Apparatus and method of detecting interfaces between well fluids

A reverse circulating cementing apparatus for cementing a casing in a wellbore, the casing and the wellbore defining an annulus therebetween, the apparatus comprising:

• a sensor coil disposed substantially on a lower end of the casing, the sensor coil adapted to be mountable around an outer perimeter of lower end of the casing;
• a transponder device disposed substantially adjacent a fluid interface formed between a first fluid and a cement slurry, the sensor coil adapted to detect the transponder as the transponder approaches the lower end of the casing, the transponder being implanted into a protective rubber ball, the transponder adapted to send a Radio Frequency Identification signal to the sensor coil;
• a valve disposed within the casing;
• and
• a host electronics package adapted to receive a signal from the sensor coil and to send to a signal to the valve to close the valve, the host electronics package functionally adapted to close the valve when the sensor coil detects the transponder and sends a signal to the host electronics package when the fluid interface approaches the lower end of the casing as the cement is pumped down the annulus.

A reverse circulating cementing apparatus for cementing a casing in a wellbore, the casing and the wellbore defining an annulus therebetween, the apparatus comprising:

• a sensor coil disposed substantially on a lower end of the casing, the sensor coil adapted to be mountable around an outer perimeter of lower end of the casing;
• a transponder device disposed substantially adjacent a fluid interface formed between a first fluid and a cement slurry, the sensor coil adapted to detect the transponder as the transponder approaches the lower end of the casing, the transponder adapted to send a Radio Frequency Identification signal to the sensor coil;
• a valve disposed within the casing;
• and
• a host electronics package functionally adapted close the valve when the host electronics package receives a signal from the sensor coil and sends a signal to the valve to close the valve, when the sensor coil detects the transponder and sends a signal to the host electronics package, when the fluid interface approaches the lower end of the casing as the cement is pumped down the annulus.