BOREHOLE LOCATION SYSTEM CONCEPT 

DEMOHSTRAT I ON TESTS 

Prepared for 

UNITED STATES DEPARTMENT OF THE 1NTE:RIOR 

BUREAU OF MINES 

DEVELCOJ INC, 

404 TASMAN DRIVE 

SUNNYVALE, CA 94086 

FINAL REPORT 

Contract No. 301 77074 

DEMONSTRATION OF A BOREHOLE LOCATION SYSTEM 

May 5, 1978 
The views and conclusions contained in this 

document are those of the authors and should 

not be interpreted as necessarily representing 

the official policies or recommendations of the 

Interior Department's Bureau of mines or of the 

U. S . Government. 
L 

4. Title aad Sobtitie 5. Report Dace 

BOREHOLE LOCATION SYSTEM CONCEPT Submitted May 5, 1978 

DEMONSTRATION TESTS 6 

r 

hrbTis) T.C: Moore 8. Pertorring Orgaaixation ~eport NO. 

(this pase replaces old Title Page) REPORT DOCUMENTATION PACE rn 

1. Report No. 

404 Tasman Drive r 

11. Contract or Grant No. 

Sunnyvale, CA 94086 501 77074 

13. Type of Report t 

L.H. Rorden 

C. Kwonq 

3. Perforr~ng Orpntzatiocr Jaw and Address 

DEVELCO , I NC . 

12. Sponsoring Orsanizrriocr Name and Addrear 

U. S. '~ureau of Mines , Branch of Procurement 

2401 E Street, N.W., Washington, DC 20241 

H.R. Eveland, C.O.; H.K. Sacks (PMSRC) TPO 

2. 

1 132-780505 

10. ProJecc/Taak/Uork Unit No. 

i I 

15. Supplementary Notes I 

I 

3. Recipient 'a Aecerrion NO. I 

I 16. Abstract 1 This report describes the feasibility test of an electromagnetic method for locating 

, boreholes, with or without casing, that have been drilled in conjunction with mining 

operations but whose location with respect to the tunnel is not precisely known. The 

first tests were conducted with the cooperation of the Kerr-McGee Corporation, Church 

Rock Mining Operations, New Mexico, in September 1977. These tests demonstrated that 

accuracies of better than 15% of range and +I0 of bearing can be achieved with a 

simple system and setups. Subsequent tests, in January 1978, on a horizontally drilled 

pipe 1 ine river crossing application, by Ti tan Contractors of Sacramento, Cal ifornia, 

demonstrated that accuracies of better than one-half percent of range and a few tenths 

of one degree of bearing can be achieved by using refined techniques. The demonstration tests were done at ranges on the order of 130 to 200 feet but the method is 

capable of working at much greater distances. 

I?. Originacor'm Key Uordr 

Borehol e Location 

Horizontal Drill ing 

Mine Surveying 

Underground El ectromagnetic 

Undersround Naviqation 

I 

18. Availability Statement 

I 

! 

1 J 

19. U. 5. Security Clrr8if. of tho Report 

Uncl assi fi ed 

20. U. S. Security Claaaif. of This Page 22. ?rice 

Unclassified 

21. No. of Pager 

68 
FOREWORD 

This report was prepared by Develco, Inc., Sunnyvale, California, 

under USBM Contract Number 50177074. The contract was initiated 

under the Industrial Hazards and Communications Program. It was 

administered under the technical direction of Pittsburg Mining and 

Safety Research Center with H. Kenneth Sacks acting as Technical 

Project Officer. H. R. Eveland was the contract administrator for 

the Bureau of Mines. This report is a summary of the work recently 

completed as a part of this contract during the period of May 1977 

to January 1978. This report was submitted by the authors on May 5, 

1978. 

There were no inventions or patents disclosed as 2 result of work 

performed on this contract. 

We would 1 ike to thank Dr. H. K. Sacks of the USBM Pittsburg Mining 

and Safety Research Center, and Rodger F. Sturgeon and his associates 

of the Kerr-McGee Corporation, Church Rock Operations, for their support and assistance. We are also grateful to Sandia Corporation and 

the Department of Energy for allowing use of the ELF receiver supplied 

by Develco for a previous project. We would also like to thank 

Martin Cherrington and others of the Titan Contractors Corporation 

for their support. 
TABLE OF CONTENTS 

Page 

1 . INTRODUCTION ........................... 5 

2 . THEORY OF OPERATION ........................ 6 

2.1 Locator Equations ....................... 6 

3 . EQUIPMENT DESCRIPTION ...................... 12 

4 . RESULTS ............................. 20 

4.1 Setup ............................ 20 

4.2 Demonstration Test Results at Vent #I . 1-4 Haulage Drift . . 24 

4.3 Demonstration Test Results at Vent #I . 1-5 Haul age Drift . . 29 

4.4 Demonstration Test Results at- Vent #5 . 1-4 Haulage Drift . . 33 

4.5 Calculated Results ..................... 37 

4.6 Error Discussion ...................... 40 

5 . CONCLUSIONS AND RECOMMENDATIONS ................. 42 

REFERENCES ............................... 46 0 

APPENDICES 

I Measured Data at Vent tl/l-4 Haulage Drift ......... 47 

I1 Measured Data at Vent #1/1-5 Haulage Drift ......... 51 

I11 Measured Data at Vent #5/1-4 Haulage Drift ......... 54 

IV Demonstration of an El ectrornagnetic Navigation Method on 

Titan Contractors Large Bore Drilled River Crossing at 

Greens Bayou. Houston. Texas January 1978 ......... 58 
LIST OF FIGURES 

Fi gure Title Page 

Appendi x 

Figure 

Table 

1 

HoleLocatorGeometry ................... 7 

Vertical Field Pattern at Receiver ............. 9 

Horizontal Field Pattern at Receiver ........... 9 

Borehol e Location Demonstrati on Equipment ......... 13 

Borehole Location Demonstration Equipment Block Diagram . . 14 

Plot of Field Strength at 2 Hz .............. 16 

Receiving (Magnetometer) Station Setups .......... 21 

Ventilation Shaft tl. 1-4 Haulage Drift Layout ...... 25 

Magnetic Field Plot Vent $1; 1-5 Haulage Drift ...... 26 

Ventilation Shaft fl. 1-5 Haulage Drift Layout ...... 30 

Magnetic Field Plot Vent fl ; 1-5 Haulage Drift ...... 31 

Ventilation Shaft $5. 1-4 Haulage Urift Layout ...... 34 

Magnetic Field Plot Vent #I; 1-4 Haulage Drift ...... 35 

#I Vent/l-4 Level Survey Summary ............. 48 

#I Vent/l-5 Level Survey Summary ............. 52 

#5 Vent/l-4 Level Survey Summary ............. 55 

Greens Bayou Drilling Profile .............. 61 

TABLE 

Borehol e Location Demonstration Equi prnent ~eneral 

Characteristics ...................... 19 
1 . INTRODUCTION 

This report describes the feasi bi 1 i ty test of an electromagnetic method 

for locating boreholes, with or without casing, that have been dri 1 led 

in conjunction with underground mining operations but whose location 

with respect to the tunnel is not precisely known. The Bureau of Mines 

has conducted successful experiments1 with uncased holes where a transmitting magnetic dipole antenna, operating at a frequency of about 1000 

hertz in the borehole, was located by triangulation methods from within 

the tunnel. However, the relatively high frequencies used do not permit direct application to cased holes and triangulation is not practical 

in some situations. The method used in the demonstration tests overcomes 

these 1 imi tations by using very 1 ow frequencies to penetrate the casing , 

and a vector field detector which obta~ins hole location information from 

a single position in the tunnel. The detector can be located more than 

100 feet from cased boreholes, or even further for uncased holes. In 

addition, the method has potential value in other mine surveying problems 

which are discussed in this report. 

The tests were conducted with the cooperation of the Kerr-McGee Corporation, Church Rock Mining Operations near Gallup, New Mexico on September 

9 through 12, 1977. They have had hole location problems, and inquired 

at the Bureau of Mines for a solution which provided a real case to demonstrate the method proposed by Develco in 1976. The test objectives were 

first to demonstrate the technique by making measurements on a known 

ventilation shaft, and then to verify the relative position of a new 

ventilation shaft with respect to a new haulage drift being tunnelled 

towards it. Existing components, and some new prototype equipment, was 

assembled without consideration of fie1 d operation design in order to 

achieve an inexpensive demonstration, These objectives were successiully 

accomplished as discussed in the following sections. Subsequent to the 

Kerr-McGee operation, an appl ication involving the horizontal dri 11 ing of 

pipe line river crossings was encountered which offered an opportunity to 

test the method as a means of drilling navigation which may also be of use. 

in mine operations. The successful results of this cooperative effort are 

described in Appendix IV and were of considerable benefit in refining techniques. 
2. THEORY OF OPERATION 

The borehol e 1 ocation sys tern incorporates a borehol e transmitter, generating an ac magnetic dipole moment at low frequencies (a few hertz to 10's 

of hertz typical ly) to penetrate steel casi ngs with mi nimum attenuation, 

and a 3-axis receiver. The receiver is set up in a mine drift close to 

(100 to 200 feet typically) the expected hole location, and the transmi tter is lowered in the borehole to about 100 to 200 feet above the 

drift, i.e., about the same order as the distance from hole to receiver. 

