This document discusses the development of an innovative logging while drilling (LWD) system using underground georadar (UGR) technology. It aims to improve navigation and maximize oil recovery from directional drilling. Key challenges include developing compact antenna designs that can operate in harsh downhole conditions and suppress leakage between antennas. The proposed system uses stepped frequency continuous wave radar with two receiving antennas to differentiate between leakage and boundary reflections. A prototype has been developed with antennas placed inside stabilizer blades to displace drilling fluid and achieve over 45dB leakage suppression without an antenna spacing. The design provides stable characteristics and anisotropic signals that can detect boundaries within 1-5m and estimate properties like propagation velocity.

1. Dr. Sergey Bondarenko,Dr. Sergey Bondarenko,
Sergey.Bondarenko@gmail.comSergey.Bondarenko@gmail.com
Innovative Solutions for Logging While Drilling

2. 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.

3. Main Geonavigation GoalsMain 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.

4. Project MotivationProject Motivation
4
Principal Problems of Existing Methods and DevicesPrincipal Problems of Existing Methods and Devices
Potential Opportunities of GeoradarsPotential 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 always
α >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 used
inductive methods don’t provide a high contrast because they “don’t see” the
boundary
principally, and estimate only some proximity to it by comparison to a threshold)
2. Overall Dimensions Problem (Sounding depth, R, is proportional to transceiver
antenna 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 large
transceiver antenna spacing decreases the rate of climb of drilling angle)
L
R

5. 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

6. 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.

7. Key Borehole Radar RequirementsKey Borehole Radar Requirements
7
 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.

8. Innovative Approach:Innovative Approach: Creation of Controlled ConditionsCreation of Controlled Conditions
8
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.

9. 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.

10. SFCW Method (illustration)SFCW Method (illustration)
10
t
ufu
t
Δf
Δt
Directional Synthesis
Synthesis by
Weighted Processing

11. 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.

12. Basic Concept: Prototype FlowchartBasic Concept: Prototype Flowchart
12
S2
S1
Digital Signal Processing
USB,
Bluetooth
Antenna Unit
Ph. 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 Channel
Mix
ADL5801
Reference Channel
Ph. Shifter (R499.101.000)
Receiver
ADL5565ADL5565
Transmitter

13. 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.

14. Prototype: General ViewPrototype: General View
14

15. Antenna Unit: Constructive DetailsAntenna Unit: Constructive Details
15
97 мм 68 мм 120,6 мм38 мм
0.7 м
Substrate Coating

16. Antenna Unit: Main AdvantagesAntenna Unit: Main Advantages
16
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 antennas
The 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.

17. Antenna Unit: Parametric StabilityAntenna Unit: Parametric Stability
17
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 МГцf=100 МГц

18. Antenna Unit: Space Signal AnisotropyAntenna Unit: Space Signal Anisotropy
18
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
90о
90о
Aquifer : Clay (εr =20; σ=0.1 S/m)

19. Azimuthal ScanAzimuthal Scan
19
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
Magnitude,dB
Angle, degree
45о
180о
315о

20. 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.

21. Residual Leakage CompensationResidual Leakage Compensation
21
 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
дБ
Р
= −

22. 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
its
concentration 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 the
antenna effectively radiates over the entire frequency range (Fig. 3). After multivariable numerical computer
optimizations 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

23. Propagation Medium Parameter EstimationsPropagation Medium Parameter Estimations
23
 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:
( ) ( ) ( ) ( ) ( ) ( )[ ] ( )ωωωωωωω 1111 rfarneartt HHRHHSS ⋅⋅+⋅⋅= ( ) ( ) ( ) ( ) ( ) ( )[ ] ( )ωωωωωωω 2222 rfarneartt HHRHHSS ⋅⋅+⋅⋅=
( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ){ }1 1 1 2 2 22t r far r far rS K H R H H R H Hω ω ω ω ω ω ω ω ωΣ  = × × + × × + × × 
( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ){ }1 1 1 2 2 22t r far r far rS K H R H H R H Hω ω ω ω ω ω ω ω ω∆  = × ×∆ + × × − × × 
( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )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 Hω ω ω ω ω ω ω ω ω ω= × × = × + ∆ = × −      
( )
( )
( )
( )
( )
( )
,
t t
Н
S
Н
S S
S
ω ω
ω
ω ω
ω
∆
Σ ∆
Σ = =

24. Propagation Velocity EstimationPropagation Velocity Estimation
24
 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
L
t near r L R
R
R
L H H H H Vϕ ϕ ϕ ϕ
ω ω ω ω ω τ
τ
ϕ ω+ + =
≈ × × × → × × − × → =
( )
( ) ( )
( )
( ) ( )
( )
( ) ( ) ( ) ( ) ( )1 1 1
1
1 1 1 1,
1ˆ 0.5 exp
2 r r r far r
r
far far rH H
r
S L H
S R H
V
R
L
R
H
H ω ω ϕ ϕ ϕ
ω ω ω
ω ω ω ω ω ϕ ω
ω ω
∆
∆ ≈ + =
−  
= ≈ × ×        → × × × − × ÷
×  
( )
( )
( ) ( ) ( ) ( ) ( ) ( ) ( )
( ) ( ) ( ) ( ) ( ) ( ) ( )
1 1 1 2 2 2
1 1 1 2 2 2
2
2
r far r far r
r far r far r
H R H H R H H
H R H H R H HS
S ω ω ω ω ω ω ω
ω ω ω ω ωω
ω
ω ω
∆
Σ
×∆ + × × − × ×
=
× + × × + × ×
( )
( )
( ) ( ) ( ) ( )
( ) ( )
1 1
1 1
/ 0.5
1 0.5
r r far
far
H H R
S
HS
R H
ω ω ω ω
ω ω
ω
ωΣ
∆
∆ + × ×
≅
+ × ×
( ) ( )1 10.5 1farR Hω ω× × <<
( )
( )
( )
( )
( ) ( ) ( )
( )
( ) ( )1 1 1 1
0
1
0.5 0.5 expr
r
r
far far rH
r H
H
R H R H
VH
R
S
S
ω
ω
ω
ω ω ω
ωω
ω ϕ
ω
ω
Σ
∆
→
∆ ∆  
≈ + × × → × × × − × ÷
 

25. System Dynamic RangeSystem Dynamic Range ((SDR)SDR)
25
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 dB
due 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
power
Output receiver noise power

26. 26
Thank you for attention.Thank you for attention.
(Be in cooperation?!)