An engineered fluid formulation was designed to provide a 114-pcf non-damaging drill-in fluid for the Unayzah A and B sandstone reservoirs. Employment of potassium formate high density brine and manganese tetra oxide weighting agent provided superior drilling properties that delivered reduced formation damage, improved thermal stability, and lower drilling costs.

The use of acid-soluble manganese tetra oxide allowed engineers to increase the density of potassium formate drilling fluids and extend the density window above that offered by calcium carbonate. The reduced particle size (D50= 1 micron) and the spherical shape of the manganese tetra oxide reduced friction and drag. This improved control of equivalent circulating density (ECD) and plastic viscosity (PV) and significantly lowered rheological profiles. These optimal properties were maintained at temperatures exceeding 155°C.

Laboratory testing confirmed high performance features such as:

  1. Excellent hole cleaning characteristics

  2. Thin filter cake with low lift-off pressures

  3. Low differential sticking potential

  4. Low treatment cost during drilling and re-use capability

  5. Superior rheological performance compared to high solids content oil-based fluids

  6. Improved drilling performance and hydraulic efficiency with the formate base system.

The vertical well in the Unayzah A and B sandstone reservoirs was completed with zero hole problems. The potassium formate/manganese tetra oxide system provided superior performance and stability even with elevated bottomhole temperatures in the tight gas formation. This paper reviews the laboratory design and development as well as the field application of the high performance, brine-based drill-in fluid.

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