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A Robust Torque and Drag Analysis Approach for Well Planning and Drillstring Design
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5/28/2018 A Robust Torque and Drag Analysis Approach for Well Planning and Drillstring Design
1/16
Copyright 1998, IADC/SPE Drilling Conference
This paper was prepared for presentation at the 1998 IADC/SPE Drilling Conference held inDallas, Texas 36 March 1998.
This paper was selected for presentation by an IADC/SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of thepaper, as presented, have not been reviewed by the International Association of DrillingContractors or the Society of Petroleum Engineers and are subject to correction by theauthor(s). The material, as presented, does not necessarily reflect any position of the IADC orSPE, their officers, or members. Papers presented at the IADC/SPE meetings are subject topublication review by Editorial Committees of the IADC and SPE. Electronic reproduction,distribution, or storage of any part of this paper for commercial purposes without the writtenconsent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print isrestricted to an abstract of not more than 300 words; illustrations may not be copied. Theabstract must contain conspicuous acknowledgment of where and by whom the paper waspresented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A., fax01-972-952-9435.
AbstractThis paper presents a novel torque and drag analysis approach
and demonstrates its robustness when used with a versatilecomputer program. Torque and Drag analysis remains an
important evaluation process for assessing drilling feasibility
of directional wells, minimizing the occurrence of catastrophic
drill string failures and avoiding premature termination of the
drilling operation before reaching planned target depth.
From a draft well plan, the drilling engineering analysis isinitiated with the development of a representative analyticalmodel using selected entries in a Torque and Drag computer
program. Several parameters and instances of evaluation are
needed to capture the physical behavior of modeled systems
and to produce technically sound results.
The availability of computational tools have not necessarily
improved the drilling engineering process or enhance the
quality of recommendations without a methodical approach
and application of results.
To minimize the iterative steps required to reach an
interpretable result, the analytical process as presented in thispaper is accelerated with a directed search and a convergence
to the determinant drilling variables. The novel approach
narrows - the design search domain and tests sensitivities of
well-plan characteristics, simulates drilling conditions andapplicable drillstring - to the dominant operating factors that
determine the boundaries of application.
A record extended reach well (MD/TVD ratio of 2.9) with alateral displacement of approximately 6,000 ft. was drilled in
the GOM using this approach to select tubulars and t
position in the well with respect to dogleg severity, inclina
and target objectives.
IntroductionSuppose we define Drilling Mechanics analysis as consis
of a number of well-established activities, including W
path planning, Torque and Drag analysis, Drillstring de
and the selection of Drilling Systems. The subject of this p- well-path design and, torque and drag analysis - maintai
strong interest in the petroleum industry.
The process of well-path planning and drillstring design
given geological targets are subject to Bottom Hole Assem
(BHA) directional performance, torque and drag analy
Hydraulics analysis and mechanical strength of drillstcomponents has seen progressive development, the cur
surge in Extended Reach Drilling (ERD) operati
Horizontal re-entries and other complex drilling programan excellent testimonial. Torque and drag analysis compr
well-path description and drillstring load modeling pro
aimed at simulating the same mechanics and characteristica real-life drilling operation. Torque and Drag analysis is nconsidered a valuable tool used primarily for design, plann
and application screening of drilling and completion system
However, evolution of successful approaches has been dog
by heuristic concepts and rules of thumb which are effective when non-linear situations exist or when decisi
become sensitive to quantitative measures rather
qualitative indicators. It is our belief that the evidcomplexity of run-time problems does not permit solut
based only on the experience of the drilling group.
The design and troubleshooting ability of those who under
such analysis should not be limited to historical experien
and performance of the applied drilling system if the pro
use of computational tools and methodical approaches en
thorough and concise evaluation of the drilling program. implementation of model-derived analytical solutions sho
be brought about by providing a framework for sys
behavior dynamics to evaluate the possible system stcreated in the modeling process.
IADC/SPE 39321
A Robust Torque and Drag Analysis Approach for Well Planning and Drillstring DesigOpeyemi A. Adewuya, SPE, and Son V. Pham, SPE, Baker HughesINTEQ
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2 YEMI ADEWUYA, SON PHAM IADC/SPE 39
A robust modeling process is based on the logical
representation of system states as functions of interval
objectives at the modeling stage, providing solutions forextremely complex interplay of variables without necessarily
simplifying the system model. The approach we propose uses
available theoretical foundations and analyses, combined with
the extensions to conservative criterion offered by practice to
arrive quickly at feasible parameters for hole Dogleg Severity(DLS), optimum tubular properties, and scope of drilling
feasibility.
This paper is presented in two sections, in the first section
beginning with Well Planning Considerations we discuss the
Torque and Drag implications of the Well-path TrajectoryMethod used in survey calculations for the well design.
Completing this first section is a discussion on the attributes
that makes this proposed modeling approach robust and the
steps demonstrating its value - minimized iteration time and
ease of implementation - using an example well is outlined. Inour conclusion we summarize, with emphasis, the most
valuable components of that process.
Well-planning Considerations
Well-path Trajectory Method:Many methods for calculating well-path trajectory have
been formulated to represent a suitable plan to reach
geological objectives. There are basically six different
methods, which have been widely used in the directional
drilling applications, are the Tangential, Average Angle,Balanced Tangential, Mercury, Minimum Curvature and
Radius of Curvature method. All except for the Tangential
method demonstrates relative accurate representation of thewell-bore trajectory [16]. Readily available computational
tools naturally leads to the use of the more demanding
Minimum Curvature Method in order to maximize on survey
calculation accuracy.
While the variation in survey calculation methods plays aminor role in the overall torque and drag analysis, it does
contribute to the overall accuracy and thoroughness of the
well-path design. Therefore Minimum Curvature Method isthe formulation of choice and is consistently utilized in the
well planning process.
