A Laboratory Method for Screening Foaming Agents Used in Air-Gas Drilling Operations
Authors: Behrens R.W. , Rice H.L. , Becker K.W. 
Published: December 2007

Abstract
An apparatus has been designed and built for the purpose of studying factors affecting the foaming performance of available and potential air-drilling surfactants. The principal feature of the apparatus is a constant-head device which allows foaming of test liquid in a chamber at a constant rate, called carry-over rate; this rate is determined by direct measurement of the volume of liquid supplied to the test chamber in any given time interval to replace test-chamber liquid having been converted to foam and carried out of the test chamber by air or other compressed-gas stream. A study of variables connected with the apparatus and composition of test solutions and effects on various air-drilling surfactants has resulted in development of a laboratory screening method which has correlated with observed results during field testing in gas-mist drilling operations. Laboratory foaming performance data, collected by the constant-rate method and by the standard Bureau of Mines carry-over method, are compared with observed field results. A theory is developed connecting foaming performances of surfactants directly to type of injection water used in air-gas mist drilling, as opposed to the type of formation water being produced in the drilled well and commonly thought to be responsible for adverse effects on foaming surfactants.

Background
Since the advent of air-drilling operations, large numbers of surfactants have appeared on the market for use as "foaming agents". That such agents have been found useful is attested to by the fact that, in 1955, only a few air-drilled wells employed them, whereas today several thousand air-drilled wells employ these agents; and, in addition, they are being used to increase gas production in water-logged wells. Some surfactants do a "cleaner" job than others on an equal-concentration or an equal-cost basis. Therefore, methods are needed (such as bottle-testing techniques in treating oilfield emulsions) which would enable surfactants to be "screened" systematically and significantly. Several methods have been used to screen surfactants for potential use as air-drilling foaming agents. Although no standard method exists in the air-drilling industry for such screening, the Ross-Miles method has been widely accepted in the screening of foaming detergents. This method involves measurement of the height of foam generated by dropping a test liquid into another portion of the test liquid from a specified height at a specified temperature, and also measuring relative foam stability by observing height readings at given time intervals. A laboratory modification of this method has involved high-speed Waring-Blendor agitation of test liquid containing surfactant, pouring foam into a large graduated cylinder, measuring foam volume and measuring the time required for a certain body of liquid to be broken from the foam. A gas-lift type of screening method has been employed by Dunning, et al, of the U. S. Bureau of Mines. In this method, test liquids are foamed out of a column by gas, and the foam is broken; liquid collected at various intervals is used to establish a relative carrying capacity of a foam generated by surfactants in a wide variety of test liquids. A modification of this type of carryover testing has been described by Lummus and Randall: the gas-lift operation is carried out in an apparatus similar to field air-drilling design as various test media are converted to foam and carried out of an annulus along with drill solids for measurement. A fixed quantity of liquid is involved in this operation, which closely resembles conditions encountered in a gas-well clean-out because hydrostatic head continuously decreases as liquid is foamed-out. Air drilling involving slugging or misting presents different conditions than found in clean-out operations. Here, one might consider that the mixture of produced (formation) water and/or oil and injected water containing foaming agent (mist) being carried steadily out of the hole with high air-gas velocities constitutes a dynamic system with a reasonably constant balance of pressures; i.e., there is essentially no hydrostatic-head variation. As air-drilling technology advances, the trend is toward mist drilling and away from slugging operations because air drillers are learning where to mist successfully, thus avoiding those locations which produce copious amounts of water.
JPT
P. 143^