Yield stress behaviour of formulated water based drilling fluid with tannin additive

Deflocculant is added into water based drilling fluid to disperse the flocculated clay that has an adverse effect on rheological properties at a temperature above 120°C. Currently, commercial deflocculants introduced have negative environmental effect. Therefore, by using plant derived additives could help resolve the weakness, since they are nontoxic and inexpensive. This study aims to evaluate the potential use of tannin from Rhizophora Mucronata to act as deflocculant agent in water based drilling fluid. Three different concentrations of tannin which are 2g, 4g, and 6g were added to the drilling fluid and its rheological properties and filtration properties along with density and pH were measured. It was observed that the addition of tannin decreased the rheological properties such as plastic viscosity, yield point, and gel strength. Furthermore, the filtrate volume and filter cake were also decreased due to the effect of tannin additive. Addition of 4g of tannin to the base fluid has been found to be the optimum concentration of tannin that exhibited the best deflocculant behaviour in water based drilling fluid. In addition, the relationship between shear stress and shear rate were constructed based on three different rheological models which are Bingham Plastic, Power Law, and Herschel-Bulkley. The result showed Herschel-Bulkley model was best representing the yield stress behaviour of water based drilling fluid with tannin additive.