from GeoTimes Website
They start in thin layers of source rock and, from there, buoyantly rise to the surface. On their way up, the hydrocarbons collect in little rivulets, and create temporary pockets like rain filling a pond. Eventually most escape to the ocean.
And, this is all happening now, not millions and millions of years ago, says Larry Cathles, a chemical geologist at Cornell University.
He's bringing this new view of an active hydrocarbon cycle to industry, hoping it will lead to larger oil and gas discoveries.
By matching the chemical signatures of the oil and gas with geologic models for the structures below the seafloor, petroleum geologists could tap into reserves larger than the North Sea, says Cathles, who presented his findings at the meeting of the American Chemical Society in New Orleans on March 27.
This canvas image of the study area shows the top of salt surface (salt domes are spikes)
in the Gas Research Institute study area and four areas of detailed study (stratigraphic layers).
The oil fields seen here are:
Tiger Shoals, South Marsh Island 9 (SMI 9), the South Eugene Island Block 330 area (SEI 330), Green Canyon 184 area (Jolliet reservoirs)
In this area, 125 kilometers by 200 kilometers, Larry Cathles of Cornell University and his team
estimate hydrocarbon reserves larger than those of the North Sea.
Image by Larry Cathles.
Cathles and his team estimate that in a study area of about 9,600 square miles off the coast of Louisiana, source rocks a dozen kilometers down have generated as much as 184 billion tons of oil and gas - about 1,000 billion barrels of oil and gas equivalent.
According to a 2000 assessment from the Minerals Management Service (MMS), the mean undiscovered, conventionally recoverable resources in the Gulf of Mexico offshore continental shelf are 71 billion barrels of oil equivalent.
But, says Richie Baud of MMS, not all those resources are economically recoverable and they cannot be directly compared to Cathles' numbers, because,
Future MMS assessments, Baud says, may
include unconventionally recoverable resources, such as gas
percent of the Gulf's total hydrocarbons are hidden in the
subsurface, representing about 60 billion barrels of oil and 374
trillion cubic feet of gas that could be extracted. The remaining
hydrocarbons, about 20 percent, stay trapped in the source strata.
Determining the ratio between the younger and older hydrocarbons, based on their chemical signatures, is key to understanding the migration paths of the oil and gas and the potential volume waiting to be tapped.
Another important key to understanding hydrocarbon migration is "gas washing," Cathles adds.
new process his research team discovered in the Gulf work, gas
washing refers to the regular interaction of oil with large amounts
of natural gas. In the northern area of Cathles' study area, he
estimates that gas carries off 90 percent of the oil.
Using such information in combination with the active hydrocarbon flow model Cathles' team produced and already existing 3-D seismic analyses could substantially improve accuracy in drilling for oil and gas, Colling says.
ChevronTexaco, which funds Cathles' work through the Global Basins Research Network, has been working to integrate the technologies. (Additional funding comes from the Gas Research Institute.)
And deep water changes the business plan. With each well a multibillion dollar investment, the discovery must amount to at least several hundred million barrels of oil and gas for the drilling to be economic.
Chemical signatures and detailed basin models are just more tools to help them decide where to drill, he says.
Working in an area with more oil by at least a factor of two than the North Sea, he says he hopes that his models will help companies better allocate their resources.
But equally important, Cathles says, is
that his work is shifting the way people think about natural
hydrocarbon vent systems - from the past to the present.