The Introduction of an At-Bit Natural Gamma Ray Imaging...

SPWLA 53rd

Annual Logging Symposium, June 16-20, 2012

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THE INTRODUCTION OF AN AT-BIT NATURAL GAMMA RAY

IMAGING TOOL REDUCES RISK ASSOCIATED WITH REAL-TIME

GEOSTEERING DECISIONS IN COALBED METHANE HORIZONTAL

WELLS

Aaron J. Wheeler, Thomas Billings, Allan Rennie, Rick Lee, Robert Little, Cornelis Huiszoon,

Paul Boonen

PathFinder - A Schlumberger Company

Copyright 2012, held jointly by the Society of Petrophysicists and Well Log

Analysts (SPWLA) and the submitting authors.

This paper was prepared for presentation at the SPWLA 53rd Annual Logging

Symposium held Cartagena, Colombia, June 16-20, 2012.

ABSTRACT

Logging While Drilling (LWD) measurement selection

is an exercise in risk management where potential

drilling hazards with or without a specific measurement

are weighed against their benefits. The assessment

compares value added to real-time steering decisions

for the area specific character of the target reservoir,

mechanical limitations of the drilling and completions

assemblies and economics. LWD borehole images are

commonly used to place complex, long reach lateral

wells into the optimal section of the reservoir. The

major advantage of the use of images is that they

indicate the direction in which bed boundaries are

crossed (top-down or bottom-up). Additionally, the bed

dips can be calculated which aid in constructing a

realistic structural model of the formations of interest.

Typically, the LWD tools, including the imaging

measurement(s), need to be positioned in the

bottomhole assembly (BHA) above the mud motor or

rotary steerable system (RSS). This results in a

measurement point that is some 40 ft to 80 ft behind the

bit. Considering the relatively shallow depth of

investigation of most imaging measurements, the

images do not represent the current position of the bit in

the stratigraphy - the bit may already have drilled out of

the zone before this is identified on the images. A real-

time at-bit natural gamma ray imaging tool was

developed as a solution to position the image

measurements as close to the bit as possible to reduce

the reaction time for time critical geosteering decision

making processes.

The new tool consists of two separate subs. An

instrumented stand-alone sub containing the

measurement sensors is located directly above the bit.

A wireless telemetry system is used to transmit the data

across the mud motor to the second sub which is

connected to the bottom of the conventional MLWD

toolstring. The at-bit measurements are then transmitted

to surface via conventional mud pulse telemetry. The

real-time at-bit measurements consist of a natural

gamma ray curve, eight sector natural gamma ray

image and dynamic inclination.

The tool has been extensively used in the drilling of

coalbed methane wells in a complex folded and faulted

environment in laterals up to 5000 ft long. The coal

seam targets are selected based on offset well log data.

The character of gamma ray readings for the targeted

coal is evaluated along with the density measurements

to generate the initial geosteering model(s) for the well

to be drilled. While drilling, the geosteering model is

continuously updated with the at-bit gamma ray

measurements and the dip of bedding planes is

computed. In a challenging geological structure with

the rate of penetration that can commonly exceed

100ft/hr, multiple steering decisions may be required

every hour in order to position the well in-zone.

Deciding on the correct course of action after crossing a

fault can be particularly challenging – is the fault

upthrown or downthrown? At-bit gamma ray images

have enabled a repeatable decision making process to

maintain well position within the coal seam where

every foot in zone translates into revenue for the

operator.

INTRODUCTION

Geosteering is the directional positioning of a wellbore

based on evaluation of geological criteria and real-time

downhole measurements. The interactive approach of

geosteering leverages technology and personnel from

multiple disciplines to optimally position the wellbore

to maximize production. All geosteering applications

benefit from measurements that are made as close to the

bit as possible because this allows for expeditious

steering decisions. When encountering lithological

change, shortening the bit to sensor spacing directly

reduces the time between drilling, logging, and

interpreting the changes to implementing revisions to

the wellbore’s trajectory. In the following sections, we

discuss criteria for selecting logging measurements for

a specific geosteering application, followed by a

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detailed description of the at-bit gamma ray imaging

tool. Next, we discuss real-time measurements utilized

to meet the challenges of drilling horizontal wells in

coalbed methane (CBM) reservoirs. Two case studies

are presented that illustrate the value of geosteering

with at-bit natural gamma ray images for drilling

horizontal wells within coalbed methane reservoirs.