In the case of operation without communication between the drift and 

the surface, the transmitter is then lowered in known steps of 5 to 20 

feet, at intervals of a few minutes, to permit data logging at each stop. 

The number of data points will depend on the data reduction technique 

used and the data quality. For the simple graphical methods used in the 

denionstration a large number of points are preferable, but an estimate 

can be calculated from 2 points at appropriate locations. 

2.1 LOCATOR EQUATIONS 

For the geometry illustrated in Figure 1, the radial and tangential 

magnetic. fi el d components at the receiver, which result from a vertical 

magnetic dipole with a moment m operating through a steel casing with 

an attenuation A, are as follows: 

2Am cos e Hr = w 

- Am sin 0. H8 - w 

These expressions assume that the attenuation due to the earth's conductivity is negligible for the short ranges and low frequencies involved 

in this case. 

Since the receiver is a 1 eve1 ed 3-axi s vector magnetometer, the vertical 

and horizontal components actually measured are related to these expressions by 

v r 

H =H cos 0 - H, sine =- [2 cos28 - sin2$] 4rr 
HOLE LOCATOR 

FIGURE 

GEOMETRY 

1 \ c -* 
and 

Hh = H 

r 

sin 9 + He cos 8 = - [3 sin 0 cos el. 4rr 

Using the expressions 

sin 8 = D/r 

cos 8 = Z/r 

the field's rectangular components can be expressed in terms of the 

vertical and horizontal distance from the transmitter to receiver, Z 

and D, respectively, as 

H =- AM (2Z2 - D2) (Z2 + ~~)-q~ = H : 

v 47T Z 

where $I is angle of the horizontal field with respect to the receiver 

coordinates . 

These latter expressions have characteristic patterns which are plotted 

in Figures 2 and 3, normalized to the maximum vertical field at Z=O which 

is defined as the transmitter antenna (center) elevation equal to the 

recei ver elevation. 

The direction, or bearing azimuth (A ), of the borehole from the receiver 

Z 

is given directly by the direction of the horizontal field 

4 = arctan . X 

This is best evaluated at the horizontal field maximum which occurs when 

the transmitter is located at Z = +0/2. Quadrant resolution must be determined from the relative phases of components. The simplest way to 

do this is by observation of the relative polarity of the three components with respect to the antenna's flux line direction. It can be . . 

seen that when the receiver is below the transmitter, the direction from 

the receiver to the transmitter is opposite to the phase of the horizontal 
FIGURE 2 

VERTICAL FIELD PATTERN AT RECEIVER 

FIGURE 3- 

HORIZONTAL FIELD PATTERN AT RECEIVER 
components with respect to the vertical component (e.g., if the measured 

values of X, Y and Z are in phase and defined a; +, the direction to the 

transmitter is -X, -Y). The reverse is true when the receiver is above 

the transmi tter. 

The distance D, or range, of the borehole from the receiver can be determined in several ways. The most accurate way would be to correlate 

all data points with the above equations using a computer; but this was 

beyond the scope of this program. However, under the relatively good 

si gnal -to-noise conditions expected, sui tab1 e accuracy can be achieved 

in this appl ication by simpler graphical or computational methods. For 

example, the value could be obtained from the derivative of the horizontal field at its peak, as inferred above, but the peak is too broad to 

permit any more than a rough estimate in practice. 

In those cases where the borehole extends sufficiently below the receiver 

elevation, the distance D can be determined from the distance traveled 

by the transmitter between zeroes of the vertical field, at Z, and ZB, 

using the relationship 

0 = [kfi z], 

FO 

If the lower vertical field zero cannot be obtained the horizontal field 

zero crossing, Z,, which occurs at zero elevation, can be used instead, 

SO 

An a1 ternate procedure is to calculate D by determining the rate of 

change of the horizontal field, at Z=0, with respect to the known change ., 
and 

therefore 

There are, of course, many cases where the borehole does not reach down 

to the same elevation as the receiver. In these instances it is either 

necessary to extrapolate, if the resulting accuracy is adequate, or to 

use a more i nvol ved calculation procedure. 

These equations are strictly applicable only when the borehole axis, or 

the path that the transmitter follows, is perfectly parallel to the 

receiver vertical axis. Although a detailed error analysis is beyond 

the scope of this report, an idea of the effects of a ti1 ted axis and 

other causes can be obtained from the results discussed in Section 4.6. 

Again, it would be possible to resolve all such factors with a more complex measurement and/or data reduction calculation. 
3. EQUIPMENT DESCRIPTION 

The equipment illustrated in Figure 4 was used in order to demonstrate 

the borehole locator concept feasibility as simply as possible. The 

solenoid type magnetic transmitting antenna was directly driven , through 

2000 feet of 2-conductor, 12-gauge cable supplied by Kerr-McGee, to avoid 

the complexity of building a low power resonant antenna for downhole use. 

A simp1 e push-pull type transmitter was built to drive the antenna since 

standard amplifiers are not readily available to operate at the high current levels and low frequencies required. A standard Develco Model 105395 

Fluxgate Flagnetometer was used to provide a compact, precisely orthogonal 

3-axis receiver sensor. The ELF receiver, which was previously supplied 

by Develco to Sandia Laboratories for other prototype test work, was modified and used to provide coherent signal detection. Since signal phase 

is important, a stable crystal oscillator was built for both the receiver 

and transrni tter. In addition, a spare preamp1 ifier was adapted to compensate for the signal reduction resulting from the casing attenuation. 

The ventilation shaft casings at the Kerr-McGee Mine are typically 5 feet 

in diameter and 5/8 inch thick at the elevations of interest. (There is 

one shaft, Vent #3, with 7/8 inch thick casing at the bottom but no measurements were made in it due to a last minute change. The casing data 

for the two test shafts are based on available data for Vent #5, and 

Vent B1 is believed to be the same.) The steels used are based on ASTM 

specifications A441 and, sometimes, A36. Both are roughly .2% carbon 

steels, and although there is no specific electrical data on these alloys, 

the information published by ~ozorth* for carbon steel seems to be typical. That is, the relative initial permeability, po, is on the order of 

100 (quenched) to 200 (annealed) and the conductivity is on the order of 

5 to 8 x lo6 Siemens/meter. An estimate of the casing attenuation was 

made based on the formulas in a paper by ~henfeld.~ The calculations 

suggested that attenuation could be on the order of 3 to 6 dB at 2 Hz, 

8 to 12 dB at 4 Hz, and 16 to 22 dB at 8 Hz. The field measurements 

suggested the actual attenuations were on this order although precise 

confirmation could not be obtained. 
- --- -- 

TRANSMITTER 

RECEIVER 

Figure 4A. BOREHOLE 
FREO - 

EXT SELECT 

INPUT 2,4,8 Hz 

0 

40 Vdc INPUT 

(optional) 

I 

I 115 Vac 

R = 352 

POWER 

SUPPLY 

L 

R =8.4ri 

T 3s2 

POWER CRYSTAL 

OSCILLATOR AMPLIFIER 

& DIVIDER 

R " 2.4 S2 A 

A 

LA 2 .4 Hy (low level) J 

w 

---- 

I_------ 

"RF" GAIN [;;, OUTPUTS 

1 ; w 

I 

-4 

P 

1 

I 

MODEL 10539 

-11 

I 

0 I I 

1 BAND PASS 

NOTCH ac PREAMP GUADR

TKIAXIAL - FILTER I FILTER . 1. DETEC

MAGNETOME- I 

TER 

i I.. A 

1 1:; I b 

I D, 

1 PREAMP AND 

* 'ilf" 

I PACK 

1 

I 

L-----* 

-- I SUPPLY SELECT 

Figure 48. BOREHOLE LOCATION N3WISTRATION 115 Vac 

EQUIPMENT BLOCK DIAGRAM I 

BATTERY 

CHARGER 

I . 

