In the 1990s, the wells drilled in the Dan field, located in the Danish sector of the North Sea, were primarily completed with sand fracture treatments separated with packers and pipe, which include sliding sleeves [Ref 1]. The zones were stimulated with normal 20/40 mesh sand with a tail of resin coated sand to keep the sand in the fracture.As water injection was introduced in the Dan field, some water induced fracturing of the chalk reservoir occurred. In the production well DFE-05, a fracture created by a water injector hit the sand fractured zone in the well. Most likely causing damage to the resin coated seal in the zone and loose sand formed erosion holes in the tubing. Maersk Oil investigated the possible options to isolate the damaged zone without restricting the access to the well below the damaged zone. The investigation revealed that one option was to pump an environmental friendly colloidal silica gel into the zone to lock the sand in place.Several onshore tests with frac sand and colloidal silica gel showed that it was possible to displace the uncured gel into a sand/water mixture and get the gel to set up. The resulting leak rate through a gel/sand plug at high differential pressure was low, and the sand was successfully held in place by the gel.During the course of the intervention job the primary target zone of the gel was treated with good results. The neighbouring zone above the treated zone was also found to be producing sand. This zone was therefore treated as well. After the gel had cured, the inflatable bridge plugs used to place the gel correctly were removed and the well cleaned up and production restored from the remaining zones.Six months after the treatment, the well is still producing at a stable rate with only minor traces of sand. The successful job has created valuable learning about the colloidal gel technology and the way it can work in sand fractures.

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.