1. Drilling Engineering_ A Complete Well Planning Approach
----NealJ.AdamsTommie Charrier, Research Associate~~~~!n~c~Z~
Tulsa, OklahomaII
2. Copyright @ 1985 by PennWell Publishing Company 1421 South
Sheridan Road/P. O. Box 1260 Thlsa, Oklahoma 7410] Library of
Congress cataloging in publication data Adams, NeaI. Drilling
engineering. Includes index. I. Oil well drilling. I. Title.
TN87I.2.A33 ]985 ISBN 0-87814-265-72.Gas well drilling. 622'
.33884-1110All rights reserved. No part of this book may be
reproduced, stored in a retrieval system, or transcribed in any
form or by any means, electronic or mechanical, including
photocopying and recording, without the prior written permission of
the publisher. Printed in the United States of America
3. AcknowledgmentsMany people and companies must be
acknowledged for their assistance in the preparation of this book.
Undoubtably, I will faiUo mention all of them. To them I sincerely
apologize for the oversight. . ' Above all else, I must acknowledge
the ladies in my life who tolerated my moodiness. Crystal Adams
gave to this effort in ways that I probably will never know or
understand. My daughters, Donna and Holly, were deprived of a daddy
on many occasions when I felt obligated to write, proofread, or
research. To these ladies, I say "thank you" or "I'm sorry,"
whichever seems mostappropriate..Tommie Charrier must be given
credit for his valuable assistance during the last stages Of the
book. Tommie spent countless houts researching, proofreading, and
checking the problems as well as doing much of the dirt work.
Undoubtably, the completion of this book would have been prolonged
considerably without Tommie's assistance. Thanks to the typists
involved in this effort. Barbara Everett typed the first half of
the book. Karen Trahan, affectionately known as "Giggles," did a
fine job on most of the last half of the book. Cindy Dupont, who
typed my first book several years ago, completed the text. My
publisher must be acknowledged for its faith, advice, and valuable
assistance. Kathryne Pile, PennWell's Editorial Director, has
supported my efforts since she "rescued" my first book several
years ago. Bill Moore, Drilling Editor for the Oil'& Gas
Journal. has been a valuable friend and editor since my first
article was published in OGJ in 1977. Although their editiQg often
bruised my ego, the resultant product was better. For that
improvement, I will always owe them a debt of gratitude. Many
industry personnel provided information or discussions used in this
book. Some are as follows: George Abadjian, Hydril Inc. Kris
Anderson, Tri-Service Drilling John Campbell, Golden Engineering
Inc. Bill Carington, Sweco v
4. viAcknowledgmentsTommie Charrier, Adams and Rountree
Technology Inc. Stan Coburn, Hy~l Inc. Cindy Dupont, Admns and
Rountree Technology Inc. Dave Evans, NL McCullough Inc. B.D.
"Cowboy" Griffith, Wilson Directional Drilling Inc. Richard Hamala,
Hydril Inc. Dennis Hensley, Dennis Hensley & Associates Bill
Ireland, Golden Engineering Inc. Aubrey Kaigler, WESTEC Don
Kallenbak, Tetra Resources Inc. Elmo Lum, Gulf Oil Corporation
Jerry McWilliams, Chromalloy Inc. Bob Meghani, Hydril Inc. Leonard
Morales, N.L. Baroid Bill Moore, Oil & Gas Journal Kris Mudge,
Formerly of Hydril Corp. Stanley Palmer, Gulf Oil Corporation Jim
Pittman, Western Oceanic Inc. Don Remson, Western Oceanic Inc. Dr.
Steven P. Rountree, Drilling Measurements Inc.Evan L. Simmons,Gulf
Oil Corporation.Karen Trahan, Adams and Rountree Technology, Inc.
Les White, Swaco Bob Wilder, Western Cementing Sources Larry
Williamson, Chromalloy Drilling Fluids Ron Young, N.L. Baroid Dr.
Crane Zumwalt, Western Oceanic Inc. Industrial brochures and
manuals provided valuable sources of information. Companies that
provided pertinent items are as follows: Adams and Rountree
Technology Inc. American Petroleum Institute Baker Oil Tools Inc.
Brandt Cameron Iron Works Comet Drilling Inc. Delta Drilling Inc.;
Bill Goodsby Densimix Inc, Alan D. Thibodeaux Diamond M Drilling,
Oksona Pawliw Dresser Atlas, Susan Burt Dresser Magcobar Inc.
Dresser Security Dresser Swaco Inc. Dyna-Drill
5. AcknowledgmentsviiEastman Whipstock Inc., Charles Criss
& Horace Stephens Fluor Drilling Inc., J.R. Fluor II
Gearhart-O~ens Grant Oil Tool Company, Jeff Sebrell Gray Tool Co.
Hughes Tool Co. International Assoc. of Drilling Contractors Kelco
Rotary Inc. Lee C. Moore Corp., J.R. Woolslayer Marathon LeTourneau
MGF Drilling Moran Drilling, Rick Lisnbe NL Acme Tool Co., Dave
Roscher NL Atlas Bradford, Norm Whitaker NL Baroid NL Hycalog NL
Information Services NL McCullough, Dan Chambers NL MWD, Bob Radtke
NL Shaffer NL Sperry Sun NL Well Services Norton-Christensen OMSCO
Industries Inc., Diane Anderson Schlumberger-Analysts Inc.
Schlumberger Inc. Smith Tool Division of Smith International, Ray
Manchester and Lane Peeler Sonat Offshore Drilling Inc., John C.
Cole Sweco Inc. Texas Iron Works Inc. Vallourec Vetco Western
Oceanic, Inc. Wilson Downhole Services WKM Zapata Offshore Inc.,
Linda Romans The American Petroleum Institute and the Society of
Petroleum Engineers must be given credit for information in this
work. These organizations are unparalled and for many years have
been major building blocks in the petroleum industry's growth. In
many ways, my association with the SPE has provided me with a type
of professional growth unattainable from any other source.
6. To My Grandmother Ollie Mae Barrett who has always been a
major source of inspiration since I was a young boy and To My Wife
Crystal Adams who is my best friend and companion as well as the
heart of our family
7. PrefaceMy goal for this book was to prepare a document that
could serve as a guide for most drilling and well planning
applications. I believe it contains a good blend of theory and
commonly accepted practices. In addition, most concepts have been
presented both narratively and with example problems so the
drilling engineer using this book can make good, logical decisions
when special situations arise. Drilling topics must be presented in
some logical format. I chose to discuss each item in this book in
the order in which it would be encountered during well planning and
drilling. For example, since historical drilling data must be
gathered before selecting a casing string, the chapter on drilling
data acquisition precedes c~sing design. For the most part, I
oriented the book toward planning and drilling abnormal pressure
wells. The obvious reason is that they generally pose the most
difficult problems and have higher drilling costs. Subnormal
pressure wells are considered in this book since they have unique
problems. This book does not specifically address drilling problems
in a separate chapter. Instead, I elected to discuss drilling
problems in the context in which they affect casing design,
drilling fluids, etc. In addition, my first book, Well Control
Problems and Solutions, covered many major drilling problems
extensively. Future editions of this current book may contain
separate chapters to address this issue. I have included example
and homework problems in this text. A solution set may be available
from the publisher in the future for the homework problems and the
case study in the Appendix. Approximately three years of my time
has gone into writing this book. I have attempted to develop the
best piece of work that I could while observing the constraints of
time, scope of the text and length of topic discussion. I sincerely
welcome comments from any industry member concerning improvement or
expansion of any topic within the text. xi
8. xiiPreface.I have made significant use of the wealth of
petroleum literature available in the public domain. I apologize to
a particular author(s) if I failed to acknowledge the appropriate
reference at the end of each chapter. This matter will be corrected
in future editions if notified by the appropriate author. Well cost
estimating, Chapter 19, was written in 1982. The prices used as
illustration in this chapter are no longer current. Ironically at
the time of preparing this Preface, the drilling costs in 1984 are
much lower than those in 1982. Undoubtably, this book contains
slight errors that our countless hours of review and proofreading
did not uncover. This chore is one of the most difficult in writing
a book. I will appreciate notification by any industry member of
errors in the text. Above all else, I hope that this book proves
beneficial to the drilling engineers that use it in their everyday
work. Neal Adamsj
9. ContentsPrefaceixAcknowledgmentsxiI. Introduction to Well
Planning1Well Planning Objective, Classification of Well Types,
Fonnation Pressures, Planning Costs, Overview of the Planning
Process2. Data Collection9Offset Well Selection, Data Sources, Bit
Records, IADC Reports, Scout Tickets, Mud Logging Records, Log
Headers, Production History, Seismic Studies3. Predicting Formation
Pressures39Pressure Prediction Methods, Origin of Abnonnal
Pressures, Seismic Analysis, Log Analysis4. Fracture Gradient
Determination97Theoretical Detennination, Field Detennination of
Fracture Gradients xiii
10. Contentsxiv5. Casing Settirig Depth Selection116Types of
Casing and Thbing, Setting Depth Design Procedures6. Hole Geometry
Selection139General Design Procedures, Size Selection Problems,
Casing and Bit Size Selection, Standard Bit-Casing Combinations7.
