An improved test protocol for high temperature carrying capacity of drilling fluids exemplified on a sepiolite mud

Drilling fluids with a high carrying capacity can improve the rate of penetration only if they maintain their suspending properties under downhole conditions. Testing, however, is generally performed by hot rolling fluids at the expected temperatures and measuring rheology after cooling which can produce misleading results. Therefore, a new test protocol was developed using a sepiolite water-based fluid and a xanthan gum-based reference system designed for drilling high temperature wells. First the static carrying capacity of the fluids was evaluated by suspending simulated cuttings and aging them statically before evaluating the samples visually. With conventional testing, both fluids seemed to retain their suspending capability after aging equally, however, only the sepiolite fluid maintained its excellent suspending property up to 150 °C (302 °F) in the static carrying capacity tests. This was confirmed by HTHP (150 °C/302 °F) viscosity measurements thus showing the importance of testing under actual conditions.