Subsea drilling templates and tieback engineering offer savings

The use of pre-drilling with templates and tiebacks is an optimum choice for marginal fields where additional reservoir data are needed and where drilling-to-production time needs to be reduced.

The methodology can be cost effective when executed by experienced and skilled engineers. During the late 1970s and 1980s, pre-drilling was increasingly utilised to enhance project economics. For both oil and gas reservoirs, drilling wells while jacket and topsides structures were under construction reaped significant rewards. Once wells were tied back and completed, platform production could often be achieved shortly after first production.

With the increased demand for pre drilling, the major wellhead companies enhanced the mudline tieback equipment for both jackup and semi submersible drilling. Surface wellhead equipment was developed to allow space-out with mandrel type hangers. Additionally, pre-drilling template designs were optimised for installation by mobile drilling vessels, making available major cost savings in pre-drilling economics.

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Template viewed through lower rig deck


In recent years, with the development of smaller hydrocarbon accumulations and the advent of substantially lighter platforms, there has been an increased tendency to drill through jackets once in position, rather than using a pre-drilling template methodology. These small platforms have a much reduced fabrication cycle. The perceived complexity and increased costs associated with well tiebacks had made a number of operators prefer platform drilling options. These preferences were fuelled by bad experiences from early pre-drilling and tieback campaigns, when issues were less understood and planning was less extensive.

With many technical operations that occur infrequently, limited knowledge and experience often lead to budget overruns. This is particularly the case for template and tiebacks, where many aspects of the equipment and operations occur at the interface between drilling, structural and mechanical engineering. I such instances, the services of a specialist provider can add significant value to the project by identifying risks and remaining uncertainties, as well as optimising processes based on other operators’ experiences .An individual operator may carry out a template and tieback program in a region every 5 years or so. In a similar period, a specialist provider experiences involvement in more than 20 times that work scope.

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A variety of Claxton templates being installed


Once again, however, operators are evaluating the pre-drilling option for their developments. Successful tieback of wells is now normal where there is adequate planning and manufacture of cost effective drilling templates, and there are many such examples around the world. With the benefit of experience, a typical rig-installed drilling template is in place within 24 hours, with an average well tieback taking less than 48 hours. As the oil sector has matured, field developments are increasingly marginal. Even the larger accumulations have substantial technical challenges and hence reduced economics. Operators are therefore increasingly looking to innovative use of known technologies to reduce costs. Focus with marginal fields is now on the earlier re-use of appraisal wells in order to acquire more reservoir data, and the decoupling of drilling and project schedules in order to mitigate risk and cost over runs. The increased cost of template and tieback hardware is often offset by time savings afforded by batch drilling or completion processes. Refining economic models and replacing annual historical coarse inputs with monthly reports, makes the “time value” of money (through discounting) penalty less onerous in advancing drilling for compressed field development schedules. This scenario is entirely appropriate for short development schedules.

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