Bit Planning152Drill Bits, Drag Bits, Rolling Cutter Bits, Diamond
(and Diamond Blank) Bits, Rolling Cutter Bit Design, Watercourses,
Bearing -Lubrication System, Bit Sizes, Bit Body Grading, Bit
Classification, Bit Cones, Diamond Bits, Polycrystalline Diamond
Bits, Drilling Optimization, Matching the Area Average, Bit
Selection, Formation Hardness and Abrasiveness Mud Types,
Directional Considerations, Rotating Systems, Coring, Bit Size8.
Drilling Fluids Selection227Purposes of Drilling Fluids, Types of
Drilling Fluids, Introduction to Drilling Fluids Chemistry, Field
Testing Procedures, General Types of Additives, Specialty Mud
Additives9. Cementing278Purposes of Oil Well Cementing, Cement
Characteristics, Cement Additives, Slurry Design, Cementing
Equipment, Displacement Process, Special Cementing Problems10.
Directional Planning331Purposes of Directional Drilling, Design
Considerations, Calculation Methods, Directional Drilling
Techniques
11. Contentsxv35711. Casing and Tubing ConceptsPipe Body
Manufacturing, Casing Physical Properties, Pipe Connectors38612.
Casing DesignMaximum Load Concept, Gener!ll Casing Design Criteria,
Surface Casing, Intermediate Casing, Intermediate Casing When Used
with a Drilling Liner and the Liner, Production Casing, Special
Casing Design Criteria13. Tubing Design Tubing Design Criteria,
Packer and Seal Arrangements, Producing Conditions Affecting Tubing
Design; Burst, Collapse, and Tension Evaluation14. Completion
Effects on Well Planningand Drilling430 _452Reservoir and
Production Parameters, Surface and Subsurface Completion Equipment,
Types of Completions, Packer Fluids, Completion Factors Affecting
the Well Plan and Drilling15. Drillstring Design488Purposes and
Components, Drillpipe, Drillpipe Tool Joints, Drill Collars,
Stabilization, Drillstring Design, Drill-Collar Selection,
Drillpipe Selection, Lateral Tool Joint Loading16. Rig Sizing and
Selection534Rig Types, Power Systems, Circulating System, Hoisting
System, Derricks and Substructures, Mud Handling Equipment, Rig
Floor Equipment, Blowout Preventers, Rig Site Preparation, Special
MODU Drilling Considerations
12. xviContents65317. Special Drilling LogsTemperature Log,
Radioactive Tracers, Noise Logging, Stuck Pipe Logs, Cement Bond
Logs, Casing Inspection Logs, Mud Logging, MWD, Electromagnetic
Orienting Tool, Ultra-Long-Spaced-Electric Log (ULSEL), Magrane
II67818. HydraulicsPurposes, Hydrostatic Pressure, Buoyancy, Flow
Regimes, Flow (Mathematical) Models, Friction Pressure
Determination, Jet Optimization and Planning, Surge Pressures,
Cuttings Slip Velocity19. Well Cost Estimation:AFE
Preparation740Projected Drilling Time, Time Categories, Time
Consideration, Cost Categories, Tangible and Intangible Costs,
Location Preparation, Drilling Rig and Tools, Drilling Fluids,
Rental Equipment, Cementing, Support Services, Transportation,
Supervision and Administration, Tubulars, Wellhead Equipment,
Completion Equipment'774APPENDICES A-Case study (homework problem)
B-Brine fluid tables C-AFE work sheets D-Drilling equations
E-Drillpipe tables F-Casing and tubing tablesINDEX774 782 800 821
828 847955
13. ChapterIntroduction to Well PlanningIWell planning is
perhaps the most demanding aspect of drilling engineering. It
requires the integration of engineering principles, corporate or
personal philosophies, and experience factors. Although well
planning methods and practices may vary within the drilling
industry, the end result should be a safely drilled, minimum-cost
hole that satisfies the reservoir engineer's requirements for oil
.and gas production. . The skilled well planners normally have
three common traits. They are experienced drilling personnel who
understand how all aspects of the drilling operation must be
integrated smoothly. They utilize available engineering tools, such
as computers and third-party recommendations, to guide the
development of the well plan. And they usually have a "Sherlock
Holmes" characteristic that drives them to research and review
every aspect of the plan in an effort to isolate and remove
potential problem areas.Well PlanningObjectiveThe objective of well
planning is to formulate a program from many variables for drilling
a well that has the following characteristics: . safeminimumcost
usableUnfortunately, it is not always possible to accomplish these
objectives on each well due to constraints based on items such as
geology and drilling equipment, i.e., temperature, casing
limitations, hole sizing, or budget. Safety. Safety should be the
highest priority in well planning. Personnel considerations must be
placed above all other aspects of the plan. In some cases, 1
14. zDrilling Engineeringthe plan must be altered during the
course of drilling the well when unforeseen drilling problems
endanger the crew. Failure to stress crew safety has resulted in
loss of life and burned.or permanently crippled individuals. The
second priority involves the safety of the well. The well plan must
be designed to minimize the risk of blowouts and other factors that
could create problems. This design requirement must be adhered to
vigorously in all aspects of the plan. Example 1.1 illustrates a
case in which this consideration was neglected in the earliest
phase of well planning, which is data collection.Example 1.1 A
turnkey drilling contractor began drilling a 9,000-ft well in
September 1979. The well was in a high-activity area where 52 wells
had been drilled previously in a township (approximately 36 sq mi).
The contractor was reputable and had a successful history. The
drilling superintendent called a bit company and obtained records
on two wells in the section where the prospect well was to be
drilled. Although the records were approximately 15 years old, it
appeared that the formation pressures would be normal to a depth of
9,800 ft. Since the prospect well was to be drilled to 9,000 ft,
pressure problems were not anticipated. The contractor elected to
set lO%-in. casing to 1,800 ft and use a 9.5-lb/gal mud to 9,000 ft
in a 9~8-in. hole. At that point, responsibility would be turned
over to the oil company. Drilling was uneventful until a depth of
8,750 ft was reached. At that point, a severe kick was taken. An
underground blowout occurred that soon erupted into a surface
blowout. The rig was destroyed and natural resources were lost
until the well was killed three weeks later. A drilling consultant
retained by a major European insurance groupconducteda study that
yieldedthe followingresults:.l. All wells in the area appeared to
be normal pressured until 9,800 ft. 2. However, 4 of the 52 wells
in the specific township and range had blown out in the past five
years. It appeared that the blowouts came from the same zone as the
well in question. 3. A total of 16 of the remaining 48 wells had
taken kicks or severe gas cutting from the same zone. 4. All
problems appeared to occur after a severe 1973 blowout taken from a
12,200-ft abnormal pressure zone. Conclusions 1. The drilling
contractor did not research thoroughly the surrounding wells in an
effort to detect problems that could endanger his well or
crews.
