Applications of Foam Cement

Abstract

ABSTRACT Foam cement offers a versatile and economical means of cementing wells with low density, high strength material. Several common applications of foam cement are available, and these include placing strong cement across weak or highly fractured zones without losing circulation; filling vugs or porous thief zones; or simply as an inexpensive light-weight filler slurry. The various aspects of slurry design, including their methods of determination, are discussed. It was found that thickening times could be determined directly on the foam cement in existing equipment with only minor modifications; the fluid loss and the rheology could be measured directly with no modifications; and the compressive strengths were determined in a special cell to prevent water invasion from the curing chamber. Since these parameters are determined by the nitrogen content, their relationships to density are also discussed. Job procedures for pumping foam cement are discussed in two methods, i.e., constant nitrogen rate (variable foam density) and constant density (variable nitrogen rate). Included in this discussion is the description of an improved atomizer for generating foam cement. From yard tests utilizing field equipment, it was found that this device improved the foam stability by means of better disbursement of the nitrogen in the cement slurry. The computer program which calculates the surface gas injection rates to achieve the desired density at specified depths is discussed and evaluated. Case histories are then presented to illustrate the effectiveness and versatility of foam cement as well as its relative ease of application. The case histories deal with repairing casing leaks and lost circulation problems in weak formations.