CA-3070238-C - SLUG FLOW INITIATION IN FLUID FLOW MODELS

Abstract

A method for modeling slug flow includes receiving a fluid flow model including a representation of a conduit and a multiphase fluid flow therein. A slug bubble birth rate is determined in the multiphase fluid flow. The slug bubble birth rate is determined based at least partially on a difference between a slug front velocity and a slug tail velocity. A slug bubble is initiated in the fluid flow model based at least partially on the slug bubble birth rate. Data representative of the slug flow is displayed in the fluid flow model after the slug bubble is initiated.

Inventors

• Chris John Lawrence
• Zheng Gang Xu

Assignees

• SCHLUMBERGER CANADA LIMITED

Dates

Publication Date

20260505

Application Date

20170719

Claims (18)

1. CLAIMS: 1. A computer-implemented method employing at least one processor having processor-implemented instructions to perform operations for modeling slug flow in multiphase fluid flow within one or more conduits, the operations comprising: identifying conditions for slug precursor formation in a region where the multiphase fluid flow is separated; in the event that conditions for slug precursor formation are identified, determining a slug birth rate in the multiphase fluid flow; identifying conditions for slug bubble precursor formation in a region where the multiphase fluid flow is dispersed; in the event that conditions for slug bubble precursor formation are identified, determining a slug bubble birth rate in the multiphase fluid flow; initiating a slug in a fluid flow model of the multiphase flow based at least partially on the slug birth rate; initiating a slug bubble in the fluid flow model of the multiphase fluid flow based at least partially on the slug bubble birth rate; and displaying data representative of the slug flow in the fluid flow model after the slug is initiated or after the slug bubble is initiated, data representative of the slug flow in the fluid flow model for use in modifying one or more properties of a fluid flow or changing control settings in a real-world pipeline network.
2. 2. The method of claim 1, wherein the conditions for slug precursor formation and the conditions for slug bubble precursor formation involve satisfaction of a minimum slip condition by the multiphase fluid flow.
3. 3. The method of claim 2, further comprising calculating the minimum slip condition based at least partially on a difference between the slug front velocity and the slug tail velocity, wherein the minimum slip condition is satisfied when the slug front velocity is less than the slug tail velocity.
4. 4. The method of claim I, wherein: the conditions for slug bubble precursor formation involves determining that a probability of slug formation exceeds a threshold number, wherein the probability for slug formation is based on determining a number of slug bubbles for the one or more conduits for one or more time periods based at least in part on the slug bubble birth rate.
5. 5. The method of claim 4, wherein the threshold number is a random or pseudo-random number selected in a predetermined range of numbers.
6. 6. The method of claim I, wherein determining the slug bubble birth rate comprises: determining a first difference between the slug front velocity and the slug tail velocity; determining a second difference between a maximum number density of slug bubble precursors and a local number density of slug bubbles for the one or more conduits; and determining the slug bubble birth rate based on the first difference, the second difference, and a diameter of the one or more conduits.
7. 7. The method of claim 6, wherein initiating the slug bubble comprises probabilistically initiating the slug bubble based on a probability of slug initiation, and wherein the probability of slug initiation increases when the first difference increases, the second difference increases, or both increase.
8. 8. The method of claim I, wherein determining the slug bubble birth rate comprises determining the slug bubble birth rate based at least in part on a degree of instability of local dispersed flow and a spatial density of slug precursors.
9. 9. The method of claim I, further comprising modifying one or more properties of a fluid or a flow in a real-world pipeline network, or changing control settings in the real-world pipeline network, in response to the slug bubble being initiated, wherein the real-world pipeline network corresponds to the fluid flow model.
10. I 0. A computing system, comprising: one or more processors; and a memory system comprising one or more non-transitory computer-readable media storing instructions that, when executed by at least one of the one or more processors, cause the computing system to perform operations for modeling slug flow in multiphase fluid flow within one or more conduits, the operations comprising: identifying conditions for slug precursor formation in a region where the multiphase fluid flow is separated; in the event that conditions for slug precursor formation are identified, determining a slug birth rate in the multiphase fluid flow; identifying conditions for slug bubble precursor formation in a region where the multiphase fluid flow is dispersed; in the event that conditions for slug bubble precursor formation are identified, determining a slug bubble birth rate in the multiphase fluid flow; initiating a slug in a fluid flow model of the multiphase fluid flow based at least partially on the slug birth rate; initiating a slug bubble in the fluid flow model of the multiphase fluid flow based at least partially on the slug bubble birth rate; and displaying data representative of the slug flow in the fluid flow model after the slug is initiated or after the slug bubble is initiated, data representative of the slug flow in the fluid flow model for use in modifying one or more properties of a fluid flow or changing control settings in a real-world pipeline network.
11. 11. The system of claim 10, wherein the conditions for slug precursor formation and the conditions for slug bubble precursor formation involve satisfaction of a minimum slip condition by the multiphase fluid flow.
12. 12. The system of claim 11, wherein the operations further comprise calculating the minimum slip condition based at least partially on a difference between the slug front velocity and the slug tail velocity, wherein the minimum slip condition is satisfied when the slug front velocity is less than the slug tail velocity.
13. 13. The system of claim 10, wherein: the conditions for slug bubble precursor formation involves determining that a probability of slug formation exceeds a threshold number, wherein the probability for slug formation is based on determining a number of slug bubbles for the one or more conduits for one or more time periods based at least in part on the slug bubble birth rate.
14. 14. The system of claim 13, wherein the threshold number is a random or pseudo-random number selected in a predetermined range of numbers.
15. 15. The system of 10, wherein determining the slug bubble birth rate comprises: determining a first difference between the slug front velocity and the slug tail velocity; determining a second difference between a maximum number density of slug bubble precursors and a local number density of slug bubbles for the one or more conduits; and determining the slug bubble birth rate based on the first difference, the second difference, and a diameter of the one or more conduits.
16. 16. The method of claim 1, wherein: the conditions for slug bubble precursor formation involve determining that density of slug bubbles present in the conduit is not exceeding density of slug bubble precursors.
17. 17. The method of claim 16, wherein: the density of slug bubble precursors is based on a delay constant and a local mixture velocity of the multiphase flow.
18. 18. The method of claim 16, wherein: the density of slug bubbles present in the conduit is based on distances to nearest slug bubbles using a slug tail profile model.

