Catastrophism

The tragedy of Sumatra and those countries affected by the recent tsumani brings into sharp focus the forces we geoscientists try to understand. The event brings to mind the theory of Catastrophism: sudden geologic change that reshapes the earth.

Asteroid strikes, volcanoes, earthquakes, floods, landslides, and tidal waves are all examples of sudden geologic change. Asteroids leave craters (astroblemes), volcanoes leave well-defined flows or ash falls, but the effects of earthquake (except faults), floods, landslides, and tidal waves are difficult to identify in the subsurface.

The images from the air over Sumatra are stark: coastal beaches denuded, barrier islands washed away, cut, or reduced in area by one-half or more. We hear much about the surface destruction at the water’s edge, but little about the sediment churning on the submarine slopes and canyons of the Indian Ocean as a result of the waves.

Where did all that fluidized sediment go? Down gradient, of course, flowing off the continental shelves into the canyons, filling seafloor holes, carving canyon walls, and splaying outward into various channel-levee deposits and fan forms. These deposits are the reservoirs of the future. They harken to earlier-deposited, similar structures geoscientists ponder each day.

Tsunamis are formed from offset of the seabed by earthquakes or by landslide displacement at the coast. While small earthquakes affect only the immediate region, a major undersea earthquake extends the force and effect of the energy release across the whole basin through the water. The resulting deposits are flat lying and tend to blend into the general depositional layering, but they are linked by the one event. This linkage to earthquake activity, if identifiable, can be used to predict sediment package formation and distribution from seismic data.

How many of the deepwater deposits we chase are the results of major sediment-loosening events like tsunamis? Can we link their deposits to events to form a predictive tool to aid future exploration? Understanding the Earth’s processes and unraveling the sedimentation history puzzle is a worthy challenge and full of oily promise.

Impact stimulation

Applied Seismic Research Corp. (ASR) announced a new form of oil recovery called Hydro-Impact Technology. The new approach uses seismic wave stimulation to shake loose oil trapped in existing wells. ASR developed the low-cost procedure to enhance oil recovery in depleted fields. Abandoned wells can be restored, and the yield can be increased in currently producing fields.

“Given the economic driving force of today’s energy market, an invention that increases the amount of oil recovered from existing wells is truly a technology of worldwide importance,” says Bill Wooden, vice president, Applied Seismic Research.

The technology produces shockwaves with a power ranging from 2-10 million W (compared to 10-100,000 W for vibroseis) and a pressure at the wave front in excess of 3,000 psi. The shockwaves travel 1.5 mi/sec and can cover distances of well over 1 mi in all directions, releasing previously non-moveable oil.

EXPLORATION

North Sea survey

In support of the UK’s 23rd License Round over the East Shetland platform, Fugro Multi Client Services (FMCS) highlighted a reconnaissance grid of 2D non-exclusive seismic data acquired in 1999.