1 I 

b A I I POWER FREQ 
An iron cored solenoid was used as the transmitting antenna, or magnetic 

dipole source, in order to provide adequate signal levels through the 

shaft casing with a structure of convenient size. The core of the antenna 

consists of a stack of soft electrical steel alloy, laminated to minimize 

eddy current loss, approximately 0.8 inch x 2 inch x 5 feet (0.02 x 0.05 

x 1.5 meters) in size and weighing about 28 pounds (12.7 kg). The core 

was wound over nearly the full length with about 1100 turns of 16-gauge 

magnet wire to achieve core saturation, and maximum magnetic moment, with 

a roughly square wave current on the order of 3 amperes peak. The moment 

of the fundamental component at 2 Hz was approximately 1750 A*m2 peak or 

1240 A.m2 rms, based on the field measured at a known radius, which agrees 

with the value predicted. (The effective moment at higher frequencies was 

slightly less because of waveform and response variations.) The core 

assembly was potted in a fiberglass tube for hydrostatic protection resulting in a final assembly approximately 3 inches in diameter by 7 feet long 

and weighing about 50 pounds. Centralizers were used in case it was necessary to keep the antenna away from the casing walls. Their size was significantly less than the casing diameter but it is believed the antenna 

was nearly in the center of the hole when it was hanging free. 

The equatorial field (He = Hz at Z=0) signal strengths produced by a 

moment of 1240 A*m2 rms at 2 Hz operating through casing, with the calculated attenuations above, are plotted in Figure 5 as a function of radial 

range. The maximum magnetometer noise is on the order of 5 uG, or 0.4 

mA/m, peak to peak in the bandwidth from 1 to 10 Hz. The rms noise in a 

unit bandwidth, BbJ, can be calculated from5 

Noise (rms) = Noise P-p - OW4 = 26 U~lml~, 5m 5m 

Thus the equivalent magnetometer noise levels in the minimum receiver 

post-detection bandwidth of .025 HZ, as discussed below, is 4.2 pA/m rms. 

It can be seen from Figure 5 that in order to achieve a signal-to-noise 

ratio of on the order of 30 to 40 dBy which is necessary for satisfactory 

use of the simple graphical methods described in Section 2.1 , at ranges 

over 100 feet that operation at 2 Hz is necessary. 

It is important to note that although the magneto-meter noise level is 

relatively high, for general receiving purposes, this may not be a disadvantage in many applications. For example, Bensama's4 data on coal 

mine noise at less than 60 Hz suggests that typical mine noise is on 

the same order as the magnetometer noise in many cases and even worse 

in some (e.g., as high as 1 mA/m in a 3-4 Hz bandwidth). Thus a better 

detector would not be of any help if this data can be considered representati ve of the ma jori ty of mines . Of course, in those cases where 

longer ranges, etc., are very important and environmental noise is not 

a factor, a field coil arrangement could achieve much better performance 

without too much trouble. 

The output of each magnetometer axis is manually switched to the "Sandia" 

ELF receiver for amp1 ification, detection and fi 1 tering. 

From Figure 5 it can be seen that gains from 70 to 130 dB are needed to 

give output signals on the order of several volts over the range of signal levels of interest. Since the ELF receiver has a maximum gain of 

60 dB (30 dB each in pre- and post-detection amplification) it was necessary to add 70 dB of prearnplification. This was achieved by mounting a 

preamp1 ifier assembly in the battery box, as close to the magnetometer 

as possible to minimize noise pickup, and adding an ac coupled 60 Hz 

input notch filter, to prevent dc or ac saturation. However, the dc outputs were brought to separate connectors so the magnetometer could be 

used as a compass for alignment purposes, if necessary. 

Two 12-volt (nominal), 4.5 ampere-hour Gel Cel batteries were used to 

supply the magnetometer and receiver and provided an operating life in 

excess of 90 hours at current drains of less than 50 rrA. A charging circuit was built into the batteryipreamplifier case and which was used 

along with the receiver power supply when ac power was available. 

The primary reason for using the "Sandia" ELF receiver, in addition to 

availabi 1 i ty, is that it provides the coherent detection to determine 

the signals' absolute ampli tude and phase required in this application. 

In this case, since the signal and local oscillator phase relationship 
is arbitrary but constant, the detection is done with the normal and 

quadrature components of the local oscillator. The amplitude and relative phase of the signal can be calculated from the quadrature-detected 

dc components 

I = V cos 8 and Q = V -sin 8 

where V is the ampl'itude, and 8 is the relative electrical phase angle 

in this case. 

The most direct method of insuring that the transmitter and receiver 

phases remain constant is to use the oscillator in one, and wire a 

reference signal to the other. Although this was not feasible in the 

Kerr-McGee mine case, provisions were made to do so since it wi 1 1 be 

useful in some cases (e. g. , Ti tan, Appendix IV) . Since the original RC 

oscillator in the ELF receiver had too much drift for this application, 

a crystal control 1 ed osci 11 ator and d i v i der was constructed to rep1 ace 

it. At the same time, receiver operation was changed from selectable 

values of 5, 10 and 20 Hz to 2, 4 and .8 Hz to insure adequate signal 

strength with casing attenuation predicted above. An identical oscillator was also constructed for use in the transmitter. Although there was 

some observable drift when the transmitter and receiver were at significantly different temperatures, it was low enough to obtain a consistent 

set of data. 

The receiver also provided the required fi ltering. A predetection filter 

with a bandwidth of about 0.27 times the center frequency suppressed the 

signal harmonics. A selectable post-detection low pass filter determined 

the receiver noise bandwidth; the 0.5 Hz position was used under high 

signal conditions and provided relatively quick settling; the 0.025 Hz 

bandwidth provided the required noise suppression under relatively low 

signal conditions. In addition, simple averaging was used under some 

condi ti ons when more accurate res ul ts were desi rabl e. 

Table 1 provides a summary of the demonstration equipment's general 

characteri sti cs . 

- 18- 
TABLE 7 

BOREHOLE LOCATION DEMONSTRATION EQUIPMENT 

GENERAL CHARACTERISTICS 

TRANSMITTER 

Opera ti ng Frequency : 2, 4, 8 Hz 

Dri ve Current (square wave) : 23 A peak 

Magnetic Dipole Moment 

( Fundamental Component) 1240 A.m2 rms 

RECEIVER 

Operati ng Frequency : 2, 4, 8 Hz 

Post Detection Bandwidth: .5, .(I25 Hz 

Sys tem Gain (approx. ) : 70 to 130 dB 

System Noise Level (equivalent 

in .025 Hz BW): <4.2 rlA/m rms 

3-AXIS PIAGNETOMETER (MODEL 105395) 

Range : 

Scale Factor: 

Accuracy: 

Li neari ty : 

Axi s A1 i gnment : 

Frequency Response : 

Broadband Noise: 

+1 gauss* each axis 

5 V/G 

4% of full scale, 0-60°C 

<+0.17! of full scale 

<+O.ZO relative to case referenced 

coordinates 

<5 pG p-p 0.1 - 1 HZ 

<5 pG p-p 1-10 HZ 

<50 pG p-p 10-500 HZ 

lo3 *1 gauss equi val ent to A/m i n free space. 
4. RESULTS 

4.1 SETUP 

Three cased hole location measurements were made at the Kerr-McGee 

Urani um Mine, Church Rock Operations in Gal 1 up, New Mexico on September 

10 and 11, 1978. These consisted of a first measurement on the 1-4 level 

of the mine, at a depth of about 1500 feet and about 50 feet from the 

operational ventilation shaft #I; a second on the 1-5 level (about 130 

feet below 1-4 and level with the vent bottom), about 80 feet from 

Vent #I; and a third in the 1-4 level about 130 feet from the new shaft 

for Vent #5 which had not yet been reached by the tunneling. The first 

two measurements served as a check on system operation, since the location of Vent tl is fairly well known, and the last provided Kerr-McGee 

with a position check on the "unknown" location of Vent #5. The 5-foot 

diameter vents were lined with 0.625-inch thick steel casing (Specification A441) at the depths of interest. 

It was necessary to conduct these tests on a weekend so that Vent #1 

could be shut down, which is not permitted during a normal working shift. 

On Saturday, repair work was being conducted on the only hoist shaft, 

which was operated intermittently, so movements had to be carefully timed. 

This did not leave time to accurately measure the receiver locations for 

Vent 87 so they had to be rechecked, as well as possible, later. There 

was not much time for actual measurements at Vent #5 on Sunday either 

due to the long distance from the elevator shaft (2 miles), lack of communications in the new tunnel, and the surface setup time over the new 

shaft. However, in spite of the difficulties and because of fine support 

from the Kerr-McGee maintenance crew, a very successful set of measurements was obtained. 

