Black shale is a common source rock in deepwater settings. The standard oil-generation model has organic matter being deposited as separate particles within the shale.

Th 94181

Source rocks

Black shale is a common source rock in deepwater settings. The standard oil-generation model has organic matter being deposited as separate particles within the shale. This organic matter is then transformed into oil and gas over time under overburden pressure and heat. Now more is being learned about black shale and the role its mineral constituents play in oil generation.

An article in a recent issue of Science examined the role of clay minerals in black shale and their effect on the transformation of adsorbed organic carbon into oil and gas. The authors present an alternative model where amorphous organic matter envelops clay minerals and is adsorbed onto the clay surfaces during deposition. The key in this approach is the large surface area available in clays to hold carbon-rich organic matter for future transformation.

Detrital smectite or smectite mixed layer illite-smectite have the largest reactive surfaces for holding organic matter. Smectite by itself has the largest surface area of the clays analyzed and is associated with high total organic content (TOC) values in source rocks.

The minerals dispersed in the shale act as catalysts to convert the adsorbed organics into kerogen, oil, and gas. Geologists should have potential source rocks analyzed for clay types, as well as kerogen type and TOC, for a more complete understanding of the history and oil producing potential of the rocks.

German survey

TGS-Nopec announced the start of a 2D seismic survey offshore Germany. The Zephyr 1 will perform 3,650-km non-exclusive project on the western German shelf. Final data will be available during 3Q 2002, following processing in TGS-Nopec's facility in Bedford, UK.

While the new survey is being gathered, TGS-Nopec will reprocess 6,700 km of older 2D data, which is being filled-in by the new shooting.

Ice flows

Recent environmental press articles have released a "wail of despair" regarding large blocks of ice detaching from the mainland of Antarctica. The alarm has to do with the false assumption that a release of Antarctica's floating ice contributes to future sea-level rise or indicates a warming of the oceans due to the effect of greenhouse gases.

Nothing could be further from the truth. Floating ice has no effect on the sea level, since it is already floating at volumetric equilibrium with the ocean. More importantly, a release of floating ice means there is outward pressure from higher altitude ice masses flowing off the frozen continent. Ice on land ultimately flows downhill and into the sea.

In a recent edition of Science, an article devoted to the mass balance of the West Antarctic Ice Sheet found strong evidence for ice-sheet growth of around 26.8 gigatons per year. The ice mass thickens at about 25% of the snow accumulation rate, so the ice sheets are actually thickening and expanding. This process sends ice outward from land onto the ocean as a floating ice shelf.

Glacial processes are complex. Authors who ascribe broad greenhouse effects to normal geologic processes are ill informed and should be challenged. The geoscience community needs to step forward and correct such junk-science statements.

On a more positive note, the release and eventual melting of large ice blocks frees the sediment load entrained within the ice mass. Such ice-rafted debris creates well-sorted clastic rock bodies that can become future petroleum reservoirs in deep marine settings.

Climate controller

Radiation from the sun ultimately controls the Earth's climate. This rather obvious connection now has been confirmed by Gerard Bond and his team at the Lamont-Dougherty Earth Observatory. Their work compared ice-rafted debris fragments from the North Atlantic with solar activity recorded in carbon-14 isotopes. The overlaid curves show a correlation coefficient of 0.4-0.6, dramatically consistent. While the heat flow linkages from the outer atmosphere to the oceans are not fully understood, it is apparent that, in the broadest sense, the sun is Earth's true climate controller.


4D seismic

Sonsub was awarded a patent on a new device to permanently deploy cable arrays for 4D seismic. US patent number 6,350,085 B1 describes a submersible drum deployment system that allows seismic cable to be laid out from the drum onto the seabed while the drum is suspended on a riser cable attached to a surface vessel.

Th 94181
Sonsub's patented 4D-cable laying system uses a large drum to convey the cable to the seabed and an ROV to guide cable placement.
Click here to enlarge image

The system is portable and can be used with a vessel of opportunity, since it doesn't require special handling. When deployed with the aid of a remotely operated vehicle (ROV), the 4D seismic cables can be laid in accurate patterns, which can include 90-degree turns. This new system could expand the number of deepwater fields monitored and minimize the cost of seismic operations for routine oil production tracking.

Drilling data

IHS Energy Group announced Drilling Wire on the Webtrademark, a web-based service that allows tracking all current US active drilling and completions. Subscribers can access information on new permits, staked locations, drilling wells, and completions from any Internet access point.

The service allows subscribers to search for personalized criteria, such as completion dates, operators, depth, and locations. Users can define an area of interest, such as the drilling progress of wells that meet certain criteria, and they can receive instant e-mail notification of new activity. Also included is the Energy News on Demandtrademark service, which offers editorial news, lease sale data, regulatory activity, legislation, and petroleum prices.

More in Geosciences