| Popis: |
Continous or batch treatment of low pressure wet gas wells with foaming agents is a common and cost-effective method to sustain production from such wells. The foam additives convert well liquids into water/gas foams lowering the bottomhole hydrostatic pressure and increasing brine unloading from the well, thus preventing well "drowning" resulting in lower or ceased gas production. However, foaming surfactants being good wetting agents may accelerate the casing corrosion process and work against corrosion inhibitors. This effect would be particularly severe in deep wells having high bottomhole temperatures. Foaming properties and steel corrosion rates were tested on fluids formulated with anionic, cationic, non-ionic and amphoteric foamers combined with the main categories of corrosion inhibitors. In most cases, there was a negative effect of corrosion inhibitors on foams or even a complete chemical incompatibility for some combinations. Occasionally, addition of certain corrosion inhibitors improved a foam's persistence and quality. However, the effect of a few percent of condensate seems to be stronger than 300 ppm of corrosion inhibitors. Additives had the greatest effect on the performance of non-ionic and amphoteric surfactants. The effect of foaming agents on steel corrosion is not uniform. In most cases a surfactant offers some corrosion protection at mild conditions. Most foaming agents accelerate corrosion rates at high temperatures. Few chemicals produced spectacular corrosion. Mixtures of foaming agents and corrosion inhibitors usually are less corrosive than foaming agents applied without any corrosion protection. However, no single component corrosion inhibitor reduced the corrosivity of such mixtures to an acceptable level. The results indicate that wells that are being treated with foaming agents should also be treated with an appropriate corrosion inhibitor. For any particular application a proper combination of foamer/corrosion inhibitor should be selected. More consideration should be given to the properties of the foamer/corrosion mixture, than to those of the individual components. |
