Segregated pathways mechanism for oil and water flow through an oil-based gelant

Abstract

Excessive water production during oil and gas recovery is often controlled by the injection of polymer-based gels into the near well-bore formation. Certain polymers and gels, when placed within a porous rock, are known to reduce the water permeability much more than oil permeability (often known as disproportionate permeability reduction, DPR). Different mechanisms have been postulated to explain the relative permeability change, one of the most widely accepted of which is the mechanism of segregated pathways. The key element of this mechanism is that a water-based gelant will follow the water pathways, producing a gel in these pathways, thereby reducing the water permeability. Likewise, an oil-based gelant should follow the oil pathways and preferentially reduce the oil permeability. A series of two-phase flow experiments were performed in transparent micromodels under both water-wet and oil-wet conditions to test this hypothesis. An oil-based gelant, a solution of tetramethyl orthosilicate (TMOS) in oil that preferentially reduces water permeability, was used. This is in contrast to the relative permeability effects reported for most oil-based gelants. The tetramethyl orthosilicate oil-based gelant follows the oil pathways, but only reacts with the water, to produce a silicate gel. The gel therefore dramatically reduces the water permeability in the water-occupied regions, and also induces the formation of new water paths between the oil and the gel. The results from studies in water-wet and oil-wet media confirm that the flow of oil-based gelant through the oil paths, and its subsequent reaction with water, produced a significant reduction of water flow but less change in the oil flow. Visual and quantitative evidence that segregated paths cause a preferential reduction in water permeability, and a disproportionate permeability reduction, are presented.