Wednesday, April 21, 2010

drilling differences

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?

6 comments:

Silver Fox said...

Neat post! I linked to this at the bottom of mine, because my post was linked to on FB by the GSA - so I'm getting a little extra traffic. Sending some your way!

I've only been around a water-well rig once, really (although we've had them on site with other people managing them). The water well drillers (2?) did their own thing with me just checking in because we wanted to see what rocks they were going through. They were pretty clean-cut compared to exploration drillers. And wore hard hats back when they weren't required.

OnDrill said...

I my company "drill boss" is calling supervisor. And yes, i think is big diffrence between water well or geology drilling and gas /oil drilling.

Chuck said...

SG, what is your typical depth to groundwater? We were 36-76 meters in the desert, but as few as 12 when looking for perched U in paleochennels.

Anonymous said...

Nowadays, I sit more horizontal wells than vertical wells. This means I also have to supervise the directional drillers (consultant drillers responsible for steering the well), making sure we stay in the formation or zone of interest, and watching out for (and responding to) all the fun that Mother Nature throws at us (faults, unexpected dip changes, shale plugs, incised channels, karst, pinch-outs, chert (death to drill bits), lateral facies changes...you name it). All this stuff makes horizontal drilling more interesting (I think) and I prefer it to vertical drilling.

As for the work schedule, it's usually one wellsite geologist on call 24-hours, but I try to keep "normal" hours as much as possible, typically working from about 6:00 am to 10:00 or 11:00 pm. We stay on the location, in industrial accommodation ("trailers" or "shacks"), which are usually 10' x 40' skid units, and relatively comfortable: central heating, A/C, microwave, satellite TV, gas stove, gas BBQ, private bath & bedroom, laundry room, etc. Jobs can last anywhere from 1 or 2 days to months, but commonly in the range of 1 to 3 weeks. It's becoming more common now to have 2 geologists at the location, working 12-hour shifts--especially on horizontal wells--due to the high penetration rates (30-50 m/hr is usual, 60-100+ m/hr is not uncommon), and the need to have a fresh set of eyeballs watching things all the time.

--Howard

Anonymous said...

"Anybody want to chime in with differences for oil drilling?"

I guess that's my cue. OK, here's how oil & gas drilling works, at least from my perspective in the western Canada oil patch:

There are definitely some big differences from your enviro/water well drilling and Silver Fox's mineral exploration drilling. First off, oil & gas drilling is a round-the-clock operation--always. There are either 3 crews on 8-hour shifts or--more usual nowadays--2 crews on 12s. A drilling crew is typically 5-man and includes a driller; a derrick hand (who handles pipe up in the derrick when the drill pipe is being tripped into or out of the hole; he is also responsible for maintaining the drilling mud--a very important job); a motor hand (looks after the rig motors, pumps, power plant, other mechanical duties); and two floor hands (make and break pipe connections on the drill floor, and general labour around the rig, including catching samples for the geologist). Some crews will also have a lease hand, who helps out with odd jobs around the rig (garbage, scrubbing, painting, laundry, pumping out ditches, etc.). The drilling crews answer to a rig manager, also known as a toolpusher, or just "the push". There are also 3rd party contractors who haul drilling water and operate a vacuum truck, and a whole compliment of other service people who come and go depending on what operations are underway. All of these people are coordinated by and answer to the "Company Man", AKA "Drilling Supervisor" or "The Consultant" who works for the oil company, either as an employee, or more commonly as a consultant.

Then there's the wellsite geologist (WSG). My primary job is to log drill cuttings, which are caught by one of the floor hands, typically at 5-metre intervals, though I will catch 1-metre or finer spot samples if we're approaching or drilling through an important zone of interest. Cuttings are bagged in labelled cloth bags and brought to my trailer, where I sieve them (kitchen sieve, on top of a #80 or #170 mesh sieve), wash, dry and store them in plastic vials: http://www.petrocraft.ab.ca/product_details?gocart6=product_id%3D113

The cuttings are then examined and described for lithology, porosity, estimated permeability, and oil staining. Using these data (plus penetration rate, ditch gas readings and sometimes gamma ray log readings), I maintain a continuous "strip log" of the well lithology, and report to the client on a daily or more frequent basis.

Coring, which used to be routine on almost every well, is pretty much a thing of the past: in the last 8 years, I've cut core on two wells, so core logging, while still a responsibility, is rare.

(continued in next comment...)

Cheers,
--Howard (Calgary, Canada)

Short Geologist said...

@ chuck: I'm usually in a pretty temperate/wet climate, so depth to groundwater is generally from, um ground surface to 5 meters.