Mission: As the Nation's principal conservation 

agency, the Department of the Interior has responsibility for most of our nationally-owned public 

lands and natural and cultural resources. This 

includes fostering wise use of our land and water 

resources, protecting our fish and wildlife, preserving the environmental and cultural values of 

our national parks and historical places, and providing for the enjoyment of life through outdoor 

recreation. The Department assesses our energy 

and mineral resources and works to assure that 

their development is in the best interests of all 

our people. The Department also promotes the 

goals of the Take Pride in America campaign by 

encouraging stewardship and citizen responsibilityfor the public lands and promoting citizen participation in their care. The Department also has 

a major responsibility for American Indian reservation communities and for people who live in 

Island Territories under U.S. Administration. 
Report of Investigations 9291 

In-Mine Test of the Bureau of Mines 

Preproduction Wireless Survey 

System 

By Stephen J. Kravits and John Millhiser 

UNITED STATES DEPARTMENT OF THE INTERIOR 

Manuel Lujan, Jr., Secretary 

BUREAU OF MINES 

T S Ary, Director 
Library of Congress Cataloging in Publication Data: 

Kravits, S. J. (Stephen J.) 

In-mine test of the Bureau of Mines preproduction wireless survey system / by 

Stephen J. Kravits and John Millhiser. 

p. cm. - (Report of investigations; 9291) 

Includes bibliographical references. 

1. Coalbed methane drainage-Directional drilling. 2. Boring. I. Millhiser, John. 

11. Title. 111. Title: Wireless survey systems. IV. Series: Report of investigations 

(United States. Bureau of Mines); 9291. 

TN23.U43 [TN844.5] 622 S-dc20 [622'.82] 89-600247 

CIP 
CONTENTS 

Page 

Abstract ........................................................................... Introduction ........................................................................ Acknowledgments .................................................................... General description of wireless survey system operation ........................................ Wireless survey system in-mine test ....................................................... Testsite ......................................................................... Directional drilling equipment ......................................................... Hydraulicdrill .................................................................. Downholemotor ................................................................ Wireless survey system time study ...................................................... Problems encountered .............................................................. Conclusions ........................................................................ References ......................................................................... Appendix-Electronic design, mechanical design, operation of wireless survey system, and recommendations . 

ILLUSTRATIONS 

Time required to survey versus borehole depth ........................................... Downhole guidance probe .......................................................... Uphole receiving transformer and uphole receiver processor ................................. WSS operational schematic ......................................................... Hydraulic drill feed frame .......................................................... Downholemotor ................................................................. Triplepistonpumps ............................................................... Plan view of horizontal borehole ..................................................... Vertical section of horizontal borehole ................................................. Comparison of available drilling time with WSS and wire-run survey instrument ................... WSSblockdiagram ............................................................... Downhole guidance probe block diagram ............................................... Sensor package and canister ......................................................... Signal processing and transmission circuitry ............................................. Current inducing transmitter ........................................................ Sealed lead acid batteries ........................................................... Batterypack .................................................................. Sensor canister and outer collar ...................................................... Uphole receiving transformer block diagram ............................................ Uphole receiving transformer ....................................................... Uphole receiving transformer and gas handling equipment .................................. Uphole receiver processor showing operating display ..................................... Uphole receiver processor block diagram ............................................. Uphole receiver processor .......................................................... 

TABLES 

1 . WSStimestudy .................................................................. 10 

A.1 . Specifications of Develco ........................................................... 13 

A.2 . Downhole guidance probe channel assignment ........................................... 16 

A.3 . A-D converter scaling factors ........................................................ 16 

A.4 . Power amplifier and downhole guidance probe output ...................................... 16 
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

hp 

in 

kHz 

lb 

rnA 

ampere 

ampere hour 

ampere hour per day 

decibel 

degree Celsius 

foot 

gauss 

gallon per minute 

hertz 

hour 

horsepower 

inch 

kilohertz 

pound 

milliampere 

rnA h milliampere hour 

MHz megahertz 

mV millivolt 

min minute 

ms millisecond 

pet percent 

psig pound (force) per square 

inch, gauge 

s second 

s/h second per hour 

v volt 

V ac volt, alternating current 

V dc volt, direct current 

V/G volt per gauss 

W watt 
IN-MINE TEST OF THE BUREAU OF MINES 

PREPRODUCTION WIRELESS SURVEY SYSTEM 

By Stephen J. ~ravits' and John ~illhise? 

ABSTRACT 

The U.S. Bureau of Mines preproduction Wireless Survey System (WSS) and its performance during 

an in-mine test are discussed in this report. The WSS was developed to reduce downhole surveying time 

in order to increase the efficiency of drilling long horizontal methane drainage boreholes in coal. 