Constraints Definition and Management:
Most engineering systems are designed to operate within
specified set of constraints which may be limitations on
operating load levels, modes or overall system response. Theconstraints define the lower and upper bounds of selecteddesign variables and in terms of design performance becomes
a yardstick for measuring compliance.
To allow for efficient processing of design steps, a
mechanism for defining constraint properties at each designstage is necessary [see Figure 1].
1.Structural (Surface location and Target coordinates)
Geophysicists and geologists work together to select takepoints and target intersection requirements. Candidate surface
locations are chosen based on proximity, log
requirements, criteria to maximize slot recovery opportun
and minimization of drilling costs for trajectory and ancilresources required to complete a well.
The choice of surface location relative to ta
coordinates define the design space for the trajectory of
well. The geometric elements of the well are prescribed
other factors which include drag and allowable curvaturedrilling tools in applicable hole size.
2.Geometric specifications:The variables which shape the geometry of directional
plans are Kick-off Point (KOP), Build-up Rate (BUR),
inclination and casing program. Rehashing what is comm
knowledge today, have been the subject of much research, clear that the depth of kick-off has a significant contribu
on the torque and drag characteristics and horizontal reach
well.
Build-up rates are a matter of connecting points along
wellbore to intersect target coordinates, but the choice ooptimal BUR is determined by hole size, drilling
capability, anticipated drag effects and an over-all evaluaof the drilling objectives.
3.Casing Program:
The casing design process requires the selection o
casing program to meet at the minimum design requirem
such as imposed mechanical stress (hoop, radial and tri-axand loads (burst, collapse, tensile) among other prerequis
which include estimated life-cycle of well, future re-e
work, formation isolation and casing wear tolerance.
Strategic casing placement to extend drilling assemperformance, although an opportunity cost issue, can
justified by using the example well presented later in
paper. For the work on which this paper is based, the caprogram was specified for inclusion in the well-plan.
4.Geological obstacles:
Crooked well-paths or 3-D trajectories are not w
profiles of choice. Furtive views of local geology obtafrom seismic data provides information on enroute geolog
obstacles such as sensitive shales, unstable sandst
stringers, dips, faults and the prominent water or gas sa
subtended by the oil bearing reservoir.5.Drilling system operational compatibility:
From an automated well design tool, BUR necessary
connect geometric markers (End of Build, End of Hold, etcobtained routinely, optimization of the well-design is achie
when consideration is given to the interval hole size
applicable performance drilling system.
Top hole sections necessarily are large holes requiringuse of large diameter tools. The mechanical constraints oflarge diameter tools limits the degree of curvature that can
used in the top hole section.
In addition, the lower bending capability leads to h
lateral loads and the attendant drag and torque effect. The of collar-based Measurement While Drilling (MWD) t
introduces even greater rigidity which places further limita
on planned well-bore curvature.Conventionally, most top hole sections are dri
5/28/2018 A Robust Torque and Drag Analysis Approach for Well Planning and Drillstring Design
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IADC/SPE 39321 A ROBUST TORQUE AND DRAG APPROACH FOR WELL PLANNING AND DRILLSTRING DESIGN
vertically to a selected kick-off depth, to allow drilling large
hole sections and setting conductor casing. However when
trajectory efficiency requires early directional work, relativelysmaller hole size i.e. 12-1/4 can be drilled out of large casing,
enabling the use of higher BUR. When the interval TD is
reached, the hole is opened up to 17-1/2, as was done in the
example well, to accommodate a 13-3/8 casing string.
In smaller hole sizes, BUR ranges cover a wider spectrumallowing flexibility in trajectory geometric properties. At the
high end of this wide spectrum is a drilling assemblylimitation posed by push-through radius. That discussion is
beyond the scope of this work.
So far we have discussed constraints as defined in the
preamble to this subsection, suppose a constraint were to beused to advantage, for instance, designing a well path to
maximize drilling assembly rotation and exploiting the drop
tendency of the drilling assembly from gravitational effects to
track the well into the target location.
Drillstring Torque and Drag Modeling and Design
Drilling engineering algorithm developers are constantlystriving to produce sophisticated computational engines from
mathematical representations of drill string dynamics which
offer greater accuracy and more realistic results. While the
computational engines improves, the results produced are
more intricate and refined. The impressive developments inareas such as trajectory simulation are to be immensely
appreciated but each step brings its own problems for the end-
user.
Software Tools:
Robust analysis of modeled multivariate systems require
considerable computational processing before meaningfulresults are obtained. The Torque and Drag analysis tool used
in this work is one of the seven module suite of Baker Hughes
INTEQproprietary drilling engineering software tools.
In the Torque and Drag calculation mode the software
computes the surface-to-bit load, stress and lateral forceinformation for rotary and oriented drilling operations at user-
specified evaluation depths. Operating load cases including
magnitude, location and mode of occurrence (e.g. drilling,rotating-on-bottom, tripping, etc.)
The computational engine allows fast and rigorous
engineering mechanics analysis of the modeled well-trajectoryand casing configuration, drillstring and drilling parameters,
based on a continuous elastic beam column theory. From the
vast array of state-of-the-art analytical solutions, the relevant
solutions for Euler, sinusoidal, helical buckling and postbuckling behavior, drillstring torsion and load displacementhysteresis in buckling mode transition was the focus in this
application [2].
Availability of computational tools facilitate fast and
accurate iterations which will naturally be incorporated intodrillstring optimization processes.
Well-plan Drillstring Optimization - Supplementary
Issues:
In Extended Reach directional wells, what remain
protracted optimization issue is not simply DLS minimiza
but the effect of the inter-play between inclination, azimuchange, drag and buckling.
Micro-loading studies into sensitivities of drillstrin
varying well-profile pursue the quantitative indexing
dominant load factors towards achieving optimization.
reported by Payne and Abbassian [4], critical well-binclination i.e. angle at which pipe no longer falls at o
weight, is one of the several factors that shape ERD well-bdesign [see Figure 2].