LOGGING MEASUREMENT SELECTION

Evaluating the objectives for the project will help

determine what logging measurements will be required

by narrowing down key questions relevant to the area.

Objectives for different intervals of the wellbore may

vary. How thick is the target formation? Is there enough

control for geometric steering or is geological steering

required? What are the dogleg severity requirements for

completions? Is there an oil-water interface? What

lateral geological variations are expected to occur? Will

natural fracture identification be required? Are there

any known or anticipated faults to be encountered?

During the planning stages, the exercise of assigning

steering decision values for individual logging

measurements within a specific target formation and the

adjacent formations is assessed for horizontal

wellbores. Through evaluation of offset well logging

data, the characteristics for the area are determined and

objectives are made to minimize well placement

uncertainty for geological steering.

The advent of a variety of LWD tools from shallow

high resolution imaging to deep bed boundary detecting

measurements allows for multiple BHA combinations

to meet a variety of objectives for any given area. The

challenging task is to minimize the operating cost while

insuring that enough measurements are employed to

accurately position the wellbore efficiently.

AT-BIT NATURAL GAMMA RAY IMAGING

TOOL

To add to the drilling industry’s measurement offerings,

an at-bit natural gamma ray imaging tool has been

developed for nominal collar sizes of 4 ¾ in, 6 ¾ in and

8 in. Each tool consists of two separate subs: an

instrumented stand-alone sub containing the

measurement sensors and a telemetry sub which acts as

a transceiver.

The measurement sub is typically located between the

positive displacement mud motor and bit. It houses a

single gamma ray scintillation detector that is used in

the generation of at-bit images. The large crystal of the

gamma ray detector enables high precision images. The

placement of the detector towards the outside of the

tool aids in providing azimuthal sensitivity as the tool

body shields the detector against gamma rays from the

backside. This azimuthal sensitivity was further

enhanced by incorporating high-density tungsten

shielding material behind the detector. In a uniform

formation, approximately 90% of all gamma rays

detected will have originated from the “front,” i.e. the

half of the formation that the detector faces (figure 1).

Figure 1. Cross section of the measurement sub.

Gamma counts are sampled 100 times per second. A

set of magnetometers and accelerometers provide a

measurement of (azimuthal) detector position. A

patented weighting algorithm is used to compute

average counting rates for each azimuthal sector of the

image (Haugland, 2006). Typically, the real-time

image is presented with 8-sectors. Memory data can be

processed into a larger number of sectors where a 16-

sector image is typical. All gamma ray data are

presented in API units.

A wireless telemetry system is used to transmit the data

across the positive displacement mud motor to the

telemetry sub. This electromagnetic “short hop”

telemetry system allows for real-time data to be

received from the measurement sub that is placed

between the bit and motor, without the need for a wired

motor (figure 2).

Figure 2. At-bit gamma ray imaging tool subs.

“FRONT”

“BACK”

Detector

Outer tool housing

Borehole

Antennas used for

“short hop” communication

Measurement sub

Telemetry sub

Detector

Outer tool housing

Borehole

Telemetry sub

Measurement sub

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The telemetry sub, as shown in figure 2, mechanically

connects to the bottom of the conventional toolstring to

complete the measurement and transmission system

within the BHA.

The at-bit measurements are transmitted to surface via

conventional mud pulse telemetry in conjunction with

measurements acquired from additional LWD tool(s) in

the BHA. The advantage of this at-bit gamma ray

imaging system is BHA flexibility in selecting a motor

specific to the target formation.