15. 3Introduction to Well Planning2. The final settlement by
the insurance company was over $16 million. The incident probably
would not have occurred if the contractor had spent $800 to obtain
proper drilling data as the drilling consultant had done. Minimum
Cost. A valid objective of the well planning process is to minimize
the cost of the well without jeopardizing the safety aspects. In
most cases, costs can be reduced to a certain level as additional
effort is given to the planning (Fig. 1-1). It is not noble to
build "steel monuments" in the name of safety if the additional
expense is not required. On the other hand, monies should be spent
as necessary to develop a safe system. Usable Boles. Drilling a
hole to the target depth is not completely satisfactory if the
final well configuration is not usable. In this case, the term
"usable" implies the following:. .The hole diameter is sufficiently
large so an adequate completion canbe made. The hole or producing
formation is not irreparably damaged.sCJ)o oWell planning
effortFig. 1-1Well costs can be reduced dramatically if proper well
planning is implemented
16. 4DrillingEngineeringThis requirement of the well planning
process can be difficult to achieve' in abnormal pressure, deep.
zones that can cause hole geometry or mud problems.Classification
of Wen Types The drilling engineer is required to plan a variety of
well types, including the following: . wildcatsexploratoryholes
step-outsinfills reentriesGenerally, wildcats require more planning
than the other types. Infill wells and reentries require minimum
planning in most cases. Wildcats are drilled on a certain location
where little or no known geological information is available. The
site may have been selected because of wells drilled some distance
from the proposed location but on a terrain that appeared similar
to the proposed site. The term "wildcatter" was originated to
describe the bold frontiersman who was willing to gamble on a
hunch. Rank wildcats are seldom drilled in today's industry. Well
costs are so high that gambling on wellsite selection is not done
in most cases. In addition, numerous drilling prospects with
reasonable productive potential are available from several sources.
However, the romantic legend of the wildcatter.will probably never
die. Characteristics of the well types are shown in Table 1-1.Table
1-1 WeD Type Characteristics Well TypeCharacteristicsWildcat No
known (or little) geological foundation for site selection.
Exploratory Site selection based on seismic data, satellite
surveys, etc.; no Step-out Infill Reentryknown drilling data in the
prospective horizon. Delineates the reservoir's boundaries; drilled
after the exploratory discovery(s); site selection usually based on
seismic data. Drills the known productive portions of the
reservoir; site selection usually based on patterns, drainage
radius, etc. Existing well reentered to deepen, sidetrack, rework,
or recomplete; various amounts of planning required, depending on
purpose of reentry.
17. Introduction to Well Planning5Formation Pressures The
formation, or pore, pressure encountered by the well significantly
affects the well plan. The pressures may be normal, abnormal
(high), or subnormal (low). (Chapter 3 gives details on pore
pressure and detection.) Normal pressure wells generally do not
create planning problems. The mud weights are in the range of
8.5-9.5 lb/gaI. Kicks and blowout prevention problems should be
minimized but not eliminated altogether. Casing requirements can be
stringent even in normal pressure wells deeper than 20,000 ft due
to tension/collapse design constraints. Subnormal pressure wells
may require setting additional casing strings to cover weak or low
pressure zones. The lower-than-normal pressures may result from
geological or tectonic factors or from pressure depletion in
producing intervals. The design considerations can be demanding if
other sections of the well are abnormal pressured. Abnormal
pressures affect the well plan in many areas, including the
following: . casing and tubing design mud weight and type selection
casing setting depth selection cement planningIn addition, the
following problems must be considered as a result of high formation
pressures: kicks and blowouts differential pressure pipe
stickinglost circulation resulting from high mud weights heaving
shaleWell costs increase significantly with geopressure. Because of
the difficulties associated with high-pressure exploratory well
planning, most design criteria, publications, and studies have been
devoted to this area; the amount of effort expended is justified.
Unfortunately, the drilling engineer still must define for himself
the planning parameters that can be relaxed or modified when
drilling normal pressure holes or well types such as step-outs or
infills.PlanningCostsThe costs required to plan a well properly are
insignificant in comparison to the actual drilling costs. In many
cases, less than $1,000 is spent in planning a $1 million well.
This represents VIO 1% of the well costs. of
18. Prospect developmentMud plan.Cement plan Bit
program~------Drillstring designRig sizing and selectionFig.
1-2Flow path for well planning
19. 7Introduction to Well PlanningUnfortunately, many
historical instances can be used to demonstrate that well planning
costs were sacrificed or avoided in an effort to be cost conscious.
The end result often is a final well cost that exceeds the amount
required to drill the well if proper planning had been exercised.
Perhaps the most common attempted shortcut is to minimize data
collection work. Although good data can normally be obtained for
less than $2,000-$3,000 per prospect, many well plans are generated
without the knowledge of possible drilling problems. This lack of
expenditure in the early stages of the planning process almost
always results inhigher-than-anticipatedrillingcosts. d.Overview of
the Planning Process Well planning is an orderly process. It
requires that some aspects of the plan be developed before
designing other items. For example, the mud density plan must be
developed before the casing program since mud weights have an
impact on pipe requirements. Fig. 1-2 illustrates a commonly used
flow path for a well plan. Bit programming can be done at any time
in the plan after the historical data have been analyzed. The bit
program is usually based on the drilling parameters from offset
wells. However, bit selection can be affected by the rimd plan,
i.e., the performance of PCD bits in oil muds. In addition, bit
sizing may be controlled by casing drift diameter requirements.
Casing and tubing should be considered as an integral design. This
fact is particularly valid for production casing. A design criteria
for tubing is the drift diameter of the production casing, whereas
the production casing can be affected adversely by the
packer-to-tubing forces created by the tubing's tendencies for
movement. Unfortunately, these calculations are complex and often
neglected. The completion plan must be visualized reasonably early
in the process. Its primary effect is on the size of casing and
tubing to be used if oversized tubing or packers are required. In
addition, the plan can require the use of highstrength tubing or
unusually long seal assemblies in certain situations. Fig. 1-2
defines an orderly process for well planning. This process must be
altered for various cases. The flow path in this illustration will
be followed, for the most part, throughout this text.References
Adams, N.J. Unpublished material from consulting work, relating to
legal expert witness studies.
20. 8DrillingEngineering Adams, N.J. WeLL ontrol Problems and
Solutions. Tulsa: PennWell, 1979. C Moore, Preston. Drilling
Practices Manual. Tulsa: PennWell, 1974. Records, Louis R., Sr.
Personal discussions, 1981-1983.
21. Chapter2Data CollectionThe most important aspect of
preparing the well plan, and subsequent drilling engineering, is
determining the expected characteristics and problems to be
encountered in the well. A well cannot be planned properly if these
expected environments are not known. Therefore, the drilling
engineer must initially pursue various types of data to gain
insight used to develop the projected drilling conditions.Offset
Well Selection The drilling engineer is usually not responsible for
selecting well sites. However, he must work with the geologist for
the following reasons: I. Develop an understanding of the expected
drilling geology 2. Define fault block structures to help select
offset wells that should be similar in nature to the prospect well
3. Identify geological anomalies as they may be encountered in
drilling the prospect well A close working relationship between
drilling and geology groups can be the difference between a
producer and an abandoned well. An example of geological
information that the drilling group may receive is shown in Fig.
2-1. The geologists have found significant production from E.B.
White #2. Contouring the pay zones has yielded the contour map in
Fig. 2-1. The prospect well should encounter the producing
structure at the approximate depth as the E.B. White #2. A
trimetric plot (Fig. 2-2) is useful as a conceptual tool. It adds a
third dimension not presented in Fig. 2-1. The drilling engineer
can view the projected targets and develop a better understanding
of the goal. 9
22. 10DrillingEngineeringFig.2-1Contour mapMaps that show the
surface location of offset wells are available from commercial
cartographers (Fig. 2-3). These maps normally provide the well
location relative to other wells, operator, well name, depth, and
type of produced fluids. In addition, some maps contour regional
formation tops.
23. Data Collection11Fig. 2-2Trimetric plotThe map in Fig. 2-3
is defined according to township, range, and section. In some rare
cases, a specific township and range may have several hundred
sections. This scheme is used throughout the United States except
in Texas where the wells are u.sually located by county and
abstract (Fig. 2-4). Selecting the offset wells to be used in the
data collection is important. Using Fig. 2-3 as an example, assume
that a 13,000-ft prospect is to be drilled in the northeast comer
of Section 30, TI8S, RI5E. The best candidates for offset analysis
are as follows:
24. 12Drilling Engineering...,....... e..,.'.' t. /' .10400Fig.
