Experimental Investigation of Rheological and Filtration Behavior of Water-Based Mud Using Response Surface Methodology (RSM)

Abstract

Rheological and filtration properties of water-based muds (WBM) are essential for optimum
drilling fluid applications. Numerous difficulties are associated with mud rheological and filtration
characteristics including poor cuttings transport, loss circulation, formation damage and suspension of
cuttings. This study investigated the impact of a readily available sago starch as a rheology modifier and
filtrate reducing agent in water-based mud system. The effects of sago starch in addition with DUO-VIS on
rheological and filtration properties of water-based mud were assessed in terms of plastic viscosity (PV),
yield point (YP), apparent viscosity (AV), filtrate volume (FV) and filtercake thickness (FCT). All tests
were carried out at a standard temperature and pressure conditions utilizing response surface methodology
(RSM). RSM was employed by considering central composite design (CCD) and taking three factors:
bentonite, sago starch and DUO-VIS concentrations. Plastic viscosity, yield point, apparent viscosity, filtrate
volume and filtercake thickness were considered the responses in the design. Bentonite, sago starch and
DUO-VIS concentration were ranged from 1-5 ppb, 2-8 ppb and 0.5 to 2 ppb, respectively. Experimental
results showed that sago starch improved the rheology of mud with an optimum concentration of sago starch
i.e., 8 ppb in addition with 3 ppb of bentonite and 1.25 ppb DUO-VIS. Moreover, it was noticed that filtrate
volume and filtercake thickness were also reduced with increase in starch concentration. It was concluded
that sago starch exhibited an acceptable rheology as recommended by API.