Logically, lower inclination angles produces less drag,
lacks the well-bore support (cradling effect) needed to man
the severity of buckling. An interesting observation presented by Payne and Abbassian though empirical, ident
the sensitivity of hole inclination to type of operation
briefly stated, a high KOP well profile is favorable to a
1/4 hole by 9-5/8 casing/coiled tubing run, while a low K
well profile is preferred for an 8-1/2 hole by 5-1/2 liner/pruns.
Steering in well-bores with azimuthal and inclinachanges combined with long tangent sections presen
challenge to the transmission of mechanical forces. Pre
orientation of tool-face in the presence of significant tor
couples (normal/contact force, circular frictional d
aggravates the uncertainty of heading and achieving geomdrilling objectives.
Process for achieving Analytical Robustness withWell-path and Torque and Drag Modeling
Well-path Modeling:
To account correctly for the degree of variation of dogseverity in finite course lengths two approaches was exam
by the authors. One approach uses a user-specified maxim
relative noise amplitude based on a scale of 0 - 10 to prod
random net well-path tortuosity nominally ranging from 02.0 deg/100 ft. [1], while the definition given by Dr. Ra
Dawson suggest the correction of the well-path by the addi
of a sinusoidal variation to the inclination and azimuth an
over 1,000 ft. course lengths [17]. Different methodsapplying tortuosity to a well-plan may result in the s
average dogleg severity [see Figure 3] but from
observation, of the drilling operation, applying a random nfactor is more representative of a tortuous well path compa
to a cyclic factor applied by the tortuosity equation [see Fi
3, Equation 3-A]
The Tubular Buckling Theories Compared:
The available theoretical foundations on which tub
buckling has been developed can be grouped into
categories, namely conservative and extended models.
models that can be classified as conservative criteria consof the combined work of Lubinski, Dawson/Pas
Chen/Cheatham and, Sextro and He/Kylinstad.
The recent developments by Wu/Juvkam-Wold qualifiean extended criteria model [1]. The differences between
5/28/2018 A Robust Torque and Drag Analysis Approach for Well Planning and Drillstring Design
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4 YEMI ADEWUYA, SON PHAM IADC/SPE 39
two classes of criterion is enumerated in terms of scope of
application and impact on modeling.
Conservative Theories: Critical buckling loads predictedby the Dawson/Paslay equation are much lower than actual or
operating critical loads. In addition, the equation represents
the mechanical behavior of long finite tubular elements and
produces erroneous results for short elements [15].
The critical buckling load limits predicted by Chenindicated a 40% increase in load during sinusoidal to helical
buckling transition and an 18% increase in the magnitude ofcritical load required to initiate buckling.
Extended Criteria Theories: A full understanding of the
premises on which the buckling theories proposed by Wu and
Juvkam-Wold is important to recognizing their relevance toresulting load behavior of modeled drilling assemblies.
Directional wells with long tangent sections and hole
inclination approaching critical angles with respect to friction
are stereotypical of the parameters which validate the
suitability of the extended buckling theories. At lowinclination angles where the contribution of tubular weight to
axial compressive force is greatest, the Wu and Juvkam-Woldbuckling equation [12] suffices with the critical length and
axial load term. The He & Kyllinstad work contributed the
effect of wellbore curvature to the development of
mathematical basis for assessment of critical buckling loads.
In essence, the normal forces due to curvature as an additionalresistance modulus is added to the force term [15].
A broad comparison of the two classes of criteria can be
summarized in terms of common factors namely the normal
force and the stiffness terms. Invoking the conservativebuckling criteria assesses buckling loads based a quotient of
unit stiffness and normal force, while the extended buckling
criteria assumes higher indices for modifiers to stiffness andnormal force terms.
In summary, the reason for enumerating the differences
between the conservative and extended buckling assessment
approaches is to draw our attention to the quantitative quality
of analytical work based on these models. In practice, factorssuch as hole friction, wellbore inclination and curvature affect
the initiation of buckling and un-buckling discriminatorily
contributes to the torque and drag analysis.Extended-reach wells by virtue of design and required
tubular configuration manifest loads at higher thresholds and
are best analyzed with models based on extended criteria.Frequent occurrences of drillstring failures or completion
string collapse would have dogged ERD save that there are
favorable interplay of influencing factors which make current
theories poor predictors.
The Genealogy of a Robust Torque and Drag Modeling
Approach
Multiple Analytical stations:Traditionally the drillstring design process tended to focus
on meeting minimum safety requirements in the string, for
example design based on mechanical ratings, size, drillingmode, casing points and relative component function. Also,
emphasis was placed on drillstring applicable only at
whereas in most cases stations such as KOP, casing poi
whipstock exits and build-turn sections present greater drilchallenges.
A common assumption is that the analysis at TD of
well-plan will yield the limiting parameters for the dril
applications of the entire well-path - which neglects
varying tool size utilized and changing geometry of the wbore. Due to the weight and complex load bea
characteristics of different size drillstring components inecessary to perform computational analysis for each h
interval to better understand and optimize on the w
bore/drillstring interactions.
Correct interpretation of the drilling program enaeffective drilling mechanics analysis of the drillstring and
quality of results approach close approximations.
Reflective of Actual / Changing Hole Conditions:The initial torque and drag modeling allows us
systematically develop a thorough understanding of
interaction between well-bore, drillstring components operational parameters [see Figure 4]. By discretely selec
modeling stations or evaluation intervals, drilling parame
(ROP, WOB, RPM) that best describe hole condit
(lithology, temperature, hole cleaning, mud properties, e
can be applied for a representative model that approacactual drilling condition.
