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Page added on August 4, 2014
Natural Fracking: How Long Did It Take?
Hydraulic fracturing is in the news because more natural gas has meant substantially fewer carbon emissions – and it has also been implicated in a variety of environmental issues.
Man is doing what nature has always done, albeit on a different time scale. A new GSA BULLETIN study examines how long it takes natural Earth processes to form hydraulic fractures and whether the formation is driven by sediment compaction, oil and gas generation or something else. Plus, in order to make environmental models about modern hydraulic fracturing production, it’s important to know what role these natural fractures play.
The process of fracture formation by a natural increase in pore-fluid pressure has previously been referred to as natural hydraulic fracturing. Researchers work to understand these fractures through examination of fluid inclusions trapped in minerals within the fractures. In this study, András Fall and colleagues conclude that natural hydraulic fractures formed over time spans of 33 to 35 million years, driven by the slow generation of natural gas.
(A) Location map of the Piceance Basin, Colorado, with major gas-producing fields.
(B) Stratigraphic cross section across the northern Piceance Basin.
Credit: A. Fall et al. and GSA Bulletin
Natural fractures provide important pathways for the flow of water, natural gas, and oil in geologic formations, including unconventional tight-gas sandstone oil and gas reservoirs targeted for production by hydraulic fracturing. These fractures play an essential role during well completion and production by connecting pores in the reservoir rock storing oil and gas to the hydraulic fracture and wellbore that allow production. “Sweet spots,” or zones of higher than average permeability, have been attributed to the presence of these open fractures.
Successful prediction of zones of increased fracture abundance provides an opportunity to minimize drilling and completion costs as well as the environmental footprint of production. Successful prediction of natural fracture occurrence and their hydraulic properties requires models of fracture formation that are based on realistic mechanical, hydraulic, and chemical principles that can be tested against core, well-log, and production data.
A. Fall et al.,’Natural hydraulic fracturing of tight-gas sandstone reservoirs, Piceance Basin, Colorado’, GSA BULLETIN, 30 July 2014, http://dx.doi.org/10.1130/B31021.1
3 Comments on "Natural Fracking: How Long Did It Take?"
rockman on Mon, 4th Aug 2014 11:30 pm
“…conclude that natural hydraulic fractures formed over time spans of 33 to 35 million years, driven by the slow generation of natural gas.” Perhaps in the formations they studied. But there are other causes such as structural “bending” (geologic term: folding) of a brittle rock. During the 90’s the Austin Chalk (a naturally fractured carbonate “shale”) in Texas was THE hottest oil play on the planet. Eventually frac’ng horizontal wells in the AC became more common. But initially great horizontal wells, comparable to current EFS completions, were completed without frac’ng. Ultimately the dynamic was deciphered. Long after the initially soft rock hardened and became brittle relatively gentle structural folding occurred.
Imagine a sheet of brittle material being placed over a football and downward pressure is slowly applied. Forces above the football would crack the material at roughly 60 degrees to the long axis of the football. Discovering where such “extensional fractures” occurred in the AC was critical to making good wells. Once these structures were identified horizontal wells were drilled to intersect the EF’s.
But there was a minor hitch: since the EF’s were present when the wells were drilled one of two situations tended to happen: a well would try to blowout if the mud weight was too low or, if the MW were two high, it would flood the fractures with drilling mud destroying much of their productivity. So a very exciting solution was developed: let the well blowout while drilling it. Essentially a controlled blowout with the oil being diverted to a large number of portable storage tanks (a 1,000 bopd was not uncommon) and the NG diverted to a flare tower (1 to 2 million cubic feet per day was not uncommon). Needless to say anxiety levels were very high while drilling. Once the well was drilled it was often completed “open hole”… no casing was run in the hz lateral.
But money was there to be made and folks were willing to take the risk. Needless to say only the most skilled hands were used to drill such wells. BTW the AC trend eventually covered several times the areal extent of the current EFS boom. There are still a few AC wells drilled now but it’s glory days have long passed. As I just posted elsewhere all oil/NG plays are “bubbles”. They either burst when prices drop or when most of the viable locations have been drilled. In the case of the AC bubble it simply died of old age.
Dredd on Tue, 5th Aug 2014 8:26 am
“Hydraulic fracturing is in the news because more natural gas has meant substantially fewer carbon emissions – and it has also been implicated in a variety of environmental issues.” – Science 2.0
Contra: “Insanity is sometimes defined as doing the same thing but expecting a different result. Psychologists define perseveration as repetitive behavior that interferes with learning. Whatever we call it, that seems to be what is happening. And whatever it is, it doesn’t make sense. Natural gas is not the bridge to clean energy; it’s the road to more climate change.
…
Natural gas is falsely promoted by the Obama Administration and energy corporations as a “bridge fuel” that will allow American society to continue to use fossil energy over the coming decades while emitting fewer greenhouse gases than from using other fossil fuels such as coal and oil.
On this basis, President Obama is providing total support to a massive expansion of hydraulic fracturing (fracking) for natural gas within the U.S. He seeks sufficient quantities to last for many decades, allowing the U.S. to export liquefied natural gas and oil throughout the world.” (When Indoctrination Is Enlightenment – 5)
Nony on Tue, 5th Aug 2014 3:28 pm
I’ve been doing some reading on the natural fractures. Sometimes they help stimulation, other times hurt it (there is an interaction). In the Austin Chalk, a lot of the production is right from the fractures themselves and stimulation of horizontals is not effective. In the Marcellus, the types of fractures (jointed) interact well with stimulation. In the Barnett, they generally also help but it’s a mixed bag.