Laboratory Observations of an Advancing Boiling Front in a Porous Medium and Correlation to Self Potential Measurements

Abstract

We present new laboratory observations of an
advancing boiling front radiating from an injection
point in a simulated geothermal reservoir. The Berea
sandstone model is a 26 cm cube that is either heated
to a dry 125ì?Í?î©C, or saturated with 145ì?Í?î©C steam in two
separate testing configurations. Cool water is applied
at the sample center, and the advancing boiling front
is identified by a radial array of 4 temperature sensors
spaced at 1 cm intervals from the injection point.
Using this data, the location of the vaporization front
is observed, and temporal variations noted.
Temperature information is correlated to self
potential measurements made at the injection point.
We show that these measurements can identify the
point at which local fluid flow changes from 2-phase
water / steam to single phase water, or that point
when 2-phase flow ceases at the injection point. This
is made possible by a large difference in resistivity
between water and steam, and the resulting increase
in self potential coupling for 2-phase flow.
Furthermore, pressure fluctuations resulting from 2-phase
flow in a porous medium can be observed in
the self potential record and used to indicate the state
of local pore fluid. Extrapolation of this work to field
sites will lead to a better understanding of
vaporization at injection points and more economical
injection strategies.