It also enables narrowing the drillstring design sea
domain and improves ability to test sensitivities of drillst
well-bore interaction in the following modes: rotary drillslide drilling and tripping. By closely evaluating the diffe
drilling modes we can determine safe drilling lim
Operational limits consist of the applicable WOB withbuckling the drillstring, tripping capabilities and fricti
tolerences.
On a scale of significance, friction factor and WOB
dominant contributions to the torque and drag effectsdrillstring application.
Trade-Offs:Traditionally, the objective of Heavy Weight Drillp
(HWDP) application is to contribute to string weight a
mean to transfer weight to the bit. However well curva
impose a limit on the functional relevance of the HWString weight in the curve produces greater normal loads
contact forces.
As hole friction changes, the ability to maximize HW
functional performance is affected by the rate at whiccompressive state or a tension state is approachedmaintained. In cased hole, when friction becomes a prop
of the contacting materials and imposed loads, the functio
HWDP can be exploited to a higher degree.
A secondary mechanical characteristics of HWDP isinherent capacity to withstand relatively higher compres
loads [12]. By strategically utilizing this load characteri
of HWDP we can meet complex and challenging drilobjectives which would not otherwise be successful w
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IADC/SPE 39321 A ROBUST TORQUE AND DRAG APPROACH FOR WELL PLANNING AND DRILLSTRING DESIGN
normal drillpipe application.
Optimization requires an evaluation of the load and drag
distribution of the well based on the selected drillstring. Inaddition, optimal use of HWDP requires correct assessment of
required length, location in the borehole and balance of
performance in mitigating buckling while maximizing
transmission of the weight to bit.
In drilling work of horizontal wells with long laterals, theeffective application of HWDP is becoming more of a science
than a convention. This emerging functional use of HWDP forsustainable transfer of weight to the bit is becoming critical to
achieving lateral length target displacements and reach target
depth.
The inverted drillstring configuration is now anestablished arrangement of drillstring assemblies. An inverted
drillstring arrangement places the HWDP above regular
drillpipe.
The common belief supported by static force analysis of
weight-derived axial force indicates that half the amount of
this force is available at hole inclinations greater than 60i.e.
the weight of HWDP element x cos(60) weight of HWDP x0.5. Although this guideline is generally acceptable for non-critical applications advance well-bore construction requires
methodical computational drillstring analysis which takes into
account friction factor, trip analysis, WOB and other drilling
optimization and constraining parameters.
Presentation of Model Analysis:Graphical representation and summary tables simplifies
complex data sets for quick and accurate interpretations andserve as an invaluable communications tool. The extensive
knowledge captured from the modeling process needs to be
communicated to all team members.When used as a monitoring or look ahead tool on the field,
deviation from predicted outcome can be flagged early and
corrective measures taken. In the next section the application
of this approach on the field is discussed using the example
well. Logical presentation of data allows the operational teamto easily and quickly assemble feedback information
facilitating easy understanding of complex relationships
between modeled and output variables.
Execution of results and recommendations isstraightforward and less prone to misinterpretation by field or
implementation staff because of the graphical highlights thatlimit additional processing.
Example Step-through Modeling Process
This methodology was first used in an extended reach wellwith a MD/TVD ratio of 2.9 and a lateral displacement of
6000 ft. In this section the application of the components ofthe robust modeling thesis enumerated thus far as it applies to
the different phases involved in the design and eventual
successful drilling of the well is presented.
Wellpath Planning of Example WellPreliminary well design requirements was developed by a
multidisciplinary team composed of the operator and ser
personnel.
The example well [see Figure 5] consist of a 20 dr
pipe set at 300 ft., an initial drill-out 12-1/4 hole kicks
beginning at 3/100 ft. and end-of-build reached at 1ft.,MD with final heading of 341.23. The 12-1/4 hole is
entered and opened to a 17-1/2 conductor hole to be dri
with a 5/100 ft. build rate, building to a 40 inclination1,500 ft.,MD.
Beyond the planned 13-3/8 conductor set depth, cu
building would be continued at 5/100 ft. to an intermed
end-of-build inclination of 83 at 2,373 ft.,MD. The inclination is held to the end-of-hold depth at 6,317 ft.,MD
A two section drop was designed to intersect a target s
for which the complete coordinates (orientation and de
definition was unknown. The two section drop would facil
a slide and search drilling operation and a controlled drop of 1.5/100 ft. to reach the bottom hole location.
Fit for Purpose Well Design: the combination build-
of 3/100 ft. and 5/100 ft. used in the kick-off after drivep
is installed was chosen after careful evaluation of its potentorque and drag implications. The curvature produced by
strategically chosen combination build rates is intendedprovide a less aggressive trajectory thereby reducing nor
forces and lateral loads that affect the drag distribution in
bore-hole drillstring interface.
The magnitude of build-up rate used in curved sect
follow a scheme that locates the smaller BUR, 3/100 ft. at
beginning of the curve section and the larger BUR, 5/10at the end of the curve. By following this scheme the ab
to maintain WOB and stable string is ensured and lateral lin the curved section of the hole is evenly distributed.
Surface Casing Location: the choice of set depth for
surface casing was informed by the following reasons:
provide a cased hole to place HWDP for effec
transmission of WOB in the drilling of the target.
provide a reduced friction channel to minimize dand torque.
to enable rotation of the drillstring in the tang
section and smooth bore-hole with less doseverity and the ability to drill to target depth.
introduce a significant hole-cleaning advantage
offered by placing the surface casing about midwa
the tangent section, since half the section is cased-the hole cleaning requirement for the tangent sec
is halved.
Production Hole Design for Maximum Rotary drilling
expected drop tendency: this hole section consist of a ltangent section and a drop of inclination in the end in orde
search for the target sand. Both the tangent and angle d
section allows us to employ the natural tendency of drilling assembly and maximize drilling in the rotary mode
The challenging aspect of ERD is the ability to p
sufficient WOB in the sliding mode in order to main
directional control. By planning on the natural drop tendeof the drilling assembly we can minimize the need for s
5/28/2018 A Robust Torque and Drag Analysis Approach for Well Planning and Drillstring Design
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6 YEMI ADEWUYA, SON PHAM IADC/SPE 39
drilling and therefore maximizing operational success.
