Incorrect file associations could be the result of underlying issues within your PC system. As such it is highly recommended to scan your PC for invalid registry entries, unused processes and other unfavourable system settings to identify slowdown issues.
The MWD file type is primarily associated with 'MWD'.
MWD = Measurement While Drilling
A number of different vendors produce software for use with MWD hardware. These include, but are not necessarily limited to: BenchTree, XXT, GE Honeywell. Program names include: BenchTree, XXT, QMWDPC.
These should be text files.