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Shell Casing and Tubing Design Guide

Chapter 1

Shell Design Philosophy

Shell Design Philosophy.............................................................................................................2

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1. SHELL DESIGN PHILOSOPHY

Shell wells share the foundation of being designed and constructed based upon historicaloperating experience and a long tradition of operating and producing integrity in many differentparts of the world. This shared philosophy has resulted in Shell being recognized for itscompetency in well design but also being criticized for conservatism and risk aversion in the past.Future wells will be designed and built based upon maintaining this commitment to competencyand integrity, but will use risk-balanced innovation and adaptation to be able to cope with moredemanding well designs in a cost-leadership environment.

The well will be designed around three factors: the needs of the completion to provide optimumproduction over its lifetime; the need for reliable pressure containment over the life of the well;and the cycle time required to put various design options into production. Completionrequirements and production schedules should be defined early and drive both the tubing and thecasing design. Technology should be used aggressively to accommodate the well completioninstead of compromising on the completion design by assuming what can be accommodated basedon past practice. The completion concept forms the basis for the overall well design “from theinside out.”

The new well design taps into both historical learnings and recent innovations through sharing ofbest practices with global staff having decades of experience through the use of networks such asthe Wells Global Network and training programs. Reliance on historical learnings does not meanthat new designs copy past wells. Instead this means that past learning experiences should be afoundation for the innovation of each new well design. This Design Guide is intended to fosterthe creation of new casing and tubing design opportunities which link to both historical andcontemporary learnings. The latter is to be achieved through a commitment to keeping this Guideevolutionary. Risk assessment will ensure that design integrity is maintained.

The basic design process will still be the same all across Shell. In principle, two Shell engineersworking with the same well conditions in different parts of the world will come up with the samebasic well design. However, in the end, their detailed well designs may differ, taking account ofhistorical learnings, local expertise, and local innovation of the particular operating company.This is the reason that Shell has introduced the layered design process discussed later in theGuide.

The engineer doing casing or tubing design should have awareness of general trends in industrywell design, but the engineer also should keep well abreast of and leverage the innovations andnew learnings being generated by Shell. When new technologies, innovative ideas, or newbusiness conditions demand and enable innovative new well designs, the design of casing andtubing should be taken to the cutting edge at which well and operating integrity can be maintainedthrough prudent management of risk. However, the innovation of casing and tubing designshould not reflect the initiative of an individual engineer; it should reflect the consistentevolution of local design practices within an operating company.

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Shell wells must make more rapid use of new and evolving technologies. This is supported bythe large annual investment in technology, and part of the responsibility of the well engineer is tokeep abreast of the new technology and rapidly exploit the technology for the benefit of increasedproduction or reduced cost at managed risk. The aggressive use of new enabling technologyshould not be done at the expense of prudent risk management incorporating historical learnings.Shell will innovate faster than its competition, but will use prudent risk management to do this.The Guide can be used to help rationalize changes in design practice specific to the conditions oflocal operating companies. The casing and tubing should be designed to provide well integrityand innovation at the lowest possible cost while always managing risk. Risk should not beavoided in an absolute sense, but instead risk should be managed by evaluating the likelihood ofevents occurring, the likely consequences, and their impact over the total lifetime of a well.

Risk management should include both the risks to well control over pressures and fluids and therisks to competitive cost and position. Design changes should evolve either by taking a series ofincremental evolutionary steps linked by well successes, or by taking large leaps forward with theguidance of a risk assessment and hazard evaluation that supports the large step change. Everylarge change in well design should be accompanied by a risk assessment that is documented bythe engineer. This risk assessment can be either qualitative or quantitative. The risk assessmentcould entail a comprehensive study, but it also could involve just the engineer making anddocumenting (1) a subjective evaluation of the likelihood that events will happen; (2) thelikelihood that particular consequences will occur; and (3) the acceptability of this combination oflikely events and consequences. Shell wells therefore must be designed with the documentedmanagement of risks, not with the avoidance of risks.

Casing and tubing design should be done as a marriage between design concepts and operatingskills. This is one reason that Shell has introduced tiers for design practice. The basic design caserepresents the most conservative option for design possibilities and for control of the well.Designs with higher but still prudent risk represent the next tiers up in well design. These higher-risk designs are desirable for their benefit to well efficiency, and these should be implemented onan OU level. However, they should only be implemented when risk assessment indicates thatadequate controls are in place to manage safety and maintain well integrity; and only when thehighest well control skills are in place to manage the higher-risk well.

Where innovative design leads to the use of new equipment, part of the risk assessment should beto consider the value brought by the new equipment, the likely start-up performance of the newequipment, and the likely consequences of unforeseen issues with the new equipment. Newequipment should be used when the risk assessment suggests that the risk is acceptable in light ofthe added value.

A Shell well should be a quality design and should use quality equipment in order to make thedesign both optimized and fit for its purpose. Shell has a commitment to quality in well designand equipment, because the risks of an innovative well design can be managed only through aquality process. Quality does not necessarily mean use of the most expensive equipment. Instead,quality means use of the right equipment for the application. Quality in the well design may bebased on historical experience with equipment (that is, field-proven or grandfathered equipment),or quality may be based on testing a design concept and qualifying the equipment for the service.For either of these approaches, the equipment must be shown to be fit for the application.

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Like pipe and connections, Shell also provides quality stress analysis through the use of designsoftware to Shell standards. Delivery of the quality well is achieved partly through the Shell useof design software. The well design will be based on triaxial stress design and use of the samesoftware shared by all operating companies across Shell. Software expertise is one of the keycore competencies of Shell engineers. Shell uses its historical experience and large number ofwells drilled annually to share design best practices among different operating companies. Thecommonality of design software is one of the vehicles for this sharing of best practices.

Shell operating companies take responsibility for ownership of the tubing and casing design. Thetubulars design is not contracted out to third parties. Where support calculations are provided bycontractors, the work is supervised and owned by Shell engineers. This is done because of theimpact that tubulars design has on lifetime well reliability, cost, risk, and delivery. This approachis part of what makes the well a “Shell well.”

Tubing design should seek to maximize through-tubing accessibility to the reservoir. Industry-wide emphasis on lifecycle cost saving has raised awareness of the benefits of performingoperations such as perforation optimization, production logging, selective stimulation, zonalabandonment, and improved wellbore clean-out at reservoir level through the tubing. For fullflexibility and increased reliability in these operations, it is important not to inhibit the passageand operation of the tools involved. This requires the elimination of unnecessary restrictions inwell completions, i.e., maximizing the completion through-bore, together with a suitable matchingof the tubing and production liner sizes in cases where tiebacks are not used. A directconsequence of this is the desire for simplified well completions. The completion shouldemphasize overall life cycle production optimization, operational simplicity with respect to wellmonitoring, well servicing, and future workover requirements.