HR: 0800h
AN: H21C-1353    [Abstracts]
TI: Fluid Mechanics of Borehole Flowmeters
AU: * Clemo, T
EM: tomc@cgiss.boisestate.edu
AF: Boise State University, Center for the Geophysical Inivesitgation of the Shallow Subsurface 1910 University Dr., Boise, ID 83725-1536 United States
AU: Barrash, W
EM: wb.cgiss.boisestate.edu
AF: Boise State University, Center for the Geophysical Inivesitgation of the Shallow Subsurface 1910 University Dr., Boise, ID 83725-1536 United States
AU: Johnson, T C
EM: tcj.cgiss.boisestate.edu
AF: Boise State University, Center for the Geophysical Inivesitgation of the Shallow Subsurface 1910 University Dr., Boise, ID 83725-1536 United States
AB: The sensitivity of an electromagnetic flowmeter to flow in a borehole is dependent on flow entering the well above the entrance of the flowmeter. This dependence influences the calibration of flowmeters that are freely hanging in a borehole or use a centralizer, but not flowmeters using a skirt or packer to force the entire wellbore flow through the flowmeter. A mathematical model based on conservation of momentum has been developed to simulate the flow around and through the flowmeter. The model has been numerically implemented in an axis-symmetric version of MODFLOW-2000. The numerical model has been calibrated using data from a laboratory simulator of flow to a 4 inch ID screened well in a highly-permeable homogeneous aquifer. The influence of inflow above the entrance is clearly evident in the laboratory data which mimics data acquired at the Boise Hydrogeophysical Site. The most dramatic influence occurs near an unperforated region, where two sections of the screen are connected. The laboratory data reveal that the flow through the flowmeter decreases as the tool moves upward into the region, even though total flow through the wellbore at the entrance of the flowmeter is increasing. Then, as the entrance of the flowmeter passes through the unperforated region, flow through the flowmeter increases despite constant total flow in the unperforated region. The ratio of flow through the flowmeter to flow through the borehole is a non-linear function of absolute flow rate and flow entering the screen along the sides of the tool. The ratio is too complex to be completely ascertained from physical calibration of the flowmeter. A numerical model is needed. Interpretation of flowmeter measurements without considering dynamic calibration can be misleading. We use PEST to estimate hydraulic conductivity in a layered aquifer from the combined flowmeter and aquifer model using axis-symmetric MODFLOW. A parameter estimation program such as PEST or UCODE is required because each flowmeter measurement position requires a separate MODFLOW simulation.
DE: 1828 Groundwater hydraulics
DE: 1829 Groundwater hydrology
DE: 1835 Hydrogeophysics
DE: 1847 Modeling
DE: 1894 Instruments and techniques: modeling
SC: Hydrology [H]
MN: Fall Meeting 2005