Abstract
The Cannonball Field is a one Tcf gas condensate development offshore Trinidad producing at a sustained rate in excess of 800 MMcf/D from three wells. The completion design selected was 7⅝ inch production tubing with an open-hole gravel pack. The initial well (CAN01) has produced at 333 MMcf/D. These rates are higher than typically experienced which has raised concerns concerns about the resultant potential for metal erosion. As a result, a rigorous erosion study was initiated. The objective was to quantitatively evaluate erosion at various rates over the life cycle of the well to appropriately design the completion and select the appropriate materials.
The erosion nodes within the completion - changes in flow direction (e.g. a tee such as in the wellhead) and/or flow constrictions - were identified as: the tree; a landing nipple profile near the surface; and a formation isolation device (FID) positioned in the gravel pack assembly. The key parameters were defined as particles of sharp sand, with a diameter of 50 microns, at a concentration of 0.1 lbs/MMcf. Erosion rates were calculated using the erosion model - Sand Production Pipe Saver (SPPS) - developed by the Erosion/Corrosion Research Center, University of Tulsa, USA. Erosion rates were calculated over the life cycle starting at initial rates of 280 and 400 MMcf/D. Erosion rates were also calculated with and without a liquid film (a protective layer on the pipe wall that can reduce the erosion rate). Erosion results (without a liquid film) at all nodes exceeded BP's erosion limit; however, the erosion results with a thin liquid film were mostly below the company's erosion limit. Determination of the presence and thickness of the liquid film was critical. A multi-phase pipeline simulation calculated that a sufficient liquid film would exist at all critical areas. Erosion of the tree was further assessed by computation fluid dynamics (CFD) models, which identified several hot spots; thus, additional cladding of all flow-wetted surfaces and rounding of the outlet corner was required. The Cannonball completion design, including the tree, was determined to be capable of sustained rates up to a maximum 400 MMcf/D. The three (3) well development, where initial rates have been as high as 333 MMcf/D, has been on production for several years without any erosion issues.
