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PART I - MULTIPHASE PIPELINE & SLUG CATCHER DESIGN GUIDE CPTC NOVEMBER 1994 1 M

PART I - MULTIPHASE PIPELINE & SLUG CATCHER DESIGN GUIDE CPTC NOVEMBER 1994 1 Multiphase Pipeline Design Guide PART I - MULTIPHASE PIPELINE & SLUG CATCHER DESIGN GUIDE CPTC NOVEMBER 1994 2 PART I TABLE OF CONTENTS SECTION 1.0 - INTRODUCTION 1.1 Objective and Scope..................................................................................................................................................... 1 1.2 Definition of Terms........................................................................................................................................................ 1 SECTION 2.0 – OVERVIEW OF MULTIPHASE FLOW FUNDAMENTALS 2.1 Design Criteria.............................................................................................................................................................. 11 2.2 Velocity Guidelines ....................................................................................................................................................... 11 2.3 Flow Regimes............................................................................................................................................................... 13 2.4 Pressure Gradient......................................................................................................................................................... 16 2.4.1 Frictional Losses .......................................................................................................................................... 16 2.4.2 Elevational Losses........................................................................................................................................ 17 2.4.3 Acceleration Losses...................................................................................................................................... 18 2.4.4 Allowable Pressure Drop............................................................................................................................... 20 2.5 Pressure Gradient Calculations...................................................................................................................................... 20 2.6 Section Highlights......................................................................................................................................................... 21 SECTION 3.0 – STEADY STATE DESIGN METHODS 3.1 Pipeline Design Methods............................................................................................................................................... 25 3.2 Steady State Simulators................................................................................................................................................ 26 3.2.1 Phase Equilibrium and Physical Properties.................................................................................................... 26 3.2.2 Pipeline Elevation Profile .............................................................................................................................. 28 3.2.3 Heat Transfer ............................................................................................................................................... 30 3.2.4 Recommended Methods for Pressure Drop, Liquid Holdup, and Flow Regime Prediction................................................................................................................................ 33 3.2.5 Interpretation of Results................................................................................................................................ 35 3.3 Section Highlights......................................................................................................................................................... 38 SECTION 4.0 – TRANSIENT FLOW MODELING 4.1 Transient Flow Modeling (General) ................................................................................................................................ 41 4.2 Use of Transient Simulators........................................................................................................................................... 42 PART I - MULTIPHASE PIPELINE & SLUG CATCHER DESIGN GUIDE CPTC NOVEMBER 1994 3 4.3 Section Highlights......................................................................................................................................................... 43 SECTION 5.0 – SLUG FLOW ANALYSIS 5.1 Slug Flow (General) ...................................................................................................................................................... 45 5.2 Slug Length and Frequency Predictions......................................................................................................................... 46 5.2.1 Hydrodynamic Slugging................................................................................................................................ 46 5.2.2 Terrain Slugging........................................................................................................................................... 51 5.2.3 Pigging Slugs............................................................................................................................................... 53 5.2.4 Startup and Blowdown Slugs........................................................................................................................ 55 5.2.5 Rate Change Slugs ...................................................................................................................................... 56 5.2.6 Downstream Equipment Design for Slug Flow............................................................................................... 56 5.3 Section Highlights......................................................................................................................................................... 59 SECTION 6 – EXAMPLE PROBLEMS 6.1 Example Problem – 1 Low Gas/Oil Line Between Platforms .......................................................................................... 63 6.1.1 Line Size...................................................................................................................................................... 65 6.1.2 Slug Length Prediction ................................................................................................................................. 75 6.1.3 Slug Frequency and Length by Hill & Wood Method ...................................................................................... 80 6.2 Example Problem – 2 Gas Condensate Line .................................................................................................................. 88 6.2.1 Table 1, Wellstream Composition ................................................................................................................. 89 6.2.2 Table 2, Pipeline Evaluation Profile ............................................................................................................... 90 6.2.3 Pipeline Simulation Comparison ................................................................................................................... 92 SECTION 7.0 – REFERENCES .................................................................................................................................................... 106 FIGURES I: 1-1 Flow Regimes in Horizontal Flow................................................................................................................................... 8 I: 1-2 Flow Regimes in Vertical Flow ...................................................................................................................................... 