After the Arab Oil Embargo, my dad (Agronomist) established a USDA farm/nursery in NW Colorado for the propagation/reintroduction of native plants after coal and oil shale strip mining. But it never really got off the ground. There was a lack of technology to make oil from oil shale. At that time, in that neck of the woods, oil shale was the "buzzword". But that lack of technology combined with the environmental blowback killed it.
I think it is fantastic they have the ability to make use of shale deposits.
@Smokin Joe
Do you guys have any reading recommendations beyond Wikipedia?
Howdy,
@bigheadfred !
Sorry I haven't responded sooner, I was up all night picking intermediate casing point on the well I'm on and had to get some sleep.
These guys have put together a pretty good primer, and it touches on drilling, fraccing, and what's involved, with bits from a few sources. It is directed toward the Illinois Basin area (local for them), but the basics are the basics, and those are pretty well covered.
https://www.woolseyenergy.com/media/files/WOC-Drilling-Brochure.pdfI'd be happy to answer any questions I can, and if I can't, I'll find the answers for you, so feel free to ask.
I know a little about the Green River Oil Shales, having worked in the Piceance Basin, south of Rifle, CO many years ago on horizontal gas wells for Oryx. The facility over by Parachute didn't work economically, trying to cook the oil out of the mined shale, and the Government project (Project Rulison part of Project Gasbuggy) had its problems, too, as the fenced off area south of Rifle attests (and one up on the Book Cliffs). There is a lot of oil bound in those shale beds, and some day someone will figure out how to get it out--seems there are a host of ideas that have been tried, and I have little doubt others are in the works.
Another interesting aspect of those shales is the preservation of insects--in some beds the preservation is amazing, I have found fossil gnats and mosquitoes, bot fly larvae, and other odds and ends in them up by Rio Blanco and Douglas Pass.
Keep in mind that the shale in these plays is the source rock, the origin of the organic material the hydrocarbons form from, be they gas or oil or both. For now, most 'shale plays' are actually releasing the trapped oil in laminations and beds of siltstone, 'tight' sandstone, and other rocks which have low permeability and would be difficult (and prohibitively expensive) to produce using vertical wells.
Resources: Sedimentary Rocks
https://www.britannica.com/science/sedimentary-rockAnd in pictures and outline form apparently for a course at U WVa (nice presentation) and downloadable
http://pages.geo.wvu.edu/~kammer/g100/SedimentaryRocks.pdf(Sometimes it helps to put a face on the rocks)
For the oil and gas industry, beyond the type of rock, there are some properties which are important, and are affected by rock type, mineral content, and the arrangement of the particles in the rock--and what has happened to the rock since it formed.
It is the space within the rock, between grains, in dissolved cavities, even in voids created by fossils (
porosity), how well those spaces are connected and allow flow from one space to another (
permeability), and the fluids in those spaces which determine whether a formation (rock layer) can produce oil or gas (and make money, too).
Shale has lots of porosity. It is composed of extremely small fragments, usually clay minerals, often contains organic material (plant or animal fossils or both), so it is a great place to form and trap hydrocarbons. But those pore spaces, although abundant, are seldom interconnected, so whatever hydrocarbons form tend to be trapped in the rock and only released over a very long period of time. When that happens, those fluids migrate into the pores in adjacent, more porous rock, usually upward, but sometimes downward to where the pressure in the pores is lower than it is in the shale. The Three Forks is one such case, where oil and gas from the Lower Bakken Shale have been squeezed downward into the silt, dolomite, and sand in the upper part of the Three Forks.
Siltstone is a little coarser than shale, has fewer but larger pore spaces (if they aren't filled by clay or other minerals), but the interconnections are still so small that fluid can't readily flow from one space to another. While that flow can happen and often does, it takes a long time for those fluids to move around. Too long for some driller who is waiting for a paycheck.
As the grains in the rock become coarser, the pores become larger, and the interconnections better, so fluid can flow and accumulate (and be produced) better, so sandstone (coarser grains, larger pores yet) is a better reservoir and can be produced with vertical wells.
Lots of things can happen to that rock to either make that porosity or permeability better --or worse, but the big ones involve folding the rock during episodes of mountain building, fracturing associated with that folding and or even faulting, and minerals deposited or removed by fluids passing through.
Those rocks are commonly conceived of as being in nice layers, and sometimes even are, but often, especially in the case of low permeability reservoirs, are in discrete lenses, separated by permeability barriers, in 'pods' which are not interconnected. They may even be lenses in and dispersed throughout the shale that is the source rock, but it is tough to produce oil from limited units of tight rock.
That's where horizontal drilling comes into its glory, because it offers the ability to connect a bunch of those reservoir pods to a single wellbore. That is further enhanced by hydraulic fracturing, which generates fractures which not only make the permeability within the lens better, but can also connect multiple lenses near to the wellbore that the wellbore did not penetrate directly. During a frac, those created fractures are propped open by sand grains pumped in with the frac fluid (or some other
proppant, including ceramic beads, but sand is the most common). That creates pathways for the oil or gas trapped in the tight reservoir lenses and tight rock to escape to the wellbore, and even allow more oil or gas to escape from the source rock.
At times those fractures intersect natural ones, and that can work even better.
Some more on sedimentary rocks and oil reservoirs:
http://infohost.nmt.edu/~petro/faculty/Adam%20H.%20571/PETR%20571-Week3notes.pdfI'd be happy to answer any questions you have.