Torque and Drag Analytical Stations:
The analysis for the example well was performed for all
hole intervals (surface, protective and production). For each
scenario defined by well-bore design, select BHA and
drillstring, drilling parameters and imposed loads, the analyst
must model all possible configurations and must take intoaccount the combination of several interacting or related
factors. The reality of such undertaken is that modeling is astudy of non-deterministic events, a phenomenon amplified by
the number of cases required to test the influence of each
factor. Unarguably, a guided search to test sensitivities of
factors is indispensable, providing a precise experimentaldelineation to reduce the number of iterations.
Due to space constraints we will only use the analysis of
the TD point of the production interval to highlight the robust
methodology. The selection of the 8-1/2 production interval
clearly demonstrates slide drilling and tripping concerninherent in all ERD.
For this cycle of evaluation, we will closely scrutinize theresults in the form of Summary Data Tables and the Drilling,
Tripping and Frictional Sensitivity Analysis. As will be
demonstrated, the format of the data presentation leads to a
thorough and logical interpretation of the modeled results.
Drilling Sensitivity Analysis: in this scenario we willisolate WOB to determine its affect on the drillstring during
the drilling of specific intervals. The modeling consist of
varying the WOB while constraining to the same frictional
factor, drilling assembly and other rig parameters.Since the operation calls for the use of a water based fluid
system the frictional values of .25 and .30 was chosen, based
on a historical database, for casing and open-hole sectionsrespectively. The model results will therefore lead to an
operational WOB boundary based on a realistic frictional
estimation.
Selection of WOB is based on tools specifications as well
as operational parameters. The operational WOB expected foran 8-1/2 hole section will range from 0-25 klbs. The
modeling take points will analyzed at 0, 15, 25, and 50 klbs
WOB in order to view the dynamic condition reflective of theoperational performance.
We will now interpreted the actaul data grouped in a table
and graphical format. The result summary table allows us toeasily compare the models results with the specification of the
5 drillpipe. The initial analysis was performed on a
drillstring consisting solely of drillpipe [see Table 1]. We can
quickly learn that any WOB above 10 klbs will result in anegative Hook Load at surface and enter into the helical
buckling regime at the top 500 ft. of the well-bore, as seen
from the graphical representation [see Figure 6].
A comparison of the analysis using the preliminary versus
the same sensitivity analysis of the modified drillstring [seeTable 2] will demonstrate the value of the simple method in
integrating complex variables.
The placement 4,000 ft. of HWDP in the modifieddrillstring was not derived from only the Drilling Sensitivity
Analysis but the Tripping Sensitivity Analysis was a m
contributing factor.
Tripping Sensitivity Analysis: these sets of analysis similar parameters as set for the Drilling Sensitivity Anal
which was performed using the preliminary drillstring.
main objective for this type of analysis to determine
location and amount of HWDP needed (if any) in order to
to TD while still having sufficient WOB availableovercome any ledges.
The graphical results [see Figure 7] indicates, interpolating between the 0 and 15 klbs trip curve, that
ledge requiring WOB over approximately 5 klbs canno
applied with the current drillstring. Contingency plan requ
the force of at least 15 klbs for any ledges encounter duthe drilling process and therefore modifications must be m
to the preliminary drillstring.
The information capture from the trip analysis lead to
replacement of the drillpipe with 4,000 ft. of HWDP at the
section of the preliminary drillstring. Subsequently, selection of the amount of HWDP leads to the strat
decision to set the 13-3/8 casing string at 4,000 ft.,MDencompass the heavier weight drillpipe in a stable will-b
and therefore reducing the overall torque and drag affects.
Friction Sensitivity Analysis: this final sensitivity anal
completes the torque and drag evaluation of the 8-
production hole interval. Determining the tolerable frictioperating range assist in making the decision to incorpo
the type of mud system, lubricious additives, drillpipe rubb
hole cleaning equipment, stringent fluid parameters, etc.
the drilling program.The graphical results in this case [see Figure 8] shows
adequate load transfer and helical buckling can be feas
mitigated by modification of the drillstring design rather tupgrade to the more costly oil-based mud system.
economical decision, from a frictional perspective, i
contingency plan to incorporate the use of the water-ba
fluid system with a stringent solids removal program andaddition of lubricious additives as contingency.
Interpretation and Field Implementation:
In recent publications and papers it has been implicexpressed that there are discrepancies in the analytical res
and recommendations put forward by drilling ser
companies, and the expectations of operators during crudrilling operations or at planning stages. Drilling serv
companies share objectives for success of drilling projects
would undertake a rigorous drilling mechanics evaluation
an mechanical application match of the prescribed drilsystem.
The procedure developed to integrate well plann
drillstring design and torque and drag analysis h
demonstrates is fruitfulness through field use and observat
On the technical merit, we have seen the torque, drag, frictional trends distinctly matched with the modeling resu
In cases where the trends diverge or differ parameters diffe
from the ones chosen for modeling were identified accounted for in changes made to the operational paramete
5/28/2018 A Robust Torque and Drag Analysis Approach for Well Planning and Drillstring Design
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IADC/SPE 39321 A ROBUST TORQUE AND DRAG APPROACH FOR WELL PLANNING AND DRILLSTRING DESIGN
A secondary merit of the modeling process in the field
communications and implementations. Through the format of
the result presentation, explanation and support of the designparameters were clearly understood and plans were carried out
as specified.
