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.

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 YesYes

YesA2b2 not reached on

buildNo

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 noYes

Yes (BHA#5) NoYes, 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

Ch

an

ge

of

serv

ice

pro

vid

er

GEOSTEERING SCORE CARDWell

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