Simultaneous Acid Diversion and Water Control in Carbonate Reservoirs: A Case History From Saudi Arabia

Abstract

Abstract Acid diversion and water control are usually addressed as two separate issues. Associative polymers can be used to simultaneously achieve effective diversion and water control during a single treatment. A polymer-based treatment was applied in an offshore, perforated vertical well with two sets of perforations in a carbonate reservoir in Saudi Arabia. The acid treatment was needed to restore the productivity of the upper set of perforations and reduce water production from the lower set of perforations. Experimental studies were carried out to investigate the potential use of associative polymers to control water mobility and act as an acid diverter. Coreflood experiments were conducted on reservoir cores at downhole conditions (temperature of 200°F and pressure of 3,500 psi). Extensive lab testing showed that associative polymers had no significant effect on the relative permeability to oil. However, the relative permeability to water was significantly reduced. This paper presents a case history where an associative polymer was applied during matrix acid treatment of a damaged well. The treatment included stages of associative polymer solutions and 20 wt% HCl with additives. Post stimulation treatment production data showed that oil rate increased by 11-fold; whereas water rate decreased by 3-fold; resulting in a reduction in the water-cut from 75 to 14 vol%. The PLT test confirms that the associative polymer was very effective in diverting the acid to the oil zone. The PLT showed that the upper set of perforations was producing most of the fluid, which further confirmed that the associative polymer was effective in reducing the relative permeability to water.