Slide Drilling Limitations Leading Towards State-of-the-
art Drilling Technology:The frictional drag in the drill ahead direction in the well-
bore relative to the string poses a limitation to the ability toslide. The severity of this frictional drag is dependent on well-
bore profile, traversed formation type and bore-hole geometry.
We can observe the tremendous reactionary load difference
between the sliding and rotating drilling model [see Table 1 &2].
Recently, torque reducers have seen prolific use in solving
the problem by isolating would-be contact points between the
tool-joints/drill-stem and the well-bore. Torque reducers can
be defined as active if they rotate relative to drillpipe orpassive if non-rotating.
However, in ERD wells the severity of frictional drag issuch that contact points become pseudo-fixed points along the
drill-string producing increasing sensitivity to WOB. The
following approaches have been touted as successful antidotes
for excessive drag,
Increased mud lubricity
Low friction drill-pipe protectors
Running DC or Heavy-Weight Drill-Pipe (HWDP) in
near vertical well sections
Boost weight transfer with Bumpers, and Thrusters forsmooth WOB application
Use extended or double-power section motors toincrease stalling resistance.
And, recently Rotary Closed Loop Drilling Systems , anadvancement over the Variable Gauge Stabilizer emerged as apanacea for overcoming critical drag limitation in ERD wells.
Otherwise, drilling mechanics practitioners emphasize
qualifying drillstrings and well-sections for rotation, that may
otherwise present drag limitation.
ConclusionA novel well planning and torque and drag analysis
approach and demonstrates its robustness when used with a
versatile computer program. The value of using a methodicalprocedure in the evaluation of a drilling program can clearly
appreciated through:
Application of the state-of-the-art theories and
computational algorithms
Incorporating the dynamics of the field operation intothe planning and modeling process by carrying out
drilling, tripping and frictional sensitivity analysis
Multiple points of analysis ensures a thorough and
precise understanding of well-bore/drillstring
interactions from surface to TD
Advance deployment of HWDP for efficient weighttransfer to bit and integration into the drilling
assembly as a load bearing member to miti
drillstring helical buckling
Logical and simple presentation of data thro
tabular and graphical summaries to represent compmodeling systems
Useful communications tools to be incorporated
the drilling program for precise field implementa
and appreciation of model optimization Refinement and proven through field usage
AcknowledgmentsThe authors wish to thank the respective managemen
Baker Hughes INTEQ for permission to prepare and pub
this paper. The support of the following people are gratefacknowledged during the initial stages and final preparatio
this work: Thomas Dahl, Steve Dearman, Keith Fisher, D
Gaudin, Spencer Harris, Pat Havard, Raymond Jackson
Les Shale.
References
1. Baker Hughes INTEQ Torque and Drag v.4.1. Progr
Users Guide
2. Baker Hughes INTEQ, Drilling Engineering Softwv.3.20, Marketing Documentation
3. Batchelor, B. J., and Moyer, M. C., Selection
Drilling of Recent Gulf of Mexico Horizontal WeOTC 8462 (May 1997)
4. Payne, M. L., and Abbassian, F., Advanced Torque-a
Drag Considerations in Extended-Reach Wells, S
35102 (March 1996)
5. Ruddy, K. E., and Hill, D., Analysis of BuoyanAssisted Casings and Liners in Mega-Reach We
IADC/SPE 23878 (February 1992)
6. Guild, G. J., Hill T. H., and Summers, M. A., Designand Drilling Extended Reach Wells, Part 2 , Petrole
Engineer International (January 1995)
7. McKown, G. K., Drillstring Design OptimizationHigh-Angle Wells, SPE/IADC 18650 (February 1989
8. Maurer Engineering Inc., Horizontal Technol
Manual - DEA 44 September 1994
9. Payne, M. L., Duxbury, J. K., and Martin, J.
Drillstring Design Options for Extended-Reach Dril
Operations, PD-Vol. 65, Drilling Technology, ASETCE, 1995
10. Callin, J. K., and Hatton, P., Drillstring Consideratand BHA Design for Horizontal Wells, Internal Eastm
Christensen Paper(now Baker Hughes INTEQ)11. Chen, Y. C., Lin, Y. H., and Cheatham, J. B., Tub
and Casing Buckling in Horizontal Wells, JPT, p191, February 1990
12. Morris, E. R., Heavy Wall Drill Pipe A Key Membe
the Drill Stem, Presented at the Joint Petrole
Mechanical Engineering and Pressure Vessels and Pip
Conference, Mexico City, Mexico, September, 197613. Wu, J. and Juvkam-Wold, H. C., Buckling and Loc
5/28/2018 A Robust Torque and Drag Analysis Approach for Well Planning and Drillstring Design
8/16
8 YEMI ADEWUYA, SON PHAM IADC/SPE 39
of Tubulars in Inclined Wellbores, PD-Vol. 56, Drilling
Technology, ASME ETCE, 1994
14. Brett, J. F., Beckett, A. D., Holt, C. A., and Smith, D. L.Uses and Limitations of a Drillstring Tension and
Torque Model to Monitor Hole Conditions, SPE 16664,
September 1994
15. McCann, R. C. and Suryanarayana, P. V. R.,
Experimental Study of Curvature and Frictional Effectson Buckling, OTC 7568
16. API Bulletin D20, Directional Drilling SurveyCalculation Methods and Terminology, American
Petroleum Institute, December 1985
17. Maurer Engineering DDRAG8 Torque and Drag Us
Manual18. Hill, T. H., Summers, M. A., and Guild, G.
