American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

Abstract

Over sixty wells have been treated with hydraulic fracturing techniques with foam as the fracturing fluid. These foams contained as much as 95% gaseous phase; most treatments used foams with gas contents in the 65% to 85% range. Foam has several desirable properties for use as a fracturing properties for use as a fracturing fluid: high sand-carrying and sand-suspending capability, low fluid loss, low hydrostatic head, low pressure drops due to friction, quick fluid recovery, low formation damage, and no reduction of fracture conductivity due to fluid ingredients. Most applications of foam as a fracture fluid have been in low permeability gas reservoirs. Several permeability gas reservoirs. Several oil reservoirs have also been successfully treated, however. Cost of the treatment is approximately the same or slightly less than a treatment with conventional fluids of comparable volume and rate.

Introduction

Foams used as fracturing fluids are dispersions of gas, generally nitrogen, in a liquid, generally water, with a small amount of surfactant foaming agent added. Volumetric gas content (referred to as foam quality) is generally between 65% and 85%. Qualities as high as 95% have been used. Surfactant content is commonly 0.5% to 1% of liquid volume. Stability is increased by addition of more surfactant, whether foaming agent or gelling agent. Such foams are homogeneous mixtures with a narrow range of bubble size, mean bubble size less than 200 microns, and are stable for periods of several hours.

During a fracture-treatment operation, the liquid phase passes through a blender and is mixed with sand and then passes through the injection pump which raises the pressure to required injection pressure. Surfactant foaming agent is added downstream of the injection pump and gas is introduced with a tee or lateral downstream from the surfactant. Foam is generated at the point of gas introduction (see Figure 1). The gas is transported to the site and stored in cryogenic tanks and added to the injection stream at line pressure.

The foams used for fracturing are similar to those described previously by several investigators.

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