Borehole survey data are electromagnetically transmitted from the WSS7s downhole guidance probe, via 

the drill rod, to the uph'ole subsystem in less than 1 min per survey transmission, regardless of borehole 

depth. The WSS7s in-mine test consisted of providing borehole survey data during the directional drilling 

of a 2,538-ft horizontal methane drainage borehole in the Pittsburgh Coalbed. By considering available 

drilling time, which does not include hydraulic drill downtime and the time spent traveling portal to 

portal, 24 shifts were needed to complete the borehole. Of the available drilling time during the tcst, 

50 pct of the time was spent drilling and 50 pct surveying and maintaining the WSS to keep it 

operational. Previous Bureau experience indicates drilling efficiency was increased 108 pct because of 

the WSS, in comparison with using a commercially available wire-run directional survey instrument at 

10-ft intervals. 

 i in in^ engineer, Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA. 

2~resident, ISE, Inc., Aldie, VA. 
INTRODUCTION 

The U.S. Bureau of Mines pioneered the development 

and has demonstrated that the technique of methane control by horizontal boreholes is an effective method for 

removing methane from coalbeds in advance of mining and 

controlling methane emissions during mining (1-4): For 

horizontal boreholes to be effective, they must be accurately drilled simultaneously maintaining vertical trajectory 

within the coalbed and horizontal trajectory on the desired 

course. Maintaining this degree of drilling accuracy can be 

difficult, requiring frequent directional surveys of bit inclination and azimuth, usually at 10- to 20-ft drilling intervals. The time required to survey at this frequency 

using conventional wire-run survey instruments increases 

with borehole depth (fig. 1). Previous Bureau experience 

with boreholes drilled to depths of 1,000 ft or greater has 

shown that the time spent surveying can occupy as much 

time as the drilling operation (5-6). Consequently, drilling 

productivity is reduced as the time required to survey 

increases. To address this problem, the Bureau developed 

a preproduction WSS. 

This report provides a description of the WSS and its 

performance during an in-mine test. Electronic and mechanical design information concentrating on the WSS 

operation and assembly are provided in detail in an appendix along with suggested design modifications for a 

production model WSS. 

- 

KEY 

Wireless survey system ----- Wire-run tool 

0 

500 1,000 1,500 2,000 2,500 

HORIZONTAL DEPTH, ft 

Figure 1 .-Time required to survey versus borehole depth for 

the permissible wire-run survey instrument and WSS. 

ACKNOWLEDGMENTS 

The cooperation provided by personnel at BethEnergy are dedicated to Donald Raab, mining engineer, 

Mines, Inc.'s, Eighty-Four Complex, Livingston Portal, coordination of mine personnel duties; John Ronto, 

Eighty Four, PA, was critical to the successful in-mine test construction foreman, drill site preparation; Thomas 

of the preproduction WSS. In particular, special thanks Decass, surveying engineer, drill site preparation; and 

Thomas Mucho, mine manager, project approval and 

assignment of mine personnel; of BethEnergy Mines, Inc., 

3~talic numbers in parentheses refer to items in the list of references Eighty-Four Complex. 

preceding the appendix. 
below by shales, clays, or other materials that are more 

conductive. Therefore, these materials tend to offer a 

good return path for the signal between the ends of the 

drill string. Data or drill string currents are detected by 

the uphole receiving transformer. 

The uphole receiving transformer is a very sensitive 

current toroidal transformer constructed to allow the drill 

rod to pass through. After the data signal is amplified, it 

is transmitted by cable to the uphole receiver processor 

where it is demodulated. Finally, the processor evaluates 

and converts the raw data into usable information including inclination, azimuth, orientation of the downhole motor's bent housing and status of the downhole batteries, 

etc. Inclination, azimuth, and survey depth are entered 

into a Hewlett PackardWP-15C calculator programmed 

with a radius-of-curvature program used to calculate the 

borehole's elevation and coordinates. Regardless of borehole depth, surveys, take less than 1 min each to complete. 

The electronic design, mechanical design, operation, and 

assembly of the WSS are explained in the appendix. 

Figure 2.-Downhole guidance probe. A, Transmitter; 

8, batteries and canister; C, battery-transformer cable; 

D, electronics and canister; E, sensor package and canister. 

'~eference to specific products does not imply endorsement by the 

U.S. Bureau of Mines. 
Figure 3.-Uphole receiving transformer (left) and uphole receiver processor (right). 
Figure 4.-WSS operational schematic. 
Figure 5.-Hydraulic drill feed frame. 
Figure 6.-Downhole motor (shown equipped with 2" bent housing and polycrystalline diamond cutter bit, 

although lo bent housing used during in-mine test). 
Figure 7.-Triple piston pumps used to supply water flow of 60-70 gpm at 500 to 1,000 psig to power the downhole motor. 
Figure 8.-Plan view of horizontal borehole. 

