Summary
Excessive gas and/or water production is a common problem encountered
throughout the lifetime of oil-producing wells. High-producing gas/oil or
water/oil ratios are normally responsible for both rapid productivity decline
and increased operating costs caused by gas or water processing. The result is
often a premature shut-in of wells because production has become uneconomical.
Foamed gels have been used as selective barriers to counteract disproportionate
gas/oil and/or water/oil ratios in oil production. However, research on the
effects of critical parameters such as wettability of the porous medium and
pore geometry on foamed-gel-blockage performance remains incomplete.
In this work, microscale experiments, which involve the magnified
observation of flowing and trapped foamed gel in etched-glass micromodels, were
performed. The purpose of this research is to provide new insights into the
sensitivity of foamed-gel-blockage performance as a function of porous-media
wettability (strongly water-wet or strongly oil-wet systems) and pore
geometry.
The experimental results indicate that foamed gels presented higher blocking
efficiency in strongly oil-wet systems than in strongly water-wet systems.
Under these experimental conditions, foamed gels exhibited higher blocking
efficiency at lower pore-body-/pore-throat-size aspect ratios. The plugging
treatment exhibited stability after subsequent steps of gas and brine
injection. Ultimately, these results indicate that the combination of foam and
gel systems has technical advantages that make foamed gels superior
mobility-control and plugging agents.
Introduction
In porous media, foam is a gas (or immiscible liquid) dispersed in a second
interconnected liquid partially comprising thin, surfactant-stabilized films
called lamellae (Morrow 1990). The surfactant used to impart stability to the
mixture concentrates at the gas/liquid interface to reduce interfacial tension
and form stable lamellae. Foams are structured, two-phase fluids that are
compressible in nature (Schramm 1994). Fig. 1 is a schematic representation of
a 2D slice of a general foam system. The bulk liquid is at the bottom of the
foam structure, and the gas phase is at the upper side. The gas phase is
separated from the thin liquid film by a 2D interface, or lamella, which is
defined as the region that encompasses the thin film, the two interfaces on
either side of the thin film, and part of the junction to other lamellae. The
connection of three lamellae, at an angle of 120°, is referred to as the
plateau border (Schramm 1994; Bernard and Jacobs 1965).
Foams have been of great practical interest because of their widespread
occurrence and their important properties. In the oil and gas sector, foams may
be applied or encountered at all stages in the petroleum recovery and
processing industry, such as in oilwell drilling, reservoir injection, oilwell
production, and process-plant foams (Schramm 1994).
The usage of foams for enhanced-oil-recovery (EOR) processes can be
classified into two main groups: foams for mobility control or
gas-injection-well treatments and gas-blocking foams for oil-production-well
treatments. When foams are used for mobility control, the most important
parameter is the viscous performance of the foam, while in the case of
gas-blocking foams, the fundamental issue is their capability to divert
unwanted fluids (Schramm 1994). In these applications, the foam is usually
prepared in situ by coinjection of gas and surfactant solution. As the mixture
of gas and surfactant solution flows through the porous rock, rapid shear
strain occurs and leads quite naturally to the generation and stretching of
bubbles within the pores. The texture of the foam (that is, the size of the
bubbles) depends mainly on the size of the pores. Similarly, the number of
bubbles that exist will be determined by the balance between the rate of
generation of lamellae and the rate of decay. The rate of generation depends on
pore sizes and porous-media complexities, and it should be roughly proportional
to the flow rate. The rate of decay is the result of several simultaneous
processes such as lamellae rupture and coalescence that cause bubbles’
breakdown (Schramm 1994).
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
21 May 2004
- Meeting paper published:
17 April 2004
- Revised manuscript received:
28 October 2006
- Manuscript approved:
9 November 2006
- Version of record:
20 April 2007
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