Multi-Zone Cased Hole Frac-Packs and Intelligent Well Systems Improve Recovery in Subsea Gas Fields

Abstract

Abstract A nine well subsea development project has been completed using cased hole frac-packs for sand control and an innovative multi-zone intelligent well system to improve recovery from a series of shallow, low pressure, gas reservoirs. In these wells, cased hole frac-packs have been installed to provide reliable sand control over the long, low net-to-gross, sand/shale target sequence: typically, three to six frac-packs per well. This outer cased hole frac-pack completion is then augmented with a multi-zone intelligent well system, consisting of isolation seals, surface controlled zonal isolation valves and downhole pressure/temperature gauges. The intelligent well system is run as a separate inner string to provide flow monitoring capability and allow shut-off of zones producing high water volumes. This critical water shut-off capability eliminates the risk of one or more high water production zones loading-up and killing adjacent low-pressure gas zones with associated loss of reserves. To date, a total of nine wells have been completed and are being successfully produced from three subsea gas fields. To maximize recovery from the fields' numerous but relatively thin gas reservoirs, production wells are completed over three to six separate intervals. These frac-packed intervals are then grouped to allow flow control and pressure/temperature monitoring to occur through up to six surface operated Interval Control Valves and associated downhole gauges. This combination of sand control and intelligent well control has provided an ability to perform multi-rate flow tests and pressure build-up tests on each reservoir interval to detect the start of water production or identify other impending production issues. After roughly five years of production service to June 2017, four of the 34 zones completed in the nine well project have had to be shut-in to eliminate high water production. These water shut-off actions performed via the surface controlled interval control valves are estimated to have improved gas recovery factors from 50% to 60% without requiring rig intervention. This paper will describe the reservoir challenges, completion design and operating practices employed in this successful program.