Two part poster from the Operations Geology Conference, Aberdeen 2012.

1. Geosteering questions asked every moment of every day:
• Where are we?
• What has been achieved?
• Where are we going?
Answers given by: well inclination, azimuth, correlation,
lithology, biostratigraphy, reservoir porosity, saturations,
formation dip (density image) and comparison with the
pre-drill Geological Model derived from seismic and offset
well data.
The key to the whole geosteering process is Teamwork,
Collaboration, Communication and Cooperation; with all
team members aware of the Well (often reservoir
section) Objectives. The team is an integration of
“geology and drilling” and the Operations Geologist
plays a key role in that integration.
• WSG (often the wellsite Geosteering focal point)
• Rig Drilling Supervisor
• Directional Driller
• LWD / MWD operators
• Data loggers and Mudloggers
• Communicate with “base” team members:
Operations Geologist, Project Geologist / Modeller,
Petrophysics, Drilling.
THE ROLE OF THE OPERATIONS GEOLOGIST
AND WELL-SITE GEOLOGIST IN GEOSTEERING DATA ANALYSIS
AND THE MEASUREMENT OF GEOSTEERING QUALITY
Dr Stephen Crittenden
Horizontal drilling and sophisticated geosteering techniques have
changed the economics of some oil and gas fields particularly
those with low relief structural traps and thin hydrocarbon
columns. The field development relies upon the safe drilling of a
number of closely spaced wells with long horizontal sections
often comprising a multilateral configuration. The development of
such fields is often made difficult by complex stratified reservoirs,
variation in the consolidation of the sediments and changes in
bedding dip, and subseismic faults, flexures and fractures
making geosteering horizontal wells for long distances a
challenge. The experience gained from drilling the initial Field
Development wells is utilised iteratively to plan and drill
subsequent development wells. This has resulted in smoother
trajectories with fewer surprises such as unexpected changes in
RSS inclination due to “geology” and in a better geosteering
quality.
From an analysis of well data sets from a number of fields
worldwide (literature search and personal experience) it is
recognized that the main requirements for safe and effective
geosteering are seven-fold.
i. Tools that are manoeuvrable with the ability to drill with
precise and continuous steering.
ii. High quality and continuous real time logs and drilling data
(for example gas, torque, ROP, WOB) – WITSML.*
iii. High quality real time log images (for example resistivity,
density) and real-time porosity and Hydrocarbon Pore
Volume.
iv. LWD / MWD sensors as close to the bit as possible with GR
and inclination “at the bit”.
v. High quality biostratigraphical data while drilling.
vi. An understanding of the interaction of tool behaviour and
geology (for example lithology, bedding, consolidation of
sediment, chert beds / nodules).
vii.Pre-planning and real-time geo-modelling update while
drilling.
TEAMWORK
QUO VADIS?
1. INTRODUCTION
Poster 1
WHAT IS GEOSTEERING?
The WSG maintains a Diary of the Main Geosteering Events /
Decisions and Data Status.
• Brief record of status, decisions and forecast.
• Record inclination and azimuth at bit real time.
• Record last survey.
• Record going up or down through stratigraphic layers
(depths). Density image “smiles or frowns”.
• Record Biozone as indicated by the fossils observed.
• Record: ROP, WOB, RPM, Torque, Lithology and
Formation.
• Record MWD values: GR, Resist., Density, Porosity.
• Record quick look saturations /Reservoir properties.
• Record Steering Response.
The well path is plotted: measured depth / TVDSS.
POSTER OBJECTIVES
GEOSTEERING DIARY
An Example of The Data Stream
The objectives of this poster are twofold: 1) to document briefly
some observed, and well known, geosteering behaviour of Rotary
Steering System tools (RRS) and 2) to present a proposed, albeit
preliminary, “new method” to measure Geosteering Quality as a
quantifier of performance.
2. GEOSTEERING DATA ANALYSIS
Purpose of the post well analysis (pre-planning):
• to make geosteering a high quality (successful) process.
• ultimately to reduce well costs.
