Historically wells were drilled, to as great a degree as possible, vertically downwards. There was the occasional meander, and this had to be corrected, after running a borehole survey, to make sure that the drill eventually arrived at the intended target. But in making those corrections, so a technology evolved that allowed wells to be steered at deliberate angles, and then the light dawned, and deviated wells could be steered away, at designated angles from the initial well, and out to some additional nearby possible sources.

When directional drilling first was developed, the process occurred in a series of steps. Remember that the wells are usually cased with a steel liner. So the first thing that has to be done is to cut a window in that casing. There are several ways to do this, one of the more efficient of which is to use a high-pressure stream of mud from a jet nozzle, that has had a certain amount of sand added to the mud. This abrasive jet can eat through the steel and cut out a segment so that the drill bit can reach and attack the rock.

Now we have to make the drill deflect, and the easy way to do this is to slide a wedge into the hole right at the point where the window is. This wedge is known as a whipstock and is very carefully aligned and set into the borehole with the inclined side set so that as a new drilling bit slides down the hole it will be kicked off into the window, and as it begins to drill it will penetrate the rock in the required direction.

The hole can be started with a smaller bit until the hole is well established (maybe several feet into the new well) and then this pilot bit is removed and a full-scale bit put on the bit to allow the drill to continue creating a new hole moving out from, and down from, the new start to reach the new target either by a straight shot, or by drilling over to the vicinity of the new end point, and then kicking back over to the vertical to drill down into the new oil reservoir. The process is not that complicated, and with practice one can then drill a number of different wells out in different directions from that original hole. And from one location, or platform, one can then collectively extract the oil from an increasingly large surrounding area of the reservoir.

I said "historically" because when they tried this in Western Siberia they ran into a problem. The quality of Soviet steel was not that good at keeping the bit turning down and through that bend. And so they had to come up with a different approach. And that, is next week's story.

This is a series of highly informal posts that are aimed at giving some background to what goes into drilling and production from oilwells. Earlier posts in the series are:

the drill

using mud

the derrick

the casing

pressure control

completing the well

flow to the well

working with carbonates

spacing your well

As ever, if this is not clear, or if there is disagreement then please feel free to post, and I will try and respond.

Acknowledgement - the idea for this post came from browsing through "Russian Oil Supply" by John D. Grace, which is a very informative, well written, and recommended addition to a PO library.

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