Controlling excess water production in fractured carbonate reservoirs: chemical zonal protection design

Abstract

Abstract Fractured carbonate reservoirs are prone to premature water cut production at the early stage of recovery. Conventionally completed long horizontal wells, suffering from high water cut through fracture networks, need reliable and cost-effective treatment solutions to control water entry, without damaging oil-saturated segments. Protection of oil flow channels from polymer gel invasion could be a challenge in complex fractured reservoirs because of the enormity of the number of zones that may require damage protection. In this work, a chemical package system is developed, comprising three different chemical solutions. The first fluid is designed to protect the low-permeable oil-saturated zones by creating an impermeable barrier while keeping the water conductive fractures open, followed by a gelant, designed to invade, solidify, and seal off the water conductive fractures. The third treatment is designed for a complete dissolution of the protective barrier created by the first fluid. The effectiveness of this process is evaluated through a set of four core flood studies at reservoir conditions. It was observed that whereas the effective brine permeability could be reduced by 74–91%, oil effective permeability is reduced by 12–17% depending on the fracture aperture. The paper also discusses the key parameters to be addressed for successful field implementation of this technology.

Keywords

• Water shutoff
• Fractured reservoir
• High water cut
• Polymer gel
• Formation damage