This paper focuses on the unique problems that were confronted in the process of formulating and implementing a field redevelopment strategy for the Piper field, located in Block 15/17 of the UK North Sea continental shelf. The original Piper A development, including 56 directionally-drilled wells, was lost on 6 July 1988.
The process of selecting a site for the Piper B drilling template is reviewed in the context of:
the proximity of oil and gas pipeline networks serving the Tartan and Claymore platforms;
the proximity to subsea wells and debris at the Piper A site;
the presence of shallow gas hazards in areas adjacent to the Piper A site;
the requirement for directing some replacement wells to the original Piper A targets;
the requirement for directing other replacement wells to revised targets.
The drilling of Piper B redevelopment wells in close proximity to the Piper A well cluster requires an unusually rigorous and comprehensive approach to collision avoidance, as the possibility for deep intersection with existing wellbores poses a substantial drilling hazard. Key considerations in the planning and execution of Piper B directional drilling include:
the QC of survey records for the original Piper A wells;
the quantification of survey errors in the original Piper A surveys;
the assignment of error models for the calculation of positional uncertainty;
the generation and maintenance of clearance reports.
To date, six directional wells and two sidetracks have been safely drilled through the Piper B template. Strategic site selection and the highest standards of directional well planning and collision avoidance surveillance have been key ingredients of the ongoing and successful redevelopment of the Piper field.