Bubbles characterization in foam drilling fluid

Abstract

Underbalanced drilling is a type of managed pressure drilling technique which is used to drill oil and gas wells where the pressure in the wellbore is kept lower than the fluid pressure in the formation being drilled. Foam generates low Equivalent Circulation Density (ECD) which makes it a lightweight drilling fluid, apart from possessing good lubricating characteristic and hole cleaning ability. These characteristics have brought foam drilling more advantages, such as eliminate formation damage, reduce lost circulation, increase bit life and performance, and reduce possibility of differential pipe sticking. Generally, an underbalanced drilling requires a longer time to plan drilling a well and this may raise cost, however it also has the potential to raise production by up to 800% due to the improved flow of oil and gas, fewer wells are required to drain reservoirs and overall environmental footprints are smaller. Despite all the advantages of a foam drilling operation, the characterization of foam properties under drilling conditions is still incomplete and foam structures can be very complex. Foam’s stability can be expressed in the form of half-life measurement and bubble sizes and its distribution. The longer the half-life of the foam, the more stable it is. On the other hand, it can be concluded that foam with small bubble size shows rigidity at the interface while larger bubbles show mobile liquid-gas interface which will enhance the film thinning between bubbles and will be easily get ruptured. This research was conducted to find the relationship between these two different definitions of foam stability and quality. A relationship equation was created between these two definitions which showed an inversely proportional relation. Three different types of stabilizers, namely xanthan gum, glass beads, and polymer beads were examined to prolong the stability of the foam and xanthan gum was found to have given the longer half-life and smaller bubble size.