The achievement of this purpose can be aided by understanding
the steering tool behaviour and interaction with a variety of
factors both drilling and geological. This understanding will:
• Enable the identification and pre-drill planning of key
geological decision points along a planned well path
(constrained by the pre-drill geological model together with
offset well data if available) and the communication of these to
the geo-steering team prior to drilling.
• Optimize the prediction model of tool behaviour and
geosteering response along a well path.
• Assist the drillers in their choice of tools, bits and BHA. (*)
• Plan future well paths with the objective to mitigate possible
geosteering problems.
• The benefits are:
i. To maximize the feet drilled per day / bit run and to place the
well path in the best place in the reservoir.
ii. To optimize hole geometry and minimize dog-legs (minimise
overall torque and drag of the well path).
iii. To minimize unplanned exits from the reservoir due to
geosteering tool behaviour problems (non-geological).
iv. To minimize unplanned sidetracks due to geosteering tool
behaviour problems.
INVESTIGATION OF GEOSTEERING TOOL
BEHAVIOUR
The behaviour of the steering tools (Motor assemblies and RSS)
has in many field cases been inconsistent, resulting in variable
geosteering quality and performance within different sections of
well paths and with different service providers. The main
observations are:
• RSS tools drop inclination unintentionally during drilling when
building-up from firm into softer layers.
• RSS tools when deflected either up or down by a harder bed
(eg. chert in chalk) is often difficult to control (if at a high ROP)
and often the original inclination cannot be regained.
• RSS tools perform well when drilling bed parallel in softer more
porous reservoir units and is often “bounced” between a firmer
bed above and below. However, precise steering and holding
inclination is compromised at fast ROP when the bit is jetting
the formation.
• It is important that the near-bit sensors GR and Inclination are
available.
• The orientation and incident angle of the well path with respect
to bedding dip. At a low angle of incidence between well path
and bedding dip the BHA, and hence the well path, will be
‘bound’ between any firmer / harder layers. The well path will
be unable to build angle and cut across the stratigraphical
layers. This was a particular problem in some wells resulting in
a sidetrack.
Notes* : WITSML = Wellsite Information Transfer System Markup Language.
Differences in tool behaviour due to differences in BHA configuration such as
stabiliser position have not been addressed in this study.
UNDERSTANDING TOOL BEHAVIOUR
In the quest to understand tool behaviour and to understand why
geosteering “succeeded or failed”, post drilling “exploratory” analysis of
Directional Drillers Parameter Reports and data sets collected while
drilling, usually at surveys only*, was undertaken.
i. Divide well into analysis intervals / segments: for example; Heel
(build and turn) and horizontal section, for steering tool response.
The graphical results of analysis and plots were inconclusive.
• Graph of Dog-leg Severity versus Tool setting versus the Reservoir
Unit for intervals of “active steering” and “hold” modes with target
inclination setting noted.
• Graph of Inclination Hold vs. Reservoir Unit vs. Dog Leg Severity
vs. Target Inclination.
ii. Apparent from the graphical results that additional analysis was
required to measure Geosteering Quality.
Directional Driller Parameter Report
Note that on this example no indication is given of targets
Data stream delivered to the dynamic geosteering / geo-model while
drilling = real-time monitoring and re-modeling.
GEOSTEERING TARGET REPORT
BHA # Well
8.5"
Depth In: Depth Out: Tot Footage:
Inclin. In: deg Inclin. Out: % Slide:
Azimuth In: deg Azimuth Out: % Rotate:
Steer MD From TVDSS HZL UTM UTM Incl MD Target TVDSS HZL UTM UTM Incl
Course /
Distance TF
Steer
Ratio NBI Res Unit Bedding
Hit
Target
Mode (ft) (ft) (ft) (°) (ft) (ft) (ft) (°) (ft) (°) (%) (°) Y/N
R
R parallel
R smile
R frown
R smile
R
R
R
R
R
R
R
R Yes
Comments
WELL PATH
BHA / RSS
Hole Section:
TARGET
Depth interval increments toward
target depending on parameter
changes.
Target is hit these data will be identical
Target achieved.