Floor 

KEY 

Survey elevation, 11 

0 to 460 * 400 to 1,120 990 to 2,538 

4 I 111111,,1,1,1, 1 I I1 1 I I I I I 0 200 400 6 00 800 1,000 1,200 1.400 1.600 1.800 7 .Om 2.200 2.400 2.600 

HORIZONTAL DEPTH, ft 

Figure 9.-Vertical section of horizontal borehole. 
Table 1 indicates the breakdown of the in-mine test 

including drilling, surveying, etc. A typical drillingsurveying sequence includes drilling a 10-ft length drill rod, 

flushing the borehole clean of cuttings, surveying, adding 

a new drill rod, and reestablishing water circulation to resume drilling. Of the total 33 shifts to complete theaborehole, 9 shifts were spent drilling. The WSS downhole 

guidance probe was designed to be activated when the 

drilling water pressure is shut off after the completion of 

a 10-ft drill rod and the borehole has been flushed clean 

of cuttings. 

Table 1.-WSS time study 

Operation &h, shifts 

Drilling ................. Adding drill rodi ........... Surveying ................ WSS maintenance: 

Charging batteries2 ....... Downtime .............. Hydraulic drill downtime ..... Total shifts ............. 

'includes flushing borehole clean of cuttings and reestablishing 

water circulation after new drill rod has been added. 

21ncludes time spent to pull drill string from borehole to charge 

downhole guidance probe batteries and time to reinstall downhole 

guidance probe in borehole. 

During the study, a total of 2,898 ft of horizontal borehole was drilled, including 290 ft of sidetracks (fig. 9). 

Consequently, over 350 WSS surveys were conducted including bad transmissions. A total time of less than one 

shift was occupied conducting WSS borehole surveys. 

Cumulatively, five shifts were required to flush the 

borehole clean of cuttings aftcr the completion of a drill 

rod, add a drill rod after a survey was completed, and 

reestablish water circulation to resume drilling. Regardless 

of the survey system employed, the borchole must be 

adequately flushed clean of cuttings aftcr the complction 

of a drill rod to prevent blockage of cuttings and the drill 

string getting stuck. However, when using the WSS, extra 

time and attention was made to ensure that the drill cuttings were removed from the boreholc. Coal cuttings in 

the boreholc will couple the drill string and the coalbed, 

weakening and possibly shorting the data signal 

transmitted via the drill road. Of the five shifts spcnt 

flushing the borcholc, adding a drill rod, etc., two wcre 

estimated as required to ensure that the cuttings were 

removed from the borcholc. Consequently, these two 

shifts wcre included as WSS survcying time. Maintenance 

of the WSS occupied a total of nine shifts, six shifts 

charging the downhole guidance probe batteries and three 

shifts repairing the steel conduit, which provides access 

from the sensor package to the downhole electronics. 

The downhole guidance probe's battery pack consisted 

of 14 2.5 A- h, 2.1 V capacity, scaled lead acid batteries. 

By considering the current draw of a normal day of 

0.49 A - h, working one shift per day, the downhole guidance probe had to be pulled out of the borcholc about 

every 5 days for recharging, or a total of six times during 

the in-mine test (details concerning current draw of the 

downhole guidance probe, etc. are discussed in the appendix). The time spent pulling the downhole guidance probe 

out of the borehole and putting the probe back in the 

boreholc after recharging occupied six shifts. Furthermore, during the six 5-day periods (one shift per day 

worked) that the downholc guidance probe was operational in the borehole, the hydraulic drill averaged 3.33 days of 

the 5-day periods, before it needed repair. If thc hydraulic 

drill was not operational, the WSS could not be used even 

if the WSS worked. Consequently, although thc downhole 

guidance probe was operational in the boreholc, it was not 

used 10 shifts because of hydraulic drill downtirne. 

The WSS failed only once when a 0.19-in-ID steel conduit (fig. A-3) providing access from the sensor package to 

the electronics in the downhole guidance probe developed 

a small crack allowing water to enter the sensor and electronics canisters. Replacing the steel conduit and Develco 

sensor package that suffered water damage, and making 

minor repairs to the downhole electronics, took three 

shifts. 

Available drilling time is considered the time available 

for drilling, not included arc hydraulic drill downtime and 

the time spcnt traveling portal to portal. To provide a 

valid comparison between the WSS and the commercially 

available, permissible wire-run survey instrument, the nine 

shifts spent maintaining the WSS (six shifts charging downhole batteries and three shifts WSS downtime) and the two 

shifts required to adequately flush the borehole clean of 

cuttings, will be considered as survcying time. 

Figure 10 illustrates a surveying and drilling comparison 

of surveying with the WSS and wire-run survey tool while 

drilling a 2,538-ft horizontal methane drainage borehole. 