2-3Section map illustrating townships, ranges and sections.
25. DataCollection13Fig. 2-4.Texas map illustrating the
abstractsOperatorShell, 15,000ft.Union of California, 14,562 ft
Huber, 12,521 ft Exchange, 12,685 ft Houston Oil and Minerals,
17,493 ftSection (TI8S, RISE) 30 29 21 19 19Although these wells
were selected for control analysis, available data from any well in
the area should be analyzed.Data Sources Sources of data should be
available for virtually every well drilled in the U.S. Drilling
costs prohibit the rank wildcatting that occurred years ago.
AI-
26. 14DrillingEngineeringthough wildcats are currently being
drilled, seismic data, as a minimum, should be available for pore
pressure estimation. . Common types of data used by the drilling
engineer are as follows:. . . .bit records mud records mud loggjng
recordsIADC drilling reports scout tickets log headers production
history seismic studies well surveysgeological contours' databases
or service company filesEach type of record contains valuable data
that may not be available with other records. For example, log
headers and seismic work are useful, particularly if these data are
the only refe~ence sources for the well. Many sources of data exist
in the industry. Unfortunately, some operators falsely consider the
records confidential, when in fact the important information such
as well testing and production data becomes public domain a short
time after the well is completed. The drilling engineer often must
assume the role of "detective" to defin~ and locate the required
data. Sources of data include bit manufacturers and mud companies
who regularly record pertinent relative information on well recaps.
Bit and mud companies usually make this data available to the
operator. Log libraries provide log headers and scout tickets. And
inte1J1alcompany files often contain drilling reports, IADC
reports: and mud logs. Many operators will gladly share old offset
information if they have no current leasing interest.Bit Records An
excellent source of offset drilling information is the bit record.
It contains data relative to the actual drilling operation. A
typical record for a relatively shallow well is shown in Fig. 2-5.
The heading of the bit record provides information such as the
following: . . operatorcontractor rig number well
locationdrillstringcharacteristics pump data
27. :0IN V.SA~4-!-'>' -1'1...~,('-jP.1- L-'".......~
"'---Bit record for a shallow wellBIT CONDITION CODE: RP. REPAIRED
RR-RRUhFig. 2-5
28. 16Drilling EngineeringIn addition, the bit heading provides
dates for spudding, drilling out from under the surface casing
(U.S.), intermediate casing depth, and reaching the bottom of the
hole. The main body of the bit record provides the following
details:. . . . . . .number and type of bitsjet sizes footage and
drill rates per bit bit weight and rotary operating conditionshole
deviation pump datamud properties dull bit grading commentsThe
vertical deviation is useful in detecting potential dogleg
problems. Comments throughout the various bit runs are informative.
Typical notes such as "stuck pipe" and "washout in drillstring" can
explain why drilling times are greater than expected. Drilling
engineers often consider the comments section on bit (and mud)
records just as important as the information in the main body of
the record. Bit grading data can be valuable in well planning if
the operator assumes the observed data are correct and
representative of the actual bit condition. The bit grades can
assist in the preparation of a bit program for the prospect well by
identifying the most (and least) successful bits in the area. Bit
running problems such as broken teeth, gauge wear, and premature
failures can be observed and preventive measures can be formulated
for the new well. Drilling Analysis. Bit records can provide
significantly more useful data if the raw information is analyzed.
Plots can be prepared that detect lithology changes arid trends.
Cost-pef-foot analyses can be made. Crude, but often useful, pore
pressure plots can be prepared. Raw drill-rate data from a well and
an area can detect trends and anomalies. Fig. 2-6 shows drill-rate
data from a well in South Louisiana. A decreasing drill rate is
expected as shown. Sudden changes in the trend might have suggested
some anomaly, as in Fig. 2-7. This illustration is the composite
drill rates for all wells in a South Louisiana township and range.
The trend change at approximately 10,000 ft was later defined as
the entrance into the massive shale section. Cost-per-foot studies
are useful in defining optimum, minimum-cost drilling conditions. A
cost comparison of each bit run on all available wells in the area
will identify the bit(s) and operating conditions that yield
minimum drilling costs. The drilling engineer provides his expected
rig costs, bit costs,
29. D~ILL~ATEVS.DEPTH PLDT!,tElL : J.D. SITTIG ND. I OPE~ATO~'
STONE OIL COIWANY STATE' LA TOWNSHIP' 7> ~AN6E' IW o + ! ! ! !
2000 + !40006000 DEPTH'Fn 8000+SECTION' 28+++.I I.+I I+ I.! ! ! I
+I+++ ! !! I !+....I I I.+t I t I10000 + I I I I 12000 + oFig.
2-6++ 30+ + 60 90 DRILL RATE (FT/~)+ 120+ I!!O+ I I I I + 180Raw
drill rate data from a South Louisiana well (Courtesy of Adams and
Rountree Technology)Table 2-1Average Trip Times Hole (Bit)Size,
in.Depth, ft 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000
18,000 20,000Small 8.75)1.5 2.5 3.5 4.7 5.8 7.0 8.25 9.75 11.00
11.8MediumLarge(8.75-9.875)(> 9.875)3.0 4.2 5.4 6.5 7.25 8.25
9.25 10.25 11.25 12.254.5 5.75 7.0 8.0 9.0 10.25 11.50 12.50 13.75
15.0
30. 18DrillingEngineering o+++++! ! ! !4000.+! ! ! ! 8000 + ! !
! ! 12000 + ! ! ! DEPTH (FD ! 16000 + ! ! ! ! 20000 + ! ! ! !
24000+ oFig. 2-7+ .+ ! ! ! ! ++ ! ! ! ! + ! ! ! ! + ! ! !+ 30+ 60
DRILL+ 9C RATE (FT/HR)+ 120+ 150+ ! ! ! ! + 180Composite drill rate
data for a South Louisiana region. A significant trend change is
observed at approximately 10,000 ft.and assumed average trip times.
The cost-per-foot calculations are completed with Eq. 2.1: $/ft
Where: $/ft CB CR TR TT Y(2.1)cost per foot, dollars bit cost,
dollars rig cost, dollars/hr rotating time, hr trip time, hr
footage per bit runA cost-per-foot analysis for Fig. 2-5 is shown
in Fig. 2-8. Trip times should be averaged for various depth
intervals. Several operators have conducted field studies to
develop trip-time relationships (see Table 2-1). The most
significant factors affecting trip time include depth and hole
geometry, i.e., number and size of collars, and downhole tools.
Table 2-1 can be used in the cost-per-foot equation (Eq. 2.1).
31. Data Collection19o1,0002,000 IIThe intervalcost from
0-8,100 ft is $85,318tMoor4,000g;c '5.CDc5,0006,000II7,000tI
I8,0009,00051015202530$/ftFig. 2-8Cost per foot plot for the bit
run in Figure 2-5Example 2.1 Calculate the cost per foot and the
cumulative section costs for the following data; assume a rig cost
of $12,OOO/day.
32. 20DrillingEngineering Depth In, ft Well A Well BDepth Out,
ftRotating Time, hrBit Cost, $6,000 7,150 6,0007,150 8,000 8,00023
20 421,650 1,650 2,980Determine which drilling conditions, Well A
or Well B, should be followed in the prospect well. .Use a
9.875-in. bit..Solution: 1. The hourly rig cost is $500. Trip times
from 7,150 and 8,000 ft are 6.0 hr and 6.50 hr, respectively. 2.
The cost per foot for Bit #1 on Well A (6,000-7,150) ft is:$/ft =Co
+ C~ TIi + CRTT Y 1,650 + (500)(23) + (500)(6.0) 1,150=
$14.04/ftFor Bit #2: $/ft = 1,650 + (500)(20) + (500)(6.50)
850=$17.53/ft3. The cumulative cost for Well A is: Bit #1 Bit
#2$14.04/ft x 1,150 ft = $16,146.00 $17.53/ft x 850 ft = $14,900.50
Total = $31,046.504. The cost per foot for Well B is: $/ft2,980 +
(500)(42) + (500)(6.5) 2,000= $13.62/ft The section cost is
$27,230. 5. Since the cost per foot is lower in Well B, the
drilling conditions from Well B should be implemented on the
prospect well.
