A Review on Dissolvable Alloys - Part I: Development of Materials

In the trend of unconventional oil and gas explorations, the long laterals over 3,000 m are commonly fractured in multistage fracturing operations. The mill-out of the conventional and temporary isolation downhole tools, such as frac plugs or balls/ball seats, in these wells using mechanical intervention, such as coiled tubing (CT), is a challenge. This paper is to review the developments of the dissolvable alloys to be used on these tools in these long lateral wells to eliminate the mechanical intervention afterward. It includes the history and current status of the developments of the dissolvable alloys. The two types of mainstream dissolvable alloys including magnesium-based and aluminum-based alloys were developed, based on their microscale galvanic corrosion behaviors. The properties of these dissolvable alloys, therefore, depend on the chemistry, process and finally microstructure. The casting and extrusion processes will be discussed since they are very important processes to enhance properties of the dissolvable alloys. The properties including the strength, the ductility and the dissolvability are measured under various temperatures, pressures and salinities conditions. The future trend of development is also briefly visioned.