Managing Flow Assurance in Oil and Gas Production Facilities

ove bratland

Upcoming Session : 14-18 September 2015

Instructor : Dr. Ove Bratland (View Profile)

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Course Overview
Flow Assurance covers all methods to ensure the safe and efficient delivery of hydrocarbons from the well to the collection facilities. It is a multi-disciplinary activity involving a number of engineering disciplines, including mechanical, chemical, process and software engineering. Previously uneconomical fields are now being exploited in hostile environments from deep water to the Arctic. As conventional oil reserves decline, companies are developing unconventional oil fields with complex fluid properties.

Flow assurance technology often allows us to transport mixtures of oil, gas and water in the same flowline over quite long distances, and local separation by the wellheads – something which traditionally requires expensive oil platforms – can then be avoided. This has led to very significant savings in many oil and gas projects. Cost-effective and reliable multiphase transport comes with its own set of challenges, however, and requires competent flowline design and operation. This flow assurance course focuses on how to avoid problems like slugging, hydrate or wax formation, in addition to various other potential problems. how to do so in practice.

Dr. Bratland has written two books on flow assurance, and they will be used as reference during the course. The books will be given in softcopy version to the participants.

The course will include running flow assurance simulation software, and the participants are encouraged to bring their laptops. The simulations will be run in groups of 3, and so it will not be a problem if some of the participants do not bring any.

Who Should Attend
The course is intended for technical professionals who are involved in projects with flow assurance issues. Pipeline engineers or operators, well engineers, production engineers as well as flow assurance and mechanical engineers who are involved in the design, operation and optimization of the wells and flow lines are invited to participate.

While the course will touch upon theoretical aspects of flow assurance, focus will mainly be on its application to solve operational and to some extent engineering problems.

Most of the course will therefore revolve around how to avoid or solve practical problems, including how to interpret results coming out of commercial simulation software and how to recognize problems from the data available to operators.

Course Outline
Part 1: Introduction
•Presentation of participants.
•Introduction to flow regimes.
•Introduction to the most common flow assurance challenges we are faced with, and the main ways of dealing with them.
Exercise 1: The Ormen Lange field or another offshore field. Which of the problems mentioned in the introduction today could potentially create problems on this field? How were they solved? Could any of the problems have been solved in different ways?

Part 2: Friction
•The main mechanisms causing friction.
•Friction in single-phase flow, well-mixed bubbly flow, stratified flow and annular flow.
•How none-Newtonian fluids can affect the friction.
•Introduction to how terrain and flow regime affects friction and other sources of pressure drop (this is more thoroughly explained when discussing each flow regime later).
Exercise 2: Relatively simple manual calculation of the friction types described above. Illustration of how the results give us indications regarding which flow regimes to expect. Doing manual checks of results coming out of multiphase simulation programs.

Short summary of the day’s lessons.

Short repetition from day 1.
Part 1: The multiphase pipe flow equations
•The development of the equations will be shown (quite briefly), the main emphasis will be on the understanding the principles built into them and which closure correlations they require (slides and board).
•Description of what the closure terms describe, and how some of them can be estimated manually.
•Principles for steady-state solution of the equations with example illustrations.
•Heat calculations: Various types (steady-state, quasi-steady-state and fully transient), how accurate they are, and which input-data they require.
Exercise 1: Examples of ways we can check results coming out of commercial simulations by manually calculating some of the closure equations, particularly pressure drop.

Short summary of today’s lessons.

Part 2: Transient phenomena
•How various flow regimes develop.
•Flow regime maps for various inclinations, particularly vertical and horizontal.
•How to estimate the location of important points in the flow regime maps.
Exercise 2: Simulating a simple mechanical system (a mass and a spring damper) with two different integration methods. (Comment: The emphasis is on how user settings affect the simulations, the source of some of the errors we need to guard against and which sometimes my cause the simulations to ‘crash’. It is meant to give some understanding of the numerics built into commercial software, without needing to go into details about the theory. )
Exercise 3: A (simple-to-use) simulation program is used for simulating transient dispersed bubble flow in a flowline. The gas fraction is varied to investigate how it affects friction, capacity and the potential for pressure surges. The results are animated for pedagogical reasons. If time allows, another (also simple-to-use) simulation program will be used to illustrate stratified flow by an illustrative animation generated in real time.

