In offshore Oil & Gas production processes the undesired severe slug flow regime can be present. The negative impact of severe slug is crucial to the production rate and process safety. In this work, the severe slugs which occur in the well-pipeline-riser system are experimentally and theoretically investigated though mathematical modeling, laboratory experiments, control system design and analysis, numerical simulations and laboratory implementations. In general, this thesis studies the modeling and control of slugging flows which can occur in offshore well-pipeline-riser systems, from both theoretical and experimental perspectives. Some typical control-oriented mathematical models are reviewed and examined. Some extensions have been proposed for improving the model accuracies. The choice of control structure is analyzed based on the Input-Output (IO) controllability concept. All the respective studied measurements give better results than the frequently used riser topside pressure (Pt). A supervisory self-learning control strategy is developed and the results show that the decision making based on the supervisor drives the system close to the closed-loop bifurcation point, but a faster control scheme can reduce the settling time significantly. A number of anti-slug control strategies are proposed, where the robust control solution shows the best potential in both anti-slug control and production rate improvement. Simulation results show that control solutions with the riser bottom pressure Pb performs better than the ones developed for Pt. Furthermore, an alternative transmitter is experimentally investigated for online slug detection and monitoring. The transmitter is an Electrical Resistance Tomography (ERT) sensor measuring the electrical resistance over the cross-area section of the transportation channel. The results show that the transmitter can be a good alternative to conventional measurements if the oil-to-water ratio is low and the fluids are well-mixed. The severe slug’s influence on the downstream separation process is examined. It is confirmed that the riser-induced slugs entering the gravity separator has significant impact on the pressure-dropratio (PDR) controller’s tracking performance on the de-oiling hydrocyclone. Most of this thesis’s contributions have been experimentally examined

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Plant-Wide Anti-Slug Control for Offshore Oil and Gas Processes

Transportation of fluids is important in the design of chemical process plants. In the chemical process industries (CPI), pipework and its accessories such as fitting make up 20–30% of the total design costs and 10–20% of the total plant investment. Maintenance requirements and energy usage in the form of pressure drop (Δ P ) in the fluids being pumped add to the cost. Also, these items escalate each year in line with inflation. As a result, sound pipe-sizing practices can have a substantial influence on overall plant economics. It is the designer's responsibility to optimize the pressure drops in piping and equipment and to assess the most economic conditions of operations. Figure 4-1 illustrates piping layouts in a chemical plant.

4 – fluid flow

References Part 5

Title Name Signature Date Clearance Review Ayers, Lynn M Ayers, Lynn M 11/29/2018 Design Verifier Lovelady, James T Lovelady, James T 11/08/2018 Checker Lovelady, James T Lovelady, James T 11/08/2018 Document Control Approval Manville, Kira Manville, Kira 11/29/2018 Originator Irwin, John Irwin, John 11/07/2018 Other Approver Huntington, Matthew R Huntington, Matthew R 11/09/2018 Other Approver Sijgers, Frederik O Sijgers, Frederik O 11/08/2018 Responsible Engineer Joslyn, Cameron C Joslyn, Cameron C 11/14/2018 Responsible Engineering Manager Rutherford, Wally Rutherford, Wally 11/15/2018 USQ Evaluator Carlstrom, Richard Carlstrom, Richard 11/15/2018

WTP/Evaporator Transfer System Hydraulic Analysis

Entrainment curtails liquid gravity flow from vessels by raising the pressure drop (above that for single-phase flow) through the outlet piping, and reducing the static head available for overcoming the pressure drop. A similar problem can arise when a liquid is near its boiling point, or contains dissolved gas, especially if the absolute pressure at any point in the piping falls below atmospheric pressure, as occurs in a syphon. This work considers the case of liquid flowing from the bottom of an absorption column through a pipe that has been sized for full liquid flow. When the liquid level in the column is low enough, the liquid entrains gas. The resulting increase in pressure drop and reduction of head restrict the flow rate, and the liquid level rises. Eventually, the level rises high enough to stop entrainment. However, gas still in the outlet pipe causes the level to continue to rise until the gas is all swept out. Now, the outlet pipe is running full flow (as was assumed in the design), but the static head, becoming higher than was assumed, creates excessive flow, which causes the level to fall until entrainment occurs again and the cycle is repeated.

P. D. Hills

Papers

Designing piping for gravity flow