Twelve shifts or 50 pct of the available drilling time, were 

spcnt survcying (combining shifts, one survcying, nine 

maintaining WSS, and two adequately flushing tjorehole); 

while 38 shifts or 76 pct wcre required surveying with the 

wire-run tool. Therefore, surveying with the WSS was 

217 pct more efficient than the wire-run tool. Twenty-four 

shifts of available drilling time wcre required to complete 

the borehole using the WSS compared with 50 shifts with 

the wire-run tool. Consequently, drilling efficiency or 

productivity increased 108 pct as a result of survcying with 

the WSS. 

PROBLEMS ENCOUNTERED 

To conduct a WSS survey at the completion of a 10-ft 

drill rod, the borchole must be flushed clean of cuttings. 

As mentioned earlier, if not flushed adequately, the likelihood of a missed survey or bad data transmission, increases. When the time and difficulty to adequately flush 

cuttings from the borehole increased with dcpth, the frequency of bad data transmissions or no transmission of 

any data, increased, especially from a dcpth of 2,300 ft to 

borcholc completion. 
p, pp, 

raw data and system status can be observed to determine 

the integrity of the raw data transmitted including sensor 

outputs, the downhole guidance probe's analog to digital 

(A-D) reference voltage, the downhole guidance probe's 

battery voltages, etc. This information indicates whether 

,,y 

from depths of 2,479 to 2,519 ft. WSS surveys were attempted from 2,519 to 2,608 ft, but were unsuccessful 

because the downhole guidance probe had been in the 

borehole for 5.5 days and needed to be recharged. 

CONCLUSIONS 

The preproduction Wireless Survey System (WSS) 

provided the borehole survey data, on a near real-time 

basis, necessary to navigate a 2,538 ft directionally drilled 

horizontal methane drainage borehole drilled in the 

Pittsburgh Coalbed. WSS surveys were conducted on 10 ft 

drilling intervals, taking less than 1 min for each survey 

transmission, regardless of borehole depth. The WSS 

operated reliably to a borehole depth of 2,300 ft with 

82 pct of the surveys attempted successful. From 2,300 ft 

to borehole completion, only 50 pct of the WSS surveys 

attempted were successful. Difficulty in adequately 

flushing the drill cuttings from the borehole and the 

interception of several clay veins is believed to have caused 

or contributed to short circuiting of the signal current. 

By considering available drilling time, which does not 

include hydraulic drill downtime or the time spent 

traveling portal to portal, 24, 8-h shifts were needed to 

complete the 2,538 ft borehole. Fifty percent of the 

available drilling time was spent drilling and 50 pct 

surveying. Of the 50 pct surveying time, 4 pct was 

occupied transmitting survey data, 13 pct WSS downtime, 

25 pct charging the downhole guidance probe's batteries, 

and 8 pct additional time required to ensure adequatc 

flushing of cuttings from the borehole. By comparison, 

using a commercially available, wire-run permissible 

directional survey tool would have taken 217 pct more 

surveying time to complete the 2,538 ft borehole surveying 

at 10 ft drilling intervals. Consequently, drilling efficiency 

was increased 108 pct because of the WSS, in comparison 

with using the wire-run directional survey tool. 
REFERENCES 

1. Hagood, D. W., R. C. Pate, and J. W. Stevenson. Methane 

Control in an Advancing Section of an Underground Coal Mine 

(contract S0395033, Jim Walters Resourc., Inc.). BuMines OFR 94-84, 

1983, 39 pp.; NTIS: PB 84-185057. 

2. Finfinger, G. L., and J. Cervik. Review of Horizontal Drilling 

Technology for Methane Drainage From U.S. Coalbeds. BuMines 

IC 8829, 1980, 20 pp. 

3. Deul, M., and J. Ce~k. Methane Drainage in the Pittsburgh 

Coalbed. Paper in XVII International Conference of Mining Safety 

Research (Varna, Bulgaria, Oct. 3-7, 1977), pp. 9-15. 

4. Ce~k, J., H. H. Fields, and G. N. Aul. Rotary Drilling Holes in 

Coalbeds for Degasification. BuMines RI 8097, 1975, 21 pp. 

5. Prosser, L. J., Jr., G. L. Finfinger, and J. Ce~k. Methane 

Draining Study Using an Underground Pipeline, Marianna Mine 58. 

BuMines RI 8577, 1981, 29 pp. 

6. Kravits, S. J., A. Sainato, and G. L. Finfinger. Comparison of 

Rotary and In-Hole Motor Techniques for Drilling Horizontal 

Boreholes in Coal. BuMines RI 8933, 1985, 33 pp. 

7. Pittard, F. 2-718 Inch High-Torque Slimdril Motor Performance 

Data. Slimdril, Inc., Houston, TX, 1984, 21 pp. 