Slight porpoising
due to soft layers
• Service quality of Directional Drilling / LWD and MWD is a common
concept usually driven by statistical analysis (Service Company and
Drilling Dept.).
• But… Geosteering is usually not addressed regarding “Quality”.
• Perhaps best to use the term ”Quality “ rather than emotive terms of
success or failure.
Analysis of Geosteering Quality is linked to the aim of improvement of
performance. What is the use of a maximum footage drilled per day
per bit run if the wellpath is not in reservoir?
But what is the interpretation of Geosteering Quality and Performance?
There is no unique definition and no proven method of quantifiable
measurement of Geosteering Quality.
3. GEOSTEERING QUALITY
What data analysis could be meaningful for understanding tool
behaviour?
Does the data analysis support /refute observational intuition?
An obvious measure: Targets & Planned Path versus Actual Path
achieved.
What additional data / parameters are required?
Is there a need for a “central Geosteering Data Sheet” or “Geosteering
Target Report” to complement the Geosteering Diary? Yet another
form to complete!
THE MEASUREMENT OF GEOSTEERING QUALITY
• What Defines & Measures Geosteering Quality?
1. Were targets met or not and if not, to understand why not?
2. Dog leg severity
3. Optimal placement of borehole in reservoir (all other
considerations taken into account – geological model)
• How can this understanding and measurement be achieved?
• What data needs to be recorded that characterises these
measurements of quality?
• What analysis is meaningful and can it be scored and ranked?
Good / successful Geosteering results in a smooth well bore,
with minimal tortuosity, with a minimum of dog legs, with low dog
leg severity, and has hit all steering targets, is placed within good
hydrocarbon saturated reservoir, was drilled at optimum feet
drilled / day, and can be lined to total depth.
Geological Society of London Workshop
October 2012 Aberdeen
Geosteering is a technique used to drill a well bore efficiently and
in a precise stratigraphical location / horizon, usually reservoir,
and at often a very high angle (horizontal), using drilling data
collected and analysed “real-time”.
The aim is to achieve as smooth a trajectory as possible: no
severe dog-legs & no spiralling. The results of analysis and
interpretation of the real time data are used for geosteering
decision-making by the Well Site Geologist (the Wellsite
Geosteering Coordinator) & Operations Geologist such as
whether to increase inclination or to place the borehole trajectory
higher in terms of TVD. Discussion with the directional driller
results in the instruction to increase inclination or to aim for and
hit a series of forward target points. The well is not drilled
geometrically by following a profile / line to a TD target as was
the practice in the past, but is pro-actively steered so that the
well path / well bore stays in the best position in productive
reservoir. Accurate well placement means the “capturing” of
more hydrocarbons.

2.  Hydrocarbon exploration drilling and oil and gas field
development well placement is enhanced by the
improved technology available in all disciplines
associated with well drilling including tools, seismic, well
data and geological and reservoir modelling.
 The integration of the data leads to a fuller
understanding of the controls on drilling, geosteering and
for field development, the factors that affect completion
and production performance. A part of this integration is
contributed by the role of the Operations Geologist,
both in a development and exploration scenario, in
ensuring a full understanding between drillers and
geologists of the complexities and interactions of each
discipline associated with geosteering.
 Geosteering performance and quality must be able to be
measured in a consistent manner in order for
performance and quality to be improved. It is not just a
question of feet drilled per bit run or per day.
 The Geosteering Quality Score Card approach described
is a useful first step toward establishing an accepted
objective methodology for measuring quality.
G
Acknowledgments: This poster is presented with the approval of Addax Petroleum Services Ltd. The
encouragement and advice are acknowledged of Rudolf de Ruiter and Bernd Fiebig. The author wishes to
thank the numerous colleagues with whom I have worked; in many fields in many parts of the world and
who have contributed, over the years, geosteering ideas and comments and shared with me their
successful working practices. Particular acknowledgement is due to Martin Kendall, Stephen Bryant, Tim
Daley, Guillaume Durance and Julian Thompson.
Selected References
* Dr Stephen Crittenden is currently a Senior Geologist with Addax Petroleum Ltd, Geneva, Switzerland.
