Porosity Measurement Using Image Analysis
Techniques
Spontaneous
imbibition is perhaps the most important phenomenon in oil recovery from
fractured and low permeability tight gas reservoirs. Air-water
spontaneous imbibition experiments were conducted using low permeability
heterogenous limestone core plugs. The interfacial tension was changed by
adding differing amounts of alcohol to water. It was observed that the
true residual saturation of gas is very small for all cases. A much
larger pseudo-residual saturation was achieved early in the imbibition stage
but gas continued to be produced at extremely low rates until the true
saturation was reached. The gas-air spontaneous imbibition performance
was modelled using a mathematical model where the porous medium is represented
as a bundle of equal but turtous capillary tubes. Input data for this model was
obtained from thin sections using a state of the art image processing system
and a computerized microscope. It was observed that the model succesfully
explained the imbibition process in samples where pores with varying
circularity were present. Average number of pore throats meeting at one
pore in the pore skeleton (coordination number) was less than six for all
cases.
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