High-Density Monomer System for Formation Consolidation/Water-Shutoff Applications

Abstract

Summary This paper describes an in-situ polymerizable organic monomer hydrogel system for formation consolidation during deepwater drilling applications in which a water-soluble vinyl monomer solution is polymerized in-situ to seal and consolidate unstable geological zones. In deepwater wells, shallow zones may have pore pressures close to parting pressures. In these situations, lost circulation or flowing zones can be difficult to control and can lead to a complete loss of the well. Hydroperoxide and azo initiators are used for polymerizing solutions of 2-hydroxyethyl acrylate monomer in aqueous solutions of synthetic seawater, sodium chloride (NaCl), calcium chloride (CaCl2), calcium bromide (CaBr2), and zinc bromide (ZnBr2), with densities from 8.6 to 17.5 lbm/gal. These monomer solutions undergo controlled polymerizations in the formation to yield a crosslinked hydrogel matrix that can withstand high differential pressures. A similar monomer system has been used for water-shutoff applications but had never been formulated in heavy brines or used in the cool temperatures (50 to 60°F) typical of the shallow water-flow zones. The use of a high-density hydrogel for consolidation purposes would be an advantage in shallow water-flow zones because the gelant solution of the hydrogel could be spotted over, and allowed to flow into, the problem zone where the gelant flow is driven by the hydrostatic pressure of the treatment fluid. This process enables the use of the monomer system in wells where high-pressure injection of the treatment fluid into the formation is not an option. This article describes the hydrogel system's development, including gel-time curves and compressive strengths of consolidated sandpacks, and discusses factors affecting the performance and application of the system.