Wednesday, July 11, 2012

WTF is the Newark Basin?


One story that was all over the news during my break was the moratorium on drilling in Bucks and Montgomery Counties.  In addition to the political controversy there was some confusion over what would be drilled in those areas.  The assumption of some, particularly on blogs and twitter, was that any production drilling under those counties would require hydraulic fracturing and the rocks involved are the Marcellus Shale. The former is speculative (production may or may not require fracking), but the latter is wholly inaccurate. 
 
Rather than the Marcellus Shale, bedrock formations of interest under those two counties are within a geologic structure known as the South Newark Basin. The geologic question then is what is the Newark Basin?

First off, basins within the crustal bedrock are not the same as topographic ones found on the surface. At one time they were indeed low-lying surface areas, but over time they filled with eroded and/or volcanic material. So they may or may not correspond to a topographic basin today and should not be confused with watersheds in the present. The loose materials in the ancient basins (mud, silt, sand, gravel, ash, organic remains etc.) were buried, compacted and cemented to form sedimentary rocks that became part of crust.  If there were enough organic remains mixed in and subjected to the right combination of temperature petroleum, natural gas or coal may have formed.  Thus geologic basins such as the South Newark are can be prime areas for fossil fuel exploration. 
Location of the South Newark Basin from USGS report.

The Newark Basin is one of several that formed along what is now the East Coast when the Atlantic Ocean opened.  Around 220 million years ago (ma. or mega annum in geology) what is now North America was part of a much larger super continent that began to pull apart or rift. 
Formation of the Newark Basin (from USGS).

Such rifting develops when a tectonic plate is subjected to tension. Blocks of crust will slide up and down along parallel faults to allow the crust to spread and accommodate the tension.  This process forms a rift valley (a basin). In addition to earthquakes, volcanism occurs and lava will be erupted into areas of the rift basins. The East African Rift provides an excellent modern analog that shows all stages of the process.  When such rifting occurs there is not a single tear, but multiple ones branching from each other.  Along the East Coast a chain of these connected rifts eventually continued to open and formed a new plate boundary and eventually the Atlantic. The other ones were abandoned and became inactive and over time the rift valleys filled in with eroded sediments. Some have once again become topographic low points and make up parts of the valleys for rivers such as the Hudson and Connecticut.  If you're interested in more details, the Wikipedia page on the Newark Basin is fairly good and a Newark Basin site at Rutgers provides a wealth of information, although some parts may be difficult for non-geologists. 

The basin has been looked at before, but the current speculation and political brouhaha is driven by a new assessment from the USGS:
Using a geology-based assessment method, the U.S. Geological Survey (USGS) estimated
a mean undiscovered natural gas resource of 3,860 billion cubic feet and a mean undiscovered natural gas liquids resource of 135 million barrels in continuousaccumulations within five of the East Coast Mesozoic basins.
The estimated amounts in the Newark Basin are much less, 876 bil­lion cubic feet of gas, than those put forth for the Marcellus Shale (141 tril­lion cubic feet in some estimates). Even before this report there was renewed speculation in the past decade. Geologist Art Pyron,  published a review of the gas potential of the Newark Basin back in 2007 based on data from two sites drilled in the 1980s. His conclusion:
The results of drilling the two wells in the Newark basin of Pennsylvania provided an initial insight into subsurface conditions.
It allows a broad correlation of seismic data with subsurface conditions. It also exposed the fact that the subsurface characteristics of this basin are more complex than the “cookie cutter” geology that has been imposed upon it since the mid-1800s.
Reservoir analysis suggests that there is a thick, organically rich, siltstone-shale-mudstone complex in basin center that is apparently equal to other great fractured shale reservoirs.
With a thickness ranging from 2,500 ft to over 4,000 ft, the Lockatong member could host many significant local reservoirs that could produce economic amounts of relatively dry natural gas. In addition, there is a possibility that sandstones with porosity might lie in proximity to the organic shale, and could, under the proper conditions, be significantly large natural gas reservoirs. (emphasis added)
The last sentence suggests that the gas would be held in the type of reservoirs tapped by conventional drilling and not fracking. I added the emphasis to stress that the estimates are just that.  So right now uncertainty remains whether there is exploitable amounts of natural gas in this basin and what technique would be needed to recover it.

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