drilling fluid is used to aid the drilling of boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also used for much simpler boreholes, such as water wells. Liquid drilling fluid is often called drilling mud. The three main categories of drilling fluids are water-based muds (which can be dispersed and non-dispersed), non-aqueous muds, usually called oil-based mud, and gaseous drilling fluid, in which a wide range of gases can be used. Despite the excellent track record demonstrated by invert emulsion fluids, operators continue searching for a water-based system that will give comparable performance. Increasing concern is placed on environmental impact of operations, making water-based alternatives more attractive.
The main functions of drilling fluids include providing hydrostatic pressure to prevent formation fluids from entering into the well bore, keeping the drill bit cool and clean during drilling, carrying out drill cuttings, and suspending the drill cuttings while drilling is paused and when the drilling assembly is brought in and out of the hole. The drilling fluid used for a particular job is selected to avoid formation damage and to limit corrosion.
Water-Based mud (WBM) and Oil-Based mud (OBM) are the most common drilling fluids currently used and both have several characteristics that qualify them for High Pressure High Temperature (HPHT) purposes. This paper compares the different characteristics of WBM containing Multiwall Carbon Nanotubes (MWCNTs) and OBM to help decide the most suitable mud type for HPHT drilling by considering mud properties through several laboratory tests to generate some engineering guidelines.
The tests were formulated at temperatures from 120 °F up to 500 °F and pressures from 14.7 psi to 25,000 psi. The comparison will mainly consider the rheological properties of the two mud types and will also take into account the environmental feasibility of using them. The results showing that the Water-Based offers a more environmental friendly choice yet some of additives that are used to enhance its performance at (HPHT) conditions, such as (MWCNTs), thus it is necessary to develop new formulas for (HPHT) Water-Based muds that could act like Oil-Based mud but cause less harm to the environment.