dBm

Pdif_amp_max = 20 dBm

SDRreceiver = 161 dB

Noise floor

Input mixer noise power

Filtered input ADC noise power

Filtered output ADC noise powerOutput receiver noise power

26

Thank you for attention.Thank you for attention.

(Be in cooperation?!)