The receiving magnetometer was set up in an arbitrary location at each 

test station, as shown in Figure 6. No special effort was made to avoid 

conditions that might affect the results, such as the steel pipes, beams, 

rail tracks and power lines that can be seen in the photographs. Although 

the mine surveys are typically referenced to the left track, the setups 

were made roughly mi dway between the tracks for improved s tabi 1 i ty with 
VENT #1 LEVEL 1-4 

A 

VE

RECEI VIMG (M
the simple tripod used. The magnetometer +Y axis was oriented towards 

local magnetic North in each case and leveled with a bubble level. 

(The magnetometer +X axis pointed toward magnetic East and +Z axis 

pointed up. ) Due to circumstances beyond control, it was not possible 

to obtain an accurate survey of receiver locations and orientations with 

respect to "bench marks" at the time of the tests, so they were simply 

measured with a tape to the best available physical references. 

The transmitting antenna was lowered into the vents using a wire cable 

attached to the antenna's bail. Two-thousand feet of 2-conductor, 12- 

gauge "red-line" power cable was spliced to the antenna connector pigtail 

and periodically secured to the wireline, for support, during descent. At 

Vent #1, the emergency man hoist was used to lower the antenna. At the 

unfinished Vent #5, the cable was payed out on the ground and attached to 

a truck. When the approximate operating depth was reached, the cable was 

marked in measured 10- or 20-foot (probably to a couple inch accuracy) increments for controlling the distance between measurement stations. Thus, 

the transmi tting antenna measurement station locations (Z axis position) 

used for data recording are only relative and are not intended to indicate 

absolute elevation. 

Rigidly attached fiberglass strap centralizers were used to keep the 

antenna from direct contact with the vent walls but the roughly 32-inch 

(or less) overall diameter they provided was not large enough to guarantee 

exact centering in the five-foot diameter shafts. It was not practical to 

realize a large loop structure for these trials, and other structures were 

ruled out for fear of hanging up or "sailing" in the natural convection 

airflow that was estimated to be on the order of 20,000 cfm or about 

10 mph in Vent #I. (Vent #5 was filled with an estimated 800 to 1000 feet 

of water. ) Thus, the resulting &I-1/4 foot or so uncertainty in antenna 

position must be considered when comparing the measured data with the maps. 

In addition, the vents can "drift" on the order of 10 feet (Vent #5 was 

8 feet) between the top and bottom so it was hoped the 50-pound antenna 

weight would be sufficient to hold it steady and reasonably vertical even . 

if the centralizer was touching the walls. It is important to note that 

the only time the antenna was observed, from a distance at the bottom of 
Vent #I, it appeared fairly we1 1 centered (within a couple feet) and 

re1 atively steady a1 though conditions coul d have been different at 

higher elevations. 
4.2 DEMONSTRATION TEST RESULTS AT VENT 11. 1-4 HAULAGE DRIFT 

The overall layout of the receiver setup at Vent 81, in the 1-4 haulage 

drift near the lumber yard, is shown in Figure 7. The receiver station 

was plotted on the map from measurements made with respect to the vent 

casing as summarized in Appendix I. The receiver location measurements, 

relative to the tunnel wall, were made on the next day by carefully resetting up the magnetometer and measuring its position and orientation. 

Because the vent alcove door was blocked at the time of the locator 

measurements, K-M personnel measured the incremental distance from the 

door to casing at a later date. 

The temperature at the receiver location was about 64OF (1g0C) and the 

humidity was relatively low. The surface temperature was on the order 

of 75OF to 85OF so the relative phase drift between the independently 

crystal control 1 ed transmi tter and receiver was reasonable. Al though 

there was a stiff breeze blowing (estimated at 10 mph) there was no 

evidence of wind induced noise even at 2 Hz, so shielding was not considered necessary. In fact, a rough noise check made with 0.5 Hz bandwidth and a system gain of approximately 110 dB resulted in a receiver - -- 

noise output of about k.7 V peak at 2 Hz, or-an-equivalent -- - .- of - 3.-l5-p~/-mrmr - in-a - -- -.-025 Hz BW, which indicates the system was -1 imitd-by magnetometernoise. There were no indications of powerline or other sources of 

electrical noise although this was under quiescent weekend conditions 

and can't be considered typical. Thus, the measurements were made at 

.025 Hz bandwidth and 2 Hz center frequency to minimize casing attenuation effects and real i ze a maximum signal -to-noi se ratio. 

The detail receiver output data is given in Appendix I and the horizontal 

and vertical magnetic field output levels are plotted in Figure 8. Since 

this shaft continued on down for another 200 feet or so, the transmitter 

was lowered an estimated 100 feet below the assumed receiver elevation 

and then raised in 10-foot increments to get sufficient resolution for 

the relatively short range. The measurements were terminated when the . . transmitter antenna was an estimated 60 feet above the receiver, and 

shortly after the required vertical magnetic field zero crossing was observed, in order to make the man hoist operating schedule. 
MAP (VENT e) 

GRAPHICAL SOLUTIO

CALCULATED SOLUTI

SURFACE MAGNETIC NORTH 

N 13.5"E 

I 

I 

MEASURED MAGNETIC NORT

MAGNETOMETER LOCAT ION 

3' above track 

FIGURE 7 

VENTILATION ,SHAFT #1 

1-4 Haul age Drift 

LAYOUT 

The horizontal range from the receiver to the antenna can be estimated 

by dividing fi into the distance between the two vertical field zeroes 

on the graph, or 78 feet, which gives D = 55.2 feet (reference Section 

2.1). The original estimate, made from a crude graph in the field, was 

53 feet. This is only in fair agreement with the value of 58 feet scaled 

from the map even after allowing for some uncertainty of the antenna position inside the vent. From the graph it can be seen that although the 

horizontal field zero (which theoretical ly occurs when the vertical 

antenna center is at the receiver elevation) is symmetrical ly located 

between the others, the amplitude at + and - antenna elevations is not 

symmetrical. Since the graphical method requires a fairly uniform response to be accurate, this distortion was undoubtedly the major source 

of error. (Probable causes are discussed more fu1.1~ below and in Section 

4.6. ) It may be possible to get a more accurate result from the same data, 

as discussed in Section 4.5, but this is a good example of the graphical 

method's 1 imitations in a real world environment. 

Since it was not possible to observe the casing, it is not clear what the 

exact cause of the apparent change in signal characteristics above and 

below the tunnel was. It may be due to a change in casing attenuation 

resulting from a change in casing thickness (which is thought not to 

occur until another 200 feet higher) or electrical properties, other 

structures in the path, antenna ti1 t from vertical caused by the borehole 

drift, or an actual shift of the relative antenna location in the hole 

since several feet of relative antenna motion was possible even though 

it was expected to hang fairly straight. It is known there is a cutout 

in the casing for venting at the drift elevation which, judging from one 

example observed later, is probably relatively large, i .e., on the order 

of 6 to 10 feet high. This would tend to distort the field at within 10 

to 20 feet of the receiver elevation but should not affect the overall 

result in this case where a complete !jet of data above and below the 

receiver is available. Thus, the most likely causes are changes in 

casing attenuation or re1 ative position. 

The measured results for the bearing i'rom the receiver to the antenna 

are in much better agreement with the map, Figure 7. This is to be 
expected since the angle is independent of amp1 i tude variations (assuming isotropy) and ac magnetic fields are relatively undistorted by steel 

structures. For the purposes of the simple graphical analysis, the 

bearing is usually obtained from the angle between the X and Y magnetometer output components at or near the horizontal field maximum and 

vertical field zero since the resolution is best and the results are 

not significantly affected by any antenna ti1 t that may occur (see Sections 2.1 and 4.6). In this case the maximum occuring at the higher 

antenna elevations was used simply because the graphical data appeared 

to be more uniform (which is not necessarily conclusive). From Appendix 

I, the bearing angle measured at this point is seen to be 11 .6' and the 

quadrant is S(-Y) of E(+X) based on the relative electrical phase of the 

components (see Section 2.1 ) . 

