Utilization of Electrical Plasma for Hard Rock Drilling and Casing Milling

Abstract

Abstract Worldwide, the research groups have been dealing with several innovative drilling technologies. Their common aim is to significantly decrease the overall price of the drilling process, particularly to keep the high constant speed, energy efficiency and shorter drilling time. There are above twenty innovative non-contact technologies at different maturity such as: laser, water jet, plasmatorch, ultrasonic, microwave, and several others. However few of them reached Proof-of-the-Concept in laboratory and are currently developed in outside testing sites. This paper presents one of such activities – development of technology based on electrical plasma for hard rock drilling. During its development, another application was identified – milling of steel casing and cement for well Plug&Abandonment operations. Both of these applications are developed by the team of engineers led by the authors. The electrical plasma-based tool changes completely from its inception the paradigm of the drilling as well as casing milling. The most important advance in comparison to conventional plasmatorch technology is that the electrical arc with temperatures of tens of thousands of degrees Kelvin heats directly the surface, especially the radiation component, with minimalized heating of intermediate gas (the intermediate gas flow in conventional plasmatorches reduces the efficiency of heat transfer into the rock). Moreover, the arc creates area-wide, relatively homogeneous heat flow from spiral arc on the whole surface for high-intensity disintegration process. Compared to conventional plasmatorch technology, electrical plasma-based technology allows the use of electrohydraulic phenomenon, generating shock waves for the destruction and transport of disintegrated material. System also allows obtaining electrical and/or optical characteristics of the arc in the interaction with the rock to derive indirect sensory information (e.g. online spectroscopy for logging while drilling.). This paper includes the nature of challenges in both application areas – hard rock drilling and casing milling, the description of the developed solutions, the results obtained until now, possibilities of some spin-off technologies using the same core technology concluded by expected impacts. The technology has been tested on various rock types including sandstone, limestone, halite, granite and quartzite. Currently, the demonstration prototype is being tested for drilling of testing borehole in the quarry.