The unique problems associated with heavy oil production largely revolve around the issue of viscosity. Production technologies used to overcome the viscosity issue, such as steam injection and water flooding, increase produced water levels at heavy oil wells. Accurate knowledge and monitoring of any produced water is key to production optimization; however, accurate measurement of water content relies on a homogenous flow, and the high viscosity of heavy oils makes high flow velocities and thus, homogeneity, particularly difficult to achieve.
While sampling standards acknowledge the need for a homogenous flow, no such standards currently exist for oil/water measurement. API MPMS Chapter 8.2 details the various combinations of velocity, pipe installation, and mixing devices required to achieve homogeneity for sampling and one can borrow from this standard for minimum requirements for oil/water measurement. However, mixing elements and piping configurations can create a pressure drop and are still subject to inconsistencies and complications from varying fluid velocities, densities, viscosities, etc., and none of the mixing elements are capable of creating a constant velocity.
The addition of a circulation or measurement loop to the main pipeline creates a consistent environment and homogenous flow for optimized measurement conditions, regardless of varying fluid conditions. The loop utilizes a pump in line with a suction nozzle to extract a representative flow from the main pipeline for oil/water measurement and an injection nozzle to inject that flow back into the pipeline upstream of the suction nozzle. The size of the pump and mechanical design of the injector must be appropriate to increase velocity and create mixing sufficient enough to generate a homogenous flow in the portion of the main pipeline between the injection and suction nozzles. Homogeneity is maintained in the loop itself by a high velocity of 10–15 fps-well above API minimum requirements. An oil/water measurement device or OWD is placed at the pump outflow where flow conditions remain constant regardless of variations in the main pipeline.