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Severe slugging is a cyclic flow regime which causes intermittent delivery of oil and gas which usually leads to flow separator flooding, production reduction, platform trips and plant shutdown. This paper presents a novel method for severe slugging mitigation. It describes the use of a Venturi for the improvement of system stability, increase in production and recovery.
A Venturi is coupled to the pipeline-riser system upstream of the choke valve before the topside test separator for severe slug mitigation. Experiments were carried out in a 2″ pipeline-riser system which comprises of a 40 m long horizontal pipe connected to a 10.23 m high S-shape riser followed by a 5.2 m horizontal topside section. The effects of Venturi on severe slugging were investigated, gas perturbation method was used to analyse the effects of Venturi on the stability of the system, and the traditional choking technique and Hopf bifurcation technique were combined and used to investigate the stability and production increase performance of the pipeline-riser with Venturi applied.
Experimental results show that with the Venturi applied, the system achieves stability quicker than without the Venturi in the pipeline-riser and reduced the pressure fluctuation range by 57 %. In addition, combining the Venturi with the choke valve to choke the pipeline-riser (bifurcation study) stabilised the system at higher valve opening and lower pressure compared to choking the pipeline-riser with the choke valve only. For the case studied (
This is a cost-effective severe slug mitigation method, its deployment at the topside is an additional advantage when compared with other methods that require subsea deployment. The increase in brown fields due to diminishing reserves of oil from reservoirs have made oil recovery very vital. This technique will help to extend the operational life of a reservoir, thus enhancing oil recovery and flow assurance.
This paper presents a new method for severe slugging mitigation in pipeline-riser systems. It describes the use of an injectable venturi coupled to the pipeline-riser system upstream of the choke valve before the topside test separator for severe slug attenuation and system stability. An injectable venturi is a venturi tube that has an opening at its throat and a pipe inclined at 45° is inserted into this opening. Thus, gas is injected counter to the flow coming from upstream of the injectable venturi to choke the working fluid passing through the throat of the venturi.
Experiments were carried out in a 2" pipeline-riser system which comprises of a 40 m long horizontal pipe connected to an 11.75 m high S-shape riser followed by a 5.2 m horizontal topside section. The results of stability study showed that with an injectable venturi applied the system achieves stability quicker than without the injectable venturi. In addition, combining the injectable venturi with the choke valve to choke the pipeline-riser (bifurcation study) stabilised the system at higher valve opening and lower pressure compared to choking the pipeline-riser with the choke valve only. For the case studied (Vsl = 0.25 m/s and Vsg = 3.1 m/s), the critical valve opening (bifurcation point) for injectable venturi is 27% while that of pipeline-riser is 21% and their riser base pressures were 2.3 barg and 2.7 barg respectively. The low loss of energy due to the gradual change in geometry of the venturi may account for its ability to achieve stability at a lower riser base pressure. Thus, there was a 29% increase in valve opening and a 15% reduction in the riser base pressure. These practically imply an increase in oil production.
Sun, Hehui (No.1 Mudlogging Company, BHDC, CNPC) | Lao, Liyun (SWEE school, Cranfield University) | Li, Dengyue (No.1 Mudlogging Company, BHDC, CNPC) | Tao, Qinglong (No.1 Mudlogging Company, BHDC, CNPC) | Ma, Hong (No.1 Mudlogging Company, BHDC, CNPC) | Li, Huaiyu (No.1 Mudlogging Company, BHDC, CNPC) | Song, Changhong (No.1 Mudlogging Company, BHDC, CNPC)
More and more early kick/loss detection (EKLD) devices are being used in drilling operations, whether in the field of onshore or offshore drilling. In the field of deepwater and offshore drilling, high-precision electromagnetic flowmeters and Coriolis flowmeters was used to measure the inlet and outlet flow rates of drilling fluids. Good effect was achieved, but are affected by drilling fluids, space limitation of the wellsite and production costs when in the field of shore drilling, engineers usually use the paddle- flowmeter and ultrasonic liquid level meter to measure the inlet and outlet flow. It exists the problem of low measurement accuracy and prolonged warning time. In order to improve the accuracy of measurement and the accuracy of early warning, the electromagnetic flowmeter has been studied in terms of flow measurement at the outlet of on-shore drilling. The study found that the installation position of the electromagnetic flowmeter in the V-shaped test pipeline is a key factor that determines the accuracy of measurements. The influence of different fluid types on the measurement was studied by fluid dynamics. The fluid model was established using Ansys fluent software, and the boundary conditions were set in conjunction with the relevant parameters of the drilling fluid. It was found that the descending segment of the V-shaped pipeline was suitable in the state of laminar and dispersed flow. It is an appropriate mounting position for the electric flow meter; for the slug flow, the rising section is a suitable installation position. The theoretical conclusion is verified by laboratory simulation and field tests. The results of theoretical research were used to optimize the design of the test pipeline, and the problems of transient large flow passage and solid-phase debris deposition in the field were solved, and good results were achieved. An automatic grouting module was developed based on the accurate measured outlet flow data. The automatic grouting operation is very helpful for the construction process of drilling and triping, improved the safety level of well control, and laid a good foundation for the large-scale application of EKLD devices in the field of shore drilling.
Pipelines transfer production fluids from the well head to the platform and from the platform to process facilities. Water, sand or liquids like condensate could settle at the bottom of pipelines especially at low flow velocities and this has implication for flow assurance. During shutdown the settled heavy liquid (e.g. water), could result in corrosion in pipelines, while following restart stages the settled water could form a water plug that could damage equipment, while settled sand could also form a blockage that needs to be dispersed into the flowing fluid. This study looked at cases of low water cut in oil flows and, low sand concentrations in water flows. Conductive film thickness probes were used to obtain oil and water interface height and the water film velocities in water in oil flows.
Similarly values for the sand in water, sand layer profiles and sand dune velocities were investigated respectively. Comparisons are made between two cases in order to gain better understanding of the dispersal process of low loading heavier phase in two phase flows.
Severe slugging in an offshore riser pipeline imposes a major challenge to production and flow assurance in the oil and gas industry. Riser-top-valve choking has shown effectiveness in eliminating severe slugging. However, most manual-choking and active-control techniques were tuned by trial and error, resulting in an operation at a smaller-than-necessary valve position for a stable-flow condition. This imposes unnecessarily high backpressure on the riser pipeline, which leads to reduction in production. One way to overcome this problem is to design the active-control system to operate at a large valve position. However, at such an operating point, the riser-pipeline system is naturally open-loop unstable associated with severe slugging flows.
In this work, an approach to tune a robust proportional-integral-derivative (PID) slug controller at an open-loop unstable condition is proposed. First, at an open-loop unstable operating condition, a reliable linear model is derived from the nonlinear simplified riser/separator model (SRSM) developed in previous work. Then, a robust stabilizing PID controller is designed on the basis of the linearized model.
The controller was successfully applied to a 2-in. laboratory riser at Cranfield University and an 8-in. generic industrial riser system modeled in the commercial multiphase-flow simulator OLGA. Simulation on the industrial riser system shows that the proposed approaches not only can eliminate severe slugging but also can increase oil production. It also shows that the percentage improvement in oil production compared with manual choking will increase as the well pressure declines. This means that adopting active slug control is even more beneficial for mature oil fields than for relatively new fields.
The result is very significant for mature fields that are susceptible to severe slugging and low oil production because of declining reservoir pressure.