Designing and Qualifying Drillstrings for Extend
Reach Drilling, SPE DRILLING AND COMPLETI
June 1996, Vol. II, No. 2, Pg. 111-117
19. Arora, J. S., Introduction to Optimum DesiMcGraw-Hill, Inc., 1989
Table 1: Result Summary - Analysis of Preliminary Drillstring
Table 2: Result Summary - Analysis of Optimized Drillstring
Figure 1: Well Planning and Engineering Analysis Procedure
Figure 2: Critical Inclination Curve - Simple Static Analysis
Figure 3: Tortuosity Comparison Chart
Figure 4: Torque and Drag Analysis Procedure
Figure 5: Plot of Plan vs. Actual Well-path
Figure 6: Torque and Drag - Drilling Sensitivity Analysis
Figure 7: Torque and Drag - Tripping Sensitivity Analysis
Figure 8: Torque and Drag - Frictional Sensitivity Analysis
5/28/2018 A Robust Torque and Drag Analysis Approach for Well Planning and Drillstring Design
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Table 1: Result Summary - Analysis of Preliminary DrillstringREFERENCE 8-1/2" Hole Size: 5"DP to Surface
RESULTS
5"S-1
3519
.5#DP
Prem
ium
(NC50)-
API
RP7G
-----
ORIENTED ROTARY=100rpm ORIENTED
Friction Factors [csg/oh] ----- ----- .25/.30 .25/.30 .25/.30 .25/.30 .25/.30 .25/.30 .25/.30 .25/.30 .35/.40 .45/.
Weight on Bit [klbs] ----- ----- 0 15 25 50 0 15 25 50 25
Max. Tot. Eqv. Stress (MTES) [psi ----- ----- 28,044 28,992 30,490 41,126 32,988 31,646 31,458 34,736 34,584 45,0
Location of MTES [ft, MD] ----- ----- 1,060 1,960 1,630 800 650 530 530 1,210 1,060
Mode of MTES ----- ----- Pick-up Drilling Drilling Drilling Drilling Drilling Drilling Drilling Pick-up Drilli
Yield Stress [psi] 135,000 ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- --
Torque - Drilling [ft-lbf] ----- ----- 0 708 1,181 2,361 10,335 10,193 10,722 13,943 1,181 1,1
Torque - Rot-Off-Bot. [ lbf] ----- ----- 10,360 10,360 10,360 10,360 10,360 10,360 10,360 10,360 14,066 17,7
Make-Up Torque [ft-lbf] 24,645 ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- --
Torsional Yield [ft-lbf] 63,406 ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- --
Hook Load - Dril ling [lbf] ----- ----- 15,322 -4,483 -18,608 -67,353 53,735 38,764 28,762 3,690 -49,464 -99,7
Hook Load - Rot. Off Bot. [ lbf] ----- ----- 54,091 54,091 54,091 54,091 54,091 54,091 54,091 54,091 54,091 54,0
Hook Load - Pick-Up [lbf] ----- ----- 107,959 107,959 107,959 107,959 107,959 107,959 107,959 107,959 139,324 180,0
Hook Load - Slack-Off [ lbf] ----- ----- 15,322 15,322 15,322 15,322 15,322 15,322 15,322 15,322 -6,824 -39,0
Max. Allow. Hk Ld @ Min. Yld [lbf] 560,764 ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- --
Neutral Point [ft, MD from bit] ----- ----- 0 7,659 7,659 7,659 0 3,533 6,066 7,466 7,659 7,6
Table 2: Result Summary - Analysis of Optimized DrillstringREFERENCE 8-1/2" Hole Ssize: 5"DP to 9-7/8" Casing Shoe and 5"HWDP to Surface
RESULTS
5"S-1
3519
.5#DP
Prem
ium
(NC50)-
API
RP7G
5"K-5
549
.3#HWDP
(NC50)-
Dri
lco
Han
dboo
k ORIENTED ROTARY=100rpm ORIENTED
Friction Factors [csg/oh] ----- ----- .25/.30 .25/.30 .25/.30 .25/.30 .25/.30 .25/.30 .25/.30 .25/.30 .35/.40 .45/.
Weight on Bit [klbs] ----- ----- 0 15 25 50 0 15 25 50 25 Max. Tot. Eqv. Stress (MTES) [psi ----- ----- 26,183 26,796 27,478 35,219 28,275 27,949 28,207 32,626 28,006 28,6
Location of MTES [ft, MD] ----- ----- 6,797 4,323 4,323 4,563 4,053 4,053 4,053 7,458 4,323 4,3
Mode of MTES ----- ----- Drilling Drilling Drilling Drilling Drilling Drilling Drilling Drilling Drilling Drilli
Yield Stress [psi] 135,000 55,000 ----- ----- ----- ----- ----- ----- ----- ----- ----- --
Torque - Drilling [ft-lbf] ----- ----- 0 708 1,181 2,361 13,877 14,063 14,480 14,291 1,181 1,1
Torque - Rot-Off-Bot. [ lbf] ----- ----- 13,889 13,889 13,889 13,889 13,889 13,889 13,889 13,889 19,008 24,1
Make-Up Torque [ft-lbf] 24,645 29,400 ----- ----- ----- ----- ----- ----- ----- ----- ----- --
Torsional Yield [ft-lbf] 63,406 51,375 ----- ----- ----- ----- ----- ----- ----- ----- ----- --
Hook Load - Dril ling [lbf] ----- ----- 45,305 26,547 13,124 -26,884 99,227 84,245 74,246 49,202 -23,972 -77,2
Hook Load - Rot. Off Bot. [ lbf] ----- ----- 99,717 99,717 99,717 99,717 99,717 99,717 99,717 99,717 99,717 99,7
Hook Load - Pick-Up [lbf] ----- ----- 165,662 165,662 165,662 165,662 165,662 165,662 165,662 165,662 204,021 253,4
Hook Load - Slack-Off [ lbf] ----- ----- 45,305 45,305 45,305 45,305 45,305 45,305 45,305 45,305 15,085 -26,9
Max. Allow. Hk Ld @ Min. Yld [lbf] 560,764 691,185 ----- ----- ----- ----- ----- ----- ----- ----- ----- --
Neutral Point [ft, MD from bit] ----- ----- 0 7,019 7,344 7,659 0 3,534 5,544 6,463 7,659 7,6
Note: Critical results
Reference limits and specifications
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Figure 1: Well Planning and Engineering Analysis Flowchart
Preliminary Well-Path DesignConstraints Definition
- Surface Location and Target
Coordinates
- Rig Specifications
- Geological Specifications and
Obstacles
- Drilling Systems Operational
Compatibility
Anti-Collision Anaysis
Initial Well-Path
Approval
Preliminary Drillstring Design
Yes
No
Completions Program
Fluids Program
Bit Program
Hydraulics Analysis Torque & Drag Anaysis
Optimal Well-Path
and Drillstring Design
Optimized Drillstring Design
No
Develop Drilling Program
Yes
Perform Drilling Operation
Collect Useful Drilling Parameters
Torque (surface, down-hole), Weight On Bit
(surface, down-hole), Friction Factor (caing,
open-hole), Drag (slack-off, pick-up), Rate
of Penetration, Rotary Speed, Pump Rates,
Fluids Properties, Bit Performance, etc.
