After more than 30 years of development and refinement, the technology for formulating halide-based brines for drilling and completion-fluid duty is relatively mature. Nevertheless, the halide brines still exhibit certain performance deficiencies that can significantly limit their utility.
Laboratory tests indicate that a series of organic brine systems based on the alkali metal salts of formic acid have a promising range of properties that are superior to those of the halide brines in nearly all respects. The outstanding features of the formate salts are:
- They can provide high-density brines that are non-hazardous and appear to be compatible with oilfield hardware. - They are environmentally responsible and readily biodegradable. - As powerful anti-oxidants, they can protect viscosifiers and fluid-loss polymers against thermal degradation up to temperatures of at least 150C. - They are compatible with formation waters containing sulphates and carbonates.
It is anticipated that formate brines will soon find application as high-performance drilling and completion fluids in a number of demanding operational environments where conventional fluids have difficulties in meeting the required performance specifications.
Following the first use of clear, high-density brines as packer fluids in the late 1950's, a range of specialised salt solutions have been developed for placement across oil and gas production zones, to prevent formation impairment during drilling, completion and workover operations. The full potential of brines as high-performance drilling fluids has yet to be realised on a wide scale, although this situation may soon change with the growing awareness of their advantages for slim hole and shale drilling.
The industry-standard clear brine fluids normally comprise concentrated aqueous solutions of one or more alkali-metal and alkaline-earth-metal halides, sometimes with zinc bromide, formulated to provide the required performance characteristics at lowest possible cost. The technology for formulating halide-based fluids is now relatively mature, yet a number of difficulties still exist (particularly with the higher-density calcium bromide and zinc bromide compositions) that can significantly limit their applicability.
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