In September 1999, Statoil completed Well A-13 in the Are formation ofthe Heidrun field with a 130-m openhole gravel pack. After only a few days of production, a high gas-to-oil ratio (GOR) required the operator to shut the well in. Free gas was believed to be flowing from a gas-filled sand located immediately above the 9 5/8-in. casing shoe. Production analysis indicated a high-permeability flow channel between this layer and the upper zone of the gravel pack. The operator and a major service company jointly evaluated different chemical gas shut-off systems and several placement methods. A new generation of organically crosslinked polymer gel technology was selected. In addition, the operator desired that the gel be injected with open-ended CT and without mechanical packers to reduce operational risk. Therefore, a chemical diversion system was required for protecting the lower zone.
In February 2000, a temporary blocking agent consisting of a crosslinked hydroxypropyl guar polymer was placed in the lower part of the gravel pack. Then, the permanent sealant was injected into the gas-producing zone. After 72 hours, CT was used to wash the well. Finally, the well was lifted with production gas. The entire operation was completed in a single run with CT.
Currently, the well is producing oil at a rate of350 Sm3/d and no significant free gas. Production paid for the cost of the sealant treatment within 1 month. Additionally, this treatment prevented the operator from having to recomplete and sidetrack the well. This paper describes the well's gas-flow mechanism, the polymer gel systems used for sealing the gas-flow zone, the placement technique, and the operational aspects of the selective gas shut-off treatment.