by rockdoc123 » Sun 12 Apr 2015, 19:47:11
$this->bbcode_second_pass_quote('', 'T')he Bakken is a variant of a conventional reservoir and it is extremely misleading to compare to fracked tight gas fields like the Marcellus.
You just cannot get the flow of gas through shale-like reservoir rock compared to sandstone and dolomite. No amount of fracking can increase shale-like rock porosity to that of sandstone. All that fracking does is produce a large surface area for slow outgassing from the tight rock matrix. This gas flows towards the well through the fracture channels. It does not flow towards the well at any commercially viable rate from the part of the rock, which is most of it, that is not fractured.
The Bakken has several producing layers. The first production actually came from the upper shale unit but was followed by success in the middle tight dolostone unit. That being said more and more wells are focusing specifically on the upper and lower shale units in the Bakken which behave as a typical shale play. Elm Coulee Field has seen considerable activity to this end as of late.
The middle dolostone is by no means a conventional reservoir, it is tight dolostone with a permeability of as low as 0.01 millidarcies and is classifed by anyone active in the business as unconventional. This permeability is, of course, much higher than typical shale permeabilities which are in the nanodarcy range. But gas will not flow through that low of permeability without the aid of a fracture. The difference in reservoir behavior is that the permeability difference between the middle Bakken tight dolostone matrix and a propped fracture is somewhat less than the permeability difference between the upper Bakken shale matrix and a propped fracture. Because the flush production comes from the fracture the actual IP rate (initial production) for upper or lower Bakken shales can easily be as high as for the middle Bakken. Where production differs is the middle Bakken will have slightly less early decline rate and will stabilize at a higher flat rate. That being said in reality the upper, lower and middle Bakken are one system with hydrocarbons from the upper and lower units replenishing hydrocarbons as they are produced from the middle unit. In this sense the middle unit is an intermediary conduit. Claiming the middle Bakken is a conventional play is completely inaccurate.
As to your statement
$this->bbcode_second_pass_quote('', 'N')o amount of fracking can increase shale-like rock porosity to that of sandstone
Once again shows you are confusing porosity with permeability. There is no intent to increase porosity through fracking; the intent is to increase permeability.