8. Kravits, S. J., A. Sainato, and G. L. Finfinger. Accurate 

Directional Borehole Drilling: A Case Study at Navajo Dam, New 

Mexico. BuMines RI 9102, 1987, 25 pp. 

9. Sammarco, J. J. Intrinsically Safe 5-V, 4-A Rechargeable Power 

Supply. BuMines IC 9223, 1989, 11 pp. 

10. Marsh, J. L. Hand-Held Calculator Assists in Directional Drilling 

Control, Part 2 - Calculating Borehole Sensor Outputs. Pet. Eng. Int., 

July 1982, pp. 79-88. 
APPENDIX.-ELECTRONIC DESIGN, MECHANICAL DESIGN, OPERATION 

OF WIRELESS SURVEY SYSTEM, AND RECOMMENDATIONS 

The following appendix explains in detail the WSS's 

electronic design, mechanical design, operation, and recommends design modifications for a production model 

WSS. The Mine Safety and Health Administration 

(MSHA) granted the Bureau Experimental Permit No. 

EP-569-0 for use of the WSS by the Bureau in BethEnergy 

Mines, Inc., Mine No. 60. The downhole guidance probe 

was evaluated as explosion proof and the uphole receiving 

transformer and uphole receiver processor intrinsically 

safe. 

WIRELESS SURVEY SYSTEM DOWNHOLE 

GUIDANCE PROBE 

The WSS's downhole guidance probe is positioned 

directly behind the downhole motor as shown by figures 4 

and A-1. The downhole guidance probe consists of sensors, electronics, batteries, and transmitter. Figure A-2 is 

a block diagram of the downhdle guidance probe. 

Downhole Guidance Probe's Sensors 

The Develco MWD (Measurement While Drilling) 

Sensor, Model 106470, was selected as the sensor package 

for the WSS's downhole guidance probe because of its offthe-shelf availability, inherently precise alignment, and 

Uphole receiving 

transformer 

receiving 

Downhole 

guidance 

probe 

small size of 1.5-in-OD by 24.5 in. in length (ligs. 2 and 

A-3). The Develco sensor package comprises three single 

axis flux gate magnetometers, three single axis servo accelerometers, and a temperature sensor. Within the sensor 

package, the axis of each magnetometer and accelerometer 

are precisely aligned to be mutually orthogonal to each 

other. Consequently, when the sensor package is placed 

within its aluminum canister and assembled in the copper 

beryllium outer collar (assembly and mechanical design of 

the downhole guidance probe are discussed later), one 

magnetometer and accelerometer are aligned with the axial 

direction of the probe and two magnetometers and accelerometers are aligned radially. 

The Develco sensor package is used to accurately measure the orientation of the downhole guidance probe with 

respect to the Earth's magnetic and gravitational field 

vectors. In addition to the three magnetometers and accelerometers, the Develco package is equipped with a temperature sensor. When surveying deep vertical wells 

drilled for oil and gas exploration or production, which is 

a more typical application of the Develco package, monitoring the temperature is essential so that scnsor errors 

caused by extreme temperatures (100" C plus) can be 

corrected. Although the output of the temperature sensor 

is transmitted, extreme temperatures are not cncountered 

when drilling horizontal methane drainage borcholes in 

coal. The manufacturer specifications of thc Develco 

sensor package are provided in table A-1. 

Table A-1 .-Specifications of Develco Model 106470 sensor package 

Each axis magnetometer: 

Output: 5 V/G (Earth's field typically 0.7 G) 

Alignment: 20.2" 

Offset: 20.003 G 

Linearity: 20.2 pct full scale 

Each axis accelerometer: 

Output: 24.5 V/G (Earth's field typically 1 G) 

Alignment: 20.2" 

Offset: 20.003 G 

Linearity: 20.1 pct 

Power: 20-30 V dc at 100 mA (max) 

Dimensions: 24.5 in. in length by 1.5-in-OD 

Figure A-1 .-WSS block diagram. Weight: 4 Ib 
Figure A-3.-Sensor package and canister. A, Electronics; 6, 3/16-in-OD steel conduit; C, sensor-electronics transition piece; 

Dl sensor canister; El sensor. 
8.4 s. The remainder of the master clock outputs are 

disabled until a survey is initiated. 

scale factors. 

i I 1 D i 

Scale, In 

Figure A-4.-Signal processing and transmission circuitry. A, Batteries; 8, electronics canister; C, steel conduit for sensor wires; 

D, battery canister; E, battery end plug with O-rings; F, electronics; G, sensor-electronics transition piece; H, sensors. 
Table A-2.-Downhole guidance probe channel assignment 

-- 

channel' Assignment 

1 . . . . . . . Magnetometer X axis, 2 1.0 G 2 5 V. 

2 . . . . . . . Magnetometer Y axis, 2 1.0 G 2 5 V. 

3 . . . . . . . Magnetometer Z axis, 2 1.0 G 2 5 V. 

