Upper and Lower Eagleford in Eastern Gonzales County

Can anyone shed any light on if there is an upper and lower producing zone for the Eagleford in the Eastern Gonzales area? Specifically in the Shiner area at the county line on hwy 90. It appears that the EOG spacing is suddenly increased from typically around 300 feet to between 550 to 600 feet. I'm curious if the wider spacing is to allow for additional drilling in between wells at a different elevation.

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Let me check some logs in that area to confirm, but my past experiences in this specific area showed that the overall Eagle Ford section was thinning overall and leaving you with only a single EF target zone.

However, some operators in this area have been chasing a target zone in the overlying Austin Chalk (sometimes calling it the Marl).

More after I check.

PS - EOG increasing lateral spacing may also be an indication that they believe that 330' spacing is too close in this area and that there was too much overlap of stimulated fracture volumes.

As noted in first email, I confirmed that the EF section is thinning in this part of the county and that only a single LZ / target zone if viable (in my opinion).

From a regional perspective, the EF section thins from SW to NE as you move toward the San Marcos Arch area (roughly the Gonzales / Lavacao County border). Then the section starts to thicken up as you move NE thru Fayette County into the other counties along the trend.

Mark, I'm specifically looking at wells involving the Zimmerman Unit. The elevation depth at the end radius to start the lateral for the 8 wells associated with the Zimmerman Unit ranges from 11,652 to 12,323. I have to assume that the 671 ft elevation variation between these wells, at the drilled spacing, would indicate the target zone in this area. I'm getting the data from the actual rig reports so I'm not sure how accurate this information might be. What minimum thickness is desired for the stacked lateral drilling in the EF?

DJC, thanks for that specific info.

I am assuming this is the Zimmerman unit that sits in far NE Gonzales Co near the County Line. Five permits on file - two wells drilled and on production (2012 and 2014). Older EOG production and frac approach. TVD's of the target zone in the Eagle Ford around 11,640-11,650'.

These two have produced about 520 MBO since being put online - my EUR projection shows them to be able to make another 150-200 MBO over the remaining well life assuming no mechanical problems.

GOR increasing a lot over past several months as bottom hole pressure is drawn down. This is to be expected.

EF here is only about 100' thick. Laterals appear to be landing in the middle of the EF on these two wells. Frac is then contained by the underlying Buda Lime. And can propagate upward into the Lower Austin Chalk.

It is good that you are getting rig reports - this is real and accurate data. Are you also getting directional survey information? Completion Information?

I see only the 14H and 15H as having been drilled and completed (info above). Are they drilling the 11H, 12H and 13H? No info on the Tx RRC site or my other sources on any activity on these three wells (all permitted in 2015 I think).

You mention 8 wells in Zimmerman unit - I only see five permits called Zimmerman in this area.

Your reference to the 11,652' and 12,323' data points is a bit confusing to me - is this drilled depth? TVD? You reference a 671' difference in elevation - that would indicate that these are TVD numbers.

Considering the thickness of the Eagle Ford and the depths you have noted (assuming that they are TVD values), the deeper of the two is in the Buda Lime below the Eagle Ford. But only if these are TVD numbers.

If this is the case, I would be a bit surprised, the best secondary target here would be Lower Austin Chalk in my opinion. Penn Virginia has been doing very well drilling that interval in their assets in this same area.

Buda is not a good producer in this area. Natural fracture play that is pretty marginal at best.

As to your question about minimum thickness to do stacked or wine rack Eagle Ford lateral drilling - I would say at least 300' and ideally more. Of course, it all depends on reservoir quality. Areas to the SW in Karnes County are ideal for this approach (plus add in a Lower Austin Chalk). The Zimmerman area is a pretty lean area as to Eagle Ford - the production from these first two wells tend to confirm that.

I figure you will have some more questions after reading my comments. Fire away.


  Zimmerman wells 11, 12 and 13 were never drilled. The Jamestown 1, 2 and 3 replaced the Zimmerman 11, 12 and 13 and the most recent Atlantic 1 and 3 have been drilled and completed within the past 2 years. The starting locations of the Zimmerman, Jamestown and Atlantic are all very close to each other. Additionally the Aggie 1, 2 and 3 have been drilled and are awaiting completion. I did not include the Aggie wells in my original comments/question since the starting location is much further North than the previously mentioned wells but do pass through the Zimmerman unit.

Thanks for that additional info.

In looking at the permit plats and directional surveys (all public record on the Tx RRC site), the Zimmerman, Jamestown and Atlantic laterals are all drilled parallel to each other and about 330' to 390' apart.

Directional surveys for 5 of the 6 (one for Atlantic 2H not yet on file) show TVD's in the 11,610-11,710' range.

