Abstract

A renewed interest in utilizing foamed cement slurries in wells where conventional slurries pose difficulties has increased the need for equipment capable of accurately monitoring and reliably controlling the necessary additives. These additives typically include nitrogen and a foaming agent. The goal is to have a completely automated control technology for the liquid additives and nitrogen. A fully automated system will also incorporate a cement mixing unit with automatic density control, with the additives metered in proportion to the base slurry rate. Proper pumping equipment selection is essential, but it is the flow monitoring technology selected that ultimately determines the accuracy of the additives. While process control technology for liquid additives is well established, metering and control technologies for automating nitrogen addition are less mature, and are critical to the proper execution of a foamed cement job.

Prior knowledge of slurry designs for a particular drilling program allows suitable components to be selected for use in an automated system, ensuring properly generated foamed cement slurries. The corollary is also true - that knowledge of the limitations of the equipment used to generate the foamed cement can lead to optimization of slurry design. Software is generally used to generate the ideal rates for base cement slurry, nitrogen, and liquid additives to obtain an optimum foamed cement slurry for a particular well. It is important to know that a software-generated solution that combines equipment capabilities with slurry and well requirements is technically feasible.

This paper describes the equipment and methods used to monitor and control the nitrogen and liquid additives used in foamed cement slurries. Additionally, the limitations of the nitrogen pumping and metering equipment, and how these limitations affect foamed cement job design, are discussed. Techniques to modify job parameters based on equipment performance parameters are also discussed. Charts from field evaluations of the developed system are included.

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