There is an uncertainty of about .5' in the measurement of the receiver 

coordinate orientation (see Appendi x I), and possibly sl ightly more from 

the subsequent casing location measurement. Therefore the minimum has 

been used in plotting bearing on the map, Figure 7, since it illustrates 

a worst case result - a larger physical angle between the receiver and 

vent axis would put the bearing closer to the vent center. From Appendix I, it can be seen that the measured bearing angle for most transmitting antenna locations is fairly uniform. The 5.8' value is clearly a 

bad value and can be discounted so the overall average is about 11.7' 

which is in good agreement with the value used. The maximum value is 

12.1' and would not result in any significant change in estimated position. Thus the bearing estimate appears to be accurate to within 2.5' 

and certainly no more than 51' and is entirely consistent with the relatively crude orientation measurements and the uncertainty of antenna 

position in the vent. 
4.3 DEMONSTRATION TEST RESULTS AT VENT #I . 1-5 HAULAGE DRIFT 

These measurements were also conducted at Vent #I but about 130 feet 

below the previous station, in a blinld location near a training school 

facility off the 1-5 haulage drift, as shown in Figure ,9. Again, the 

receiver station is plotted on the map from tape measurements with respect to convenient reference points (see Appendix 11) but this time without any line of sight "advantage.' It was not possible to obtain a 

receiver axis orientation measurement, due to time constraints, so KerrMcGee personnel went back some time later and measured the direction of 

local magnetic North at the same position and instrument height. It is 

believed this should be quite reproducible because all structures are 

fixed as shown in the photograph (Figure 6), and this seems to be the 

case, judging from the results. 

The temperature at this receiver location was about 74OF (24OC) and the 

humidity was relatively high which started to have a small effect on 

receiver offsets. There were no specific noise measurements, but the 

receiver signals were about the same as before so the system was probably 

still magnetmeter noise limited. The measurements were again made at 

.025 Hz bandwidth and 2 Hz center frelquency. 

Since the shaft could be observed through a hole in the vent alcove baffle, the antenna was lowered until it was just off the bottom. It 

appeared to hang free, was roughly centered (within a couple of feet) 

and apparently steady. The vent had a very large cutout (about 3 or 4 

feet wide, but the height could not be determined) on the backside (away 

from the receiver) which undoubtly contributed to the "bottom effects" 

in the data. The shaft bottom appeared to be concrete lined and a couple 

feet higher than the tunnel floor. There was very little time for measurements, because of the need to check and secure the vent shaft before 

the end of the day, so the antenna was moved in 20-foot increments until 

the vertical magnetic field zero crossing could be resolved. 

The detail receiver output data is given in Appendix I1 and the horizontal and vertical magnetic field output levels are plotted in Figure 10. 

In this plot the data is seen to be distorted and somewhat inconsistent. 
I 

I 

\ 

1 

I , 

I 

1 

C3 

0 

1 

MA

M

MAGNETOMETER 

FIGURE 9 i 

VENTILATION SHAFT #l 

1-5 tlaulage Drift 

LAYOUT , 

Part of this is a result of the lack of resolution due to widely spaced 

antenna stations. However, the rapid reduction of attenuation near the 

bottom, due to the cutout and open end, is probably the most significant 

factor. It results in relatively higher signal levels near zero elevation and gives an inaccurate impressicn of the zero crossing location. 

By extrapolating the data points as indicated, the apparent distance 

between the horizontal and vertical zero crossings is 55 feet and the 

apparent horizontal range to the antenna axis is fi times that, or 77.8 

feet (see Section 2.1). The original rough field estimate was 79 feet. 

This is not too far off from the 81.5 feet scaled from the map and is 

a reasonable first estimate a1 though Section 4.5 suggests a more accurate 

result can be obtained from the same data. 

By using the data from near the horizontal field maximum (Appendix 11), 

as in the previous case, the bearing angle is estimated to be 42.7" and 

the quadrant is N(+Y) of E(+X) based on the relative electrical phase of 

the components (see Section 2.1). This is in very good agreement with 

the angle of 42.2" to the vent center scaled from the map and is consi stent with the possible actual location of the antenna in the shaft. 

From Appendix I1 it can be seen that the measured bearing angle for most 

antenna locations is again fairly uniform. The value of 47.5" at "+20" 

could have resulted from incorrect data recording so if it is discounted 

the overall average is 42.0" with a k.7' variation. Since the KerrMcGee measurement of magnetic North is probably accurate to better than 

0.5', the bearing estimate appears accurate to within '1' and is consistent with the uncertainty of antenna position in the vent. 
4.4 DEMONSTRATION TEST RESULTS AT VENT #5. 1-4 HAULAGE DRIFT 

The receiver was located near the working face of the new tunnel being 

constructed to connect with Vent #5 as shown in Figure 11 . Its orientation was measured with respect to the tracks as shown in Appendix 111. 

In this case, the location along the tunnel was later accurately measured with respect to survey station P-1089 by Kerr-McGee personnel. An 

attempt to recheck magnetic North with respect to the tracks was not 

successful , apparently because the tracks had been advanced another 40 

feet by the time the measurement was attempted. 

The temperature in this area was about 84OF (2g°C) and the humidity was 

extremely high (probably 99%) because of the poor air flow (surface 

temperature was about 74OF). The protection of the crude demonstration ' 

equipment proved to be inadequate for these conditions and the receiver 

had to be taken to an area with better ventilation, sprayed with demoisturant and sealed with tape. After this the receiver offsets returned 

to nearly normal values and operated satisfactorily. Again, there were 

no specific noise measurements but noise levels appeared to be about the 

same as for the first case, i .e., magnetometer limited, which would be 

expected because ambient noise was probably even lower than before. 

These measurements were also made at 0.025 Hz bandwidth and 2 Hz center 

frequency. 

The detailed receiver output data is given in Appendix I11 and the horizontal and vertical magnetic field output levels are plotted in Figure 12. 

The bottom of the new ventilation shaft is nearly the same as that of 

the tunnel. Since there was no convenient communication with the surface, the antenna was lowered far enough to be sure it was on the bottom, 

then raised in scheduled increments at predetermined times. However, it 

can be seen from Figure 12 that there was no signal change until about 

40 to 50 feet of cable was pulled out. This indicated that the antenna 

had hung up (and ti1 ted) at an elevation of about 25 feet above the receiver, on some "junk" that was known to have been dropped in the hole. 

The subsequent data is very uniform and consistent, possibly because 
, MEASUWD MAGNETIC NORTH (+Y) 

' SUW'ACE MAGNETIC NORTII 

N 13.5~ E 

VENTILATION SHAFT #5 

I 

11-4 Haulage Drift MAG

LAYOUT I 

antenna motion was damped better in this water-fil led hole. (The anomolous point at +I30 is possibly due to a local increase in attenuation 

at that level. ) 

Although there is some chance the antenna orientation was still not 

perfectly vertical at the +50 location, this point appears reasonably 

consistent on the graph and was included in the extrapolation to determine the horizontal field zero crossing. This results in a distance 

between zero crossings of 95 feet and an apparent horizontal range to 

the antenna axis times that or 134.3 feet (see Section 2.1). The 

original field estimate was 130 feet based on a rough plot. The distance scaled from the map is 128.5 feet and the difference is probably 

because the +50 data is slightly in error as suggested by the fact that 

the bearing result at this point is significantly off (see Appendix 111). 

Again, the analysis in Section 4.5 suggests a more accurate result can be 

calculated. 

Using the data from near the horizontal field maximum (Appendix 111), 

as in the previous cases, the bearing angle to the antenna axis is estimated to be 11. lo and the quadrant is N(+Y) of E(+X) based on the relative electrical phase of the components (see Section 2.1). From Appendix 

111, the average bearing angle of all data points, except +50, is 11.5" 

and the variation is +.7" and -1.2O. Since the magnetometer orientation 

accuracy is estimated to be better than 0.5', the bearing estimate is 

probably accurate to on the order of t1° or about twice that which can 

be attributed to antenna position uncertainty. In any case, the bearing 

is again in very good agreement with the map. 
4.5 CALCULATED RESULTS 

In order to check the consistency and overall accuracy of the data ob- v 

tained in these measurements a series of calculations was done using 

the procedures developed for the horizontal dri 11 i ng appl icati on described in Appendix IV. While the results of this preliminary analysis 

cannot be considered conclusive, because many subjective decisions were 

involved, there was a consistent tendency to converge on answers that 

were in agreement with the map and near or within the limits of antenna 

position uncertainty. The primary value of this exercise was in achieving a general understanding of the factors which affect the field measurements under real conditions and in concei vi ng procedures for improving 

the accuracy of the method. 

The data analysis consisted of using an iterative type calculation which 

finds the best theoretical fit with up to 6 data points. By running 3 

or 4 cases, the probable erroneous data points could be identified and 

the theoretical case producing the lowest error, i .e. , the best fit with 

the final data points used, was determined. The general criteria used 

in determining "bad" data points to be avoided in the calculation were 

significant inconsistencies in the horizontal and vertical field strengths, 

or bearing angle or results that were in gross disagreement with the map. 

