A Robust Torque and Drag Analysis Approach for Well Planning and Drillstring Design

5/28/2018 A Robust Torque and Drag Analysis Approach for Well Planning and Drillstring Design

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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


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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


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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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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


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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


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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


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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


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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)




Rotary Drilling

- WOB #1 (No 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


11/16

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


12/16


13/16

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


14/16

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]


15/16

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


16/16

A Robust Torque and Drag Analysis Approach for Well Planning and Drillstring Design

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Transcript of A Robust Torque and Drag Analysis Approach for Well Planning and Drillstring Design