GEOSTEERING QUALITY PARAMETERS
1. Were drilling targets & Way Points met or not? This is
influenced by the Steering Tool, the Directional Driller and
the geology. The hole must not be oversteered.
2. Hole geometry = Tortuosity, Dog Leg Severity and
torque & Drag. This is influenced directly by the
Directional Driller and the BHA plus to some extent the
geology.
3. In Good reservoir = Porosity%, Hydrocarbon %,
staying in the reservoir. This is influenced by the
Geosteerer, the Directional Driller and geology.
Can these parameters be measured in a Ranking System
that distinguishes low and high quality?
THE INFLUENCES ON GEOSTEERING QUALITY
Geology
• Formation character
• Reservoir quality
• Fractures and faulting (large and small)
• Saturations: Hydrocarbons and Sw (water)
• Pore pressure, fracture gradient, stress orientation
• The geological model, key markers and decision points
Well bore geometry and placement
• Well path (planned versus actual)
• Tortuosity, spiralling / porpoising (planned vs. actual)
Mud / Drilling Fluid
• OBM or WBM (hole cleaning, cuttings beds, stability)
• ECD
• Additives
Directional Drilling Tools
• Rotary Steerable tools
• Steerable motor
• Bit Type: Tricone / PDC etc.
• BHA configuration – stabilisers etc.
• LWD / MWD sensor to bit distance
Personnel
• Experience level overall
• Familiarity with the field / drilled area geology
• Experience with the tools
• Pre-planning
MEASURING GEOSTEERING QUALITY
• Judgement applied to the whole well?
• Judgement applied to certain well sections?
• Judgement applied to each Geosteering decision?
• Direct Physical Measurements
• Dog Leg Severity, steering force, inclination.
• Torque & Drag.
• LWD / MWD Tools measurement – NBI, GR, Resist,
Neut/density, Image logs.
• Side tracks due to steering failure and geology.
• Unplanned Trips – bit change, tool change.
• In reservoir or not? CGI log real time.
• Was the target met? Steering tool response. Planned
versus actual well path.
Are these Direct Physical measurements easy to interpret in
terms of geosteering quality?
• Indirect Measurement (interpreted) : a response to the
geosteering quality.
• Score or Rank the measurement of what variables and
how?
• Analyse and interpret the results.
Well path: simple to complex
Experience Learning Curve
Wells in Drilled sequence Well 1 Well 2/1 Well 2/2 Well 3/1 Well 3/2 Well 4/1 Well 5 Well 6/2B Well 7/1 Well 7/2 Well 7/2A
Pre-Reservoir Meeting plus Lessons Learnt Yes Yes Yes Yes Yes Yes Yes
HEEL / BUILD SECTION / Land in A2b2 BHA#4 BHA#4 BHA#4, BHA#5 BHA#1 BHA#2
A2 / A3 boundary drop in inclin., unintended build A3 not reached A3 not reached A3 not reached No drop observed A3 not reached Yes Yes Yes Yes A3 not reached slight
A2b2 (softer layer) inclin drop unintended No No No Yes (eg 12,010ft) Yes Yes Yes
Yes
Yes
A2b2 not reached on
build
No
recovered Yes Yes Yes (set new target) No (set new target) Yes No (tripped for Motor)
Deflection up/down (hard layer) Yes Yes No Yes (eg 14,700ft) Yes Yes none observed Yes Yes Yes Slight
recovered Yes Yes Yes Yes Yes No (trip for Motor) Yes (time drilled) No Yes
Service Provider A RSS Yes Yes Yes
Service Provider B RSS "1" Yes Yes Yes Yes Yes
unintended build (failed to hold or to drop) ? Yes (10,200ft)
unintended drop (failed to hold or climb) Yes ? Yes Yes
fail to hold angle ? Yes Yes
Service Provider B RSS "2" Yes Yes BHA#2
unintended build (failed to hold or to drop) Yes No
unintended drop (failed to hold or climb) Yes Yes Yes
fail to hold angle Yes Yes
Vortex Motor Power Pack Motor Yes Yes Yes Yes Yes Yes BHA#2
Mud Motor Assembly Yes Yes Yes BHA#1
Initiated ST from casing and or Whipstock? no Yes Yes
Remedial to correct a 'dive' / inability to build no
Yes
Yes (BHA#5) No
Yes, inability of
motor to build
Sensor Offsets
NB Incln Yes No (failed) Yes Yes No No - 13.6ft
NB GR No (failed) Yes Yes (intermittent) No No
GR 79.01ft 102.49 ft 6.83 ft (RSSGR) 33.19ft 89.28ft
D & I 116.09ft 136.39 ft 8.03 ft (RSS D&I) 66.65 ft 13.6ft
Res 78.76ft 96.29 ft 43.17 ft 89.11ft
Density 137.75ft 144.21 ft 37.15 ft 138.69ft
Neutron Poros 140.96ft 147.46 ft 44.01 ft 141.85ft
TARGET MET Yes Yes Yes Yes Yes No (porpoised) No
No - partial (dropped in
A2b2)
No
No, Only A2c1. The
A3 was not reached.