In addition, data points in the immediate vicinity of the Vent tl openings 

were avoided. The final theoretical curves that resulted are plotted as 

the solid lines in Figures 8, 10 and 12. The calculated range and azimuth that are consistent with these curves are tabulated in Figures 7, 

9 and 11. 

Three separate cases were calculated using the data for Vent 41 at the 

1-4 level. The first used arbitrarily selected data at + and - antenna 

elevations (relative to the receiver) and resulted in a curve that was 

in fair agreement with the data overall and matched the + elevations best. 
The average error* between the data and theoretical curve was 7.81, the 

calculated range was 57.8 feet and azimuth was 11.6'. Since there was 

a clear difference between the (+) and (-) elevation results, the next 

case used only (-) elevation data points. The final average error was 

4.7%, range was 59.1 feet, and azimuth was 11.9'. However, while the 

curve fit with (-) elevation points was better, it still wasn't good, 

which indicated data inconsistencies possibly due to shifts in relative 

antenna position. Next, only (+) elevation points (except 10 and 20) 

were used which resulted in an average error of 2.6% and the best general 

fit with (+) elevation data as shown in Figure 8. Although the irregularity at +40 feet is not understood, the calculated range and bearing 

of 58.4 feet and 11.7' is in general agreement with the other results. 

The results of the calculations for Vent #1 at the 1-5 level were not 

quite as good, probably because there were so few data points, but the 

answers were within reason. By using the data points at +40, 80 and 

100, which seemed to be the most consistent, an average error of 4.6% 

was obtained for a calculated range and azimuth of 81.4 feet and 42.7'. 

This is very close to the results scaled from the map. The theoretical 

curve calculated for this case, plotted in Figure 10, clearly illustrates 

the distortion at the bottom resulting from the large. cutout, etc. At 

the +20-foot point there was variation in bearing angle and amplitude 

that may have resulted from antenna tilt if it first contacted the vent 

walls in this region. The relatively lower amplitude values that occured 

at +60 may have been due to a local increase in casing attenuation. 

The best theoretical fit with the data was obtained for Vent $5 as 

shown in Figure 12. This may have resulted from the fact that antenna 

motion was much better damped by being under water as mentioned earlier. 

*The average error is defined in terms of the 3 dimensional magnetic field 

vector, and is the sum of the differences between the data and theoretical 

amplitudes divided by the sum of the theoretical amplitudes for the data 

points used in the calculation. 
By eliminating the data at +50, which still did not appear normal although ascent had started, and at +130, which was singularly inconsistent, a result with an average error of 1.5% was obtained. The calculated 

range for this case was 131.4 feet and the bearing was 11.6°. Although 

the range is slightly in excess of that which could possibly be attributed 

to antenna location certainty, it is still in good agreement with the map 

in terms of percent of range. The bearing is in good agreement with the 

other values. 

In conclusion, the discrepancies between the various theoretical cases 

and the actual data was not great and was generally consistent with 

antenna position uncertainty. This indicated a convergence on answers 

that were real and not coincidental which suggests that procedures can be 

developed to first 1 imi t data requirements then automatical ly select the 

best points to produce the most accurate results. 
4.6 ERROR DISCUSSION 

The primary sources of error in the relatively simple demonstration of 

the hole location technique, described above, are: 

1. Uncertainty of antenna location in the borehole because of 

a) The small centralizer used which resulted in a general position 

uncertainty of r1.5 feet. 

b) The vertical ventilation shaft drift of about 0.3' which could 

result in 0.5 foot displacement in 100 feet of travel if followed 

directly. 

c) Sudden changes in relative antenna position (either large ti1 t 

or lateral displacement) caused by wind, antenna or cable contact with the casing walls or irregularities, etc. 

d) Errors in measuring vertical antenna station position. 

2. Receiver station location surveying errors which could easily be on 

the order of 0.5O to 1' and 1 foot considering that all positions 

were established from several measurements by different people. 

(Includes errors in positioning receiver with respect to North and 

vertical. ) 

3. Nonuniform signal response from different transmitting antenna stations due to such causes as 

a) Openings in the casing walls or at the bottom itself. 

b) Variations in expected range Cue to shifts of relative position 

in the casing (see 1). 

c) Local increases in attenuation due to unknown structures on the 

casing itself or in the direct path to the receiver. 

4. Noisy signals due to electrical (e.g., the magnetometer) or mechanical (e.g., wind) variations that 1 imited resolution. 

5. Map scaling inaccuracies up to 1 foot and 0.25" because of paper 

stretch and the small scale used which limited data comparison. 
6. Limitations of the graphical method because of geometric distortions 

or lack of sufficient data. 

7. Limitations of the calculation methods because of possible errors 

in choosing the "correct" (uniformly con'sistent) data points. 

It was beyond the scope of this program to perform a detail error analysis or conduct a rigorously controT,led system cal ibration experiment. 

Thus a definitive statement of the locator method's inherent accuracy 

limits cannot be made at this time. However, the fact that such consistent results were obtained in all three cases suggests they can be fairly 

used to indicate performance capabi 1 i ty since the uniformity is unlikely 

to be coincidental and there were no known sources of large systematic 

errors. 

Therefore, we would estimate that a fairly simple system used in somewhat uncertain condi tions (e. g. , reasonabl e position unknowns, casing 

variation unknowns, etc. ) should be able to achieve range accuracies of 

a - couple feet to r5%, for ranges of greater than 100 feet, when using 

the graphical solution, and bearing accuracies of better than ?lo. The 

accuracy can probably be readily improved to on the order of less than 

1 or 2% of range and k.5' of bearing angle by making even simple improvements such as precisely orienting the antenna in the hole and measuring 

receiver location, taking more data points or knowing more about the 

casing structure. The horizontal drill ing experience, described in 

Appendix IV, suggests that range and bearing accuracies of better than 

one-half percent and a few tenths of one degree, respectively, can be 

achieved by using a more elaborate approach such as two receiver stations and computer calculations. The latter approach would have the 

added advantage of being able to compute borehole tilt which can be on 

the order of 5" in some situations. 
5. CONCLUSIONS AND RECOMMENDATIONS 

The feasibility tests of the borehole location concept described in this 

report have shown that 

1. Location of cased, as well as uncased, holes can be achieved so the 

method will be useful in a wide variety of mine applications. 

2. Accuracy is not significantly affected by the variety of potentially 

disturbing influences commonly found in mines such as steel structures, tracks, power lines, etc. 

3. Very reasonable accuracy (range <+5%, bearing <+I0) can be achieved 

with a relatively simple system and crude setups which makes it inherently suitable for use in a mine environment. 

4. Considerably improved accuracy (range <+2%, bearing ~2.5") can be 

achieved with the same basic method using refined techniques which 

would make it a very useful aid for more general and precise mine 

surveying work. 

The operating range of the test system is estimated to be on the order 

of 150 to 200 feet with casing attenuations of about 6 dB, as encountered 

in the actual measurements, which appears useful for many applications. 

If the casing attenuation is on the order of a couple dBy which would be 

typical of smaller diameter holes and/or thinner casings, the same system 

would be capable of satisfactory operation at ranges of 250 to 300 feet 

or more. By using a larger antenna and/or a more sensitive receiver, 

accurate operation at considerably longer ranges is conceivable. Thus, 

the ability to make blind measurements of range with fair accuracy could 

be a valuable aid in general surveying work, when the potentially more 

accurate conventional methods are very difficult to use, as well as in 

hole locator work where it is the only satisfactory way to make a direct 

measurement. 

.. The high accuracy of the bearing measurements, while not entirely unexpected, was surprisingly immune to effects from the variety of the steel 
structures found in the mine and this may be of considerable value in 

itself. The measured values of local magnetic north varied as much as 

12" between the three measurement locations which represents a very large 

error for any survey work that attempts to use magnetic measurements. 

(The nominal value of magnetic north at the mine location is approximately 

Nl3.5"E). Because it is so simple to determine, bearing might also provide a much quicker but accurate fix om location when circumstances permit, as in the original Bureau of Mines trials, ;is as a quick check as 

tunneling progresses towards a target. 

It is clear that the locator concept has technical merit and potential 

advantages in some obvious mine applications. In addition, like any 

successful new tool, it is conceivable that it may generate many new 

applications. However, its success and acceptance will depend more on 

the ability to demonstrate significant cost savings, for mines, than on 

its technical advantages or ease of use. 

