An exploratory investigation of Nd:YAG laser welding in high pressure gaseous environments

In oil and gas exploration, there are advantages to be gained from exploiting new pockets of hydrocarbons by branching laterally from existing casings, in addition to drilling new wells. These so-called multilateral wells require a junction to be constructed and sealed. Thus there is an interest in examining the feasibility of using a fibre delivered focussed laser beam for cutting and welding steel pipe materials in the branching operation. In production, any such process would be required to function in an environment which comprises high density mud, a temperature possibly in excess of 100°C and pressures up to 500bar. This paper reports on a series of trials to examine the use of fibre delivered Nd:YAG laser power for welding in a high pressure gaseous environment, to simulate the downhole conditions. The work involved the design and manufacture of a pressure chamber equipped with access, via a sapphire window, for the laser beam. To simulate the welding process, material samples in the form of small diameter discs, were rotated inside a chamber under the focussed laser beam, to perform a series of melt runs in high pressure gaseous atmospheres of helium and argon. The results of these trials are presented, which include what is believed to be the first laser melt run produced under a pressure of 500bar.