I've never seen an HO model of an oil rig or production platform except at the airport in Houston, but I don't know if they were HO scale.
Oilfield rigs come in a variety of shapes and sizes, from the smallest work-over spud barge to the mamoth semi-submersibles or deep water platforms. There are in-land barges for drilling in marshes and swamps. No kits as far as I know.
What part of the world are you modeling? You'd be hard pressed to find an offshore rig up here in Massachusettes where the lead footed whiners don't want drilling off of the coast, but in the Gulf of Mexico west of Florida you will find a bunch. California makes the oil companies dress up thier rigs to look like skyscrapers, so they won't offend those who can see through the smog. The ocean creatures don't seem to mind.

Those would be boring to model anyways.
Era also plays a part, somewhat if you are worried about historical accuracy. IMHO, a model of a small jack-up rig orinland barge would be so cool.
Jack-ups usually have 3 legs and are thus laid out in a triangular shape, which will take up more room. you wouldn't have to model it standing this high. I think they were adding the leg sections at this point of its construction or refurb. The triangular legs are the most interesting and the most complicated, your choice.
Some have tubular legs. This is a nice compact rig and is still probably too big for a layout if done to scale, but if it were built 3/4 size you may be ble to fit it. I don't have any definite dimensions, but a rough guesstimate of the drill floor and surounding weather shiething around it looks to be about 30' x 30', so the whole thing looks to be 75' x 175-200' including the heliport.
The inland barge is basically the rig superstructure, living quarters, ancillary drilling equipment all on a barge. This one is probably about 150' long and 50' wide. That's a small jack-knife rig as it looks to hold a double (2 joints) of pipe, or tubing.
I've spent some time on a few of these in the GoM, but I am no expert. I'm sure there are a few others that could expound on this subject. I've always thought the airport models were so fascinating. You could sped hours just looking at them. But, there was/is something wrong with them:curse: . None of them were ever weathered!
EDIT: KCS, I didn't realize that you were in Shreveport. Go take a ride down to Amelia, just on the other side of Morgan City. When you cross over the bridge look right. There will be oodles of offshore oilfield equipment in all phases of construction. You could stop off in New Iberia and visit the Port of Iberia. There are RR tracks there and I believe they are still being used to supply a pipe coating company.