Abstract
Laboratory equipment has been designed specificallyto study effectively the microscopic structure offlowing foams at high pressures. In addition, application of foaming-agent optimization techniquesto design stable foams at varying foam qualities isdemonstrated at high pressures - i.e., 500 to 2,000psig (3448 to 13 792 kPa). Capillary viscosity datafor these foams is established and correlated with avideo-photomicroscopic study of the flowing foamand their designated bubble qualities. Foaming-agent screening information from the tests is providedindicating the foaming-agent generic chemistry thatallows optimal foam stability under high-pressure conditions.
Introduction
The study of contemporary foam rheology has arather interrupted history beginning with Fried'swork in 1961 on a foam drive process, which was followed by Raza and Marsden's 1965 paper onrheology and streaming potential. During 1969Blauer et al. studied foam flow properties andmade successful comparisons of data obtained incapillary viscometer tests and actual oilfield tubulardata. These investigations lead to the development ofdata and calculated procedures for using high-qualityfoams as fracturing fluids to transport proppanteffectively with extremely low formation damage as aresult of smaller amounts of water or liquid incontact with the formation.
With all the theoretical depiction of flowing foamstructure, it was felt that a study was needed to showvisually the actual flowing foam under pressure. Thiswas undertaken in a study' where oil-foamingsurfactant concentrations were optimized using anapparatus similar to ours. (The majority of foamstimulation treatments use aqueous bases, and thisstudy was conducted exclusively with them.)
The goal of this project was to design equipmentthat could be adapted to a TV camera/microscopesystem to allow videotaping of flowing foam in aview cell under pressure. To study effectively thechemical nature of four different surfactant foams, the temperature was kept at 80 deg. F (26.7 deg. C)throughout the study. Also, one foam quality of88%, or 88% nitrogen and 12% water was chosenusing 2% KCl water as the liquid phase. Selected pictures from the videotape are presented to show thesuccession of bubble-structure change with pressure.In addition, the effect of surfactant concentration (which had been thought to play a small role, if any, in the rheology of foams) is shown. This allows aneven greater ability to optimize surfactant concentration in the production of stable foams forstimulation.
The subjective bubble-quality scale of Holcomb etal. is refined by showing the average bubblediameters at various study pressures and is demonstrated photographically in Figs. 1 through 3.For the viscosity tests through the capillaryviscometer system, a constant 1,000-psi input pressure was maintained for the generation of foam.
Testing Apparatus, Procedure, and Chemical Additives
The high-pressure test apparatus was designed tomeet the rate requirements for a laboratory testsample of 700 cm (liquid) or more. The system iscapable of pressures to 3,000 psi (20 683 kPa). The pump is a Williams Oscillamatic TM single-strokemodel with a pressure rating to 10,000 psi (68 946kPa). All main lines are 6.35 mm in diameter. Trunklines to the gauges are 3.175-mm-diameter tubing.All tubing in the apparatus is 316 stainless steel. (SeeFig. 4.)
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