Joint Cross Well and Single Well Seismic Studies at Lost Hills, California Page: 2 of 39
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post- and pre-injection data revealed an increase in Poisson ratio of up to 5%. Both,
velocity and Poisson estimates indicate the dissolution of C02 in the liquid phase of
the reservoir accompanied by a pore-pressure increase.
The single well data supported the findings of the cross well experiments. P- and
S-wave velocities as well as Poisson ratios were comparable to the estimates of the
cross well data.
The cross well experiment did not detect the presence of the hydrofracture but
appeared to be sensitive to overall changes in the reservoir and possibly the presence
of a fault. In contrast, the single well reflection data revealed an arrival that could
indicate the presence of the hydrofracture between the source and receiver wells, while
it did not detect the presence of the fault, possible due to out of plane reflections.
Key words: cross well seismic tomography, P-wave and S-wave velocities, Poisson
ratio, single well seismic imaging, C02 sequestration, enhanced oil recovery
A subsurface C02 injection pilot program is currently being operated by Chevron
USA Production Company in the Lost Hills, California, oil field (Figure 1). This
pilot program, which is partially funded by the U.S. Department of Energy (DOE)
as an enhanced oil recovery (EOR) project, is ideally suited for design and testing of
geologic sequestration concepts including subsurface monitoring techniques.
Lost Hills Diatomite
The reservoir at Lost Hills is comprised of diatomite which consists of approxi-
mately equal parts biogenic silica, clay, and silty-sands. As the diatomite is buried
at higher pressures and temperatures, the silica, which is initially in a form called
opal-A, undergoes a phase transition to opal-CT and subsequently to quartz (Isaacs,
1982). Hydrocarbons are found in all three phases with enhanced production from
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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/m1/2/: accessed October 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.