Browsing by Author "Tandoh, Henry"

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    Slug flow control in an S-shape pipeline-riser system using an ultrasonic sensor
    (Elsevier, 2021-12-11) Nnabuife, Somtochukwu Godfrey; Tandoh, Henry; Whidborne, James F.
    Slugging flow poses significant challenges to the offshore multiphase flowline and riser systems. Slug flow is characterized by an uneven flow regime whereby pipeline pressures, temperatures, or flow volume rates fluctuate. One of the most common causes of severe slugging is low pressures which causes buildup of fluid over time, consequentially causes flow and pressure oscillations. This mostly occurs in vertical risers or wells. The negative effects of severe slugging have prompted numerous studies, investments, and efforts to reduce or eliminate the slugging flow. Several active slugging control techniques have been investigated in the oil and gas industries for decades. However, many of these techniques still run the risk of limiting hydrocarbon production due to inappropriate over choking. Other challenges for active slug control include the fact that some systems rely mainly on subsea measurements such as riser base pressure, and most of these subsea measurements are costly, difficult to maintain, not always available, and can be unreliable. As a result, to achieve an efficient slugging control performance, reliable, robust, and efficient measurements that are more sensitive to slugging flow for control are required, which is the motivation for this work. The control of riser slug flow using non-radioactive, non-invasive, and non-intrusive Continuous-wave Doppler ultrasound has been investigated in this work, and provides good control performance. It achieved a larger valve opening than an open-loop unstable system. This outperforms manual choking, which maintains stability at a much lower valve opening.
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    Slug flow control using topside measurements: a review
    (Elsevier, 2021-11-19) Nnabuife, Somtochukwu Godfrey; Tandoh, Henry; Whidborne, James F.
    Slugging flow is a condition caused by a liquid obstruction at the riser base. It exhibits cyclic behaviour. The cycle consists of a protracted time of no gas production at the riser's top, followed by the arrival of a liquid slug with a length greater than the riser height, and ultimately the breakthrough of a significant gas surge. The cycle time might range from a few minutes to a few hours, depending on the system size and flow conditions. In offshore oil production, feedback control is a practical and cost-effective way to prevent slug flow. To control the flow rate or the pressure in the pipeline, adjusting the choke valve opening on the topside facility is generally utilised as the control input. From a practical standpoint, designing a control system based on topside data rather than seabed measurements is preferable. Controlling the topside pressure alone is difficult and ineffective in reality, but combining it with the flow rate results in a more reliable control solution. Measuring the flow rate of a multiphase flow, on the other hand, is difficult and expensive. All the topside measurements-based slug control techniques was critically reviewed and necessary recommendations for enhanced control performance provided. In conclusion, this review acknowledged that slugging is a well-defined flow pattern, yet despite having been studied for several decades, current slug control methods still have robustness issues. Slug flow problems are expected to become even more intense in the future as a result of longer vertical risers driven by deep-water Exploration and Production (E&P).
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    Slug flow regime in a flowline with U-shape riser
    (Elsevier, 2022-10-29) Tandoh, Henry; Nnabuife, Somtochukwu Godfrey; Cao, Yi; Lao, Liyun; Whidborne, James F.
    A suitable initial point for understanding multiphase flows is a phenomenological description of the mechanism of geometric distributions or flow patterns that are observed. The challenge however is the prediction of the flow patterns for a combination of flow operating conditions and the characteristics of the phases as well as points of transition from one pattern to the other. Different flow patterns occur in different pipeline configurations for which U-shape risers are part. In the quest to stabilise unstable slug flow in the U-shape riser, an experimental study of gas-liquid flow mixture is conducted to understand the behaviour of the flow in the riser. This paper seeks to understand the flow dynamics in a 2-inch internal diameter U-shape pipeline riser system with much emphasis on unstable slug flow. The initiation of this flow instabilities in the U-shape pipeline riser system and the impact of the downcomer on the flow behaviour is investigated experimentally. Understanding the flow behaviour in the U-shape riser could help in developing effective control techniques to stabilise the multiphase flows in the flowlines. Experimentally, flow patterns observed from the U-shape pipeline riser configuration is used to develop a flow regime map which was then compared to that observed in literature and similarly to a purely vertical riser with similar pipe diameter. Thus, a slug envelope was developed for the U-shape riser to help identify which regions slugging could occur in the system.