9 I: 2-1 Horizontal Flow Regime Map......................................................................................................................................... 23 I: 2-2 Vertical Flow Regime Map............................................................................................................................................. 24 I: 5-1 Taitel-Dukler Liquid Holdup Predictions.......................................................................................................................... 60 I: 5-2 Stages in Terrain Slugging ............................................................................................................................................ 61 I: 5-3 Pipeline Slugging.......................................................................................................................................................... 62 I: 6-1 Liquid Holdup for Example 1, Year 12............................................................................................................................ 101 I: 6-2 Inlet Pressure for Example 1, Year 12............................................................................................................................ 102 I: 6-3 Liquid Flowrate Out of Line, Example 1, Year 12............................................................................................................ 103 I: 6-4 Gas Flowrate Out of Line, Example 1, Year 12............................................................................................................... 104 PART I - MULTIPHASE PIPELINE & SLUG CATCHER DESIGN GUIDE CPTC NOVEMBER 1994 4 I: 6-5 Liquid Holdup Predictions for Example 2........................................................................................................................ 105 PART I - MULTIPHASE PIPELINE & SLUG CATCHER DESIGN GUIDE CPTC NOVEMBER 1994 5 SECTION 1.0 - INTRODUCTION 1.1 Objective and Scope The simultaneous flow of gas and liquid through pipes, often referred to as multiphase flow, occurs in almost every aspect of the oil industry. Multiphase flow is present in well tubing, gathering system pipelines, and processing equipment. The use of multiphase pipelines has become increasingly important in recent years due to the development of marginal fields and deep water prospects. In many cases, the feasibility of a design scenario hinges on cost and operation of the pipeline and its associated equipment. Multiphase flow in pipes has been studied for more than 50 years, with significant improvements in the state of the art during the past 15 years. The best available methods can predict the operation of the pipelines much more accurately than those available only a few years ago. The designer, however, has to know which methods to use in order to get the best results. Part I of this guide consists of seven sections. The fundamentals of multiphase flow in pipelines are discussed in Section 2.0. The third section describes the use of steady state simulation methods. This section of the guide helps the designer choose the best methods for the project, and it gives guidelines to use in designs. The fourth section of the report briefly describes transient flow modeling. The fifth section describes slug flow modeling, giving suggestions on the best methods to use in slug flow simulation. The sixth section includes two sample problems, based on actual designs, which illustrate the design steps used in analyzing the pipeline designs. 1.2 Definition of Terms In discussing the design of multiphase pipelines, it is necessary to define several terms used repeatedly throughout this text. Near Horizontal and Near Vertical Angles The term "near horizontal" is used in this guide to denote angles of -10 degrees to +10 PART I - MULTIPHASE PIPELINE & SLUG CATCHER DESIGN GUIDE CPTC NOVEMBER 1994 6 degrees from horizontal. The term "near vertical" denotes upward inclined pipes with angles from 75 to 90 degrees from horizontal. Flow Regimes In multiphase flow, the gas and liquid within the pipe are distributed in several fundamentally different flow patterns or flow regimes, depending primarily on the gas and liquid velocities and the angle of inclination. Observers have labeled these flow regimes with a variety of names. Over 100 different names for the various regimes and sub- regimes have been used in the literature. In this guide, only four flow regime names will be used: slug flow, stratified flow, annular flow, and dispersed bubble flow. Figure I:1-1 shows the flow regimes for near horizontal flow, and Figure I:1-2 shows the flow regimes for vertical upward flow. Descriptions of the flow regimes 1. Stratified Flow - at low flowrates in near horizontal pipes, the liquid and gas separate by gravity, causing the liquid to flow on the bottom of the pipe while the gas flows above it. At low gas velocities, the liquid surface is smooth. At higher gas velocities, the liquid surface becomes wavy. Some liquid may flow in the form of liquid droplets suspended in the gas phase. Stratified flow only exists for certain angles of inclination. It does not exist in pipes that have upward inclinations of greater than about 1 degree. Most downwardly inclined pipes are in stratified flow, and many large diameter horizontal pipes are in stratified flow. This flow regime is also referred to as stratified smooth, stratified wavy, and wavy flow by various investigators. 2. Annular Flow - at high rates in gas dominated systems, part of the liquid flows as a film around the circumference of the pipe. The gas and remainder of the liquid (in the form of entrained droplets) flow in the center of the pipe. The liquid film thickness is fairly constant for vertical flow, but it is usually asymmetric for horizontal flow due to gravity. As velocities increase, the fraction of liquid entrained increases and the liquid film thickness decreases. Annular flow exists for all angles of inclinations. Most gas dominated pipes in high pressure vertical flow are in annular flow. This flow regime is referred to as annular-mist or mist flow by many investigators. PART I - MULTIPHASE PIPELINE & SLUG CATCHER DESIGN GUIDE CPTC NOVEMBER 1994 7 3. Dispersed Bubble Flow - at high rates in liquid dominated systems, the flow is a frothy mixture of liquid and small entrained gas bubbles. For near vertical flow, dispersed bubble flow can also occur at more moderate liquid rates when the gas rate is very low. The flow is steady with few oscillations. It occurs at all angles of inclination. Dispersed bubble flow frequently occurs in oil wells. Various investigators have referred to this flow regime as froth or bubble flow. 4. Slug Flow - for near horizontal flow, at moderate gas and liquid velocities, waves on the surface of the liquid may grow to sufficient height to completely bridge the pipe. When this happens, alternating slugs of liquid and gas bubbles will flow through the pipeline. This flow regime can be thought of as an unsteady, alternating combination of dispersed bubble flow (liquid slug) and stratified flow (gas bubble). The slugs can cause vibration problems, increased corrosion, and downstream equipment problems due to its unsteady behavior. Slug flow also occurs in near vertical flow, but the mechanism for slug initiation is different. The flow consists of a string of slugs and bullet-shaped bubbles (called Taylor bubbles) flowing through the pipe alternately. The flow can be thought of as a combination of dispersed bubble flow (slug) and annular flow (Taylor bubble). The slugs in vertical flow are generally much smaller than those in near horizontal flow. Slug flow is the most prevalent flow regime in low pressure, small diameter systems. In field scale pipelines, slug flow usually occurs in upwardly inclined sections of the line. It occurs for all angles of inclination. Investigators have used many terms to describe parts of this flow regime. Among them are: intermittent flow; plug flow; pseudo-slug flow, and churn flow. Superficial Velocities The velocities of the gas and liquid in the pipe are prime variables in the prediction of the behavior of the multiphase mixture. Most multiphase flow prediction methods use uploads/s3/ multiphase-design-guide-part1.pdf