All the same landing zones (Eagle Ford) on all these wells.

Whereas the Zimmerman laterals are only short laterals (4560' to 4859'), the Atlantic laterals are in the 8200' long range while the Jamestown laterals are in the 6700' long range.

Mark, in my lease agreement we receive the daily drilling reports for each well so I get the actual data as the wells are drilled. Every well has a different elevation than the RRC. The common tangent point of the end of the radius to the start of the horizontal lateral is the point I will identify below for the wells being discussed. I'm guessing that the elevations identify the TVD's and landing zones for each well (I could be missing something in my assessment). Please note by the GIS map the locations of each of these wells are very close for the penetration points. 

Zimmerman 15 is 11,625 ft

Zimmerman 14 is 11,945 ft

Zimmerman 11, 12 and 13 never drilled

Jamestown 1A is 12,150 ft

Jamestown 2B is 12,175 ft

Jamestown 3C is 12,247 ft

Atlantic 1A is 12,323 ft

Atlantic 2B never drilled

Atlantic 3C 12,285 ft

The vertical depth (TVD) difference I mentioned initially is the depth difference between the Zimmerman 15 (11,652 ft) and the Atlantic 1A (12,323 ft) which is the 671 ft. If these elevations are the correct elevations for the TVD's, would the EF thickness be estimated to exceed the 671 ft thickness? I hope this additional information is useful.


Thanks for the additional info you have provided this AM. I have been racking my brain this AM on this - and aside from the difficulty in trying to talk about this and explain things via this site instead of being able to sit down in person and show you details and sketch out things - I think I have the answer.

First off, it is great that your lease allows you to get daily drilling reports from the operator. But in my 44+ years of experience in the oil patch, operators are VERY resistant to give up all the data on any well unless the lease specifically says that they have to do it.

  • With that being said, I am figuring you are ONLY getting the drilling report - which can be very detailed. But you are NOT getting daily and final directional survey information, plats, Gamma Ray Logs, plats and related information pertaining to the well that is being drilled. Operator will not send this to you unless it is specifically outlined for them to do so in the lease terms. 

There are a few facts in play here - the Eagle Ford is only about 100' thick in this part of the county. That is proven by the vertical logs I have looked at. Plus the studies I have done over the past several years in the Eagle Ford trend.

Another fact - the TVD of the laterals being drilled in this area (as noted in my comments yesterday) range from subsea 11,610' to 11,710'. The 100' variance between these laterals subsea landing zone depths are probably tied to a subtle structural change in the Eagle Ford across this area.

  • This is to be expected since no section in the subsurface is "flat" across any area.
  • These subsea measurements for the laterals are at the toe (end) of the laterals.

Another fact - the Tx RRC GIS mapping site is a nice tool, but it is NOT an accurate depiction of the laterals. As you know, it shows a common surface location point for a drilling pad with the laterals radiating outward from that central point. This depiction is incorrect.

  • In truth, a drilling pad will have the actual surface locations sitting about 25'-50' apart. Rigs are skidded this distance to give the operator room to set and drill each well. These wells are then drilled outward and away from this surface location so as to allow the operator to get to a subsurface position to start the lateral. And this start will be such that the lateral is 330' or whatever away from the parallel lateral in the unit. To do this, the wells are drilled out and away from the surface location - basically like a string of spaghetti that moves out and away from the surface location before hooking back to the first penetration point of the lateral / horizontal.
  • Imagine a series of sinuous "fishhooks" or "spaghetti strings" emanating from the common surface location. And by having to drill these "sinuous strings", each lateral will have a long-measured drilling depth before they get to the point of hitting their first horizontal take point in the subsurface. 

This - in my mind - is the reason for the 600'+ of difference you are seeing as noted above.

You need to access the directional surveys (MWD) from the Tx RRC site to see the true info for each lateral. I don't think that this info is being sent to you as part of the drilling reports as per your lease terms. 

  • I have attached PDF's of these surveys for the Zimmerman 14H and Atlantic C 3H. Lots of info here - but the TVD's of the laterals at the toe of these two laterals are subsea 11,652' and subsea 11,651'.
  • Note the details in these directional surveys - measured depth, correlative TVD's, azimuth, dog legs, etc.
  • Also note the details on the plats - especially the "detailed" views of the surface location vs penetration points and how for the wells have to be drilled from the surface location to get to the first penetration points.

I will send the link to the directional survey info on Tx RRC in my next posting. Note that this is all free info on the Tx RRC site.

Hope this all makes sense.


This is the link the Tx RRC site where you can find the directional surveys. They are a separate part of the completion report info link.

Note that when entering the API number for any specific well, you only have to show the county and well specific number with no hyphen

ex - "17734209" 

Oil & Gas Completions (texas.gov)



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