Less Damaging Drilling Fluids: Development and Lab Testing

The properties of the selected drilling fluid must be carefully planned to have minimal effects on the near-wellbore pore spaces. Proper mixing, monitoring, and maintenance of the drilling fluid throughout the drilling operations are as critical as the careful planning. Solids control equipment should be operated to remove the cuttings and maintain the density and rheological properties consistent. The characteristics of an effective reservoir fluid system include stability at high pressures and temperatures, proper and stable density, good filtration control, ability to transport cuttings, and minimal damage to formation pore spaces, Davidson et al. 1997. Selection of the most suitable drilling fluid additives takes into consideration numerous factors such as downhole conditions (pressure and temperature), formation type and petro physical properties, and the objective of the drilling operation. The experimental work in this paper involved rheological properties, thermal stability, API and HT/HP filtration and acid filter cake removal efficiency. Tangentional flooding showed that water based Mn3O4 drill-in fluid has the highest return permeability compared to the typical drill-in fluids (KCl/CaCO3/Barite and potassium drill-in fluids). Potassium formate drill-in fluid filtrate was not compatible with brine. This incompatibility explained its low return permeability in spite of its low solids content. Oil based drilling fluid was developed and tested with good acceptable results. Filter cake removal efficiency was showing more than 95%, indicating its removable formation damage.