Joint Cross Well and Single Well Seismic Studies at Lost Hills, California Page: 3 of 39
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fracturing in transition zones. Depositional laminations in the diatomite with vary-
ing silica content affect the system permeability (Graham and Williams, 1985). The
layers with phase transitions may exhibit enhanced natural fracturing and therefore
higher effective permeability, while other layers with lower permeability act as flow
The success of CO2 sequestration will depend greatly on the reservoir properties.
The diatomite reservoirs of central California have unusually high porosity (45-70%)
and low permeability (< 1 millidarcy). The pore size is < 5 microns while the pore
space is occupied by a mixture of water (50%), oil (45%), and gas (5%) (Perri et al.,
2000). Because of the low permeability, the diatomite reservoir is developed with 5,060
m2 (1.25 acre) well spacing. Despite this small well spacing, only 5% of the estimated
2.6 billion barrels of oil in place has been produced since discovery in 1910. In the
1970s, the production of the Lost Hills oil fields was increased by the introduction
of hydrofracturing to increase the reservoir permeability. In the 1990s, water floods
were added as an EOR technique. In 2000, Chevron USA decided to start a CO2
pilot project to study the applicability of this technique to the diatomatious reservoir.
Initial test were successful resulting in the recovery of 56-65% of the original oil in
place (Perri et al., 2000). Despite this success, the location and migration of the CO2
is not known and thus it was decided to use seismic borehole methods to investigate
whether the presence and the location of the CO2 can be determined.
Previous studies in carbonate reservoirs have shown that seismic velocity changes
are caused by CO2 injection, which can be spatially mapped using cross well seismic
surveys (Wang et al., 1998). The seismic velocity changes can be up to 10%, which
is easily detectable and mappable with modern cross well seismic surveys. There-
fore, borehole seismic surveys hold promise for mapping and long term monitoring of
Our goal is to investigate, through field testing, the suitability of cross well and
single well seismic techniques for imaging subsurface CO2 and for monitoring geologic
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Gritto, Roland; Daley, Thomas M. & Myer, Larry R. Joint Cross Well and Single Well Seismic Studies at Lost Hills, California, article, June 25, 2002; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc780276/m1/3/: accessed October 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.