Kuwait Oil Company introduced new fluid practices to improve producibility in the Minagish oolitic limestone reservoir in Umm Gudair field. The approach was designed to minimise formation damage in the reservoir section and apply a more effective filter cake removal technique during the well completion.

Experience on offset wells and results of return permeability studies showed that specially designed water-based drill-in fluids with optimally sized acid-soluble bridging particles were the preferred fluids for open hole completions on the Minagish reservoir. For removal of the cake and low permeability crush zone created by the drilling process a formic acid precursor (FAP) was used. The precursor is added to the completion fluid and reacts slowly with brine to release formic acid in the reservoir section. Conventional acidisation with HCl can cause wormholes, localised leak-off and failure to treat the entire interval effectively; FAP is in a neutral condition when placed. Localised reaction and loss zones are avoided and the released acid can act uniformly on the entire interval.

Four wells in this area were sidetracked due to depletion in pressure and increasing water cut. All utilized the same drill-in fluid. Subsequently wells UG 116ST and UG126ST were stimulated with HCl, whereas UG 38STRE and UG 110ST were treated with the FAP.. The two wells treated with the FAP had producibilities about twice those treated with HCl.

The combination of well designed drill-in fluid and FAP has shown great promise of facilitating the drilling process and increasing the producibility of the well with significant economic benefit. This paper addresses practical applications of the drill-in fluid and the breaker and reports on several additional benefits that were obtained.

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