Disclaimer: in a long note like this there will be factual and typographical errors.
Disclaimer: there is much speculation in this post.
Updates
July 28, 2019: see first comment from a geologist, correcting me. I will update/correct my original post, but can't guarantee it will be entirely correct. From the reader, in the comments:
Porosity should be the Swiss cheese analogy - generally unconnected void space.
Permeability is the level of void space connectedness.
Clays (shales) have great porosity but poor permeability.
Sands (sandstone, some dolomites) have less void space (porosity) but greater connectedness (permeability).
It’s
about particle geometry at that level - the long flat clay micelles
mostly align, creating ~20:1 preference for flow along the alignment vs
flow against (e.g. horizontal vs vertical flow). The cubic or hexagonal
pack of sand grains and ooids does not create a significant flow
direction preference, has less void space and more connectivity.
July 28, 2019: link to a great discussion regarding permeability and porosity. Scroll through the comments; much about the high water cut issue.
Link here.
One gets the feeling that before this is all over there will be myriad problems to work out, including flaring and increasing amount of produced water.
Original Post
This is an important note from a reader.
It pertains to #21903. This note won't make sense without going back and looking at the linked #21903. But the note is important enough I don't want to lose it.
That production profile from #21903 (see below) seems to be very significant, but I do not know what to make of it regarding, specifically, the big surge in gas production.
Looking at the high, relatively flat oil production, one might deduce
this is another example of a 'recharging' of the formation pressure via
'halo' from nearby frac or ... something else.
The highly elevated produced water levels show water was injected for some purpose, somewhere.
Interestingly, the flat level of produced water implies some type of controlled flowback over several months.
This, if accurate, would be in line with the restricted production
practice (choking) so as to maintain elevated, induced formation
pressure.
Not sure and, as you say, don't wish to get ahead of my headlights.
Biggest curiousity, however, is the significant 'spread' in the amount of produced gas versus produced oil.
It is a LARGE change in proportionality.
Going WAY out on a speculative limb here, but I wonder if newly opened, ultra, ultra tiny fissures (pore throats, specifically) are being blocked by the larger asphaltene molecules.
So little data is available to monitor this, but ongoing evidence for some time has implied a lot of the oil left behind is, indeed, the larger, more viscous molecules.
If this is correct (big 'if', for sure), then miscible type EOR could
prove especially effective as the remaining hydrocarbons would respond
favorably by 'thinning'.
A long, long time ago, I posted the five most important parameters when judging the potential of a basin. If I find that post, I will link it.
This comes close.
From April 29, 2012 :
A horizontal well's production potential:
- Location: maturity, porosity, permeability, trapping, TOC, thickness, 3-D seismography, arrays
- Ability of horizontal bore to remain in target zone:
- Completion: fracking, drilling fluids, stages, method, sand, ceramics
I've concentrated on most of those parameters but not porosity or permeability. It's hard for me to get my hands around the difference between permeability and porosity but talking to an "oilman" helped me understand the difference better.
Think of Swiss cheese when thinking of porosity [see comment section].
Wouldn't it be interesting if porosity was a bigger nut to crack than "fracking per se" and if solving porosity challenges was the next big technology solution? I'm way beyond my headlights here but there is so much yet to learn about tight oil.
By the way, a huge digression. Note "ceramics" in that note from April 29, 2012, above. I remember the early days of the Bakken -- all the discussion about whether to use ceramics or not. It seems that question has been answered. I don't see much ceramic being used in the Bakken these days, at least in those wells I've checked, looking specifically for ceramic.
By the way, back to the reader's observation: the significant amount of natural gas being produced in this old well compared to the well when it was first drilled / fracked. If this is "common" in the Bakken, then Lynn Helms has a huge problem with natural gas production / flaring. There are over 15,000 producing wells in North Dakota. A lot of them are old Bakken wells
Bakken wells began with file numbers in the 16XXX range. We're now at #36796. Just saying.