34. 22Drilling EngineeringThe dc-exponent method of pore
pressure calculations has been applied successfully on bit records.
Although the quantitative results should be viewed with caution,
the method is useful in many cases. The quality of the results
increases in formations with fewer sand sequences (cleaner shale).
A variety of pressure prediction techniques are covered in Chapter
3. The data required must be gathered from offset well records
(Fig. 2-9).Mud Records Drilling mud records describe the physical
and chemical characteristics of the mud system. The reports are
usually prepared daily. In addition to the mud data, hole and
drilling conditions can be inferred. Many drilling personnel
believe that the mud record is the most important and useful
planning data. Mud engineers usually prepare a daily mud check
report form. Copies are distributed to the operator and drilling
contractor. The form, Fig. 2-10, contains current drilling data
such as the following: . well depth bit size and numberpit volume
pump data solids control equipmentdrillstringdataThe reportalso
containsmud propertiesdata such as the following: . mud weight pH
funnel viscosity plastic viscosityyield point gel strength. . . .
chloride content calcium content solids content cation exchange
capacity (or MBT)fluid loss solids contentAn analysis of these
characteristics taken in the context of the drilling conditions can
provide clues to possible hole problems or changes in the drilling
environment. For example, an unusual increase in the yield point,
water loss, and chloride content suggests that salt (or salt water)
has contaminated a freshwater mud. If kick control problems had not
been encountered, it is probable that salt zones were drilled. A
composite mud recap form, Fig. 2-11, is usually prepared when the
well is completed. The recap contains a daily summary of the
properties. It may also include important comments pertaining to
hole problems. Drilling Analysis. Daily reports prepared by the mud
engineer are useful in generating depth vs days plots (Fig. 2-12).
These plots are as important to
35. CollectionData23NLBaroid ICONTFlACT~.... _J;5J DDAESS}) e s
/t:1f/ O,L C..AOOAmAEPoATFDAMA~".Depth tfll Weight 0 _Ippgl D
Ilb/eu ht Mud Gt"8dillnt IpSi/hI Funnel Viscosity tMeJql) API .1
~lticViscosi1Ycplt_Yield Point (11)/100 sq hi Get St,.ngthIIbl100
tq fll 10 secJ10 rninPlpH 0 Strip Meter Filtr818 API (ml/3D mini
API HP.HT Filtr'" Cite Thidr:,,",Imll30minlc..e.L:.'190:nnd In API
)Q.HP.HTDAlkllinily. Mud IPm)~=!..'YA/~
I.uL-p"",,-t+AAllUllini1Y.Flluate !PffMtl C8lciumDppm Sand
ContentC,-,~~.~~~~ :3t:>~ . . ~~ tt /6.o4/rI.PD(')1f/fIlA.- -'
f.~ ~.CO,;1.:('~.EXTRA COPY THE RECOMMENDATIONS MAM HEAIEON SHALL
HOT 81: CONSTRUE.D A5- AUTHORIZING THE: INFRINCIEMENT Of" ANY VALID
PATENT, AND AAIE ""DE WITHOUT ASSU TION 0" ANY LIABILITy If L
INDUSTRIES, INC. OR ITS AGENTS, AND ARIE STATIEMIENTS 0.. O~INION
ONLY.REPRESENTATIVE C,hllR1!.,9A/ MOBILEUNITFig.2-10IHOMEADOAESS
'-/IF. WAREHOUSE LOCATION-~EPHr9Icf'''').bD''Daily mud check report
form (Courtesy of NL Baroid)
36. OATf.J!d1)~ffi}BAR 0 I 0 0 I V'S, 0 N NAnONAl lEAD COMPAIiY
DRILLINGMUDRECORD
~~~:;:...~~!-~o'W~~_'__I__U5D3_ho.~k...'I"",.,,,~,,;';I-'II~11
.0110002 ~D:~.C~e.ny_ ':'.Iwol..I~ :. I1i 1121.0.11III.'OIlllT
"''''''LYS'SCOMPANV---EaD American qll WEt' Touebet.~
CONTRAcrO~!:.J1.!g. UI,,,,.,;;'1 pftt 'IUItAU -.-1. BAAOIO
~~=_~.~~I22..1eC:'l~2...J.!012Q-2~G 10". I ct>"'_ "" I I...
10/,.. VISCOSITY tU , ,., "" "0. .." I ."r. I WI-'I tLO. .."',,,,,,
1901 I cp Py1'1''' Ie n"", 1. !r.GiIBW"" .L .4 1s.c.1 ...
10...:..,_. $'!.,, -150'0 NaCI Oil 'L,0.,. NaCI Alcohol 't!..."'
"'- "'AlluviuM Methane AiroFig.3-10Velocity ranges frequently
encountered in sedimentary sections (After Fertl)
63. Predicting Formation Pressures51Seismic data analysis
methods are based on the elementary reflection analysis summarized
by Pennebaker. Let SS represent the earth's surface (Fig. 3-11).
Assume shot point 0 is at the surface. When explosives at the shot
point are detonated, acoustic energy is created in the form of
compressional waves. This seismic energy moves equally in all
directions. Energy traveling vertically strikes the subsurface
plane RR and is reflected back to the surface SS along vertical
line OPO. Energy from the shot also propagates along paths diagonal
to plane RR in the subsurface (Le., path OT) and is reflected back
to the surface along path TW. The time required for the energy to
travel the two-way paths is recorded by the geophones at points 0
and W, separated horizontally by distance X. The average velocity,
V, can be computed with Eg. 3.2: (3.2) The depth to the reflecting
bed can be determined from Eg. 3.3: (3.3) The interval velocity
from seismic profiles is the reciprocal of interval travel time.
The reciprocated values can be plotted vs depth to indicate
thes0-.xsv Rp, II I1,' 0'Fig. 3-11, ,-R"II, ,,,,','",'Concept of
the elementary reflection principle (After Pennebaker)
64. Drilling Engineering52presence of abnormal p.ressures. A
normal environment exhibits decreasing porosity as compaction
occurs. Therefore, the travel times should decrease. An abnormal
pressure zone has greater-than-normal porosities for the specific
depth and causes higher travel times. Fig. 3-12 illustrates a
seismic and sonic plot for an abnormal pressure well. Quantitative
methods for interpreting seismic (and sonic) data are presented
later in this chapter.23I...Jllnte-gratedI/1sonic4 08 1io II5
(actual). r T/ overpresSAJrfL... 6 Tlove-pressure
--I/lf/(p-edicted)f7"'/alI20Fig. 3-12J>IIIJ .Comparison of
seismically derived transit travel time and actual velocity data in
a well (Courtesy of the Society of Petroleum Engineers of
AIME)
65. Predicting Formation Pressures53Log Analysis Log analysis
is a common procedure fo~ pore pressure estimation in both offset
wells and the actual well drilling. New MWD
(measurement-while-drilling) tools implement log analysis
techniques in a real-time drilling mode. The analysis techniques
use the effect of the abnormally high porosities on rock properties
such as electrical conductivity, sonic travel time, and bulk
density. Both the resistivity (or reciprocated conductivity) log
and the sonic log presented here are based on one of these
principles. Note, however, that any log dependent primarily on
porosity for its responses can be used in a quantitative evaluation
of formation pressures. The resistivity log was originally used in
pressure detection. The log's response is based on the electrical
resistivity of the total sample, which includes the rock matrix and
the fluid-filled porosity. If a zone is penetrated that has
abnormally high porosities (and associated high pressures), the
resistivity of the rock will be reduced due to the greater
conductivity of water than rock matrix. The expected response can
be seen in Fig. 3-13. Fig. 3-13 illustrates several important
points. Since the high formation pressures were originally
developed in shale sections and later equalized the sand zone
pressures, only the clean shale sections are used as plotting
points. This excludes sand resistivities, silty shale, lime or
limey shale, or any other type of rock that may be encountered. As
the shale resistivities are selected and plotted, a normal trend
line should develop prior to entry into the pressured zone. Upon
penetrating an abnormal pressure zone, a deviation or divergence
will be noted. The degree of divergence is used to estimate the
magnitude of the formation pressures. This concept of the
development of the normal trend and noting any divergence will be
used with most pressure detection techniques. An actual field case
can be seen in Fig. 3-14. The impermeable shale section was entered
at about 9,500 ft. Although this section contained normal pressure
from 9,500-9,800 ft, as evidenced by the increasing resistivity of
the normal trend, the reversal can be seen from 9,800-10,900 ft.
