Auto Gas Lift Application in Azeri-Chirag-Gunashli Field, Azerbaijan, Caspian Offshore

Abstract

The Chirag platform is one of six BP operated platforms to produce from the Azeri-Chirag-Gunashli Field in the Azerbaijan sector of Caspian Sea. The Chirag platform was scheduled for early oil delivery but was not developed with any means of artificial lift and as the field became mature, wells experienced water-breakthrough. In the absence of artificial lift, wells can typically flow naturally up to 20-40% watercut at steady-state conditions, however restart of these wells is challenging and at some point, impossible. Historically high watercut (20-40% and above) Chirag wells were side-tracked to up-dip dry oil leg. However, sidetracking for this reason could be uneconomical and could leave reserves from main production sands unrecovered. Therefore, enabling artificial lift for Chirag wells is vital. Several artificial lift options were evaluated, including ESPs and Jet Pumps. The most attractive method proved to be Gas-lift. In the absence of surface facilities to provide gas lift injection into the wells, using high pressure shallow gas formation as a source for gas lift was identified as suitable both from technical and economical perspective. This project was the first of its kind implementation in BP and offshore Caspian. A number of technical challenges had to be solved to deliver the project: Selection of continuous and permeable gas bearing formationOptimum gas lift valve size selectionSand production from perforated shallow gas formationPlant constraints to start-up and produce the well with AGL Three formations were selected as a potential energy source for gas-lift supply. It was identified that among all three zones only one is continuous (confirmed by reservoir pressure data in the Chirag area), with a good rock properties and adjacent to a field operated by the National oil company SOCAR with long production history. The gas lift valve size was selected to deliver enough energy to continue producing the well at high WC (>40%), minimize depletion in gas formation and lessen shut-in cross-flow of the lift gas. Perforation and down-hole completion were designed to minimize likelihood of sand production from gas formation, and in the case of sand production limit erosion of downhole equipment. Thorough risk evaluations were carried out to enable start-up of the well with high shut-in tubing head pressure which was due to high reservoir pressure of gas formation and its cross-flow to main production sands. This paper will focus on describing the technical evaluations carried out to assess and solve the challenges presented above and compare current performance of the wells' vs predicted. As of today, two Chirag wells are operated with AGL and one well has AGL capability for future implementation. The AGL project is confirmed to be a reliable mean of artificial lift method for Chirag wells assuming limited depletion in shallow gas reservoir.