This paper describes the design and development of a novel, non-invasive technique for measuring the mixture density of multiphase flows using the mechanical vibration characteristics of a pipe. The instrument comprises a flexible pipe section, a mechanical actuator with a driver unit to provide the required excitation to the actuator, force and displacement sensors and signal conditioning and data acquisition units. These provide force, displacement and frequency data to a novel model which has been developed, from first principles, to accurately predict the density of the flowing multiphase mixture. Experimental results obtained from the instrument for different multiphase mixtures shows that the mixture density can be accurately and repeatably estimated to within ±1% of its true value when operated at an optimum operating frequency.
When used with auxiliary instrumentation for determining phase velocities and phase volume fractions, the density of a multiphase mixture (eg oil, water and gas) can be of key importance in accurately determining the mass and volumetric flow rates of individual phases in a multiphase production stream. Knowledge of these phase flow rates is, in turn, crucial for production optimization and reservoir management and is essential for fiscal allocation. One technique which has proven attractive for noninvasively measuring multiphase mixture density without the need for radioactive sources is densitometry based on mechanical vibration.
Several previous researchers have engaged with the problem of how to measure the density of a flowing mixture accurately without posing any health hazards to personnel and the environment. A plethora of literature currently exists describing a wide variety of density measurement instruments operated using different sensing techniques [1–7]. The core focus of this paper is to describe the design and development of a novel densitometer operated using the mechanical vibration sensing technique which, compared to other density measurement techniques, is relatively accurate and cheap and poses no health hazards to personnel and the environment.