REAL-TIME MEASUREMENTS

The basic real-time at-bit measurements consist of a

total gamma ray curve, 8-sector gamma ray image and

dynamic inclination. Figure 3 illustrates a typical real-

time log that incorporates the at-bit measurements in

addition to Measurement While Drilling (MWD) total

gamma ray, survey station inclination, penetration rate,

slide indicator, and equivalent circulating density

(ECD). The 8-sector gamma ray image provides

feature identification in which dip angle and direction

can be calculated. The at-bit dynamic inclination

measurements are plotted on the same scale as the

MWD survey station inclination. This display allows

the drilling team to monitor motor yields while sliding

and build/drop tendencies of the drilling assembly

while drilling in rotary mode.

Additional at-bit parameters monitored that are not

incorporated in the log plot shown in figure 3 are the

stick-slip severity and revolutions per minute (RPM) of

the measurement sub. The at-bit RPM measurements in

conjunction with surface drilling parameters are

monitored to revise surface weight on bit and rotary

speed to improve drilling efficiencies. Real-time

parameters available for transmission are defined in

table 1.

Included in the BHA (figure 4) is a downhole pressure

measurement that provides equivalent circulating

density allowing the drilling team to understand

downhole pressure conditions and react accordingly to

increasing (possible borehole cutting loading) or

decreasing (possible loss of borehole integrity) ECD

while drilling in real-time.

An advantageous feature of the placement of the

measurement sub below the motor is that images are

continually acquired when sliding as the measurement

sub rotates with the bit. Additionally, this close

proximity to the bit allows for timely geosteering

decisions in response to changing geological

conditions. In rotary steerable system (RSS)

applications, the imaging gamma system can be placed

directly above the RSS providing the same

measurements as operated below a PDM (positive

displacement motor).

Figure 3. Real-time at-bit image measurement log.

GEOSTEERING IN COALBED METHANE

RESERVOIRS

There are a number of reasons why horizontal wells are

important in CBM drilling (Maricic et al., 2005). The

direction, shape and position of a horizontal well can be

controlled so that an almost ideal well position can be

achieved. Proper well positioning and borehole length

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contribute to draining large areas. Drilling horizontal

wellbores is very important for sweep efficiency for

reservoir drainage. Increasing contact with the coal in

longer boreholes decreases the time for water

production and gas-flow peak will occur sooner after

the well starts producing. Horizontal CBM wells can

realize a 10:1 increase in production over vertical wells

drilled into the same coal seam.

In drilling CBM horizontal wells, the utilization of at-

bit sensors and geosteering forward modeling software

has been a successful pairing (Meszaros and Boonen,

2006). The coal seam targets are selected based on

offset well log data. The character of the gamma ray

readings for the targeted coal seam are evaluated in

conjunction with the offset density measurements to

generate the initial geosteering model(s) for the

horizontal well that will be drilled. While drilling, the

geosteering model is continuously updated with the at-

bit gamma ray measurements along with all LWD

measurements employed. The dips of bedding planes

observed in the real-time gamma ray images are

computed to support the interpretation of the wellbore’s

placement allowing for maximum coal exposure

throughout the lateral (figure 6). Geosteering with at-

bit gamma ray images enabled a reliable decision

making process while reducing uncertainties to

maintain wellbore position over lateral sections that

commonly exceed 5000 ft of displacement within a

complex environment.

HORIZONTAL CBM WELL CASE STUDIES

The following examples demonstrate the well

placement results of two CBM horizontal wells. The

first well discussed utilized at-bit natural gamma ray

measurements without gamma ray images, and did not

include the real-time geosteering forward modeling

platform. This well was drilled prior to the recent

introduction of the at-bit gamma ray imaging

technology. The second well will illustrate how the at-

bit gamma ray images reduce uncertainty in real-time

geosteering decisions when leveraged with real-time

forward modeling software for maintaining wellbore

position within the targeted coal seam. The primary

well placement objective for the CBM horizontal wells

was to provide maximum contact between the wellbore

and the coal to optimize production rates and recovery.

The geosteering illustrations as seen in figures 6-11 are

of the real-time forward modeling software displays

supplemented with the memory image data. The panel

on the left side of the display contains the offset well

data represented on a true vertical depth scale with the

horizontal well’s measured logs correlated within the

same stratigraphic column. This vertical stratigraphic

column is referred to as reference vertical depth, RVD.

