Foams as blocking agents

Because foam applications for mobility control during gas flooding have proven technically challenging and marginally attractive, the recent focus has shifted somewhat to the application of relatively small volumes of foam that are placed as gas blocking agents from the production well side. The application of foams as gas blocking agents has been discussed and reviewed numerous times in the literature. This article discusses considerations in use of foams as blocking agents.

Concept

Because foams are exceptionally effective at reducing gas permeability, they are good candidates for use in gas blocking treatments that are placed relatively near to producing wellbores. The foam’s low effective density results in the tendency for selective placement in the upper sections of the reservoir where gas, especially coning and cusping, is entering the wellbore. The obvious and major challenges that must be overcome to successfully apply foams as a gas blocking agents are to assure that the emplaced blocking foam will have adequate strength and that the metastable foam will be stable long enough to result in attractive economics.

Laboratory studies and treatment design

Treatment design and laboratory studies in support of applying foam gas-blocking treatments need to assure the following.

• Foam has adequate strength to function as intended under actual reservoir conditions, including adequate strength within the maximum permeability rock to be blocked/sealed and adequate strength to withstand the maximum differential pressure that will be encountered.
• Foam has adequate durability and stability to function as intended under actual reservoir conditions for at least the minimum intended economic life of the foam gas-blocking treatment, including adequate thermal stability, adequate stability to the reservoir oil and to the salinity of the reservoir brine, and adequate stability in the presence of the reservoir minerals and lithologies to be encountered.
• Foam can be emplaced and/or generated in the desired reservoir volume to be treated.

Foams for reducing gas coning

The use of foams as blocking agents to reduce or eliminate gas coning in matrix-rock reservoirs has long been studied. One concept is to inject a foaming solution at, or near, the gas/oil contact (GOC). As gas cones down through the foaming solution, it is proposed that gas-blocking foam will form in situ and reduce or eliminate gas coning. More recently, it has been proposed that the foaming solution in this case should be a hydrocarbon solution. For a properly designed treatment, gravity forces will tend to promote the selective placement of the hydrocarbon foaming solution at the GOC, just as desired. Dalland and Hanssen reported on a laboratory study of this concept.

Sizing volume injected

The volume of the emplaced foam required to successfully function as a gas-blocking treatment is smaller than the foam volume required for mobility-control purposes. In concept, the volume of the foam placed through a production well needs only be large enough to provide sufficient strength and durability to assure effective gas blockage. The volume and depth of foam placement for such a treatment will vary substantially with the foam formula used, the permeability and mineralogical nature of the reservoir volume being treated, and the drawdown pressure that the foam gas-blocking treatment will experience. No exact treatment size guidelines for foam gas-blocking treatments are available. The sizing of such foam treatments needs to be determined on a well-by-well and treatment-by-treatment basis.

Polymer enhanced foams and foamed gels

A trend, which has often occurred when applying foams as gas- or water-blocking treatments from the production well side, is that the initial application of a conventional foam resulted in some blocking of gas or water flow that lasted for only a relatively short time. Encouraged by the initial favorable gas- or water-blocking performance of conventional foam treatments, but pursuing and needing longer-term gas- or water-blocking performance, the application and exploitation of polymer-enhanced foams were next pursued. Again encouraged by the improved gas- and water-flow blocking performance of the polymer-enhanced foam treatments, but still pursuing and needing even longer-term gas- and water-blocking performance, foamed gels were subsequently pursued. The application of foamed gels as a blocking-agent material for use across a broad spectrum of conformance treatments has been suggested and studied.

Hughes reports on three large-volume (~40,000 res bbl) foamed-gel treatments that were applied for conformance improvement purposes to injection wells of the Rangely field miscible CO₂ water alternating gas (WAG) project in northwestern Colorado. The three foamed-gel treatments were reported to have generated an incremental oil production rate of 155 barrels of oil per day (BOPD). Each of the foamed-gel treatments induced stabilization in the pattern oil rate. The cost of the foamed-gel treatments was said to be 40 to 50% below that of comparable polymer gel treatments that would have been conducted at the Rangely field.

Noteworthy papers in OnePetro

Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read

External links

Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro

See also

Foams

Foams as mobility control agents

Foam properties

Foam behavior in porous media

Field applications of conformance improvement foams

PEH:Polymers,_Gels,_Foams,_and_Resins