Or is it geography. I was asleep that day at school. No. I was right the first time, although most people on this board probably concentrate more on the latter. I'm not sure how many geologists (other than Kirk) follow this board but I'll ask my question anyway, even though the very geologists who could answer my question are probably sworn to secrecy for obvious reasons.

One of the head guys at Devon recently said that Devon was going to concentrate more on the northern end of their acreage because of the "higher carbonates" up there. From what I can tell he is referring to the type of rock that fractures and stays open, as opposed to the more southern acreage, where there were rumors that the higher clay content was gumming up the fractures. (I'm assuming he is basing that opinion on the Soterra Fluker well and the southern wells in East Feliciana). So the obvious disadvantage of clay is that it limits the oil output. Since most things have a downside and an upside, what would be the advantage to the higher clay content, or do we even know it yet? (Even if you don't know, if anyone knows any good oil geology blog boards I would appreciate your posting them as I haven't had much luck finding any. Oil geologists are apparently really quiet guys).

Devon has a considerable amount of it's acreage in what I would call "that southern end" and what I assume is the "northern part" is just a stone's throw from the Mississippi line which, rumor has it, Devon refused to cross. This means that in several of the parishes where they leased heavily they have a huge "clay" problem looking them in the face. Furthermore, if the depth of the play at any geographic location determines the high clay content (and I'm not saying it necessarily does), then they have an even bigger problem, since the play in Kentwood is at about the 11,500 foot mark. That zone quickly goes northwest into Mississippi and if you move strictly west from Kentwood into St. Helena parish and the Felicianas the play gets deeper pretty fast. If what I say is at least partially true, it would appear that they have their backs against the wall of the state line of Mississippi in just Tangipahoa and St. Helena for their best acreage, or at least what I will call their best acreage depending on the results of the Kentwood well. Even the northern most parts of the Felicianas might be too soft to work.

If anyone knows how to turn "clay" into "brittle rock", I would suggest you call Devon. You might have a job waiting with RREEEAALLLLYYY good pay and benefits.


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You pretty much have the general concept down - more clay, more ductile, more difficulit to frac


Very similar to Eagle Ford on many respects where the carbonate rich (brittle) section works and the clay rich areas don't work. The oil / gas is in these clay rich sections, but when you combine more ductility with more bound water (result of clay) which leads to less pore space for O&G (so less hydrocarbon storage capacity). Plus generally lower permeabilty because of more clay in the pore throats.


The clay vs carbonate rich areas in the Tuscaloosa Marine Shale is tied to the original deposition enviironment that was taking place during TMS time.

TH, there are no benefits to higher clay content.  Clay content is related to deposition environment - not a function of depth.

Basic fracturing concept - brittle is good, soft is not..

Make a brick sized block of clay and hit it with a hammer = compresses/sequeezes

Take the same block - fire it to a brick and then hit it = shatters into 100s of pieces = fractures

Shattered has a higher formation permeability than  the Clay block


Curious about this too. If you check Kirk Barrell's TMS presentation along about slide 35 it is shown actually the further north you go in the play the less calcareous and more clay-dominated the TMS becomes. What is the geologic positive of the northern TMS? I asked this question a while back and, other than TMS not being quite as deep, still don't know of a geologic reason for shift north by Devon. The northern (Amite County) wells seem to be doing well, but is this more a function of geology or more aggressive (longer laterals, more frac stages) techniques? I hope Mark, Kirk, some others who have the necessary mental high resistivity will get us an answer to the "is there a geologic reason for Devon and others to move northward?" question.

Interesting. I'm looking at page 35 right now. It's in the "Play Overview".You have a good memory. Since I'm more inclined to believe Kirk's geology than some suit's off-the-cuff remarks the mystery deepens. Never-the-less, the proof is in the pudding and the leasing activity is moving north in Tangipahoa parish according to my local sources. Kirk had a small section recently about the rumors swirling around and one of them was that that Devon had "lost interest" in the southern portion and he stated that he had heard that from several sources as well, and that he thought that that was a mistake, so he must be puzzled by this as well. 

I would have speculated that the move north was because of the Anderson wells initial success but the move north was already underway before they started flowing. Maybe they found some exceptionally good cores during the drilling phase and shared it with Devon. It would be interesting to know at what point in time Devon and Encana began sharing data. This could just be about Devon getting a good producer on line as quickly as possible to satisfy the shareholders and new partners.

Unfortunately my memory on this is "good" for a bad reason. Family property in 4N2E and 5N1W is said by knowledgeable geologists to be "too far north". I still have slight hopes though because Stone Energy--who is reportedly parternering with a major--has leased adjacent to two of our tracts and two unknown brokers are wanting but say for "conventional" Tuscaloosa and offers are very low. Hopefully time is on my side.

What knowlegeable geologists can claim that 4N-2E is too far north with any certainty?

Spring Branch---in answer to your question,Kirk Barrell feels our property in 4N-2E and 5N-1W is "too far north". I gather increased clay is the reason, but hydraulic fracture risk could also be an issue. A friend who is a geologist but more oriented to conventional Tuscaloosa rather than TMS feels the same. Don't know degree of certainty.

Thanks guys. Good info. So much for my "back against the wall" theory on play depth. I'll have to keep looking. And of course I still continue to wonder why Devon is not utilizing the full length of their Kentwood production unit for a longer lateral. As per Skip Peel's calculations even after "setbacks" on each end they still have over 1000 feet that they are not drilling.


another geology question:  what is DEEP TUSCALOOSA???

i found this article in louisiana life.  look at the map on page two.

can someone tell me the difference between the regular tms and the DEEP tms?

can it be two different leases?

Thanks for the link to the news article, B.J.J.

And yep, that's some map, too.  Pretty much lays it out for all to see.

As to your question on the possibility of "two different leases" -- that would, in fact, be possible, depending on a number of factors.

But the key phrase is "possible" -- in that it could be a bit of a negotiation to ink the first lease, whereas the hold-back on the second "non-leased" formation would then be well defined per the first signed lease.  

Joe A. seems to have a fairly good handle on "zonal" leasing.  You might wanna read his thinking on such.


The Deep Tuscaloosa they are referring to is the conventional sandstone play that traps oil and gas in large structures south of the Lower Cretaceous shelf margin. Examples of fields that produce in this trend are Judge Digby, Morganza and Port Hudson. They produce dry gas with small amounts of condensate and are very deep at ~20,000 feet. It is not the same as the TMS which is truly a shale and not a conventional sandstone reservoir. Hope that helped.


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