Continuous gamma-ray densitometry in a borehole flow meter

In-situ, continuous, downhole monitoring of fluid flow rates is necessary for optimal control and operation of a hydrocarbon well. In this paper, we will discuss an extremely simple and robust device that provides model independent measurement of oil, water and gas flow rates in multiphase flow. The device, composed of a Venturi and a gamma-ray densitometer, is insensitive to well deviation and flow regime. The densitometer utilizes an extremely low activity radioisotope source but is capable of monitoring fluid mixture density to very high precision. In the paper, we will detail the theory behind the densitometer, review flow loop measurements for oil/water and oil/gas flows, present the results of Monte Carlo modeling of the effects of natural activity on the densitometer, and show the results of a field test of the device.