Short summary of the day’s lessons.

Part 1: PVT properties, hydrates and other deposits
•Which fluid properties are relevant, and how do we determine them? Equation of state and other ways of modeling the properties. How the properties relate to Flow Assurance.
•Oil sampling: How they are done and what they can tell us.
•How to avoid low fluid temperatures (design and operational issues), and why they can cause problems.
•Pigging operations, chemical injection and other ways to prevent deposits.
•Sand management, where sand tends to become a problem, and common counter measures. Corrosion, erosion and cavitation.
•Emulsions: How they form, what they may result in (such as higher pressure loss due to friction, and also a less predictable and even varying loss). Models for estimating emulsion viscosity.
•Limits to what is currently possible (the PVT-related limitations such as inaccuracies due to representative oil samples being difficult to obtain, particularly at an early project stage; the fact that even when good samples are available, some properties are difficult to predict accurately, particularly emulsions; heat caused by hydrate formation not being accounted for in current models; the strong interaction between chemical and fluid mechanical approximations enhancing each other.)
•The Joule-Thompson effect and other real gas peculiarities affecting fluid temperature and hydrate formation.
Exercise 1: Interpreting hydrate envelopes coming out of PVT-software or flow assurance simulators. The exercise is not based on the participants running the software, but discussing the curves they are given on paper.

Part 2: Slugs
•More about different flow regimes, particularly slugging, and how two-phase flow differs from three-phase flow.
•Different types of slugs. Slug lengths and slug periods. Statistical variation.
•How to manage slugs, both operational and design issues.
•Gas lift: how to use it to manage slugs and/or increase production. Various types of gas lift, how to optimize production (mostly the example shown in chapter 19.2 in Pipe Flow 2).
•Slug catchers and slug catcher design.
•How slugs affects tendencies to get hydrates.
Example case: Active slug suppression at Statoil’s Aasgard-field or another field where active slug suppression has been suggested implemented.
Exercise 2: Interpreting simulation results showing slugging in a well and a pipeline. The participants are given the results on paper and asked questions about them.

Short summary of the day’s lessons.

Part 1: Operational issues
•Operational envelopes.
•How pressure surges and slugs may reveal themselves as pressure variations, and how to distinguish them.
•How beginning hydrate formation may reveal itself, and what to do about it.
•How way buildup may reveal itself.
•How to remediate hydrate plugs.
•Leak detection.
•Liquid loading in wet gas wells.
Exercise 1: Discussing an operational envelope for a particular field.

Part 2: Mini-project
Pick a field where flow assurance is important. Prepare a short presentation (around 15 minutes), to be presented to the other participants on the course. Expect questions and comments from the audience.
Comment: An example is kept ready by the teacher and given out to groups who do not find enough data themselves.

Short summary of the day’s lessons.

Part 1: Various subjects
•More about commercial simulation software. What existing programs can and cannot do, and how they are likely to develop in the future.
•Factors affecting internal corrosion.
•Brief introduction of multiphase flow measurement.
•Some extra considerations for flow in wells.
•Example illustration of the forces involved in annular two-phase flow.

Part 2: Exercises utilizing what has been covered during the course
Exercise 1: Interpretation of a well simulation where the flow stops. Discussion of how this can happen, and how to avoid it.
Exercise 2: Erosion calculations using API RP 14E Recommended Practice for Design and Installation of Offshore Production Platform Piping Systems and DNV Recommended Practice RP O501 Erosive Wear In Piping Systems.
Exercise 3: Heat loss calculations. Examples of how to use manual heat calculations to estimate the temperature reduction in a flowline, and how to use it to check results from commercial software.
Exercise 4: Interpretation of a steady-state network simulation.
Exercise 5: Exercise related to the Shtockman-field or another offshore gas field.
Where to find more information.

Summary and discussion of the course.