Description

SLUG FLOW INITIATION IN FLUID FLOW MODELS Background [01] Slug flow is a type of multiphase fluid flow that can occur in fluid transport lines (e.g., conduits, pipes, etc.). Slug flow most commonly occurs in gas-liquid flows, with either a single liquid phase (e.g., oil or water) or with two or more liquid phases simultaneously present (e.g., oil and water). Slug flow may also occur in liquid-liquid flows (sometimes referred to as "water slugging"). [02] Gas-liquid slug flow is an intermittent flow in which regions of separated flow with large gas pockets ("slug bubbles") alternate with regions of dispersed flow ("slugs") in which small gas bubbles are dispersed into the liquid. Slug flow can form in two ways, depending on whether the prevailing flow is separated or fully dispersed. If the prevailing flow is separated ( e.g., stratified or annular), the transition to slug flow occurs by the formation of new slugs. If the prevailing flow is fully dispersed (e.g., bubbly), the transition to slug flow occurs by the formation of new slug bubbles. [03] There are various types of slug flow, which are generally referred to by the conditions that lead to their creation. For example, operational or "start-up" slugs may occur after flow through a pipeline is started (e.g., after stopping flow) such that liquid has settled to low points in the pipe, and then restarting the flow. Similarly, "terrain" slugs may be caused by the topography of the pipelines, and hydrodynamic slugs may be caused during "normal" conditions by the presence of one or more regions where there is too much liquid for separated flow to be stable and too little liquid for bubbly flow to be stable. [04] Multiphase flow, including slug flow, may be modeled and simulated. Multi�dimensional simulation presents a challenge, however, as it may use an impractical amount of computing resources and/or time. Thus, at least for long pipelines, one-dimensional models may be employed, in which properties of the flow are averaged over the pipe cross-section. The model then describes how these averaged properties vary along the pipeline and with time. [05] Such models may implement various strategies for modeling slug flow. For example, in "slug tracking," the boundaries (front and tail) of the slugs are followed as they propagate along the pipe. Thus, the slugs and separated zones are represented on a Lagrangian grid, which is superimposed on the Eulerian grid used to solve the basic equations. In another example, "slug capturing," the underlying equations are resolved on a fine Eulerian grid, including the growth of large waves and the formation of slugs, so that each slug is represented. [06] These models may provide satisfactory results in a wide variety of contexts. However, some such methods of slug flow modeling and simulation may include long computation times, accuracy and/or stability issues, and/or tuning to match experimental or otherwise measured datasets, such as by using an iterative, trial-and-error process. Summary [07] A method for modeling slug flow is disclosed. The method includes receiving a fluid flow model including a representation of a conduit and a multiphase fluid flow therein. A slug bubble birth rate is determined in the multiphase fluid flow. The slug bubble birth rate is determined based at least partially on a difference between a slug front velocity and a slug tail velocity. A slug bubble is initiated in the fluid flow model based at least partially on the slug bubble birth rate. Data representative of the slug flow is displayed in the fluid flow model after the slug bubble is initiated. [08] A computing system is also disclosed. The computer system includes a processor and a memory system. The memory system includes a non-transitory computer-readable medium storing instructions that, when executed by the processor, cause the computing system to perform operations. The operations include receiving a fluid flow model including a representation of a conduit and a multiphase fluid flow therein. A slug bubble birth rate is determined in the multiphase fluid flow. The slug bubble birth rate is determined based at least partially on a difference between a slug front velocity and a slug tail velocity. A slug bubble is initiated in the fluid flow model based at least partially on the slug bubble birth rate. Data representative of the slug flow is displayed in the fluid flow model after the slug bubble is initiated. [09] A non-transitory computer-readable medium is also disclosed. The medium stores instructions that, when executed by at least one processor of a computing system, cause the computing system to perform operations. The operations include receiving a fluid flow model including a representation of a conduit and a multiphase fluid flow therein. A slug bubble birth rate is determined in the multiphase fluid flow. The slug bubble birth rate is determined based at least partially on a difference between a slug front velocity and a