Resolving a Water Shortcut Between Old Wells with Multiple Completion Zones: Example in the Dan Field

Abstract

In mature fields an important challenge is shutting off injection water breakthroughs. In the Dan field offshore Denmark developed with multi-zone completed long horizontal wells, the primary method now is closing Sliding Side Doors (SSDs) in the horizontal completions. A shortcoming of this method is that it does not work if there is communication between individual zones or holes in the tubing. This is the case in many of the up to 20-year-old wells.The primary goal of a recent coil tubing conveyed well intervention was to remove a shortcut between two horizontal wells: a producer with 16 sand fracced zones and an injector with 5 water fracced zones. This was planned to be done by closing one or two PSI zones in the injector. The connection could not be removed by shifting zones in the producer due to a restriction in the vertical section, making the horizontal completion of the well inaccessible.Production logging results of the shut in injector showed a substantial cross-flow from zones 1 and 4 into zone 3 via both the sliding side door and a hole in the zone. Due to the presence of cross-flow, the injection well was effectively injecting an estimated 4,000 bbl/d into the culprit zone, when closed in at surface. Due to the tubing leak in zone 3 it was not possible to stop the flow out of the zone by shutting the door, so all zones (1-5) in the well were closed, and injection was stopped. The closure of all zones in the injection well resulted in an immediate response in the production well, reducing water production with 6,000 stb/d while increasing the oil production with 1,200 stb/d.The intervention and responses in nearby wells indicated that the injection well was connected to up to three other water injection wells and up to two other production wells. In this paper the reasons for these short cuts and the impact it has on water flooding are analysed.The lack of water injection in the area has resulted in declined production in other wells, hence the future challenge for the area is finding a new way of shutting the connections either by means of chemical conformance treatment in cases of connected zones or straddles in wells with tubing holes.

Relation of acoustic impedance to stiffness and porosity of Maastrichtian chalk in Dan field, Danish North Sea

“…The chalk of the Ekofisk Formation is richer in silica and clay and can be subdivided into an upper porous unit and a lower tighter, silica‐rich unit. The low matrix permeability of the chalk and few natural fractures necessitates production to be enhanced by artificial fracturing, the use of horizontal wells and water injection (Jørgensen, 1992; Eriksen et al ., 2010).…”