Influence of modified starches composition on their performance as fluid loss additives in invert-emulsion drilling fluids

The influx of the liquid phase of drilling fluid, known as filtrate, in oil and gas producing zones can cause a significant decrease in the relative permeability of the fluids in the reservoir, and consequently, the well's productivity. The growing interest in developing non-aqueous fluids with low toxicity and good performance under extreme temperature and pressure conditions encourages research in this area. This study investigates the potential of using starch derivatives modified with vinyl esters from fatty acids, as additives to control filtrate in invert-emulsion (W/O) drilling fluids. There are no reports of the use of modified starches as additives to control filtrate in non-aqueous systems. The synthetic drilling fluids used in this study were prepared from a standard formulation, submitted to a dynamic aging process and evaluated by means of physical-chemical filtration tests at high temperature and pressure, along with electrical stability and rheological tests. The results indicate that the formulations developed from fatty esters from starch are able to compete technically with the standard drilling fluid, and the performance of these materials is associated with the degree of chemical modification of the polysaccharide.