Gas-Lift Orifice Valve – Safelift
Erling Kleppa
Vice President Technology
Petroleum Technology Company AS
Abstract
In close cooperation withStatoil, Petroleum Technology Company AS (PTC) developed a gas lift orifice valve - Safelift - with the primary purpose of being qualified as a valve barrier with leakage requirements related to ISO 14310-V1 or better.
The valve was tested and qualified to the new ISO-17078-2, ISO-14310-V1 as well as additional and even more stringent Statoil criteria in a special validation test program.
In combination with PTC's hydraulic surface annulus valve (H-SAS), which is a gas injection valve installed in the VR profile in the production tree's unihead. The H-SAS is qualified to the ISO 10423 (API 6A) standard, thus provides two independent and extremely effective well barriers for the A-annulus. With this effective artificial lift is achieved without compromising the globally recognised barrier envelopes for producing wells.
In particular this is of importance in mature fields where the key to improved oil recovery is effective artificial lift with recognised enhanced risk for gas leaks from surface- and annulus barriers approaching the limit for its economic lifetime.
In our presentation we will argue that the combination of H-SAS and Safelift greatly enhances the application of gas injection for improved recovery since the technology complies with the most stringent barrier requirements in the industry, above the current API requirements, and thus offer improved safety, improved flexibility with injection rates and extended life time due to barrier control with the gas volume in A annulus.
Supplementary Information
In addition to the barrier requirement the valve is tested to cycling reliability simulation for a 15 year lifetime and several temperature and pressure cycles from 2 to 165 C and 100 - 10000 PSI.
The valve comprises of only 5 parts and all seal areas are isolated from the flow. A special metal coating has been developed for the surface areas so that metal-to-metal effective seal is obtained through the lifetime of the valve, simulated to 15 years effective life time.
We used advanced simulation technology to establish the optimal shape of the orifice and CFD analysis to design the valve according to the gas flow for minimal damage to seal areas and moving parts to meet the barrier- and lifetime requirements.
Later we realised that this work also enabled us to flow much more gas through the valve than is possible with conventional valves available in the market. The 1 1/2" valve, with 1/2" orifice could withstand a max flow rate of 8.2 MM Sfc/day.
The immediate advantage of this is that one can maintain critical flow at a very high rate, facilitating high efficiency from the main valve.