Maintaining Well Productivity through Deployment of a Gas Lift Scale Inhibitor: Laboratory and Field Challenges

摘要

This paper will focus on the laboratory and field challenges ofmaintaining productivity in a North Sea well through scaleinhibitor deployment via gas lift. Calcium carbonate scaleformation commonly occurs during early production offormation water and in this particular well was detected on thedownhole safety valve and upper tubing. Several scalemanagement options were considered, however, thatconsidered most likely to succeed was inhibitor injection viathe gas lift system.An extensive laboratory evaluation under the North Seafield downhole conditions was undertaken in order to qualify asuitable scale inhibitor/solvent package. While theidentification of a scale inhibitor capable of controllingcalcium carbonate was relatively simple, the combination ofan aqueous based inhibitor with a suitable solvent packageproved challenging. The initial product development stagewas focused towards identifying compatible blends of varioustypes of scale inhibitors (phosphonates, polymers and vinylsulphonate copolymers) with different solvent and solventmixtures. An essential aspect of the formulation design was tominimise the potential for volatile loss from the product to thedry injection gas.Several candidate scale inhibitor/solvent packages wereput through a rigorous laboratory evaluation programme underthe harshest possible conditions likely to be experienced in thefield. From this initial review products were identified aspassing pre-defined criteria and showed good environmentalqualities with very low viscosities (5cP or less at ambienttemperature) before and after volatile loss and had very lowcorrosivity (0.01mm/y). In addition, the chemicals displayedcomplete compatibility at concentrations in excess of 50%with the completion fluid, formation water and completionelastomers, and controlled calcium carbonate scaling at arelatively low concentration.The final part of the paper will provide details of the fielddeployment experiences and challenges of the gas lift scaleinhibitors developed.