NUMERICAL ANALYSIS OF EROSION OF GAS-PIPELINE...

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NUMERICAL ANALYSIS OF EROSION OF

GAS-PIPELINE ELEMENTS

A.A. Ryabov, Kudryavtsev A. Yu., Voronkov O.V., (Sarov Engineering Center, Russia)

Haritonov A.N, Maltsev A.I., Melnikov I.V., Kiselev M.N.(Gazprom DobychaNadym)

Matt Straw (Norton Straw, UK)

STAR Global Conference 2014, March 17-19, Vienna

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Introduction


The main hydrocarbon reserves of the largest gas fields, currently developing in the north of Western Siberia, are

confined to the Cenomanian deposits in weakly-cemented sand reservoirs. High solids production is common for

operation from such deposits. Integrity management is a significant challenge faced by operators of hydrocarbon

production systems in many north of West Siberia developments. High sand production rates from weak

formations can lead to reduced hydrocarbon production due to excessive erosion and wear of production system

equipment; this is a major technical and economic issue.

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Typical zones of erosion

Choke erosion

Tee-junction erosion


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Problem statement

The simulations included a production gas as methane, produced water and sand.

A parametric study investigated the effect of sand particle size, production flow rate and

produced water flow rate. The range of parameters investigated are summarized below:

• Particle diameter: 0.01 mm, 0.1 mm, 0.25 mm.

• Sand concentration: 0.5, 2, 10, 40 mm3/m3.

• ‘Water-in-gas’ concentration–1…10 mm3/m3.


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Methodology

To solve the problem, the general purpose computer-aided engineering

STAR-CCM+ software by CD-adapco was used. STAR-CCM+ software

incorporates the models required for numerical simulation:

• multiphase flow comprising gas with a sand and/or water

• liquid films model

• erosion model

The Lagrangian model can be used alongside an erosion model to predict how

much wall material may be lost due to particles impacting a fluid boundary (e.g.

pipe wall).

The Oka-correlation, built in the STAR-CCM+ software, was chosen to calculate

the erosion coefficient. Coefficients by default are suitable for the sand eroding

0.25% carbon steel.


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Results of numerical simulations

Numerical simulations were split up to four stages:

• simulation of dry gas-sand flow to identify areas of erosion on the

pipeline elements, assess dependences of the erosion rate on flow rates,

particle concentration and size

• simulation of gas-water drops flow to identify area of liquid film

formation and its thickness

• direct numerical simulation of sand particle impingement to liquid film

to determine influence of liquid film thickness to erosion rate

• direct modeling of cavity shape in STAR-CCM+ and structural analysis

using Abaqus

For greater clarity, a new parameter, rate of wall thinning, was entered into the

case. It shows speed of destruction of the pipeline material and is calculated as

the ratio of erosion (kg/m2∙s) to steel density – 7800 kg/m3. The units used are

converted to mm/year as this is more intuitive to the reader


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Results of fluid-dynamic simulations

Location of localized erosion can be demonstrated by the case of the choke calculation, when Р=40

atm, Q=800000 m3/day, N=40.0 mm3/m3, d=0.25 mm. Three areas most exposed to erosion were

identified:

• needle (its damage leads to disturbances of the well operating regime);

• chamber wall behind the needle(its damage leads to well depressurization and cause

emergency situations);

• seat (narrowing in the choke – its damage leads to disturbances of the well operating

regime).

Needle


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Figures below show the relationship dependence of the predicted erosion on the sand loading

(concentration), particle size and gas flow rate (m3/day). As seen from the graphs, the

dependence of the erosion on the sand loading is linear. The impact of the particle velocity

and diameter on erosion is determined by exponents k2 and k3 in equation of Oka-correlation.

Thus, the erosion is highly sensitive to particle velocity, which in-turn is determined by the gas

velocity.

Dependence of general erosion

index on sand concentration


index on sand concentration


index on gas flow rate


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As mentioned previously, the system is flowing a multiphase mixture of

gas, sand and produced water. Under certain flowing conditions water may

form a film on the inner pipe wall surface, which may serve as a kind of

protection from the sand impact. However, we should answer two

questions:

• How much can the water film slow down the particles?

• Does the area of the water film fit in space the erosion area?


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To answer the first question, additional calculations were performed: direct numerical

simulation of the sand particle collision with the liquid film. As a result we obtained the erosion

attenuation coefficient depending on the initial speed of the sand particle and the liquid film

thickness.

Sand particle in water film


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To answer the second question, a series of calculations were carried out to model the water

film formation. It was found that in general zone of liquid film formation fits to zone of erosion.

So water spray in the pipe can be considered as factor of protection against of erosion.

Liquid film formation zones Erosion zones


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Strength Prediction of Pipeline Element Damaged by Erosion

For a full integrity assessment it is necessary to assess the residual strength of structural

elements exposed to erosive wear. For this to be undertaken it is necessary to understand

the geometrical form of the worn-our inner surface.

Given that the shape of the inner pipe wall surface has a direct influence on the internal flow

pattern, to determine the profile of the eroded pipe we used a so-called coupled formulation in

the simulation process where the pipe wall is moved in accordance with the erosion wear rate

(thinning velocity) during the solution progress.


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Results of simulation and comparison to field observations


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Conclusion:

• within this project we investigated the erosion processes in the elements of

the pipeline system on the base of STAR-ССМ + software. Localized zones of

erosion and erosion rate demonstrates good agreement with the observations of

the real object

• it is shown that the most effective parameter for erosion control is the flow

rate. Also investigated the effect of liquid films on the erosion rate. It has been

found that in some cases the presence of the water fraction in the flow leading to

the formation of liquid film on the tube wall can significantly reduce the erosion

rate.

• the new technique was developed to direct numerical simulation of the shape

of cavity with the aim of calculating the residual strength of the elements of the

pipeline system damaged by erosion


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Thank you for your attention


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NUMERICAL ANALYSIS OF EROSION OF GAS-PIPELINE...

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