Enhancing the Rheological Properties of Water-Based Drilling Fluid Using Micronized Starch

The water-based drill-in fluid should be designed to have a good carrying capacity (yield point) and an ideal filter cake (thin, impermeable, and fast formed). The ideal filter cake will reduce the fluid loss and decrease the formation damage. In addition, thin filter cake will help avoid the common drilling problem such as differential sticking and this will reduce the total drilling cost. The common drilling fluid additive that can be used to minimize the fluid loss is starch, which has two unique features, environmentally friendly and cheap additive. The aim of this paper is to assess the effect of using the micronized starch as a fluid loss control additive to the drilling fluid. Different starch sizes were used such as 60μm, 7μm, and 1μm. Laboratory measurements using gas chromatography, field emission scanning electron microscope, and transmission electron microscopy were used to evaluate the micronized properties. High-pressure high-temperature filtration device was used to assess the filtration properties at 250∘F and 500 psi. The effect of starch size on the drilling fluid rheological properties such as gel strength, yield point, apparent viscosity, and plastic viscosity was investigated at 80∘F. The results obtained showed that adding micronized starch to water-based drilling fluid increased the yield point and the plastic viscosity by 250% with an optimum yield point/plastic viscosity (YP/PV) ratio of 1.5. Filtration test at 250∘F and 300 psi indicated that decreasing the starch size from 60 to 1μm resulted in reducing the fluid loss volume by 50% and decreased the filter cake thickness by 35%. These results indicated that the starch micronized-based (1 μ m) drilling fluid was efficient in forming a thin, and impermeable filter cake.