The trend in the North Sea has been toward installing annular safety valve (ASV) systems for tension leg platform (TLP) completions or for gas-lifted platform production wells. To satisfy the requirements for a highly reliable annular safety system for the Norske Shell Draugen project and an impending Norwegian TLP completion project for the North Sea area, tests were initiated to investigate the feasibility of a polished bore receptacle (PBR)-based ASV system. The nipple system has the capability to handle high hang-weight and/or thermally-induced loads, and the PBR nipple, pre-installed in the casing string, will permit a variety of completion designs that can be determined later in the well-development cycle. Testing verified that 1) only a minimal pressure drop occurred through the system, 2) there were no compatibility problems between drilling/cementing operations and the PBR system, and 3) a PBR casing nipple assembly to anchor an ASV system has the capability to provide a viable alternative to use of a mechanical ASV packer and its related seals.
Demands imposed by industrial, governmental and regulatory standards concerning personnel and environmental safety on offshore platforms emphasize the need for a fail-safe annular control system. These needs can be met by an ASV system, which is designed to effectively contain flow of gas or fluid from the wellbore annulus at a point below surface, normally at subsurface safety valve installation depth. When selecting an annular safety system, proper material selection, simplicity of installation and retrieval, the number and nature of the sealing arrangements, dimensional/functional requirements, and economic efficiency are primary considerations for the operator. A review of these requirements leads to close examination of the PBR concept, which has shown capability to fulfill most of these design/operational needs. This paper will compare the primary design considerations for a packerless and a packer-based ASV system and will focus on the testing and qualification of the PBR nipple assembly to fulfill the requirements for a reliable annular safety system. Considerations of the completion design componential options are also included in the discussion to demonstrate the flexibility of this approach.
Simplicity of System Installation and Retrieval