Case History: How to Enable the Horizontal Development of Shallow Reservoirs

Abstract

Abstract Substantial volumes of oil and gas reserves have been discovered in the Norwegian sector of the Barents Sea. This will give numerous field developments opportunities in the years to come. However, some of these oil reserves are located within thin reservoir beds which maybe as shallow as 200 to 250 m TVD below mudline, which results in development drilling challenges to economically develop these reserves. The case study discussed in this paper shows how the use of a modern top hole well design can help facilitate the economic development drilling of these reserves. OMV (Norge) AS have drilled a set of exploration and appraisal wells in the production license PL 537 located about 350 km north of Hammerfest, Norway. The appraisal well "Wisting Central II" was planned as a horizontal well with three main objectives. The first objective being to prove that it is possible to penetrate such shallow reservoirs horizontally, the second one being the need for a representative production test from the reservoir and as last objective to gain appraisal information like oil water contact, reservoir data, etc. All well objectives were achieved according to plan. This paper will present one of the key technologies that enabled the 1.4 km long horizontal reservoir section, at 250 m TVD below mud line, to be successfully drilled and tested. Typically in these wells the conductor would be set 50 to 60 m below mud line which would significantly reduce the probability to successfully build the hole angle up to horizontal at the desired reservoir entry point due to the limited TVD available. Therefore, the plan was to substantially shorten the conductor, and to integrate it into a suction anchor based well foundation, a Conductor Anchor Node (CAN®) in what is now known as a CAN-ductor design. This structure provided the required load capacity and allowed the conductor to be as short as 11 m below mudline. This allowed sufficient TVD for building hole angle and achieve the horizontal reservoir entry point at only 250 m TVD below mudline. Thereby, this well could be successfully drilled as planned, to become the shallowest horizontal well ever drilled from a floating drilling unit. Since the installation of the CAN with integrated conductor is performed by a vessel ahead of rig arrival the technical benefits are further supported by an overall cost reduction as rig time is saved by not having to drill the conductor hole section and subsequently run and cement the conductor. Further cost savings are achieved due to the fact that no remedial and top up conductor cement jobs are required when using the CAN concept. To be noted is also that the wells P&A operations are simplified.