4 . . . . . . . Accelerometer single axis, Z axis 

lg = '4.5 v. 

5 . . . . . . . Accelerometer biaxial X axis lg = 24.5 V. 

6 . . . . . . . Accelerometer biaxial Y axis lg = 24.5 V. 

7 . . . . . . . Temperature, 0" to 50" C = 0 to 5 V. 

8 . . . . . . . Reference voltage, +2.500 V, for A-D 

converter. 

9 . . . . . . . Negative battery voltage monitor, -2.25 V 

nominal. 

10 ...... Positive battery voltage monitor, +2.25 V 

nominal. 

11 ...... Peak pressure drilling fluid, 5 V per 

1,000 psi. 

'channels 12 through 16 not used. 

Table A-3.-A-D converter scaling factors 

Bit Scaling factor 

'1 234567891011 212 

000000000 0 0 0 Plus full scale, plus 5.0 V. 

000000000 0 0 1 Plus full scale, minus 1 count, 

minus 4.9976 V. 

011111111 11 1 Plus 1 count, plus 0.0024 V. 

0 Zero. 

1 Minus 1 count, minus 0.0024 V. 

0 Minus full scale, plus 1 count, 

minus 4.0076 V. 

1 Minus full scale. minus 4.9976 V. 

'~ost significant bit. 

2~east significant bit. 

While data are being transmitted, the power amplifier 

is being fed with a 5.028 kHz carrier designated as the 0" 

carrier. This carrier operates for 16.4 s allowing time for 

the uphole receiver to perform automatic gain range and 

phase lock functions on the stable carrier. Immediately 

after the 16.4 s, the logic switches to all binary ones data 

modulation for 4.2 s so that the uphole receiver can establish a phase lock on the 40.6875 Hz data clock. After the 

4.2 s of all ones have been transmitted, a 32-bit preamble 

is sent. The 32-bit code is hardwired into the uphole 

receiver and is continuously monitored for bit pattern 

match. Once match is found, the receiver will open its 

data and clock lines to the uphole processor and begin 

handing the received data to the processor. Three bits of 

random data, not used, followed by 143 bits (11, 12-bit 

channels plus 1-bit parity per channel) are then sent to the 

processor. The following is the transmission sequence: 

1. Upon activating the downhole guidance probe, the 

probe transmits 16.8 s of 0" phase shift carrier (no modulation) used by the uphole receiver to establish carrier 

phase lock and auto gain range. 

2. The carrier is followed with 4.2 s of all one's data 

used by the uphole receiver to establish data clock and 

phase lock. 

3. All one's data are followed by the 32-bit preamble 

used by the uphole receiver to acknowledge that the upcoming data are real to prepare to alert the uphole 

processor. 

4. The preamble code is 

10110000110111001011000011011100. 

5. If the exact code is not recognized, the uphole receiver will ignore the remainder of the transmission. 

6. The next three bits of data transmitted are sent to 

the uphole processor, but are thrown away as meaningless. 

7. The last 208 bits are transmitted and received by the 

uphole receiver representing 16 channels of 12-bit offset 

binary data plus one parity bit per channel. Only 11 channels of data, 143 bits, are used by the processor. 

As stated earlier the output of the power amplifier is 

coupled to the drill string by the downhole transmitter 

through which an electric current is induced (fig. 2 and 

fig. A-5 and table A-4). Once all the data has been transmitted to the uphole receiver, the downhole guidance 

probe signals itself to shutdown and returns to the dormant status. 

Table A-4.-Power amplifier and downhole 

guidance probe output 

Carrier frequency . . . 5.2028 kHz 20.005 pct crystal controlled. 

Modulation . . . . . . . . 4 W nominal to input of downhole transmitter, varies with coupling conditions. 

Also note that the output signal of the 

downhole transmitter was evaluated as 

intrinsically safe by MSHA. 

Downhole Guidance Probe's Batteries 

The battery pack original design, consisted of 14 X cells 

of a sealed lead acid-starved electrolyte battery manufactured by Gates Energy, Denver, CO (figs. A-6-A-7). The 

cells each have a nominal capacity of 5 A. h with a ccll 

voltage of 2 V. The 14 cells were daisy chained together 

to provide 214 V to the downhole electronics. Flat 

printed ribbon tape was used to interconnect the daisy 

chain of 14 cells before installing them into the explosionproof battery canister. The life of the battery pack using 

X cells was expected to be adequate enough to drill a 

2,000-ft horizontal methane drainage borehole without 

requiring recharge. Recharging the battery pack is an 

operation that would require retrieval of the downhole 

guidance probe from the borehole, removal of the downhole guidance probe's outer beryllium collar, and transporting the downhole guidance probe to the fresh air 

environment to charge the downhole batteries as required 

by MSHA. 

