Investigation and remediation of active-clay contaminated sepiolite drilling muds

Unconventional gas and oil development has gained remarkable attention in recent years. However, the high content of active clays in shales makes drilling difficult. Since most formations drilled for oil and gas exploration are shales, active solid dispersion into the drilling mud is a common problem. This might results in severe problems, such as stuck pipes, circulation loss, excessive torque and drag, inadequate cuttings transport, poor log quality, poor primary cement job, and borehole instability.In this study, active clay contamination effects on sepiolite drilling muds were experimentally investigated for hostile drilling conditions. Rheological properties of both unweighted and barite-weighted sepiolite drilling muds with and without sodium chloride additions were tested at ambient to 204. °C temperatures. Filtration loss properties were determined at a 0.689. MPa pressure differential. The drill-hole cleaning efficiency of sepiolite drilling muds was investigated too. Methylene blue tests were also performed to determine the tolerance of sepiolite muds to solids accumulation.Major findings of this study inferred that sepiolite drilling muds formulated in a certain mixing order of additives provided effective rheological properties and water loss. Acquired results of methylene blue test and sufficient annular velocities for all samples strongly supported availability of these muds against active-clay contamination which is the special emphasis of this study. This is also particularly important for expensive high-angle and extended-reach wells.