Pore-scale Visualization of Foamed Gel Propagation and Trapping in a Pore Network Micromodel

ABSTRACT

This paper describes an experimental study carried out using a transparent etched glass micromodel to investigate the complex fl ow of foamed gel in porous media at pore level. Foamed gels can be used as mobility control or blocking agents to minimize excessive gas or water production in oil reservoirs. Although the use of foamed gels as an enhanced oil recovery process has been studied for some time, the mechanisms of foamed gel flow and trapping in porous media are not so clear.

In this work, the influence of foamed gel microstructure on its propagation in porous media and the effect of the configuration of gas bubbles and liquid phase (gel) inside the micromodel on blockage effectiveness were evaluated through visual observation in a transparent etched glass micromodel. The experimental observations demonstrate that foamed gel presents better characteristics for fluid profile modification and therefore superior fluid diversion capability than conventional aqueous foams. Micromodel visualization and videotaped data of foamed gel propagation through the etched glass micromodel indicated efficient residual oil mobilization. Image and statistical analysis showed that foam bubbles are reshaped during propagation through porous media. The final configuration of trapped foamed gel bubble and liquid phase (gel) inside the pore space indicated an important role in the effectiveness of fluid flow restriction.

Introduction

Foams have been applied broadly as mobility control and blocking agents in oil and gas reservoirs. Conventional aqueous foam is a surfactant-stabilized dispersion of a relatively large volume of gas in a small volume of a liquid. In porous media, foam is generated when a liquid containing a foaming agent is mixed with either an externally injected or an in situ gas (1), with the gas occupying typically 50% to 99% of the total volume.

Foam mobility measured in porous media is many orders of magnitude smaller than that of the constituent gas (2). This mobility reduction is achieved primarily because the gas phase is dispersed into bubbles, which are generally about the size of the pore channels ( 2). Additionally, fl owing lamellae encounter significant drag because of the presence of pore walls and constrictions (3). This performance makes foams suitable for three potential applications: 1) mobility control, improving the displacement efficiency of gas drive processes; 2) mobility control and flow impediment, improving the sweep efficiency of other fluid injection processes; and, 3) partial or total pore blockage, restricting the flow of undesired fluids and plugging of high permeable oil “thief” zones (4).

Performance of foam that is already capable of strong mobility control may be further improved by the addition of suitable polymer or gelant (5). Incorporating polymers into a foaming solution affects foam properties primarily by increasing the liquid phase viscosity, which enhances foam stability minimizing gas bubble coalescence by decreasing the rate of drainage and reducing the rate of interbubble gas diffusion (6, 7). The stability and performance of polymer-thickened foams can be additionally enhanced by crosslinking the polymer in the aqueous phase of the foam. A foamed gel is created by means similar to those used for aqueous foam generation.

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