Rethinking unconventional oil and gas: Kemp
total petroleum system: the natural fluid network that constrains the assessment unit" U.S. Geological Survey, 2000).
For decades, North Dakota produced millions of barrels from wells drilled into conventional oil accumulations found in the Madison and Lodgepole formations. But the source of that oil was probably the Bakken and Three Forks formations, which are continuous-type accumulations, and are now being targeted directly by fracking firms.
The result is that much of the prospecting for shale oil and gas is occurring in areas that have already produced conventional oil and gas. Frackers have turned their attention to the Anadarko Basin beneath Oklahoma and Kansas, areas that have been producing substantial quantities of oil and gas for a century.
Argentina's enormous Vaca Muerta shale formation is thought to be the source for several conventional oil fields in the region. China's Sichuan basin, which is highly prospective for shale gas, has been the home of the country's conventional gas industry for thousands of years.
The North Sea is also thought to contain substantial quantities of unconventional petroleum.
The main difference between conventional and unconventional accumulations is the ease with which oil and gas flows through the formation. Geologists measure this permeability in Darcy units. Permeability for the giant carbonate and sandstone reservoirs of the Middle East is a thousand times or more than for shale formations.
Until the advent of horizontal drilling and hydraulic fracturing, there was no way to extract oil and gas in commercial quantities from low-permeability rock formations such as shale. But by creating a network
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