Seismic Monitoring of Fluid Flow
I believe one of the next major breakthroughs in Geophysics will be in
the research area of
"4-D seismic monitoring of subsurface fluid flow."
Seismic monitoring defined
4-D seismic monitoring consists of time-lapse
3-D seismic surveys conducted over time intervals in which
interesting subsurface fluid movement can take place. Integrated
with rock physics and fluid-flow simulation,
estimates of fluid-flow geometry, permeabilities
and fluid phase-front movement in the Earth may be inferred from the
time-lapse seismic data. Seismic monitoring offers us the
possibility of finally being able to estimate where and how fluids are
flowing in the Earth.
Why is monitoring fluid flow important?
Seismic monitoring of subsurface fluid flow has the potential
for immense impact in: oil and gas energy resources,
groundwater and environmental studies, global warming issues
related to massive methane hydrate deposits, and earthquake
prediction related to pore-fluid pressurization before fault failure.
Oil and gas energy resources
Hydrocarbons fuel the world's economy, including transportation,
power generation, and manufactured goods that we depend on.
Most of the Earth's potential oil and gas reserves have already
been found and are currently being rapidly depleted.
Because we do not understand the complexity of flowpaths
and flow barriers in oil reservoirs, we leave behind at least as
much oil as we produce in each reservoir due to inefficient production
strategies. I believe seismic monitoring will become an
interactive tool for understanding reservoir fluid flow, and
help us double the amount of oil and gas reserves we currently produce.
Groundwater and environmental issues
Groundwater is becoming a precious resource. High-resolution
shallow seismic surveys might be useful in monitoring water table
fluctuations with time over large surface areas to better understand
aquifer depletion and recharge. Also, it is becoming increasingly
important to monitor contaminant plumes at hazardous spill sites
to make sure clean water is not polluted. While seismic data
cannot "see" most contaminants in water, the closely related
electromagnetic surveying technique called Ground Penetrating Radar
can image contaminant plumes by electrical conductivity differences.
Methane hydrates and global warming
Methane hydrates are ice-like deposits which contain huge amounts
of trapped methane gas. Methane hydrate deposits have been
found at continental margins on a world-wide basis. It is estimated
that the amount of methane gas trapped in the ice is at least as large
as all the conventional oil and gas reserves found to date.
This means that methane
hydrates may be a future energy resource when they are understood better.
Methane is also a greenhouse gas, and plays an important role in
global warming. Monitoring the rate at which these deposits accumulate
or dissolve could provide very useful information to climate models,
and help understand the buffering role of methane hydrates.
Finally, many methane hydrate deposits have been found near offshore
plate subduction zones. I believe there may be a link between the
location of these deposits and the fluids that are being heated,
pressurized and driven out of the saturated downgoing slab.
Monitoring subduction-zone hydrates might give a clue to the fluid
flow system in a subducting plate, and how that is related to
subduction rates, depth and magnitude of earthquakes, and chemistry
of upwelling magma at subduction volcanic chains.
Earthquake mechanisms and prediction
Earthquake seismologists believe that fluid flow has
an important role in how frequent and how strong earthquakes occur.
Fluids can lubricate fault surfaces making it easier for an
earthquake to occur. Highly pressurized pore-fluid in a fault region
might indicate that an earthquake is about to occur.
Pore pressure increases cause seismic velocity decreases which might
be monitorable over time. I can imagine a seismic monitoring experiment
consisting of a small array of geophones on one side of the San Andreas,
and a shot location on the other. Repeated shots could be fired at
reasonable time intervals (1 week?) and the seismic arrivals
at the geophone array could be analyzed to see if the velocity
(pore pressure) in the fault zone is decreasing (increasing).
This type of seismic monitoring might help to better understand the
earthquake mechanism along a fault, and perhaps be useful as
a tool to predict when an earthquake is about to occur.
For more information...
You can view a selection of my research movies
and award-winning papers on
seismic monitoring and other subjects.
I would be pleased to interact with
other researchers who have an interest in any of these topics.
Please feel free to contact me.
Copyright © 1994 by David E. Lumley; email@example.com