Case Study: Addressing the Mounting Challenge of Produced-Water Metering Inaccuracy With Nanotechnology

Abstract

_ As the energy industry strives to reuse produced water and disposal costs of produced water increase, it has elevated the need for more accurate measurement to save money. Measurement of produced water in the US unconventional market is impacted by paraffin deposition on the meters causing inaccurate readings of the volume of produced water. The industry is starting to address this growing issue by applying new technology solutions that enable lasting accuracy in the place of routine maintenance that provides a temporary solution. Most oil and gas producers face paraffin buildup on the inside surface of their electromagnetic flowmeters. These meters are typically located on the produced-water leg, downstream of production and test separators. Paraffin, a waxy substance present in crude oil production, drops out of solution as the fluid cools from the wellhead through the surface equipment. How Paraffin Impacts Metering As the fluid is transported through the pipes, it cools down, causing the paraffin to solidify and deposit on the walls of pipes and flowmeters. Separators that are designed to remove most of the paraffin via heat are still susceptible to the accumulation of small amounts of paraffin that may coat the pipe and measurement devices. Electromagnetic flowmeters are used to measure the volumetric flow rate of conductive fluids in pipelines, such as produced water. They operate by generating a magnetic field across the flow path and measure the voltage induced by the fluid as it flows through the magnetic field. The voltage is proportional to the flow velocity and the magnetic field strength, which is used to calculate the volumetric flow rate of the fluid. Electromagnetic flowmeters contain a minimum of two electrodes, composed of ceramic or metallic materials depending upon the manufacturer. The electrodes read the induced voltage of the produced water flowing through the meter. An insulating liner is placed inside the meter between the conductive fluid and the metal body. This isolates the fluid being measured from the meter body, preventing the fluid from creating an electrical short circuit. Paraffin buildup affects the accuracy and reliability of electromagnetic flowmeters as it nucleates on the electrodes and the liner of the meter. Over time, the paraffin deposition will increase around the electrodes, essentially insulating the electrodes from the fluid. At this point the conductivity of the fluid is artificially reduced, and the flowmeter will under read. If the paraffin coating on the electrodes becomes thick enough, a flowmeter will be completely insulated from the produced water, which the meter interprets as zero flow. As the paraffin coating on the liner increases, the cross-sectional area of the meter is reduced, creating a higher fluid velocity which results in the meter overreading the flowrate (Q = Av where A is the cross-sectional area of flow and v is its average velocity).