The mud weight was 9.0 lb/gal at 9,500 ft but was increased to 13.5
lb/gal at 10,900 ft. A plot of the key shale resistivity points is
shown in Fig. 3-15. Hottman and Johnson developed a technique based
on empirical relationships whereby an estimate of formation
pressures could be made by noting the ratio between the observed
and normal rock resistivities. Their data points, shown in Table
3-3, were used to construct the curve in Fig. 3-16. As they
explained, the following steps are necessary to estimate the
formation pressure. 1 The normal trend is established by plotting
the logarithm of shale resistivity vs depth. 2 The top of the
pressured interval is found by noting the depth at which the
plotted points diverge from the trend. Text continued p. 58
67. , ,.t I I d:+-ttT1 II,'q-j: i~,Ii!-d '. ..l dt :10-_.I :
:I,;'1 '_.L, ,I '! .Fig. 3-14f::-;:;..~_! . I:.';' . .
.Illustration of an electric log from' a well in which the
deposition of an impermeable shale barrier generated abnormal
pressures in the lower intervals. In this well, the barrier is from
9,500 ft9,700 ft.
68. 56Drilling Engineering'- "9,500""-9,600, -, , I I9,700+I I
Ig.: Q. 9,800+ I I(I) CII~ 9,900 /) / / / /10,000/10,100I 10,200 _
0.7f0.8////II I0.9I1.01.11.2Resistivity,ohmmeters ~Fig.3-15Shale
resistivities from the.Iog shown in Figure 3-14 are plotted vs
depth. Note the departure from the normal trend line at 10,000
ft.
69. 57Predicting Formation PressuresTable 3-3 Formation
Pressures and Shale Resistivity Ratios in Overpressured
MiQcene/Oligocene Formation, U.S. Gulf Coast Area Parish or County
and StateWellOffshore 81. Mary, La.A B B C D E FJefferson Davis,
La.G HCameron, La. Iberia, La.I JLafayette, La.KCameron, La.
Terrebonne, La.L M N 0Jefferson, Tex. 81. Martin, La. Cameron, La.P
Q R81. Martin, La. Cameron, La. Cameron, La.Depth ft 12,400 10,070
10,150 13,100 9,370 12,300 12,500 14,000 10,948 10,800 10,750
12,900 13,844 15,353 12,600 12,900 11,750 14,550 11,070 11,900
13,600 10,000 10,800 12,700 13,500 13,950Pressure psiFPG*
psi/ftShale resistivity ratio** Om10,240 7,500 8,000 11,600 5,000
6,350 6,440 11,500 7,970 7,600 7,600 11,000 7,200 12,100 9,000
9,000 8,700 10,800 9,400 8,100 10,900 8,750 7,680 11,150 11,600
12,5000.83 0.74 0.79 0.89 0.53 0.52 0.52 0.82 0.73 0.70 0.71 0.85
0.52 0.79 0.71 0.70 0.74 0.74 0.85 0.68 0.80 0.88 0.71 0.88 0.86
0.902.60 1.70 1.95 4.20 1.15 1.15 1.30 2.40 1.78 1.92 1.77 3.30
1.10 2.30 1.60 1.70 1.60 1.85 3.90 1.70 2.35 3.20 1.60 2.80 2.50
2.75AfterHottmanand Johnson,1965 *Formation fluid pressure
gradient. **Ratio of resistivity of normally pressured shale to
observed resistivity of overpressured shale: R",{n/R'h{ob)'
70. 58Drilling Engineering0.4 0.5~ .~ 0.6 c6It ....~ 3! Q)0.7,.
""....'" ..0.8 0.9 1.0 1.0Fig. 3-16~ "0 ::;]14.0. . ..........a:a;
C):c12.0... ... t10.0t---1.5 2.0 3.0 4.0 Normal-pressured
Rsw'observed RShEc. 16.0 ~ Q).'S CTw 18.05.0Empirical correlation
of fonnation pressure gradients vs a ratio of nonnal to observed
shale resistivities (After Hottman and Johnson)3 The pressure
gradient at any depth is found as follows: a. The ratio of the
extrapolated nonnal shale resistivity to the observed shale
resistivity is detennined. b. The fonnation pressure corresponding
to the calculated ratio is found from Fig. 3-16.Example 3.2 Plot
the following resistivity data on semilog paper. Where does the
entrance into abnonnal pressures occur? Use the Hottman and Johnson
method to compute fonnation pressures at each 1,0OO-ftinterval
below the entrance into pressures. Resistivity, ohm-m 0.54 0.64
0.60 0.70 0.76Depth, ft 4,000 4,600 5,600 6,000 6,400
71. 59Predicting Formation Pressures 0.60 0.70 0.74 0.76 0.82
0.90 0.84 0.80 0.76 0.58 0.45 0.36 0.30 0.28 0.29 0.27 0.28 0.29
0.307,000 7,500 8,000 8,500 9,000 9,700 10,100 10,400 10,700 10,900
11,000 11,100 11,300 11,600 11,900 12,300 12,500 12,700
12,900Solution: 1. 2. 3. 4.Plot the data as shown in Fig. 3-17. The
estimated entrance into abnormal pressure occurs at 9,700 ft.
Extrapolate the normal trend established between 8,000 and 9,700
ft. The observed and extrapolated resistivities at the bottom are
0.30 and 1.60 ohm-m, respectively. 5. Compute the ratio of RNonnal
and Robserved (Rn) (Rob): R='&' Rob= 1.60 0.30 = 5.333 6. Using
Fig. 3-16 from Hottman and Johnson, the formation pressure
associated with a ratio of 5.33 is approximately 18.0 Ib/gal.
Overlays. Subsequent to the Hottman and Johnson approach,
unpublished techniques were developed that used an overlay or
underlay for a quick evaluation of formation pressures. The overlay
(or underlay) contains a series
72. 60Drilling
Engineering01.,4,0005,0006,0007,0008,0009,00010,000"' Entry into
abnormalpressures L....... o#P"11,000lxtrapolated
normaltrend(tt''f:12,00013,00014,0000.10.20.3Fig. 3-170.4 o.s
0.60.8 1.0Resistivity plot for Example 3.2
73. Predicting Formation Pressures61of parallel lines that
represent formation pressure expressed as mud weight (Fig. 3-18).
The overlay is shifted left and right until the normal pressure
line is aligned with the normal trend. Formation pressures are read
directly from a visual inspection ofthe location of the resistivity
plots within the framework of theparallel lines. As an example, the
data from Example 3.2 were plotted in Fig. 3-19 and the overlay was
used to estimate the formation pressure. Different types of
overlays have been developed for pressure determinations. Some are
used with resistivity or conductivity curves, while others are used
with sonic logs. In addition, overlays have been developed for the
various geological ages for each log type. There are many pitfalls
to avoid when using an overlay. Most can be shifted left or right
but are depth fixed and therefore cannot be moved vertically.
Overlays are generally developed for one scale of semilog paper and
cannot be interchanged. This means a different overlay design if
paper sizes must be changed. Another common mistake when using the
resistivity overlay is an attempt to use it for conductivity values
by turning it over. In addition, overlays do not account for
abnormal water salinity changes. When these changes are
encountered, different techniques must be used that normalize the
salinity effect. Salinity Changes. The Hottman and Johnson
procedure, as well as the overlay techniques, assume that formation
resistivities are a function of the following variables:. . .
.lithology fluid contentsalinity temperature porosityThe
proceduresmake the followingassumptionswithrespectto
thesevariables:. . . . lithology is shale shale is water
filledwater salinity is constant temperature gradients are
constantporosity is the only variable affecting the pore
pressureFormations with varying water salinities can prevent the
reliable use of the Hottman and Johnson technique. Foster and
Whalen developed techniques for predicting formation pressure in
regions that have salinity variations. Their techniques have proved
successful and can be applied universally, although the complexity
associated with their use prevents wide acceptance. New
computerized applications help make the technique more useful.
