Asphaltene Deposition During Drilling with Emulsified Drilling Fluids

Abstract If the reservoir oil and drilling mud filtrate of drilling fluids are not compatible, mixing of these fluids in the oil reservoir can cause formation damages. For environmental reasons base oils with low aromatic content are preferred in emulsified drilling fluids. The potential for asphaltene deposition by mixing of emulsified drilling fluids and reservoir oils has been studied using stock tank oils with low and high asphaltene content. Two low aromatic emulsified drilling fluids were used, one with mineral base oil and one with synthetic base oil. Asphaltene deposition was studied both in bulk experiments and in floods using core-plugs of sandstone outcrop of low-to-medium permeability. When crude oils and mud filtrates were mixed in bulk, asphaltene deposition was detected in all cases. The formation damage was largest when the mud filtrates were mixed with the crude oil with the highest asphaltene content. During backflooding with the same crude oil, the formation damages caused by asphaltene deposition were removed. It is concluded that the potential for formation damage by asphaltene deposition is highest for reservoir oils with high concentrations of asphaltene close to the onset of asphaltene deposition. The potential will increase with decreasing aromatic content in the emulsified drilling fluids. If the reservoir oil is not saturated with asphaltenes and the damage area can be swept by the reservoir oil, formation damages caused by asphaltene deposition can be nonpermanent. If white oil is used in laboratory experiments, the potential for asphaltene deposition and removal of this damage can come out wrong.