No 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.

A new and safer, high load capacity well construction concept has been developed. This new well foundation system as installed at a Norwegian Sea well location by Det norske oljeselskap ASA, is described herein, as well as its use and recovery. Heavy Blow Out Preventers (BOP) are normally used on drilling rigs designed for deep water and arctic applications, and heavier BOPs will have a negative impact on the stability of the well head. To mitigate these negative impacts, a new suction anchor type well foundation concept; CAN (Conductor Anchor Node) has been developed. The CAN unit provides sufficient load capacity for safely carrying heavy BOPs as well as X-Mas trees, thus protecting the well from fatigue capacity "consumption" in the drilling phase. The use of the concept will also reduce cuttings and cement disposal to the sea, which may be further important aspects in arctic and sensitive marine environment areas. The CAN will also mitigate the risks of the well becoming over-loaded by undesired, accidental loads, e.g.: as a result of a rig drive off/drift off situation. This is achieved by mobilising substantial carrying capacity from the soil through the CAN's large cross sectional area and captured soil mass. This is an important aspect in view of risk mitigation and improving possibilities of applying contingency means in case of undesired events or disasters, such as the Macondo case. The concept offers significant advantages in reducing rig time; as it enables pre-rig conductor installation, thus reducing top-hole construction costs and rig failure risk exposure. The concept's viability and advantages have been demonstrated by a number of full scale applications ranging from 270 m to 1 150m water depth on the Norwegian Continental Shelf. The CAN will be a facilitator for safe jetting of conductors (only short length conductor needed), as well as being an enabler for achieving successful cement jobs (if installed by drilling and cementing), as the conductor remains supported and motionless during cement set-up.