76. 64Drilling EngineeringThe Foster and Whalen method is based
on a formation factor, F, and its relationship to the shale
resistivity and formation water resistivity: (3.4) Where: F =
formation factor, dimensionless R.. = shale resistivity, ohm-m Rw =
formation water resistivity, ohm-m The shale resistivity, Ro, is
read directly from the log. The water resistivity, Rw, is computed
from the mud filtrate resistivity, Rmr.The SP deflection is
computed from the shale base line. The formation pressures are
calculated from a plot of formation factors and the depth
equivalent approach, as previously presented. Example 3.3 will
illustrate the procedures "requiredto calculate Rwand F.Example 3.3
Use the following log data to calculate F and Rw.Assume that all
bed thickness corrections have been made. Ro = 0.980hm-m SP = - 87
mv (deflection from shale base line) temperature= 190F at 8,000 ft
depth of interest = 8,000 ft Rmr= 0.40 ohm-m at 90F Solution: I.
The SP deflection from the shale base line is used with Fig. 3-20
to obtain the ratio of Rmr.lRwc. From Fig. 3-20, a value of - 87 mv
yields 10.5 for the ratio. 2. The resistivity of the mud filtrate,
Rmf,is 0.40 ohm-m at 90F. It must be converted to an equivalent
value, Rmrc,at 190F with Fig. 3-21. From Fig. 3-21, the Rmrc 0.195
ohm-m. is 3. Combining steps I and 2:Rwc= 0.0185 ohm-m
77. Predicting Formation Pressures654. Fig. 3-22 is used to
convert Rweto Rw. or 0.028 ohm-m.5.(3.4)_ 0.98 - 0.028= 35 The SP
deflection and resistivity values should be corrected for bed
thickness and its relationship to the logging tool. (These
corrections are beyond the scope of this text.) Failure to make the
corrections will not be significant in many cases.Rwe
DETERMINATIONFROM THE SSP(CLEAN FORMATIONS) 4030 20 15 OW10.510 Omf
8 6 Rmfe4Rwe3 2 1.5 I .8 .6 .5 43+60, +40+ 200- 20-40STATICFig.
3-20-60 SP.-801 -100 -120 -140 -160 -180 -87
(millivolts)Rwedetermination from the SSP (Courtesy of
Schlumberger)
78. 66Drilling EngineeringFonnation pressure calculations are
made by defining the depth in the nonnal pressure region that has a
fonnation factor, F, equivalent to the deeper depth of interest.
The upper depth is defined as the equivalent depth, De. Eq. 3.5
describes the pressure relationships: DG Where: D De G 1.0 psi/ft=
= = ==0.465 psi/ft (De) + (D-De) (1.0 psi/ft)(3.5)deep depth of
interest, ft equivalent depth, ft fonnation pressure gradient,
'psi/ft at D assumed overburden stress gradientIf the depths D and
De are known, the fonnation pressure gradient, G, is computed as
follows:G=(1.0 psi/ft)D - 0.535De D(3.6)Example 3.4 The following
log data were taken from a well that is suspected to have
significant salinity variations in the fonnation fluids. Use the
Foster-Whalen method to calculate fonnation pressures at each of
the given depths. Assume that all appropriate bed thickness
corrections have been made to the log values. Estimated fonnation
temperatures have been previously calculated from the temperature
tools on the logging runs and are shown in the following list.
Data: Depth, ft 3,900 5,400 6,900 7,700 8,900 9,700 10,300 10,700
10,850Temperature, of 114 135 162 170 191 201 211 218 221Observed
Resistivity, ohm-m 0.76 0.76 0.84 0.96 0.99 1.23 1.02 0.93 0.73SP
Deflection, mv -70 -76 -78 -85 -90 -87 -90 -94 -90
79. ;; 0 ... .NoCIorol.l/oolCONCENTRATION~
+I.::~10TSOIppftl_017SoF_I! .. ~ . g } .. I II II . .Ii .
188i88.8.8.8 II IRESISTIVITYGRAPH20FOR NoCI75SOLUTIONS.0 40 100 ...
'"80 12'80 '" ""0 '" 70 c: 804-175 80.2100110 12050'80 140 .eo 300!
e178 200t t. ."a 0RESISTIVITYOFn_n'.n.,,_........-.-..-.. .
80. 68Drilling EngineeringDepth, ft 11,400 12,000 12,600
12,800Temperature, of. 239 250 261 270Observed Resistivity, ohm-m
1.30 1.70 2.08 1.03SP Deflection, mv -60 -57 -38 -55Logging runs:
Depth, ft 10,300 11,400 12,800Rmfat Temperature, ohm-m 0.65 at 90F
0.89 at 80F 1.03 at 90FSolution: (The actual calculation procedures
will be shown for the 12,8oo-ft depth. Results for all depths are
shown in Table 3-4.) 1. The SP deflection from the shale base line
at 12,800 ft is - 55 mv. From Fig. 3-20, a-55 mv value at 270F
correlates as follows: Rmf(c) 3.77 = Rw(c)2. The resistivity of the
mud filtrate (Rmr)at 12,800 ft is 1.03. Using Fig. 3-21, this value
is corrected from 900Pto the bottom-hole temperature of 270F: 1.03
ohm-m at 90F-0.34 ohm-m at 2700P3. The results from steps 1 and 2
are combined: Rmnc)= 3.77 Rw(c)0.34 = 3.77 Rw(c)Rw(c) = 0.090 4.
Convert Rw(c)to Rw (water resistivity) with Fig. 3-22:Rw =
0.086
81. 69Predicting Formation Pressures 5. The formation factor,
F, is computed from Ro and Rw:_1.03=12- 0.0866. The values for Ro,
Rw, and F are plotted in Fig. 3-23. 7. A vertical line is
constructed from the formation factor, F, at 12,800 ft (F = 12)
until it intersects the normal trend line in the shallow sections.
The points of intersection is defined as the equivalent depth, or
4,800 ft in this case. 8. The formation pressure at 12,800 ft is
computed with Eq. 3.6:=(1.0 psi/ft)D - 0.535 De=G(12,800 ft) (1.0
psi/ft) - 0.535 (4,800 ft) 12,800 ftD= 0.799 psi/ft = 15.4
Ib/galTable 3-4ComputedDepth, itRa, ohm-m3,900 5,400 6,900 7,700
8,900 9,700 10,300 10,700 10,850 11,400 12,000 12,600 12,8000.76
0.76 0.84 0.96 0.99 1.23 1.02 0.93 0.73 1.30 1.70 2.08 1.03Results
from Example 3.4SP Deflection, mv 70 76 78 85 90 87 90 94 90 60 57
38 55Temperature, ofohm-m114 135 162 170 191 201 211 218 221 239
250 261 2700.52 0.43 0.35 0.34 0.29 0.27 0.27 0.32 0.29 0.28 0.36
0.35 0.34Rmf(e),Rw(e),Rw.ohm-m ohm-m 0.064 0.046 0.039 0.033 0.026
0.027 0.026 0.025 0.027 0.061 0.088 0.140 0.0900.078 0.054 0.044
0.040 0.034 0.034 0.030 0.030 0.033 0.068 0.094 0.160 0.086
82. 70Drilling EngineeringRw VERSUS Rwe AND
FORMATIONTEMPERATURERmf VERSUS Rmfe FOR SALTY MUDS AND GYP-BASE
MUDS ...1f52 ~ coIi 1.0 " ::It---Ll'--L.W ,-0.5~ II::f'"~ .02e .01
IrII'LiY.-.~lrTI="== ~ ~_I I~' ,. =; ,,- +oi~,.(':t2 bm~ I!I~~I~
'--",. ,~ .002 ~JO1>OI~ .005.01,--r!: L=-_ .05 .02 -r~..1:'-Rmfe
or RweFig. 3-22,,Z;-__I~r-;1 .,,,-:. ~~t:",:'tj "=~
~I--+1:1---+-rrr~ .05::It',~~-ir 0.2 QI~W~~ii,.--~c=E ei
-'i''CI.~-0/..n-I~I...LLI.U U.ujt~W ~r-= I:::L1:::_, ~II:: I 0.1(
at Formation==E =. _c,,__-,] ;-._ II! ~-L0.2Q5;r--H ~
1.02Temperature)Rweconversion to Rw (Courtesy of Schlumberger)Sonic
Log. The sonic log has been used successfully as a pressure
evaluation tool. The technique utilizes the difference in travel
times between highporosity overpressure zones and low-porosity,
normal pressure zones. The basic relationship between travel times
can be seen in Fig. 3-24. Hottman and Johnson studied the wells
shown in Table 3-5 (see pg. 75) and developed the pressure
relationship shown in Fig. 3-25. The manner in which formation
pressures are calculated using the Hottman and Johnson approach is
similar to their method for resistivity plots, as illustrated in
Example 3.2. Observed transit times are plotted, and the normal
trend line is established and extrapolated throughout the pressure
region. At the depth of interest, the difference between the
observed and normal travel times is established. This difference is
used with Fig. 3-25 to estimate the formation pressure. The
procedure is illustrated in Example 3.5.