It is possible to get some idea of the cost advantages by considering its 

use as a locator alone. For example, in one known instance, a vent shaft 

was more than 10 feet off from its predicted location and 1 week was spent 

probing for it at a direct cost of approximately $1 600. In this case, it 

was dead ahead instead of in the right rib which required reworking the 

haulage drift. Thus, by including the rework, additional surveying effort, 

lost operating time, etc., it is likely the total extra cost of the hole 

location problem was in excess of 3 times the direct cost or on the order 

of $6000 or more. While this is probably an extreme case, and there are 

others that are no problem at a1 1, it seems that there are enough hole 

location problems in general to assume that there is an average extra 

cost of $2000 per hole as a result of the uncertainties involved. It is 

reasonable to assume a location measurement could be supplied by an outside service company for on the order of $1 000 per operation, i ncl udi ng 

equipment amortization, crew costs and expenses. 

In the Grants Mining district of New Mexico, which is composed of Church : 

Rock, Ambrosia Lakes and Crown Point, there are approximately 15 mines in 

operation now and a possibility of 30 by 1985. If the locator service is 

-43- 
priced right, a typical mine might have a use for'it as much as 5 or 6 

times a year during development phases. A total use of 20 times per 

year in the district is probably a conservative minimum average in the 

near term. Thus, it seems reasonable to estimate that some mines could 

easily realize an annual savings of $2000-$6000 and the annual market for 

the service in the district is on the order of at least $20,000 for this 

service a1 one. 

There are other factors to be considered too. As mines go deeper (e. g., 

3000 feet), hole drifts get greater and operating costs go up, so the 

potential savings are probably significantly greater. In addition, lost 

operating time due to schedul e delays , construction, and structural 

problems because too much ground is opened up and so on, are things which 

are very difficult to cost estimate but may be very important. The hole 

locator might also replace the need for, or be combined with, hole deviation and bottom surveys in some or all applications, depending on the mix 

of exploratory and service holes, which would result in additional direct 

cost savings. Thus, it would seem that when all things are considered, 

the ccst advantages would certainly be of interest to mine operators if 

the locator service were available, even though it is not yet totally 

clear whether the potential hole locator market alone is large enough to 

justify development. 

However, it is very possible that the same techniques, and perhaps even 

much of the same hardware, are applicable to a sufficient variety of 

other mining problem to materially enhance the incentives to develop 

and use them. The use as a blind surveying aid for general work and as 

a substitute for, or in conjunction with, hole deviation surveys has 

already been mentioned. It is also conceivable that the methods can be 

applied to continuous surveying and navigation in the relatively shallow 

(up to a couple thousand feet) mine drilling problems such as raise bore 

pilot hole control, deviated drilling for methane drainage, or ore body 

target verification in exploratory work. Other possible navigation 

applications include use as a target in drilling holes from the surface .- 

into existing tunnels (e.g., rescue) or driving a tunnel to a critical 

intersection. 
In summary, it appears that there are a sufficient number of technically 

and economically important applications to warrant further market investigation and instrumentation development. 
REFERENCES 

1. Dr. H.K. Sacks, Verbal Communication, U.S. Bureau of Mines, Pittsburg 

Mining and Safety Research Center. 

2. Richard M. Bozorth, Ferromagnetism, D. Van Nostrand Company Inc., 

Princeton , New Jersey, 1951 . 

3. Saul Shenfield, Shielding of Cyl indrical Tubes, IEEE Transactions on 

Electromagnetic Compatibility, Vol . EMC-10, No. 1, March 1968. 

4. W. D. Bensama, Coal Mine ELF Electromagnetic Noise Measurement, NBS Report 

10-739, April 1972. 

5. This is a commonly used expression in geophysical work for evaluating 

noise data and is based on the fact that a gaussian distribution exceeds 

k2.5~ about 1% of the time. 
APPENDIX I 

MEASURED DATA AT VENT #1/1-4 HAULAGE DRIFT 
VENT #1 

-5' 

52'4" 

---

(52.33') 

HI =3' above track bed 

#1 VENT/l-4 LEVEL SURVEY SUMMARY 
APPENDIX I 

DATA SUMMARY 

VENT # 1 ; 1-4 HAULAGE DRIFT 

GAIN SETINGS: Preamp (nom) 68 

RECEIVER ORIENTED +Z UP; +Y NORTH "RF" 0 

TRANSMITER f = 2 Hz; RECEIVER BW 2.025 Hz Detector 10 
APPENDIX I 

(CONTINUED) 

DATA SUMMARY 

VENT # 1 ; 1-4 HAULAGE DRIFT 

RECEIVER ORIENTED +Z UP; +Y NORTH 

GAIN SETTINGS: Preamp (nom) 68 dB 

I'RF" 0 dB 

TRANSMITTER f = 2 Hz; RECEIVER BW z.025 Hz Detector 10 dB 

Z 

(FT) 

0 X 

Y 

Z 

+10 X 

Y 

Z 

+20 X 

Y 

Z 

+30 X 

Y 

Z 

+40 X 

Y 

Z 

+50 X 

Y 

Z 

+60 X 

Y 

Z 

i 

I 

(v) 

+1.83 

-.31 

+2.50 

- .04 

+.29 

+2.12 

- .84 

+ .15 

'3.25 

-2.95 

+ .63 

+2.72 

-3.50 

+ .75 

+1.37 

-3.50 

+.76 

+ .27 

-2.97 

+ .66 

- .57 

Q 

(v) 

-4.89 

+.96 

-6.15 

-1.63 

+.07 

-7.77 

+3.83 

- .37 

-6.94 

, +5.32 

-1.01 

-3.93 

+6.13 

-1.24 

-1.81 

+5.20 

-1.08 

- .06 

+3.95 

- .84 

+ .95 

Iv~ tan-' f L 

(V) 

5.22 

(deg) DIRECTION 

-69.5 

1 Y IVT[ tan- X 

1.01 

6.64 

1.63 

.30 

8.05 

3.92 

.40 

7.66 

6.08 

1.19 

4.78 

7.06 

1.45 

2.27 

6.27 

1.32 

.28 

4.94 

1.07 

1.1 

(V) (deg) 

+ 

- 

-- A + 

10.95 I 

10.43 

5.83 

> 

-72.1 

-67.9 

88.6 

13.5 

-74.7 

-77.6 

-67.9 

-64.9 

-61.0 

1 5.32 

1.66 

3.94 

-58.0 

-55.3 

-60.3 

-58.8 

-52.9 

-56.1 

-54.9 

-12.5 

-53.1 

-51.8 

-59.0 

6.20 

7.21 

6.41 

5.06 

11.07 

11.61 

11.89 

12.22 
APPENDIX 11 

MEASURED DATA AT VENT #1/1-5 HAULAGE DRIFT 
LOCAL MAGNETIC NORTH' 

(KERR-MCGEE MEASU~MENT) 

b-- 2 -4 RECEIVER 4 

M 2'10" above track bed 

I 

#1 VENT/l-5 LEVEL SURVEY SUMMARY 
APPENDIX I1 

DATA SUMMARY 

VENT dr 1 ; 1-5 HAULAGE DRIFT 

RECEIVER ORIENTED +Z UP; +Y NORTH 

GAIN SETTINGS: Preamp (nom) 68 dB 

"RF" 10 dB 

TRANSMITTER f = 2 Hz; RECEIVER B'rl =.025 Hz Detector 10 dB 
APPENDIX I11 

MEASURED DATA AT VENT #5/1--4 HAULAGE DRIFT 
IVER . 

n"5 VENT 

1-4 LEVEL SURVEY SUMMARY 
APPENDIX I11 

DATA SUMMARY 

VENT # 5 ; 1-4 HAULAGE DRIFT 

GAIN SETTINGS: Preamp (nom) 68 dB 

RECEIVER ORIENTED +Z UP; +Y NORTH "RF" 20 dB 

TRANSMITER f = 2 Hz; RECEIVER BW z.025 Hz Detector 10 dB 
APPENDIX I11 

(CONTINUED) 

DATA SUMMARY 

VENT # 5 ; 1-4 HAULAGE DRIFT 

RECEIVER ORIENTED +Z UP; +Y NORTH . . 

GAIN SETTINGS: Preamp (norn) - 68 dB 

I'RF" 20 dB - 

TRANSMITTER f = 2 Hz; RECEIVER BW z.025 Hz Detector - 10 dB 

z 

(FT) 

+I 90 X 

Y 

Z 

\ 

I 

(v) 

- .64 

- .16 

- .38 

Q 

(v) 

+1.03 

+ .I9 

+.60 

IV/ tan-' 9 I 

(V) 

1.21 

.25 

.71 

DIRECTION 

I 

(deg) 

-58.1 

-49.9 

-57.6 

1 Y lvTI 

(V) 

1.24 

I 

tan- X 

(deg) 

11.67 
APPENDIX IV 

DEMONSTRATION OF AN ELECTROMAGNETIC NAVIGATION METHOD 

ON TITAN CONTRACTORS LARGE BORE DRILLED RIVER CROSSING 

AT GREENS BAYOU, HOUSTON, TEXAS 

January 1978 
ACKNOWLEDGEMENTS 

We would like to thank Dr. H.K. Sacks of the U.S. Bureau of Mines, 

PMSRC and Martin Cherrington of Titan Contractors for making this 

work possible. We also want to thank Bill Cooper for hard work 

and accurate surveying, Jim Ellison and Dennis Brown for engineering 

support, and all the other members of the Titan organization for their 

interest and cooperation. 

