AutoCAD is widely used, mostly because it's already present at a lot of places for other reasons, and therefore "free".
From a functional perspective, the bare AutoCAD that's ordinarily used is a horrible choice. Real schematic capture programs allow you to drag devices around and stretch and reroute the lines automatically, automatically generate a net list, understand the difference between inputs, outputs and just plain lines, and can do some simple error checking.
There exists an extra-cost 'AutoCAD Electrical' package from Autodesk. I get the impression that it's okay for generating ladder diagrams. I don't know if it can do schematics.
Google "schematic capture" and you'll get a boatload of ideas to start with. If you have more specific ideas you'd like to fulfill, you'll have to be more specific on the details for us to help you.
I believe Eagle is a pretty popular schematic capture program. I use gschem which is an open source program (i.e. free). But you asked for "popular" ones ;-)
From wikipedia:
"EAGLE is very popular with hobbyists because the free demo is able to create usable PCBs. (Free ECADs from some companies are crippled so that they won't save or won't print.) The only limitations of boards made with the EAGLE demo are: 2 copper layers; a maximum size of 80mm x 100mm (~3in x ~4in). The demo version of the schematic editor module can only create single-sheet schematics."
I have used Mentor Graphics schematic capture also. That was at a client's place, but I believe that the cost per seat is rather high.
CadStar was a popular mid-range package a few years ago. I haven't had any experience on it since Racal sold it to Zuken so it will have changed a lot since then. I won't comment on the pro's and con's because I've got no knowledge of the recent releases.
I usually wait before answering these types of questions to determine if the poster is a student/hobbyist or a professional. A student/hobbyist is going to be looking for suggestions on freebies (or nearly so), whereas the professional is going to be looking at multi-$k stuff. Of course, unless the person is coming into the profession fresh, these simplistic types of questions typically point to the former.
It also depends on where you are in the world and whether you need the schematic to be used for other applications such as a PCB design. And as mentioned before, whether it is for a professional application.
Since your specialization is "petroleum", you are probably interested in documenting wiring and circuits, and not in electronics and PCB layout. Is that right?
Orcad, Cadstar, Alitum (Protel), Eagle, PADS, etc. are schematic capture programs primarily designed for electronics and linking to a PCB layout tool or in some cases a FPGA/VHDL or other digital programming logic tool. The schematic capture portion of these can be used for wiring and circuit diagrams, but you are paying for a lot of features you would not be using.