Reference vertical depth is the measured depth

corrected for well inclination and bed dip. An RVD log

is the log that a vertical well would see if it were drilled

at a reference location. The reference point is usually a

point along the horizontal well trace, and in the

following examples, the wellhead is the reference point.

The middle and upper right panels display the modeled

and measured log data. Data displayed includes, but is

not limited to, rate of penetration (ROP), MWD

inclination and gamma ray, at-bit inclination and

gamma ray, at-bit gamma ray images and the modeled

gamma ray image calculated from offset well log data

in concert with the geologic interpretation.

The wellbore’s progression within the geological model

is displayed in the bottom right curtain section panel

with the y-axis representing TVD (true vertical depth)

and x-axis representing measured depth. Vertical

exaggeration may be present depending on the zoom

level utilized within the curtain section panel. The

geosteering engineer refines the geological

interpretation within this panel by adjusting formation

dips and/or adding faults to match the predicted log

data to the actual real-time log data. Dip interpretations

are independently calculated directly on the features

observed within the real-time gamma ray image panels

to support the wellbore position in reference to the

geological interpretation.

CBM CASE STUDY #1

Case study #1 displays a geologic interpretation

conducted post-well after drilling of the horizontal well

was completed (figure 5). The well was drilled with at-

bit gamma ray and inclination measurements, but

without gamma ray images and real-time geosteering

application. The targeted coal seam was encountered

shallower than anticipated. This resulted in the well

inadvertently exiting the base of the coal since the

planned landing point was too deep. From the heel of

the lateral, the well was steered up to 95.0° of

inclination to re-enter the coal seam. Approximately

25% of the total lateral was drilled out of the target

interval due to the coal seam being encountered

shallower than planned. Upon re-entering the target

seam, drilling continued at 90°-91° inclination as

planned successfully achieving the geometric goals. It

was unknown that the bed dip changed laterally to

slightly downdip while drilling continued slightly

updip. Without real-time monitoring, the well exited

the top of the coal seam and remained above the

targeted zone for the remainder of the lateral. The post-

well geosteering model and log data show that this well

was drilled in-zone for approximately 50% of the lateral

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section not achieving the geologic goals for the

horizontal well (Meszaros, 2007).

Since the gamma ray measurement utilized while

drilling this well does not contain directional

information, an alternate interpretation could plausibly

position the wellbore below the coal seam if the dip

increased locally. The correlations using standard

natural gamma ray measurements alone can provide

non-unique geosteering scenarios that can lead to

increased uncertainty within the geological

interpretations. This uncertainty can cause

complications in making timely geosteering decisions

making it more challenging to stay in-zone when

structural changes occur.

CBM CASE STUDY #2

Case study #2 illustrates the various advantages of at-

bit natural gamma ray image data in respect to wellbore

placement, proactive geosteering decisions and fault

detection through image interpretation. The curve

section was drilled with conventional mud motors,

standard MWD gamma ray measurements and real-time

geosteering modeling conducted from the wellsite.

While drilling the curve, the targeted landing point was

revised assuming consistent interval thickness from the

marker tops down to the top of the targeted coal seam

while accounting for the anticipated structural dip. The

curve was landed within the required geologic window

and casing was set at the desired depth, roughly 7 ft

TVD inside the target interval. The lateral was started

by drilling ahead utilizing the at-bit real-time natural

gamma ray image to gather the necessary logging data

to determine the formation dip.

The drilling assemblies utilized in the lateral section of

the well in this case study consisted of a 1.5° bend mud

motor, MWD natural gamma ray, ECD measurement,

and the at-bit natural gamma ray imaging tools as

shown in figure 4.

Interpreting the real-time measurements acquired from

this drilling assembly the formation dip was determined

to be relatively flat for the first 500 ft of the lateral.

