Direct Downhole Enthalpy Measurement

1
Direct DownholeEnthalpy Measurement
2
Overview

• Objective and purpose
• Approach
• Experimental results
• Future work

3
Objective and Purpose

• Find a way to measure enthalpy downhole
• Construct a device specifically to measure
  enthalpy
• Expand the use of existing measurement
  technologies
• Downhole enthalpy measurements useful for
• Reservoir modeling
• Fracture characterization
• Earlier estimates of power produced by a well
• Validating results from wellbore simulators

4
Approach

• Flowing Enthalpy
• Single Phase pressure and temperature
• Two Phase temperature/pressure and flow rate of
  each phase
• Alternatively, void fraction and phase velocities
  or slip factor could be measured
• Know how to measure temperature and pressure
• Need reliable flow rate measurements
• Keep sensors simple

5
Approach

• Phase Discrimination Sensors (PDS)
• Void fraction from average vapor liquid profile
  B(r)
• Velocity of dispersed phase from cross
  correlations
• Velocity of continuous phase from empirical
  formulations or other measurement (e.g.
  anemometry)

6
Approach

• Bulk Impedance Sensors (BIS)
• Void fraction from bulk impedance across flow
  path
• Disperse phase velocity from cross-correlation
  concept
• Alternatively use EIT theory or train an
  artificial neural network to determine the
  enthalpy directly

7
Experiments

• Phase Discrimination Sensors
• Optical window used as reference
• Resistivity probe
• Temperature probe
• Bulk Impedance Sensor
• Outward looking dual electrode probe

8
Optical Measurements

• Segmented air-water flow, 1/8 tube
• Light source on one side and phototransistor on
  the other side
• Clear signal detected when a bubble passes the
  light source

9
Optical Measurements

• Bubble flow in 1 plexiglas tube
• Same phototransistors as before but laser used as
  the light source
• Clear signal detected when a bubble passes the
  laser beam

10
Resistivity Measurements

• Segmented air-water flow, 1/8 tube
• Small electrode couple placed in the flow path
• Signal detected, but cross-talk is problematic

cross-talk
cross-talk
cross-talk
11
Temperature Measurements

• Segmented air-water flow, 1/8 tube
• Fast response thermocouple (20 ms) placed in
  segmented air/water flow
• No response detected as bubble passed the
  thermocouple

12
PDS Results - Phase Velocity

• Bubble velocities determined using the cross
  correlation function

13
PDS Results Void Fraction

• Void fraction determined from time average of air
  vs. water presencea ta/(tatw)
• More stable signals needed to determine threshold
  value
• And/or reliable reference measurements for
  calibration

14
Impedance Measurements

• Bubble flow in 6 plexiglas tube
• Electrodes placed on the outside of a submersible
  probe (1.5). Probe placed inside a larger
  plexiglas tube (6)
• Reference void fraction measured by
  gradiomanometer
• Water flow rates from 10 150 lb/min and air
  flow rates from 0 5 SCFM

Cathode
Anode
15
BIS Results Void Fraction

• Void fraction determined from a 1-Zw/Zmix
• Close to linear relationship between void
  fraction and bulk impedance for 0-25 void
  fraction
• Better fit at higher void fractions

16
Future Work

• General
• Develop or gain access to a steam-water test flow
  loop
• Obtain reliable reference measurements for
  temperature, pressure, void fraction, flow rate,
  etc.
• Phase Discrimination Probes
• Investigate high temperature options for optical
  fiber
• Experiment with optical fiber sensors in
  steam-water flow loops
• Experiments with multiple probes to obtain radial
  profile for flow parameters

17
Future Work

• Bulk Impedance Sensors
• Place multiple electrodes in two planes and solve
  for void fraction using EIT theory
• Infer bubble velocity from modified version of
  the cross correlation function
• Train an Artificial Neural Network to determine
  the enthalpy
• Attempt to solve the EIT problem using an
  outward-looking electrode setup

18
Acknowledgments

• This research was conducted with financial
  support to the Stanford Geothermal Program from
  the US Department of Energy under grant
  DE-FG07-02ID14418, the contribution of which is
  gratefully acknowledged