Torque & Drag Anaysis
Figure 4: Torque and Drag Analysis Flowchart
Drilling Sensitivity Anaysis
Tripping Sensitivity Anaysis
- WOB #1 (No Load)
- WOB #2 (Low Oper. Load)
- WOB #3 (High Oper. Load)
- WOB #4 (Max. Load)
Friction Factor Sensitivity Anaysis
- Friction Factor #1 (Expected)
- Friction Factor #2 (High)
- Friction Factor #3 (Problematic)
Preliminary Drillstring Design
Oriented Drilling
- WOB #1 (No Load)
- WOB #2 (Low Oper. Load)
- WOB #3 (High Oper. Load)
- WOB #4 (Max. Load)
Rotary Drilling
- WOB #1 (No Load)
- WOB #2 (Low Oper. Load)
- WOB #3 (High Oper. Load)
- WOB #4 (Max. Load)
Evaluation of Summary and
Graphical Results
Drillstring Optimization
Drill-String Component
Limitations and
Specifications
A thorough evaluation of the drilling
program will include this cycle of
analysis for each hole interval
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Figure 2: Critical Inclination Curve - Simple Static Anaysis
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
45 50 55 60 65 70 75 80 85 90
Critical Inclination [deg]
FrictionF
acto
r
Y
X
FW
Ff=F
N
FY
+
FX
FN
FA
FA
Summing forces in the X direction yields
the following simple relationship:
= atan1
where: = Inclination [deg]
= Friction Factor
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Figure 5: Plot of Plan vs. Actual Well-Path
0
500
1,000
1,500
2,000
2,500
3,000
0 1,000 2,000 3,000 4,000 5,000 6,000 7,000
Planned Actual
9-5/8" Casing @ 4,000'mdDepth
[ft,TVD]
Vertical Section [ft]
13-3/8" Casing @ 1,500'md
20" Drive Pipe @ 375'md
Planned TD @ 7,660'md
Actual TD: 7" Casing @ 7,075'md
12-1/4" x 17-1/2" Hole Size
12-1/4" Hole Size
8-1/2" Hole Size
0
500
1,000
1,500
2,000
2,500
3,000
0 1,000 2,000 3,000 4,000 5,000 6,000 7,000
Planned Actual
9-5/8" Casing @ 4,000'mdDepth
[ft,TVD]
Vertical Section [ft]
13-3/8" Casing @ 1,500'md
20" Drive Pipe @ 375'md
Planned TD @ 7,660'md
Actual TD: 7" Casing @ 7,075'md
12-1/4" x 17-1/2" Hole Size
12-1/4" Hole Size
8-1/2" Hole Size
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
-2,500 -2,000 -1,500 -1,000 -500 0
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Figure 6: Torque and Drag - Drilling Sensitivity Analysis
TORQUE & DRAG ANALYSIS
HELICAL BUCKLING & DRILLING LOADS
-150,
000
-100,
000
-50
,0
00
0 50
,00
0
Loads [lbf]
Hel. Buckling Load [lbf] Drlng Load 2 (WOB=15klbs) [lbf]Ext. Hel. Buckling Load [lbf] Drlng Load 3 (WOB=25klbs) [lbf]Drlng Load 1 (WOB= 0klbs) [lbf] Drlng Load 4 (WOB=50klbs) [lbf]
Critical Inclination
Critical
Region
Preliminary Drillstring
HOLE SIZE: 8-1/2"
MODE: ORIENTED
FRICTION FACTOR (CSG/OH):.25/.30 Modified Drillstring
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
-150
,000
-100
,000
-50
,0
00
0 50
,000Loads [lbf]
HWDP
Placement
MeasuredDepth[ft]
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Figure 7: Torque and Drag - Tripping Sensitivity Analysis
TORQUE & DRAG ANALYSIS
HELICAL BUCKLING & TRIP LOADS
-150
,000
-100
,000
-50
,000
0 50
,000
100
,000
150
,000
200
,000
LOADS [lbf]
Hel. Buckling Load [lbf] Trip Load 1 (WOB= 0klbs) [lbf]
Ext. Hel. Buckling Load [lbf] Trip Load 2 (WOB=15klbs) [lbf]
Pick-Up Load [lbf] Trip Load 3 (WOB=25klbs) [lbf]
Slack-Off Load [lbf] Trip Load 4 (WOB=50klbs) [lbf]
HOLE SIZE: 8-1/2"
MODE:ORIENTED
FRICTION FACTOR (CSG/OH): .25/.30
O
O Critical Trip Depth
O
Preliminary Drillstring Modified Drillstring
Critical Inclination
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
-150
,000
-100
,000
-50
,000
0 50
,000
100
,000
150
,000
200
,000LOADS [lbf]
MEASURED
DEPTH
[ft]
O HWDPPlacement
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