After the initial footage was drilled, the natural gamma

ray image log began to show sinusoidal features

indicating intersection of bed boundaries from which

formation dip was calculated. The information provided

by the image data was utilized to revise the wellbore

trajectory to follow the formation dip attempting to stay

in the middle of the target interval (figure 6). The

targeted coal seam with internal ash stringers is

identified within the geosteering interpretation figures

6-11 as the gray/blue shaded interval bounded by shale,

which is shaded light red.

A decision was made to climb in structure to get

separation from the lower ash stringer within the target

interval. At this point, the gamma ray increased from 23

to 73 API over 3 ft of TVD change in which the image

indicated an abrupt change. The feature on the real-time

image was interpreted to be a 3 ft to 4 ft upthrown fault

(Fault-A, figure 7) resulting with the wellbore

positioned directly below the target interval. Inclination

was maintained at 93° for 100 ft followed by a gradual

decrease to 91° while continuing to traverse up through

the target zone as supported by geosteering

interpretation. The uppermost stringer within zone was

encountered as the inclination was decreased below

91°.

Figure 4. Lateral drilling assembly.

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To prevent exiting the top, the well path was

repositioned to the middle of the target interval by

dropping to 89.5° and then to gradually build back to

90.5° over the next 300 ft. The image interpretation

allowed for expeditious real-time adjustments. While

continuing the build up to 91° of inclination, another

fault was encountered and interpreted to be a 6 ft

upthrown fault resulting with wellbore positioned

below the base (Fault-B, figure 7).

At this point, the inclination was built up to 94° and the

wellbore re-entered the target interval within 75 ft.

Upon drilling back into the target seam, the wellbore

was repositioned, traversing up through structure to get

back toward the middle of the coal seam. While

repositioning the wellbore higher in structure, the top

stringer was logged. This required a more aggressive

drop in inclination to prevent exiting the top. The

gamma ray image showed drilling up and then back

down through the top stringer as shown in figure 7.

Drilling continued, adjusting wellbore inclination below

the image interpreted dip angle to reposition deeper in-

zone. As the wellbore was navigated below the stringer

into the interval with lower total gamma ray response, a

formation dip change was observed. The interpreted

apparent dip changed increasing from 1.5° to 2°

downdip to nearly a 4.5° updip. The change in dip

resulted with exiting the base with 93° of inclination at

the bit (figure 8). Building inclination continued

achieving 94.8° and drilling back into the target interval

commenced.

Re-entry into the coal was confirmed by observations of

the increase in ROP, real-time natural gamma ray

images, and cutting samples. While climbing in

structure gaining separation from the bottom of the

zone, an apparent formation dip of 0.5° to 1.0° updip

was estimated. The inclination was reduced to match

the revised interpretation for the local dip of the

formation (figure 9). Over the next 1,400 ft of lateral,

the wellbore position was maintained near the middle of

the target seam with gradual adjustments in inclination

ranging between 90° to 92°. The remainder of the

lateral was drilled with only one other out-of-zone

instance, which occurred when intersecting additional

faulting (Fault-C, figure 10) with low displacement.

The remainder of the lateral was positioned between the

two stringers to the point when Total Depth was called

early due to loss of drilling fluid.

With relatively fast bit penetration rates, multiple

steering decisions were required every hour in order to

maintain position of the wellbore in-zone within this

challenging geological structure. Figure 11 displays the

entire wellbore lateral section of the target reservoir

coal seam while crossing three faults and encountering

varying formation dip changes. A 95% in-zone rate

was accomplished.

At-bit gamma ray images coupled with real-time

proactive geosteering interpretation have enabled a

repeatable decision making process to maintain the well

position within the coal seam where every foot in-zone

translates into revenue for the operator.

CONCLUSIONS

A newly developed real-time at-bit natural gamma ray

imaging tool reduces the reaction time and uncertainties

for critical geosteering decisions in the drilling of

horizontal coalbed methane wells that typically target

seams with 10ft to 30 ft of thickness.

The at-bit natural gamma ray image and dynamic

inclination system coupled with real-time geosteering

interpretation allowed the drilling and geological teams

to expeditiously steer the wellbore within challenging

geological variances. The wellbore drilled in case study

#2 achieved 95% of the lateral positioned within the

reservoir providing the operator the required coal

exposure for maximum hydrocarbon recovery.

