A 'wells-up approach' to rig design

Andy Kay, Rodrigo Rendon
Sunday, October 7, 2012

Getting the drilling facilities design process right not only ensures the operator gets the ideal rig for the job but also increases HSE and operational efficiencies and cuts rig construction and commissioning costs. Andy Kay and Rodrigo Rendon discuss the RDS approach.

Experience continues to show that many projects suffer as a result of decisions made (or in some cases, not made) during the early phases of conceptual and front end engineering. Particularly in situations where permanent fixed or floating drilling facilities are deemed the best field development solution, getting the design process right ensures the operator is provided with the ideal rig for the job, increasing HSE and operational efficiencies and reducing rig construction and commissioning costs.

In addition it’s worth bearing in mind that drilling costs account for the major part of field development expenditure; therefore any improvement in design that is translated into better operational efficiency is indeed worth pursuing.

In its 35-year history providing a comprehensive drilling facilities engineering service at every stage of design, construction and modification, RDS has developed an approach that it consistently applies during the early design stage of new-build drilling facilities. This methodology is referred to as a ‘wells-up approach’ to rig design.

This approach is nothing more than common engineering sense backed-up by strong operational experience, where the company’s understanding of the wells to be drilled becomes the foundation from which all design decisions are based. In practice it requires the rig engineering design contractor to have, during the initial stages of a project, a good understanding of the client’s well designs, drilling programme, platform interfaces and operational philosophies, levels of drilling equipment mechanization desired or needed, and regulatory requirements. This structured approach provides a clear definition of the rig equipment selection and functionality, while ensuring the rig is not over- or under-rated for the expected operational efficiency and the wells it is scheduled to deliver.

Well models

RDS utilises the well design as the key input to generate the rig basis of design. Although it is recognised that most projects during the early phases will have uncertainty around the numbers of wells and their target step-out, the client will typically develop a series of ‘model well designs’ based around increasing displacements. These well designs will show the casing setting depths, planned mud systems and weights, and the required cement programme. The well models will then be reviewed and condensed into the upper percentile in terms of complexity and a well basis of design developed to collate in one document the basis to be used for rig design.

The wells-up approach to concept selection can be loosely broken into a six-step process starting with the well design.

From the well design, the first stage is to create the rig basis of design which will entail analysing the well parameters and completing calculations such as maximum drilling torques, drag, maximum hook load and surface pressure when circulating and so forth. From this basis of design the main drilling equipment can be specified. Taking a top drive as an example: the rig basis of design will have calculated the maximum rotating torque required plus the likely hook load and by adding RDS norms which have been generated over years of drilling experience, the torque and horsepower for the top drive can be defined, allowing equipment specification to be generated and a specific top drive to suit the well selected. All other pieces of drilling equipment are specified in the same manner.

Continuing with the RDS proven process, and after all the equipment has been specified, an equipment and weight list will be generated for the rig which will allow the project to move forward on to layout drawings. Experienced layout designers will then create 2D/3D computer models to suit the specific installation type. Once the rig has been designed, the final part of the process is to generate an EPCI schedule and cost estimate, again utilising RDS’ experience in designing and building newbuild drilling facilities.

The other common sense element incorporated into early conceptual and front end engineering work is the inclusion within the team of personnel with extensive drilling operations experience. A rig manager or a person with equivalent operational experience is typically a recommended team member who adds hands-on experience during the early phase of a project. Furthermore, the client and contractor should aim for this individual to see the project through from design to operations. This proactive approach provides greater ownership and operations input into the design. It also ensures early identification and training of rig crews takes place in advance of operations. The implementation of this approach is likely to yield significant cost savings and efficiency gains given that issues identified during conceptual engineering can be rectified more easily and cost effectively than if found during the construction and/or commissioning.

RDS has been involved in some major industry projects over the years, for example Kvitebjorn, Brent, Beryl, West/ East and Central Azeri, Arkutun Dagi and Hibernia. Examples of RDS’ 2010 work include the design of twin derrick dry tree drilling facilities and a modified land rig to be located on a man-made island in the north Caspian Sea.

One of the challenges on the twin derrick job was that the platform is to produce heavy oil. Due to the increased workload of pulling submersible pumps and the substantial number of well slots, frequent intervention work would be required. This led the design to incorporate a large integrated deck for two separate intervention operations located below the drilling derrick modules, catering for simultaneous operations and allowing the continued drilling of new wells from both drilling rigs. Designing for four simultaneous operations within the working environment and maintaining a safe operation was a specific challenge for the design and resulted in an integrated engineering design and operations team working on the project. The ‘wells up approach’ was adjusted to suit the project workscope with two basis of design documents created to delineate the separate requirements of the drilling modules and the intervention work scopes.

As well as having to cope with the harsh North Caspian environment and zero discharge requirements, the man-made island design concept had to allow for skidding in both north-south and east-west directions to suit the well pattern. Typically land rigs are not designed for skidding operations and therefore the design concept had to allow for an integrated skid base, skid pad system and also cater for the increased drillfloor level due to the elevated structure. The knock on effect of having a skidding land rig means the drilling mud system has to have a long mud return gutter running the length of the well slots to allow the return of drilling mud and cutting to the mud active system located in a separate shelter. Again, due to the harsh environment and extreme temperature in the North Caspian region, the mud return gutter has to be fully insulated and self supporting.

In both these examples, the ‘wells up approach’ was successfully utilised to suit the client’s drilling requirements.

Conclusion

During the initial project stages, a focused and structured approach to defining and understanding wells is the key to bringing together ownership, lessons learned, operational drilling knowledge and a strong drive to design a rig that will provide safe, effective and trouble-free operations.

Early phase engineering work is critical in defining the economics of a development project. The appropriate performance of front-end activities will also have a direct and positive impact on project execution. It is critical that the drilling programme is properly understood, rig requirements are discussed and personnel with sufficient operations and project execution experience participate in the early phase activities. This will facilitate life of field operations and increase the level of project execution assurance before and during commissioning. OE

About the Authors

Andy Kay, a member of the RDS conceptual engineering and consultancy team, is a mechanical engineer with over 12 years’ experience on major brownfield and greenfield design, construction and commissioning projects. Lately he has specialised in the front end area of engineering definition for drilling facilities, participating in a number of conceptual newbuild drilling facilities design studies for clients such as Statoil, BP, Shell and Total.

Rodrigo Rendon, RDS’ head of business development, holds a degree in chemical engineering and has over 15 years’ experience in the international oil and gas industry. He started his career as an offshore and onshore field engineer for Schlumberger and has subsequently performed lead technical, operations and consultancy roles for clients such as Elf, Eni and BP.

Categories: Middle East Drilling Russia Rigs Design

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