RE: dspp6 Jan 2020 09:21
HH,
I only wish to add one small technical correction to your post, which in no way negates the thrust of your argument.
"I furthermore do not anticipate such a fluid path would occur in a linear manner (especially so given two different fluid viscosities), and that the passage would induce a turbulence likely to cause a vortex effect, hence the utilisation of the term “coning”.
The term 'coning' pre-dates directional and horizontal drilling, and comes from a time when most oilwells were drilled as 'straight holes', or vertical. The analogy of a well being like an open-ended straw is not completely correct, bit it'll do for now.
As 'drawdown' is applied to a well, ie negative pressure exerted on the reservoir, water in the aquifer may start to be drawn up towards the well, and the place where the water will rise the highest is directly below the well, where the 'suck' is the most concentrated. However, water to each side will rise as well, to a lesser extent as the 'suction effect' is less, distance through the formation being greater, and friction effects coming into play. So if a 3D graphic representation of this is drawn, a 'cone' of water is drawn up to the bottom of the well.
However, the well is (generally) not an open-ended straw. Instead, fluid enters through holes punched in the side of the lowermost casing. (The 'perforations'.)
If water breakthrough occurs, and bad reservoir management is employed (as was frequently the case before the phenomena were properly understood, and also for greed / commercial reasons, one way of dealing with the problem might be to actually 'suck harder', because the aggregate 'mixed' fluid column density is now greater, so it takes more suck to maintain the previous flowrate. This of course can help in the short term, but not longterm, because the 'cone' of water will rise further up alongside the wellbore, with maybe the lowermost section becoming fully 'watered out', and oil only still entering from a shallower depth.
A way of dealing with this might be to actually plug off the lowermost perforations through which most of the water is entering, but of course with the downside that you've now got less overall exposure to the reservoir.
Believe me, tens if not hundreds of thousands of wells have been run like this back in the 'bad old days': the greed factor can be high, people didn't think longterm, drilling was cheap, new fields easily found, etc. Reservoirs could be ruined.
None of the above is happening at Lancaster, though.