Yes, but heel too
deep compared
with plan.
Comments
A2c1 deepest
point. MWD
Failures. Build
achieved OK,
max DLS/100ft
4.4deg.
Deliberate 4.0
deg DL to place
well in A2b2.
Hard layers
crossed by
slowing ROP
Deliberate DL of
up to 6.0 deg
Built OK thru
A3/A2c1. Drop
associated with
A2b2. A very
unchallenging well
trajectory.
DLS to 5.6 deg
and avoided A3.
Recovered from
hard bed
deflection: 100%
force up, redn
WOB, redn
ROP. Slight
porpoising.
MWD fail shallow
test, Backup fail
shallow test, testd OK
at higher GPM. Well
path too low as MWD
failure. Stuck in hole,
free & POOH for BHA.
MWD failure, 7,857
ft MD: No NB GR.
TRIP. Drill to 14,473
ft.
Built up thru A3 / A2c
OK. i) RA sources
mismatch. Ii) MWD
Pulser jammed. iii)
Motor diffic in keeping
inclination, iii) Motor
POOH as diffic in
sliding
MWD failure. Failure
to build thru strat
layers A2c hd
streaks. POOH
change RSS BHA #
2. Failed to build
(hard layers). Bed
parallel and bound
between hard layers.
POOH for ST 7/2A.
MWD intermittent
Initiate ST with
RSS BHA#2.
Incorrect KOP
for Surveys.
MWD
Intermittent.
Heel too
deep.High
Incident angle of
well path to
bedding.
Geosteer Score (see Sheets) 14 13 13 13 12 8.6 8.6 8.5 8.6 4.3 11.3
DD Service Provider A DD Service Provider B
Changeofserviceprovider
GEOSTEERING SCORE CARD
Well
8.5"
Interval: Build and Heel
Depth In: Depth Out: Total Footage:
BHA #:
RSS:
Score
5 5
4
3
1
5 5
0
5 5
0
Total 15
5
°
Score
5 5
3
2
5
3 3
2
Total 10
4
Score
5 5
4
3
2
1
Total 5
Low Quality 3 to 6 5
Medium Quality 7 to 9
High Quality 10 to 12
Excellent Quality 13 to 14
Perfect 15 14
1
Hole Section
1: TARGETS (max score 5)
Targets met or not COMMENTS
xxxx ft
A
25 - 50 %
<25 %
75-100 %
50 -75 %
Due to inability to steer
Side tracks unplanned
None due to steering
Due to inability to steer
Score (Total / 3) =
2: HOLE GEOMETRY (max score 5)
Dog Leg Severity
all < 3.5° / 100 ft
Round trips unplanned
None due to steering
Torque & Drag
Low torque and drag
Smooth trend
all < 5.5° / 100 ft
all < 7.0° / 100 ft
Percent wellpath in planned reservoir unit
80 -100 %
60 - 80 %
Erratic trend
Score (Total / 2) =
3: PLACEMENT IN RESERVOIR (max score 5)
0 - 20 %
Score (Total / 1) =
Total Quality Score
40 - 60 %
20 - 40 %
Well GEOSTEERING SCORE CARD
Interval:
Depth In: Depth Out: Total Footage:
BHA #:
RSS:
Score
5
4
3
1 1
5
0 0
5
0 0
Total 1
0.3
Score
5
3 3
2
5
3 3
2
Total 6
3
Score
5
4
3
2
1 1
Total 1
Low Quality 3 to 6 1
Medium Quality 7 to 9
High Quality 10 to 12
Excellent Quality 13 to 14
Perfect 15 4.3
B RSS2
COMMENTS
Low quality
Heel and build
Hole Section
1: TARGETS (max score 5)
Targets met or not
25 - 50 %
7/2
8.5"
xxxx ft
<25 % Failure to build
75-100 %
50 -75 %
Due to inability to steer as above
Side tracks unplanned
None due to steering
Due to inability to steer POOh for sidetrack as failureto build
Score (Total / 3) =
2: HOLE GEOMETRY (max score 5)
Dog Leg Severity
all < 3.5° / 100 ft
