A Novel Drilling Fluid for Underbalanced Drilling

Interest in underbalanced drilling is growing worldwide. UBD, when properly designed, eliminates problems associated with the invasion of particulate matter into the formation. However, experience has indicated it is difficult to maintain a condition of continuous underbalance pressure throughout the complete drilling operation, resulting in fluid losses to the formation due to no mudcake on the borehole wall and leading to possible significant damage. So, in this paper a new drilling fluid was developed. It contains a kind of nanomaterial particles called Carbonblack. It is currently the most widely used carbon nanomaterial. This is the first time which Carbon block particles are used as a drilling fluid. Insoluble Carbon black maintains its individual particle identity through high levels of pressure. Coated with lubricant, the ultra-fine particle size penetrates openings and scratches not normally penetrable with other solids in the drilling fluid system. When overbalanced situation is happening, the Carbonblack particles can bridge and form a thin plugging layer as soon as possible in the pores or fractures in the borehole wall. This plugging layer can stop further fluid invasion into the formation.