Career shift from oil and gas TO Software/IT project Management

I do have a background in software development, but I've seen other PMs make transitions such as yours successfully. I think the most important thing is to seek companies & roles that are clearly seeking a strong project manager, not a technical leader. These come out pretty clearly in job postings and early conversations, if the focus is on managing the resources, schedules, scope, etc., or if there is less a need for that and more on someone who will take a technical lead as well. Roles for which PMP is required or strongly preferred should be your first indication that there's hope the role may be a good match -- a role or culture seeking a software lead will likely not emphasize PMP as highly.

Agree with Stephen. I recently made a transition to technical PM role even though I do not have a technical background. My current boss was looking for strong project management skills and not technical skills. A lot of the basic/necessary technical knowledge you will obtain right on the job.
So keep looking and consider doing contracting work. A lot of the tech PM roles with large companies are for contractors, so work with the 3rd party recruiting agencies and I'm sure you'll find a suitable position.