I've been asked a few questions about drilling recently, so I'll attempt to briefly clarify a few things. First of all, not all my work entails drilling, though certainly many non-drilling phases of the exploration work I do is designed to create drilling targets so that we can find some ore. For a couple looks at what I do in general, refer to these two posts, and also browse the blog using some of the tags I use, or by using the search bar in the upper left corner (those are semi-efficient ways of navigating the blog).
The two linked-to posts are attempts to cover what I do, but they are by no means thorough, and they haven't been updated with more recent posts. Short version is this: I'm a minerals exploration geologist — my work ranges from generating reconnaissance targets, staking claims (that part is usually handled by staking or surveying companies) or aquiring properties through negotiations, property evaluation in general (which can include evaluating a lot of existing data or creating new data by sampling and assaying or by running various types of geophysical surveys), mapping the geology and generating drilling targets (or not, as the case may be), drilliing said targets and hoping to get the property past a first stage, on to a second or third stage, thence onward to the time when a property can become a mine and go into production. I've also helped evaluate companies (or their properties) as part of company acquisition negotiations.
As a minerals exploration geologist I've never been near an oil rig, nor have I worked offshore (although I'd like to visit an offshore rig). I've worked almost exclusively in metals, mostly in copper, uranium, and gold, not necessarily in that order. When I log chips, rather than core, it's called chip logging. I've never seen mud logging and don't know how it differs from chip logging, but the chips I log are washed clean of mud other than fault-gouge clay or alteration clay, and they have been sieved (through a large kitchen strainer) prior to being put into plastic chip trays that hold 20 intervals (usually 100 feet).
I almost never take drilling samples while running a drilling program, whether I'm the only geologist on the program or whether I have an assistant geologist (or partner) working with me. The drillers are supposed to do that — although when I first started in the business, one set of drillers was particularly poor at collecting the samples, so I gave them some training, while getting some training myself: it was my first project. I have more than one post in draft stage about this first drilling project.
I almost always work either with rotary rigs or core rigs. These typically are capable of drilling to a couple thousand feet or more, depending on the power of the rig and the depth of the target. When I started, reverse-circulation (RC) drill rigs were rare or non-existant, and so we used conventional rotary rigs. RC rigs are standard, now, for most non-core drilling.
When I first started working around drill rigs, it was customary to have two men on the rig: the driller and the helper. Now, RC rigs usually have three men, and core rigs often have two, sometimes three. I've seen one woman on a drill rig over the years: a helper (rod man) on a core rig. The third guy on the RC rig is specifically there to take the samples, and nowadays, to make the chip trays. It became standard to have this third person sometime during the 1980's. Prior to that, geologists may have taken samples in order to get good samples, and the geologist made the chip boards and later the chip trays (these were invented sometime in the 1980's).
I have rarely had to be at or "on" a rig the entire time it was drilling. Drillers usually work 12-hour shifts; I usually don't. Sometimes, when a rig is about to get done with a hole, but the target depth is flexible (not set beforehand), I will need to be there to "call" the hole, that is, end it. That can mean being at the rig until they quit in the evening (usually at 6:00 pm) and then, if the hole needs to keep going, also being there when they start up in the morning (usually at 6:00 am). With a single 12-hour shift — which is more common on exploration rigs in the middle of nowhere than on rigs near mines, but is by no means standardized in either locale — I've usually not had to be there every morning at start up and every evening at shut down. I've often been able to run myself on a ten-hour day.
The only drillers I've seen that worked less than 12-hour shifts (more like 8 to 10), have been drillers on rigs that are more typically used for environmental-type drilling, such as what Short Geologist might be describing here.
Many RC and most core rigs will run two 12-hour shifts, in which case a geologist might be required to answer a cell phone in the middle of the night, although I've done that only rarely. A 24-hour rig will often need to have more than one geologist around, trading off night calls and other tasks. It's often possible to let the rig drill through the night, barring unforeseen and usually undesirable circumstances. Back in pre-cell days, if a rotary rig was running two shifts, a geologist might have had to go out and visit the rig if it looked like it might need down-hole logging or "calling" in the middle of the night. I did that a couple times a long time ago. Core rigs, which have usually run two shifts, don't generally need to be visited in the middle of the night because their drilling rate is so much lower than rotary rigs, usually a third to a tenth.
I hope that covers some of the questions I've been getting, both here on the blog and via email. My recent post about drilling was probably somewhat vague.
UPDATE (4/21/2010): Be sure to see Short Geologist's most recent post about drilling, for a look at what she does.
UPDATE (4/23/2010): Chuck posted a link to a neat, back-of-truck, core-logging setup he used last year. My trucks aren't usually that large!
Drilling Stories: Getting Started at Northumberland
The Unlikely Gradational Stratigraphy