Successful Water-Shutoff Case Histories in a Naturally Fractured Carbonate Reservoir in Offshore Mexico Using an Organically Crosslinked Polymer System With a Modified Tail-In

摘要

This paper presents the laboratory development and successful field implementation of an organically crosslinked polymer (OCP) system for water- and gas-shutoff applications. An overview of case histories in a naturally fractured carbonate reservoir (with BHT >250°F) in offshore Mexico where the OCP was successfully applied to reduce water production is presented. To control overdisplacement of the treatment, a modified tail-in combining the OCP system with inert particles was used to provide leakoff control, resulting in a controlled placement of the sealant. The OCP system is based on a copolymer of acrylamide and t-butyl acrylate (PAtBA) crosslinked with polyethyleneimine (PEI). To date, more than 600 jobs have been performed with the OCP system around the world to address conformance problems, such as water coning/cresting, high-permeability streaks, gravel-pack isolation, fracture shutoff, and/or casing-leak repair. The development results of this OCP system are discussed regarding its activation time and its effectiveness to limit permeability to water and provide thermal stability in sandpack flow tests at elevated temperatures. Lastly, the combination of the OCP system with inert particulates to provide fluid-loss control is discussed. The OCP system has been successfully applied to sandstone, carbonate, and shale formations in need of conformance treatments. This system has been successfully tested to withstand a differential pressure of at least 2,500 psi and is resistant to acid, CO2, and H2S environments. Because of the ability of the OCP system to withstand pressure, workover operations have been successfully performed in previously treated wells including acid-stimulation, sand-control, and frac-packs treatments, among others. An overview of case histories in which the OCP system was used in offshore Mexico is presented. This advanced water-control technology has extended the well life and profitability of the treated wells. In the past, many of these wells were abandoned because of the limited water-handling facilities.