ACKNOWLEDGEMENTS

We would like to thank Lauri Hardwick and Sophie

Jones from PathFinder a Schlumberger company for

their graphical image support.

REFERENCES

Haugland, S.M., “Enhanced measurement of azimuthal

dependence of subterranean parameters,” US patent

7,027,926, 2006.

Maricic, N, Mohaghegh, S.D., Artun, E., 2005, “A

Parametric Study on the Benefits of Drilling Horizontal

and Multilateral Wells in Coalbed Methane

Reservoirs,” paper SPE-96018 presented at the SPE

Annual Technical Conference and Exhibition, Oct 9-12,

Dallas TX, USA.

Meszaros, G., Boonen, P., 2006, “Geosteering and

Natural Fracture Identification in Horizontal Wells in

Unconventional Reservoirs,” in Resource Plays in the

Permian Basin: Resource to Reserves, Michael A.

Raines (ed.), West Texas Geological Society,

Publication # 06-117, p. 71-79, Fall Symposium, Oct

25-27, Midland, TX, USA.

Meszaros, G., 2007, “Geosteering Horizontal Coalbed

Methane Reservoirs: A Case Study,” paper SPE-

107714 presented at the Rocky Mountain Oil & Gas

Technology Symposium, Apr 16-18, Denver CO, USA.

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ABOUT THE AUTHORS

Aaron J. Wheeler is the Geosteering Operations

Manager for PathFinder, a Schlumberger company. He

received his Bachelor of Science in Civil Engineering

from Texas Tech University. He started his career as an

M/LWD field engineer with Halliburton in 1996 and

transferred to PathFinder in 1998. He has experience

working with M/LWD services for formation

evaluation, geosteering, and pore pressure evaluation.

Aaron is a member of SPWLA and SPE.

Thomas Billings is currently an Account Manager for

PathFinder, a Schlumberger company. He has 15 years

with Schlumberger holding various positions

throughout the company and started his career with

Anadrill in 1997 after receiving his degree in Electrical

Engineering Technologies. He has experience working

with multiple M/LWD tool suites, RSS Systems

services in conjunction with formation evaluation,

geosteering applications and pore pressure services.

Thomas is a member of SPE.

Allan Rennie is a business development manager and

M/LWD product champion for PathFinder, a

Schlumberger company. He has been working for more

than 20 years in technology and operations, developing

and supporting a wide range of M/LWD systems and

services for well placement, formation evaluation,

geosteering, and downhole ranging (passive/active)

applications. He holds a drilling technology diploma

from Sir Sandford Fleming College and a B.S. degree

in Geology and Physics from Acadia University. Allan

is a technology committee member for SPWLA and a

member of SPE.

Rick Lee is a Petrophysicist with PathFinder, a

Schlumberger Company, in Katy, Texas, USA. He

holds a B.S. in Geological Sciences from the University

of Birmingham in the UK. He started his career in

1990 as an SDL field engineer and later M/LWD field

engineer in the UK North Sea with Halliburton. He has

since worked in various supporting roles for LWD

operations both in the UK and USA, including M/LWD

operations coordinator, log analyst and LWD Product

Manager. Rick is a member of SPWLA and AAPG.

Robert Little is the LWD Product Line Manager at

PathFinder, a Schlumberger company in Katy, TX. He

joined PathFinder in 2001 after having worked as an

electrical engineer with Halliburton on a wireline

induction tool. Robert holds a B.S. degree in Electrical

Engineering from Rice University.

Cornelis Huiszoon is Nuclear Science Program Leader

at PathFinder, a Schlumberger company in Katy, TX.

