A Full Laboratory Study on the Physical and Mechanical Properties of a Bismuth Plug

Abstract

Well plugging and abandonment can be very expensive, time consuming and problematic. This is because it is the least considered process during a well's life cycle. Setting a plug downhole in an efficient and successful manner is governed by several factors, one of which is the type of sealant used. Portland cement, a commonly used sealing material, turned out to be an inadequate barrier material due to its porous and permeable properties, as well as its insufficient long-term sealing integrity. Bismuth, an alternative sealing material, demonstrated several distinctive characteristics, such as being non-porous, expanding after cooling, and corrosion resistant. In this study, samples of bismuth-tin metal alloys were deployed and allowed to solidify in carbon steel pipes. For comparison, cement plug samples were also prepared under the same conditions; the only prevailing difference was the plug length where that of cement was longer than that of bismuth. Both bismuth and cement samples were subjected to extensive physical, hydraulic, and mechanical push-out tests after curing. Leakage tests using nitrogen gas were also carried out on cement and bismuth samples. As a safe, economical, and environmentally friendly alternative to cement, bismuth appears to be a promising material. Preliminary results clearly manifest the weakness of cement, where high leakage flow rates and early plug breakdowns were witnessed during the tests carried on it. It was observed that short plugs of bismuth were able to withstand a higher differential pressure compared to longer cement plugs. Another interesting finding was that the bismuth plug kept on building up its strength with time even after solidifying. However, the trend of this "strength-build-up" eventually became minimal with time. Hence, the optimal curing time of the bismuth plug was concluded to be somewhere around 24 hours, unlike that of a cement plug which must be left a minimum of 5 days to cure. The aim behind the conducted laboratory experiments is to understand the sealing ability of bismuth to a steel pipe and compare its sealing performance to that of cement. This paper represents the first part of an extensive research which at later stages will be tackling the sealing performance of a bismuth plug in the annulus and its interaction with the surrounding formation.

A Full Laboratory Study on the Physical and Mechanical Properties of a Bismuth Plug