When you say investment there are differing rules.  If you are simply giving someone money to do all the actual work and your "payout" will be when (or if) the well comes in, then you have what is called a passive activity.  You don't get to take expenses or the amount of your investment until you actually sell the investment.  If the well comes in and you start receiving income then you will have royalties and be able to take certain expenses as a deduction against that income.  If you sell the investment or if, unfortunately the company doing the work goes out of business, then you would have a capital loss just as if you had bought and sold stock at a loss.

This is very simplified and there are a lot of variables in this type of situation, so you should definitely seek the advice of an Enrolled Agent with the specifics.