After having completed his physics education at the

University of Twente and the Institute for Plasma

Physics in the Netherlands, he joined Shell’s E&P

laboratory in Rijswijk, the Netherlands in 1985;

assignments followed at Bellaire Research Center in

Houston, TX and NAM in Assen, the Netherlands. In

1994, he joined Sperry-Sun’s sensor physics group to

work on the development of LWD nuclear tool

technology and he continued working on LWD nuclear

tools when he joined Baker Hughes in 2000. He joined

PathFinder in 2007. Cornelis is a member of SPWLA

and SPE.

Paul Boonen retired as Chief Petrophysicist from

PathFinder, a Schlumberger company in Katy, TX. He

holds a Ph.D. in Geology (1981) from the University of

Leuven in Belgium. He started his career in the field of

log analysis in 1981 with Geofiles consultants in

Brussels (Belgium), joined Halliburton in 1983 and

transferred to PathFinder in 1998. He worked as field

engineer, log analyst, computing center manager, and

petrophysicist in a variety of countries in Europe, North

Africa, the Far East and North America. Paul is a

member of SPWLA, SPE and AAPG.

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MNEMONICS DESCRIPTION

INC_P Static Inclination

AZM_P Static Azimuth

TGF_P Static Total Gravitational Force (TGF)

TMF_P Static Total Magnetic Force (TMF)

DIPA_P Static Magnetic Dip Angle (MDIP)

TEMP_P Static Temperature

EA_P Static X Axis Accelerometer

EB_P Static Y Axis Accelerometer

EC_P Static Z Axis Accelerometer

EX_P Static X Axis Magnetometer

EY_P Static Y Axis Magnetometer

EZ_P Static Z Axis Magnetometer

DINC_P Dynamic Inclination

DAZM_P Dynamic Azimuth

DEZ_P Dynamic Z Axis Magnetometer

DTEMP_P Dynamic Temperature

MAGXY_P Dynamic Mag XY Value (ranging)

GRC_P Total Cal. Gamma, Range 0 – 600 API

HGRC_P Total Cal. Gamma, Range 0 – 1200 API

IGR1_P 8 sector GRC Image, Range 0 – 150 AP.I

IGR2_P 8 sector GRC Image, Range 0 – 300 API



RPM_P RPM of iPZIG Tool, Range 0 – 510 RPM

SIGNAL_P 0 – 15, Strength of the Signal

RXST_P 0 – 7, Sync State, 7 = In Sync

LBATT_P Measurement Sub (LXM) Battery, AH

LTPL_P Measurement Sub (LXM) Transmit Power Level

UTPL_P Telemetry Sub (UXM) Transmit Power Level

UBATT_P Telemetry Sub (UXM) Battery, AH

SSS_P Stick Slip Severity, (0-Low, 1-Medium, 2- High, 3-Severe)

AVS_P Axial Vibration Severity, (0 -Low, 1- Medium, 2-High, 3- Severe)

LVS_P Lateral Vibration Severity, (0-Low, 1- Medium, 2-High, 3-Severe)

NBGRx X is the Number of Sectors

INBGRxx XX is the Sector Number

GRNC_P Net Cal. Gamma Derived from the Image

Table 1. Real-time at-bit parameters.

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Figure 5. Case study #1 post-well geologic interpretation of a CBM lateral where MWD and at-

bit natural gamma ray measurements without images was utilized.

Figure 6. Case study #2 geosteering display of a CBM lateral showing real-time, memory, and

modeled at-bit natural gamma ray images with dip picks and the wellbore displayed

with the resulting stratigraphic interpretation.

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Figure 7. Gamma ray image interpretation allows for time-critical steering revisions to maintain

wellbore position within the coal seam.

Figure 8. Footage drilled out-of-zone successfully minimized through real-time image

interpretation when a local formation dip increase was encountered that resulted with

exiting the base of the coal seam.

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Figure 9. Real-time steering adjustments utilized to maintain well placement within target coal

seam.

Figure 10. Footage drilled out-of-zone successfully minimized through real-time image

interpretation when a fault was encountered that resulted in steering up from the base

of the coal seam.

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Figure 11. Geosteering interpretation for case study #2 resulted with 95% of the CBM lateral

positioned in-zone achieved by leveraging imaging at-bit technology and maintaining

good communication across the drilling and geology teams.

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