The hidden treasure that is the Burket Shale
Today we are discussing the yet-untapped potential of the Burket with Gregory Wrightstone of Wrightstone Energy Consulting.
The incredibly successful Marcellus shale – along with the underlying Utica shale, which was recently reported to hold as much as 20 times more dry natural gas as was previously believed – tend to overshadow the shallower Burket-Geneseo shale, which is the black organic rich shale that lies immediately on top of the Tully Limestone, and is an Upper Devonian formation.
The play is in an early stage of development but it is already believed that it could be classified as a super-giant field – holding 30 Tcf of dry gas or more.
Monica Thomas (Shale Gas International): We are here to talk about the Burket / Geneseo Shale. I understand these are two sections of the same formation – am I correct in thinking that?
Gregory Wrightstone (Wrightstone Energy Consulting ): They’re equivalent formations – in other words the accepted terminology across most of Pennsylvania and West Virginia is the Burket, whereas the same formation in North-West Pennsylvania and New York is Geneseo. So they are laterally equivalent.
MT: You chose to talk about the Burket at the recent Hart Energy Developing Unconventionals DUG East conference. What is so important about this shale that the industry should take notice?
GW: Well, there have been around 90 wells that have been completed as producers to date. And many of those wells had significant and high production rates. Some of them as high as over a Bcf of gas in their first 6 months of production.
The analysis indicates that recoverable resources from the Burket will exceed 30 Tcf from the core areas that are identified. Which qualifies it as a super-giant gas field. Super giant being 30 Tcf or greater, which in any other area of the world would be extremely significant, but because it is located in the Appalachian basin it’s overwhelmed by its ‘big brother’ the Marcellus and now the Utica shale. So, it’s incredible that we have a super-giant reservoir this close to the north-eastern gas markets.
MT: You mentioned that the Burket is being overshadowed by the Marcellus. Would you be able to draw a comparison between the Burket and the Marcellus and Utica?
GW: The Utica is difficult to assess at this time since – and this is true particularly for the dry gas Utica – it is so early in the play development. That part of the play is still in its infancy, so the decline curves for these wells haven’t been well-established – but have been for the Marcellus, which is further along in the play development.
The Burket is also in its infancy but if we just look at the initial production into line in the south-west core area of the Burket, those wells average about 750 Mcf of gas in their first 6 months of the production data. And that compares to a little bit over 1 Bcf in the same time-frame for the Marcellus shale wells. So the production data indicates that the Burket is not quite as good as the Marcellus in its best area.
In the northern core area, the Burket wells average about half a Bcf in their first 6 months production, compared to about 1.1 Bcf from the underlying Marcellus.
So the Burket has very good production rates but significantly less than the Marcellus. Hence companies prefer to spend their drilling and completion dollars on the Marcellus rather than the Burket in many of the areas.
MT: Could you explain where Burket shale lies in relation to the Marcellus?
GW: The Burket is just above the Marcellus and ranges from less than 100 ft above the Marcellus to about 800 ft above it – moving from west to east in the Appalachian basin. So in the western area the Burket, in the best areas, lies about 200 ft above the Marcellus. Therefore one of the main concerns in this area may be that there is frack communication between the overlying Burket and the underlying Marcellus, which may complicate completions in those areas.
The Burket ranges from 4,500 ft in depth to more than 7,000 ft in depth for the deepest part of the basin, and since it’s fairly close to the Marcellus, drilling depths are similar to those of the Marcellus.
MT: How similar are these two shales? Can exploration techniques used on the Marcellus also be adopted for the Burket?
GW: I call the Burket the ‘little brother’ of the Marcellus for a number of reasons. It seems to have been deposited in similar depositional environments; they’re both located immediately above limestone, they both have been successfully completed with similar fracking technologies – with large amounts of water and sand. So the technology to both explore , develop and complete these two shales are nearly identical, for both the Marcellus and the Burket.
MT: That sounds like good news for exploration companies. Also, if they are located in the same geographical area, then if a later development of the Burket takes place, operators could use the same infrastructure that is currently built around the Marcellus.
GW: That’s true. And the best parts of the Burket overlie some of the better parts of the Marcellus as well. So we will be able to access the Burket perhaps even utilising existing pads, existing roads and pipelines.
MT: You mentioned, however, that there would be challenges?
GW: The complicating factor is in the south-west area, where the Burket is not separated from the Marcellus with a large interval. There is a possibility of communication between the two zones, and if the Burket is not completed at the same time as the underlying Marcellus, in that area, a later completion attempt on the Burket may possibly be compromised, and frack down to the underlying Marcellus.
I mean, in fracture theory, the frack goes where it wants. And when you are in a virgin pressure, the frack will tend to go up a little bit but if you’ve already produced and fracked the underlying Marcellus and produced for 10 years, then there will be a low-pressure sink, which alters the stress regime and alters where the frack might go. The frack might be compromised and not be as effective as if it was completed at the same time as the Marcellus.
Some companies have elected to complete the Burket in a stack pattern at the same time as the Marcellus and those wells appear to be performing very well.