Round trips unplanned
None due to steering
Torque & Drag
Low torque and drag
Smooth trend
all < 5.5° / 100 ft
all < 7.0° / 100 ft
Percent wellpath in planned reservoir unit
80 -100 %
60 - 80 %
Erratic trend
Score (Total / 2) =
3: PLACEMENT IN RESERVOIR (max score 5)
0 - 20 %
Score (Total / 1) =
Total Quality Score
40 - 60 %
20 - 40 %
4. CONCLUSIONS
GEOSTEERING QUALITY ASSESSMENT
Method (Direct & Indirect Measurements)
• Which variables and sub-variables are measured? How many
together adequately determine overall quality?
• What data is needed to quantify the chosen variables?
• What analysis and interpretation is needed?
• Score and Rank system devised. A score for each interval
and a combined score for the well.
1. Brown, D. 2000 (December). Geosteering: like landing in Fog. AAPG Explorer.
2. Gongora, A. & Smith, G. C. 2012. The Vincent Oil Field – Development of a
thin oil column by geosteering long horizontal wells. 74th EAGE Conf & Exhibn
SPE Europec 2012, Copenhagen, Denmark, 4 – 7 June 2012. P 175.
3. Leikness, S. & Osvoll, I. 2005. Success Factors in Troll Geosteering. Offshore
Tech Conference Houston, Texas, USA. May 2005.
4. Mottahedeh, R. 2005. Horizontal Well Geo-Navigation: Planning, Monitoring
and Geosteering. 6th Canadian International Petroleum Conference, Alberta.
2005-017.
5. Syed Hammad Zafar & Goke, Akinniranyer. 2009. KPI Benchmarking – A
systematic Approach. National Technical Conference & Exhibition, New
Orleans, Louisiana USA. 07 – 04.
Example Case Study
• The wells are from a Chalk Field in the North Sea with a
complex reservoir layering system, comprising chalks of
varying lithification, redeposited chalks, argillaceous chalks
and chert layers, and with numerous microfaults and fractures
and surface flexures.
• The data sets for landing of the wells just above or in the top
of the reservoir and for the whole of the “horizontal” section
were analysed. Only the quality assessment for “Heel and
Build” sections of two wells are illustrated for this poster.
• It is important to note that a low quality score does not
necessarily equal poor performance. The low score may be a
result of a “difficult” well in terms of planned trajectory and
geology. However, in the example well 7/2 the low quality was
mainly due to the RSS BHA (#2) inability to build through
stratigraphical layers compounded by intermittent failure of the
MWD tool signals. This was after a successful build using a
mud motor / bent sub BHA.
• The quality of the geosteering appears to fall as experience is
gained (learning curve) from drilling the sequence of wells. In
fact the heel /build section of the wells become more complex
(turn and build & geology).
THE ROLE OF THE OPERATIONS GEOLOGIST
AND WELL-SITE GEOLOGIST IN GEOSTEERING DATA ANALYSIS
AND THE MEASUREMENT OF GEOSTEERING QUALITY
Dr Stephen Crittenden Poster 2 Geological Society of London Workshop
October 2012 Aberdeen