83. 71Predicting Formation Pressures50o010.10.054,00010.I,5,000
-,-6,000j-7,000 8,0001I-9,00010,000. '811,00030 4020I"-ill
......"-12,000'..t13,00014,000 1" nnn 15,000RwFig.3-23RoRw, Ro, and
F for Example 3.4F70 90 60 8010o
84. .c 15. Q)o1 Abnormal pressuresTravel time (IL see/ft)Fig.
3-24Generalized sonic plot0.40010.0 iii!:12.0.14.0'00 C. cii
.e-C);Q jQ) U) CD-a:16.0"tJ ::> E 'E Q) iii > '5C' w.18.0
.............---1 60 seelft Fig. 3-25Empirical correlation of
formation pressure gradients vs a difference ..ttI1 4-_~.._1:IU,.1
Tr'lt.hn~nn
85. 73Predicting Formation PressuresTable 3-5 Formation
Pressure and Shale Acoustic Log Data in Overpressured
Miocene/Oligocene Formations, U.S. Gulf Coast Area .:lt"b(Sh)Parish
or County and State Terrebonne, La. Offshore Lafourche, La.
Assumption, La. Offshore Vermilion, La. Offshore Terrebonne, La.
East Baton Rouge, La. St. Martin, La. Offshore St. Mary, La.
Calcasieu, La. Offshore St. Mary, La. Offshore St. Mary, La.
Offshore Plaquemines, La. Cameron, La. Cameron, La. Jefferson, Tex.
Terrebonne, La. Offshore Galveston, Tex. Chambers, Tex. After
Hottman and Johnson, *Formation- .:ltn(sh),WellDepth, ftPressure,
psiFPG*, psi/ft1 213,387 11,00011,647 6,8200.87 0.6222 93 410,820
11,9008,872 9,9960.82 0.8421
27513,11811,2810.8627610,9808,0150.73137 811,500 13,3506,210
11,4810.54 0.864 309 1011,800 13,0106,608 10,9280.56 0.847
231113,82512,7190.9233128,8745,3240.60513 14 15 16 1711,115 11,435
10,890 11,050 11,7509,781 11,292 9,910 . 8,951 11,3980.88 0.90 0.91
0.81 0.9732 38 39 21 561812,0809,4220.78181965.fluid pressure
gradient.J,Lsec/ft -
86. 74Drilling EngineeringExample 3.5 The following sonic log
data were taken from a well in West Oklahoma. Plot the data on
3-cycle semilog paper. Use the Hottman and Johnson techniques to
calculate the formation pressure at 11,900 ft. Travel Time,
J.LSec/ft 190 160 140 120 122 105 110 99 99 98 100 100 110 100 110
101 101 105 100 110 100Depth, ft 3,400 5,000 6,600 7,300 7,900
8,200 8,600 9,000 9,200 9,400 9,600 9,800 10,000 10,200 10,400
10,600 10,800 11,100 11,400 11,600 11,900Solution: 1. Plot the data
on semilog paper as shown in Fig. 3-26. 2. The divergence from the
normal trend at 9,500 ft denotes entry into the pressured zone. 3.
At 12,000 ft, the difference between the extrapolated normal trend
and observed values is 32 /J-sec/ft. 4. Enter Fig. 3-25 with a
value of 32 /J-sec/ftand read the formation pressure at 17.5
lb/gal.
87. Predicting75Formation Pressures2,000II3,000
ItJ4,000j5,000I6,000;.g.t: a. Q)7,000a1.8,000Ii 9,000.
10,000Normaltrendfl1-11,000112,000100200300seclftFig. 3-26Sonic
data plot for Example 3.5
88. 76Drilling EngineeringBulk Density. When drilling in
nonnally pressured zones, the bulk density of the drilled rock
should increase due to compaction, or porosity reduction. As high
fonnation pressures are encountered, the associated high porosities
wiII cause a deviation in the expected bulk density trend. A
typical plot of bulk densities is seen in Fig. 3-27. The transition
from nonnal to abnonnal pressures occurs at the depth where
divergence from the nonnal trend is observed. The results from a
typical field case are seen in Fig. 3-28. The resistivity plot
shows transition zones at 10,700 and 12,500 ft. The density log
detected the lower transition zone but was unable to define the
upper transition zone due to the lack of an established trend line.
Drilling Equations. Many mathematical models have been proposed in
an effort to describe the relationship of several drilling
variables on penetration rate. Most depend on the combination of
several controllable variables and one combined fonnation property.
Several of the models are designed for easy application in the
field, while others require computerization. When conscientiously
applied, most of the available models can accurately detect and
quantify abnonnal fonnation pressures. An attempt to quantify
differential pressure is the basis of most drilling models. If this
value is known, the fonnation pressure can readily be calculated.
Garnier and van Lingen showed that differential pressure has a
definite effect on penetration. In field studies, Benit and Vidrine
found evidence that the range in differential pressure of 0-500 psi
has the greatest effect in reducing penetration. Perhaps the most
common model used by the industry is the dc-exponent. The. basis of
the model is found in Bingham's equation to define the drilling
process: 12W~ = 60Nab( dB )Where: R= bit penetration rate, ft/hrN =
rotary speed, rpm W = bit weight, 1,000 lb dB = bit diameter, in. b
= bit weight exponent, dimensionless a= fonnation drillability
constant, dimensionless(3.7)
89. 77Predicting Formation Pressures.c a. CD cI
2.202.302.402.502.60Shale density (gm/cc)Fig. 3-27Generalized shale
density plot2.70
90. 78Drilling EngineeringBULK DENSITY. gnvc:c''''.. , .
.10RESISTIVITY.,oo
,oo,...I......'.ODD10001000I.ODD...DEfrISI"'"DEWM
CN..C:UI.AnDIIII.IDWt M:OI..IIN'MEN''0000IILVW'J$I'.Gat,.. I
.I"""""lOt::: ..14'UOGCSG-.... '"0ONLV12.000',.or.
"1(,,00U"'o9$21(H.","'.',"ICUt,.i..:.t'i82CU1 I'"[LOG-$ 2'C"--:io
JXllI'I.ec"",-:h':":i-..... '.ODD.,'.ODD.roLlfo' 5('IU'o'":i-'"
......nIP GAS-..,or...,0(N$fT-. L...",18.Q.AN SHAlfW
.-....,.II.CIOCt...-,,..m(L.. .eo ... .."000......IO.OOCt..5000'.
..'6000( LOGCSG OIAMONC en1.000'LIESS''''''''' -: ........S'"..,
,,"IE....1000I ODD ~20Fig. 3-28230 ..10t'lC' HC .wERaGES2tC ..
-L~:t(..S"""''''-~.''-.;67"10lllustration of an actual case in
which shale densities are used as a pressure monitoring device.
Note that a resistivity plot is also shown. (After Boatman)Jordan
and Shirley modified Bingham's equation to the form as follows:
d=log (R/60N)/log (l2W/I,OOO dB)(3.8)where d replaces b in
Bingham's model. In Eq. 3.8, the authors introduced several scaling
constants and assigned a value of unity to the drillability
constant, a. This adaptation lumps the formation properties into a
drillability function d, which varies with depth and rock strength
or type. The manipulation normalizes the drilling variables so d
depends more on differential pressure than on operating parameters.
In field applications the d-exponent should respond to the effect
of differential pressure, as shown in Fig. 3-29.
