A simple, low-cost downhole flow logging system

Measurements of fluid flow in a well or borehole provide valuable information about the adjacent formations, including the presence of permeable features such as fractures, the presence of aquitards, and whether flow is upward or downward. Borehole flow data in groundwater wells are typically collected with mechanical spinner, heat pulse, or electromagnetic flow meters. These instruments provide excellent data, but can be expensive to purchase, and in the case of the spinner flow meter, can require significant data analysis. We have developed a simple, economical method for measuring flow in groundwater wells. The equipment consists of an electric heater that induces a heat pulse into the water column, and a submersible temperature measurement device. The heater consists of a 2000 watt cartridge heater, shrouded in a perforated steel housing, and attached to electrical cable. The heater runs on a 2000 watt generator. Temperature measurements can be made with a variety of instruments designed to measure water temperature. We used a combined water level, temperature, and conductivity meter with a flat tape to measure depths. The total cost of the heater was $639 and the cost of our water level/temperature/conductivity meter was $1,361 for a total cost of $2,000. The method consists of setting the temperature measurement device in the well at a known distance from the heat source and measuring the time required for the heated water to reach the measurement point. The elapsed time between onset of heating and the first measured temperature change at the temperature device is used to calculate fluid velocity in the well. We tested the equipment and the method in a previously-studied well and found the results to be in good agreement with previous flow measurements at the site. Laboratory tests were conducted to determine practical upper and lower limits of effective flow measurement using this system. The simple design, ease of analysis, and low cost and availability of components make this system an effective and economical tool for measuring fluid flow in wells and boreholes.