Unfortunately, the battery packs original design did not 

prove to be reliable. During lab testing and calibration at 

the surface, the flat ribbon tape connecting the X cell 

batteries failed several times. 
u 

, g y y , 

0.49 A- h would be consumed per day, which would require recharging the downhole guidance probe batteries 3 

j about every 5 days. , \ 

- ",< ic, 111 

Assembly of the Downhole Guidance Probe 

Figure Ad.-Sealed lead 

without outer case (center), 

acid batteries. X cell (left), X cell 

D cell (right). 

The outer case of each battery had already been removed (fig. A-6), while the inner diameter of the battery 

canister could not be increased because reducing the wall 

thickness would have prevented the canister from being 

explosion proof. Considering the critical timing of the 

problem, it was decided to replace the X cells with smaller 

D size sealed lead acid batteries, 2.5 A. h, 2.1 V, interconnected with larger diameter conventional wire. Obviously, the trade-off using the smaller 2.5 A. h batteries 

would result in one-half less surveying time or life in the 

borehole because the downhole guidance probe would 

need to be pulled from the borehole twice as often to 

recharge the batteries. 

The calculation for determining the battery capacity 

needed was based on several factors and assumptions. 

First, there is a continuous current drain of approximately 

The downhole guidance probe's sensors, clectronics, 

and batteries are contained within or housed by explosionproof, aluminum, 2-in-OD canisters (figs. A-3-A-4). The 

sensor and electronics canisters are joined by a copper 

beryllium transition piece while the electronics and batteries are joined by an aluminum gland with O-rings. The 

battery pack must be installed into the electronics in fresh 

air. The total assembled length of the sensor and electronics-battery canisters is about 11 ft with an approximate 

weight of 40 Ib. Once the inner canisters havc been assembled, they can be carried to the drill site in preparation 

for final assembly of the downhole transmit~cr and the 

outer copper beryllium collars. Final assembly begins by 

installing the section of the copper beryllium collar, 2.62- 

in-OD, 2.25-in-ID, 6.6 ft in length, over the sensor canister 

and threading it onto the copper beryllium transilion piece 

using pipewrenches (fig. A-8). Keeping the transmitter 

cable tucked inside the delrin centralizer belonging to the 

battery package, the copper beryllium collar with the same 

diameter as the collar already used, but 9.6 ft in length, is 

fit over the electronics-battery canister and threaded onto 
Scale, in 

Figure A-8.-Sensor canister and outer collar. A, Battery canister; 8, steel conduit; C, sensor canister; D, outer collar. 

the electronics sensor transition piece (fig. A-4). Finally, 

the transmitter cable is threaded into the downhole transmitter, followed by threading the transmitter into the outer 

collar. Assembling the downhole guidance probe's outer 

collar over the sensor and electronics-battery canisters 

takes about 1 h. 

Waterflow to the downhole motor and drill bit passes 

through the downhole transmitter to the 0.25-in annular 

space between the outer wall of the inner canisters and 

inner wall of the outer copper beryllium collar. The total 

weight of the assembled downhole guidance probe is about 

200 Ib with a length of 21 ft. 

UPHOLE RECEIVING TRANSFORMER 

AND RECEIVER PROCESSOR 

Uphole Receiving Transformer 

The signal current transmitted by the downhole guidance probe induced onto the drill string is detected by the 

uphole receiving transformer (figs. 3, A-9, and A-10). In 

addition to the high sensitivity current toroidal transformer, the uphole receiving transformer contains a 30 dB gain 

preamp and high Q or very selective passive filter with a 

centering frequency of 5.208 kHz. The preamp gain can 
Figure A-10.-Uphole receiving transformer. A, Filter-preamp 

circuit board; B, current toroidal transformer. 

be switched between 0 and 30 dB as needed by the automatic gain control circuitry of the uphole receiver to be 

discussed later. 

The uphole receiving transformer is contained within a 

watertight aluminum housing fitted onto a 4-in-ID plastic 

polyvinyl chloride (PVC) pipe and flanges that are used 

to fasten it in-line with the gas handling equipment 

(fig. A-11). 

Uphole Receiver 

The final component of the WSS is the uphole receiver 

processor (figs. A-12-A-13). As indicated by figure A-13, 

there are five major blocks that make up the receiver 

processor. 

The uphole receiver is comprised of an automatic gain 

amplifier section, phase lock loop, data demodulator, and 

All of the electronic components of the uphole receiver 

are CMOS technology to take advantage of its good noise 

immunity and low power consumption. 

Uphole Processor 

An Intel ISBC 80/24 single board computcr was used 

as the WSS uphole processor (figs. A-13-A-14). All 

software was written using program language machine 

(PLM) language primarily to expedite the construction of 

a system with in-house technology and development system. Initially, a CMOS version, off-the-shelf processor 

was planned to be used to reduce the power requirements. 

