Laboratory Evaluation of Organic Water Shut-off Gelling System for Carbonate Formations

Abstract

Abstract Water production can reduce or block oil and gas production rates. In addition, the lifting, handling, and disposal of produced water negatively impact the hydrocarbon production economics. Among several techniques for water control, crosslinked polymer systems are the most effective for certain water shut-off projects. The objective of this paper is to assess the effectiveness of crosslinked polymer system for water control applications in carbonate formations and present its optimal formulation. This paper presents a detailed lab testing of a cross-linked polymer system. The system includes a gelling agent, primary and secondary crosslinkers and an acidic activator. The evaluation covered extreme concentrations of all components, temperatures up to 212°F, differential pressures up to 1,500 psi, actual field water salinity, wide range of permeability, and extended testing time up to three months. Core-flood experiments along with Computerized Tomography Scanning and Environmental Scanning Electron Microscopy were used to assess the sweep efficiency and the strength of the gel inside the core plugs. Losses of active ingredients from effluent samples were measured using Thermal Gravimetric Analyzer. Results of carbonate core plugs were compared with that of Berea sandstone. Strength of the gel at different cross-linker and polymer concentrations was monitored using sealed glass ampoules. Gelation times were measured using bottle tests and rotational viscometers. Extreme vertices design was used to optimize the experimental work and mixture triangle was used to represent the final results. An optimal gelling system with controlled gelation time and maximum performance was attained for the targeted formation at 212°F. It was found that the gelation time was affected by the three main components of the gelling system. The acetic acid-based activator was found to have the highest effect on the gelation time. However, this activator was not effective when the gelling system was tested in carbonate core plugs. A major effort of this work was to develop alternative strategies for the ineffectiveness of acidic activator in carbonaceous formations.