C. Kwong 

T.C. Moore 

L.H. Rorden 
DEMONSTRATION OF AN ELECTROMAGNETIC NAVIGATION METHOD 

ON TITAN CONTRACTORS LARGE BORE DRILLED RIVER CROSSING 

AT GREENS BAYOU, HOUSTON, TEXAS 

Titan Contractors Corporation of Sacramento, California has developed a 

means of drilling small bore pipeline crossings under rivers and other 

similar obstructions that they have been using with a relatively high 

degree of success for the past several years. Conventional directional 

measurement techniques had been used which at best were time consuming and 

at worst led to unacceptable errors, particularly when obstacles exist close 

to the right of way. This seemed to be an ideal application for using the 

basic borehole location techniques as a means of navigating a directional 

drill ing operation that might be applicable to such Bureau of Mines problems 

as the methane drainage program and others. Therefore, arrangements were 

made to try the locator method on a radically different large bore drilling 

program that Ti tan was undertaking in late 1977. The Bureau of Mines technical officer approved the use of the equipment prepared on the borehole 

l ocator contract (501 77074). Devel co, Inc. supported special equi prnent 

design and preparation and the development of calculation programs, and 

Ti tan Contractors supported the fie1 d measurements in a cooperative effort 

to demonstrate the feasibil i ty. 

The work was successfully completed in early January 1978 when Titan succeeded in drilling a 30-inch diameter casing, for an oil pipeline, along a 

curved path approximately as shown in Figure 1. It is believed that this is 

the first time that the directional drillin~g of such a large bore using a 

steerable dri 11 bit section has ever been accompl ished, particularly in 

essentially one operation. (Because this was the first field operation of 

a radically different drill rig, the field work occured in two parts to permit some modifications - this brief account covers the final operation.) 

The navigation requirements were fairly critical because of drill ing operati on consi derations , the pi pel ine design parameters, and the existence of 

a gas line in the adjacent right of way (approximately 15 to 20 feet away 

at one point). Titan had built conventional magnetic and gravity sensors 

into the drill section and had planned to supplement this with periodic 

gyroscope measurements. However, it was exlpected that magnetic azimuth 

information would be very uncertain because of the presence of nearby pipelines, bridges, railroad tracks, barge traffic, etc., and this proved to be 

the case. Due to difficulties with the gyros, the locator system was the 

only source of azimuth information, and provided a valuable cross check on 

the other data, so the operation turned out to be of more value than a simple demonstration. 

The locator antenna was mounted in the drill section, which consisted of a 

casing with a wall thickness varying from 1/4 to 1/2 inch and various internal machinery, approximately as shown in Figure 2. Preliminary measurements 

suggested, and later calculations confirmed, that there was relatively 1 i ttle 

distortion of the transmitted field due to misalignment, the surrounding dri 11 

structures or the receiver structure. Rough measurements of signal attenuation made with the antenna at an initial location in the drill resulted in 

approximate values of 2.5 dB at 2 Hz, 5 dB at 4 Hz, and 10 dB at 8 Hz. 

The attenuation val ues were about doubled in the final location, but the 

signal strengths produced were enti rely adequate for the ranges of interest. 

The antenna drive was essentially the same as in the mines case, i.e., approximately square wave with an amplitude of about 53A producing a moment of about 

1400 Amm2 peak. However, truck batteries were connected to the transmitter 

power supply to considerably improve amp1 i tude stabi 1 i ty. 

Measurements of the fields produced at the surface were made at presurveyed 

stations as shown in Figure 3. Unlike in the borehole locator case, it is 

the instantaneous transmitter position that is important so measurements of 

the surface fields were made for at least two receiver locations (and sometimes 3 or 4 for redundancy) at appropriate distances from each transmitter 

location. This required moving the receiver, since oniy one was available, 

and took some time, so measurements were usua1:y made while a casing joint 

(about 40 feet) was being added. However, it is important to recognize that 

a high speed automatic measurement system and mu1 tiple sensors could achieve 

real time measurements while drilling. In order to achieve relatively quick 

setups with considerable alignment accuracy, the magnetometer receiver was 

mounted on a transit head as shown in Figure 4. (Fairly good results were = 

achieved with a much cruder setup in the initial work, but the refinements 

greatly improved the system accuracy and made possible the final result discussed below. ) 
transm/ttfng antenna (id) 

f/ex joint 

FIGURE 2 

Transmitting Antenna Placement 

Large Diameter Bore Machine 2-27 

TIDRIL COR PORATION 

/3 Feb. 1978 
Point of Entry 

I12 - 62 -3- 

I 

I 

- 115 * 00 STA 1/4*85.6- 

EL. 28.7 

STA N9 * 60.9- 

,STA 114-36.0- C?- EL. 28.3 

GREENS BAYOU CROSSING 

Magnetometer Stofions 

TI TAN CONTRACTORS CORP. 

14 Fob. lS7B 

- - 

STA N4-00.5-I] 

- ... - -- - -- ---- - -- - FIGURE 3 - - - -. 

EL. 29.4 

EL. 29-5 
FIGURE 4 

MAGNETOMETER/TWNS IT SETUP 

-65- 
A proprietary calculation program was prepared for the TI-59 programmable calcul ator/printer combination which took data from two receiver positions plus 

an initial estimate of distance along the desired arc and calculated the 

fol 1 owing transmitter parameters : 

Dipole moment (complex) 

El evation angl e 

Azimuth angle 

Depth from surface (OMST reference) 

Range from entry 

Distance off track (right or left) 

An iterative type program was used because of the lack of precise calibration 

data, other unknowns, and the simp1 ici ty of the TI calculator. As a result 

the calculation process was very slow and it typically took about 6 hours to 

get answers accurate within a couple of percent, which was barely consistent 

with drilling progress. (Simple single point programs were also used to get 

a quick estimate of position which was useful if the moment was accurately 

known. ) It is estimated that accuracies better than one foot were achieved 

for measurement ranges up to several hundred feet. 

A summary plot of the measurement results is shown in Figure 1 which compares 

the Develco locator data and the Titan inclination data with respect to the 

desired path. We were not able to get data or, in some cases, reduce available data at every point due to time limitations. However, the trends are 

very clear and consistent with actual events and the final result. For example, there was a consistent left track error until the pipe string started to 

roll to the right. This forced the drill into a right track error which was 

minimized and eventually recovered by steering to the left as can be seen 

from the record. The Ti tan estimate of prolfile is based on plotting their 

internal inclination measurement data by a tangential method. The Titan 

results show a clear cumulation of error in the upward direction which was 

probably due in part to instrumentation problems. Note that the locator 

method gives a true measurement of actual position at each transmitter location with an accuracy that only depends on measuring the received fields 

correctly and that does not accumulate over the path. The fact that, with 

the advice to steer hard left and up on the final section, the drill came 
out and knocked over the post marking the desired exit point, as shown in 

Figure 5, tends to substantiate this point. 

In concl-usion, this job has shown that the basic locator techniques can be 

used successfully on at least one kind of drilling navigation problem. The 

equipment can be easily designed for field use and automated to provide nearly 

instantaneous data on drill position probably even while drilling. It will 

be straightforward to adapt the calculation methods that have been developed 

to a small computer, which will reduce computation time to a few minutes at 

most. By using a more powerful antenna and a more sensitive receiver, the 

measurement ranges can be extended considerably. Also by using mu1 tiple 

sel f-compensati ng recei vers and an appropriate reference source, i t is possi - 

ble to eliminate the need for precisely surveying the receiver locations or 

to permit use where surveying is not possible, such as under water. In summary, it is clear that the method is practical and has considerable commercial 

potential. 
FIGURE 5 

DRILL AT EXIT POINT 

-68- 
TITAN REFERENCES 

M.A. Preaseau, Directional ly-Control 1 ed Horizontal ly-Dri 11 ed River 

Crossings, ASME 1977 Energy Technology Conference, Houston, Texas, 

September 21 , 1977. 

2. Gary E. Congram, Horizontal Drilling Speeds Pipeline Stream Crossing, 

The Oil and Gas Journal, March 6, 1978.