However, a CMOS version processor or equivalent was not 

off-the-shelf available and operational in time for the 

project. This created problems with respect to the required battery levels to power the transistor transistor logic 

(TTL) version processor maintaining intrinsic safety. A 

permissible high-current t 8 V battery pack was developed 

solely for the processor printed circuit board containing 

active integrated circuitry that would limit powcr levels in 

the event of fault conditions (9).' 

'ltalic numbers in parentheses refer to items in the list of references 

preceding the appendix. 
Figure A-11.-Uphole receiving transformer and gas handling equipment. A, Collar or standpipe; B, manual shut-in valve; C, gaswater separator; D, uphole receiving transformer. 

As stated earlier, due to time constraints, the software 

was implemented in the PLM language. Under this system, many subroutines for specific tasks already existed in 

the PLM library and could be easily used. The disadvantage of this software method with respect to an operational 

production system is the amount of memory overhead 

required to contain the PLM library. 

The algorithms used to process the raw survey data into 

positional information were essentially the same as those 

provided by Develco (10). One change was made in the 

calculation of inclination. Because the WSS was designed 

primarily to survey horizontal methane drainage boreholes, 

only the Z-axis accelerometer output was used to calculate 

inclination. The equation used was 4 = sin-' (V/G) where 

4 is the angle of inclination with 00 as horizontal, V is the 

voltage of the Z-axis accelerometer, and G is full-scale 

voltage for 1 G acceleration. This method was chosen 

over using the outputs of the X- and Y-accelerometers to 

eliminate the error of two sensors by only having the error 

of one. Also as sugested by Marsh (10), in order to 

eliminate the errors due to different absolute values of the 

Earth's magnetic and gravitational fields from one location 

to another, all data signals were normalized to a full-scale 

value of 1. Therefore, all equations work only on values 

of 0 to 1. 

Once the processor calculates all values for the survey 

depth, including inclination, azimuth, and orientation of the 

bent housing, it stores the data in a small portable 

Termiflex HT 1000 terminal, which is a stock item. To 

make it intrinsically safe (evaluated as part of the processor), the lithium inorganic thionyl chloride battery was 

replaced with a lithium solid electrolyte, 2.4 V Saft battery. 

The Termiflex is used as a system control device, menu 

driven, in addition to storing and displaying data. Three 

menus are available including: (1) raw data, (2) calculated 

data, i.e., inclination, azimuth, and orientation of downhole 

motor's bent housing, and (3) control. The first menu 

provides all 11 channels of raw data as indica~ed by table 

A-2. Calculated data are made available through menu 

two. Inclination, azimuth, and survey depth were entercd 

into a Hewlett Packard 15C calculator programmed with 

a radius of curvature program to determine borehole 

coordinates and elevation. Menu three is a control menu 

consisting of: message entering capability, system status 
Figure A-12.-Uphole receiver processor showing operating display and MSHA experimental permit labels. 

Input from 

uphole toroid 

preamplifier 

Figure A-13.-Uphole receiver processor block diagram. 

Receiver b Microprocessor b 

C 

Power supply Battery pack 

MSHA EP 501 

b 
providing uphole receiver gain, a monitor of the number 

of set floating bits, capability of entering a new number set 

of floating bits, and warning for low receiver batteries. 

RECOMMENDATIONS 

The preproduction WSS performed reliably during the 

in-mine test. However, the preproduction WSS would be 

in need of considerable modifications in electronic and 

mechanical design primarily in the downhole guidance 

probe, if it were made into a production model. 

In order to reduce the amount of discrete circuitry and 

the space it occupies, new advances in large-scale integration circuits (LSI) could be utilized. Off-the-shelf, small 

low-power LSI circuits could be used to replace the function of 10 to 15 circuits with a single package that would 

occupy the space of two or three of the existing circuits. 

For example, the use of a 80C85 CMOS processor would 

perform the entire control and sequencing functions currently done discretely. This family of microprocessors has 

would keep the batteries charged. These turbines and 

alternators do exist for 6-in-ID equipment used in the 

MWD industry, for oil and gas exploration, and would 

need to be scaled down. 

One other possible system improvement would be the 

addition of an upholc to downhole communication link. 

This link would only be used to activate thc downhole 

guidance probe to conduct a survey. To integrate an uphole to downhole activation link. an uvhole transmitter and 

coupling transducer to induce a signal into the drill string 

would be required. An additional transducer would not be 

required downhole because the existing transmitter would 

be used to receive the signal, only receive circuitry would 

be required. 

In the uphole receiver, LSI CMOS circuitry could also 

be employed in the receiver demodulation. Thc processor 

should be replaced with a CMOS version to reduce power 

consumption. The software could be written in machine 

or assembly language to reduce the large memory overhead required with high-level languages, which would 

reduce the power requirements.