Hello there
livioflores-ga has provided some interesting information in the
comments dealing with stability and the non-need for us to replace the
oil removed. That may very well be true in come situations and may
not effect future production from some wells.
However, nature frequently takes over where we leave off and conducts
a replacement of its own and in some cases the damage has been quite
high. Surface deformations and subsidence have taken place in more
than one oil field. - "One recent estimate placed the annual cost of
subsidence damage and mitigation within the U.S. alone at over $100
million" - From Rapid subsidence over oil fields measured by SAR
interferometry/Jet Propulsion Laboratory, California Institute of
Technology, Pasadena, California
http://www-radar.jpl.nasa.gov/s323/IntSARapps/LH-Belridge_GRL.html - -
You will find many additional references here.
From Us Department of Energy and Terralog - "Subsidence and Casing
Damage Study, California - Fluid extraction and injection operations
in several shallow diatomite reservoirs have induced significant
subsidence, surface fissures, and structural damage to wells. Terralog
has completed a detailed review and analysis of production related
subsidence and well damage. In collaboration with Lawrence Berkeley
Labs and Sandia National Laboratory, Terralog is developing improved
subsidence and damage models for these fields."
http://www.terralog.com/subsidenceexamples.htm
From Terralog - "The weight of overburden sediments above a producing
formation is supported partially by the rock matrix and partially by
the pressurized fluid within the rock porespace. When fluid pressure
is reduced by oil and gas production, more of the load is transferred
to the rock matrix resulting in formation compaction. This subsurface
compaction can sometimes produce surface subsidence with significant
displacements in the both the vertical and horizontal directions. In
extreme instances surface fissures have been created, fault movement
has been induced, well casings have been seriously damaged, and
offshore platforms have partially submerged."
http://www.terralog.com/subside.htm - - - - - In this website you will
find mathematical and elastic models, case studies and more, several
with detailed illustrations.
Induced seismicity is another situation caused by oil removal. In
other words, the removal of oil can cause earthquakes, even in regions
normally quiet when it comes to seismic activity, such as parts of
southern Texas. This from the NORSAR website: - "From oil and gas
fields the problems relating to induced seismicity have been known
since the 1920, and were 30 years later thoroughly studied at an oil
field near Wilmington, California, where the oil production triggered
a series of damaging earthquakes. In the last decade a number of
examples of earthquake activity related to oil and gas production as
well as injection of liquids under high pressure have been observed,
although not with as serious consequences as for Wilmington."
http://www.norsar.no/seismology/induced/
There may be a little confusion caused by the above statement as
"Induced Seismicity" is also a term used by the oil industry to defind
deliberate, man made 'mini-quakes' used in the finding of oil.
However, the article I quoted is clearly intended to discuss quakes
caused by the removal of oil, not the discovery of it.
This paper deals with earthquakes in Canada caused by oil and gas extraction:
"New model for induced seismicity caused by hydrocarbon production in
the Western Canada Sedimentary Basin"
http://www.mustaqeem.ca/abstract.htm
Even pumping water into the ground to try and replace the missing oil
can have negative consequences. - "Small ground motions have, in the
past, been attributed to increases in fluid pressure in rocks. The
most notable occurrence was in Colorado in the 1960s. Denver-area
residents, who had not felt an earthquake in 80 years, experienced
over 1,300 of them when the Rocky Mountain Arsenal pumped 165 million
gallons of its wastewater into a 12,000-foot-deep borehole over a
four-year period."
http://dax.geo.arizona.edu/earthscope/didyou/waterquakes.html - From Earthscope
So, the most general answer to your question about what replaces the
removed oil is "the ground above it" and as for a net deficit - yes
there is one. Sometimes the damage caused by oil depletion drags by
months or years and nobody knows just what the final outcome will be.
Only time will tell.
I hope that this, along with the material supplied by livioflores-ga
in comments will provide a fairly complete picture of what happens
when oil is removed from the ground. There may not be a "need" to
replace it from the production standpoint. But there is certainly an
economic and moral need to try and stabilize these fields in some
manner. A hundred million dollars a year in damage caused by oil
extraction is not something that can just be brushed aside by the oil
industry and government simply saying there is "no need" for
replacement.
Search - Google
Terms - oil production and earth deformity, oil production and
subsidence, oil production and earthquakes
Websites are included in the text.
If I may clarify anything, please ask.
Cheers
Digsalot |
