Water and Gas Control in Naturally Fractured Carbonate Reservoirs: Development of a Novel Polymer Gel System with Foaming Properties

Abstract

Abstract Excessive undesired fluid production of water or gas can limit the economic life and profitability of hydrocarbon reservoirs. A variety of techniques for controlling water production have been attempted within the oil industry, including mechanical and chemical treatments. Chemical treatments can become more challenging when applied in reservoirs with either natural or induced fractures. More specifically, placement control becomes a critical factor, particularly within highly fractured and depleted reservoirs. This paper presents the development and optimization to further improve a widely used organically crosslinked polymer gel system by adding foaming properties to the innovative fluid system. Referred to as a foamed conformance polymer (FCP) in this work, the system can improve placement in naturally fractured carbonate formations for water and gas control applications. The standard (nonfoamed) organically crosslinked polymer system is based on a copolymer of acrylamide and t-butyl acrylate (PAtBA) crosslinked with polyethyleneimine (PEI). This FCP system can be foamed up to 70% v/v quality to be applied within a wide temperature range (40 to 350°F) with little to no effect on gelation time, providing a stable foam that maintains sealing properties. This paper discusses the following parameters: (1) FCP advantages and considerations, (2) FCP system components to develop foam properties, (3) FCP performance testing to optimize foaming properties up to 70% v/v quality at elevated temperature, and (4) sealing capabilities of the FCP system. Addition of foaming properties to this conformance polymer gel system adds the following benefits: (1) improved placement in depleted, naturally fractured or fissured carbonate reservoirs, (2) reduced hydrostatic pressure (density can be lowered to ~2.4 lbm/gal), allowing better control of surface pressure while placing the treatment into the targeted zone, (3) improved ability to fill fractures and displace reservoir fluids by providing a system with fluid-loss control properties, and/or (4) diverting fluid properties for optimum coverage when targeting long intervals. The FCP produces a high-quality, stable foamed solution to help effectively seal natural fissures and fractures for reduced flow of unwanted water and/or gas.