Drilling Fluids rheological properties play a vital role in controlling the success of the drilling operation. Rheological parameters such as effective (or apparent) viscosity, yield point (YP), gel strength, and plastic viscosity (PV) are very important for rig hydraulic calculations and hole cleaning efficiency. The water-based drilling fluid (WBDF) consists of a mixture of different solids and polymers which are used to optimize the rheological properties. Starch is a resistance-solid additive which is used mainly to control the filtration properties and at the same time to increase the viscosity of the drilling fluid.
The main goal of this research is to evaluate the effect of using micronized starch (1 μm) on the rheological and filtration properties of water-based drilling fluid. Field emission scanning electron microscope (FESEM) was used to evaluate the starch at different particle size. Rheological properties for the drilling fluid with different starch sizes were measured at ambient condition using Fan VG rheometer while the high-pressure high-temperature (HPHT) filter press was used to conduct the filtration experiment at 200°F.
It was noted that micronized starch (1 μm) had a vital effect on the rheological and filtration properties of WBDF. The PV of the WBDF with micronized starch was increased by 158% while the YP was increased by 125% as compared with the starch of conventional size (60 μm). The apparent viscosity (AV) was increased by 137% after reducing the starch sized to 1 μm. Adding the micronized starch for the WBDF resulted in flat rheology behavior where there is no increase in the gel strength between 10 seconds and 10 minutes. The filter cake thickness was reduced by 63% while the cumulative filtrate volume was decreased by 52% when 1 μm starch is used.
This study introduced a new drilling fluid formulation that contains a micronized starch as an additive, which will help the drilling engineers to avoid many drilling issues especially the formation damage by forming an ideal filter cake.