1. n. [Drilling Fluids]
A special fluid designed exclusively for drilling through the reservoir section of a wellbore. The reasons for using a specially designed mud are: (1) to drill the reservoir zone successfully, often a long, horizontal drainhole. (2) to minimize damage and maximize production of exposed zones. (3) to facilitate the well completion needed, which can include complicated procedures. A drill-in fluid should resemble a completion fluid. It may be a brine containing only selected solids of appropriate particle size ranges (salt crystals or calcium carbonate) and polymers. Only additives essential for filtration control and cuttings carrying are present in a drill-in fluid.
See: bland coring fluid, brine, calcium carbonate, carboxymethyl starch, carrying capacity, cesium acetate, cesium formate, completion fluid, conventional mud, core, filter press, filtrate tracer, filtration, formate, formation damage, hydroxypropyl starch, particle-plugging test, sintered, sized calcium carbonate, sized salt, slurry