Silver Fox has several posts up recently about drilling. See here and here. One of the reasons I enjoy her blog is because it gives me a new perspective about the exploration biz.
Even though we are both geologists who have worked on drilling rigs, taking rock samples, our actual work is not necessarily similar because of scale differences.
When I'm in the field, collecting rock samples, it's usually just me, a driller, and a driller's helper. If I'm taking a bunch of analytical samples, I may have a helper; if the job is big or complicated, the driller may have 2 helpers. Once you get into the big jobs with multiple rigs running around at once, then you need at least one "field boss" to keep all the balls in the air - God forbid a rig runs out of work and is idle!
Sometimes, we may not care so much about the stratigraphy of the rock - we're just looking to find water-bearing zones and install a bunch of wells. In that case, we may use air-rotary methods and then I'm trying to discern something from the little chips blown up from the hole and caught in a strainer. We know we hit water when a) the rig drops, b) we get water blowing out of the hole, or c) the driller tells me (hey, sometimes I get distracted).
In other cases, we want as much detail as possible. So we'll use a diamond core barrel and collect core samples in 5-foot runs. That's when I get a traditional intact core and can spend some time doing all the traditional rock description work - where are the fractures, what do they look like, what are the minerals (if visible). I tend to set up the core where I can keep an eye on the drilling while I look at the core. If it's raining or the drilling is going fast or we're having problems, the core can get shoved in a corner and I can write everything up later.
We generally aren't in a super-big hurry to finish a particular job (unless the job got screwed up somewhere) and the margins aren't high enough to pay vast amounts of overtime, so we almost never work around the clock. In rare exceptions we work into the night, but I've never had to work past 10 pm.
Environmental geologists should (and generally do) watch the rig themselves. Why? Well, mainly because things are always changing for environmental sampling. We're often taking soil samples, which need to be legally acceptable (no cross-contamination, sampling interval is specified, don't let the samples air out, etc). We're often in high-visibility places and need to manage the public. Monitoring wells installed in the boreholes have to be done properly so that groundwater samples and other hydrologic data are again, legally defensible. And finally, environmental wells tend to be shallow (less than 150 feet in most cases), so there's always something new to do or prepare for.
So between Silver Fox and I, we've covered environmental and metal-resource drilling. Anybody want to chime in with differences for oil drilling?