Numerical Modelling and Sensitivity Analysis of Gas Kick Migration and Unloading of Riser

2019 ◽  
Author(s):  
Dalila Gomes ◽  
Knut S. Bjørkevoll ◽  
Kjell K. Fjelde ◽  
Johnny Frøyen
Keyword(s):  
Sensitivity Analysis ◽  
Transient Flow ◽  
Numerical Algorithms ◽  
Drilling Fluids ◽  
Two Phase ◽  
Worst Case ◽  
Numerical Diffusion ◽  
Flow Models ◽  
Gas Kick ◽  
Water Based

Abstract In deepwater wells there is a risk of gas entering the riser. This can be caused by gas being trapped by the BOP after a well kill operation, or it can be that the BOP was not closed quickly enough upon kick detection. With oil-based mud (OBM), gas is dissolved, and larger kicks may go undetected and circulated up in the riser by accident. If a gas kick comes into the riser, a rapid unloading event can occur. This can in worst case lead to a blowout scenario. In addition, the riser may be subject to a collapse load due to reduced liquid level inside. The unloading behavior will be different when comparing kicks in oil-based and water-based mud (WBM). For water-based muds, field experience and experiments have shown that gas can be trapped by the mud. This effect is the same that causes mud to capture cutting particles, and it is related to the non-Newtonian and time-dependent rheology behavior of the mud. The suspended gas can only be removed from the riser by circulation. The kick must therefore be of a certain volume to be able to unload the well. Modelling of the mentioned complex phenomena, with the violent transient phase seen when a large volume of gas expands as it moves towards the liquid surface in the riser, is still a challenge for numerical algorithms to do accurately and reliably. Robust handling of numerical diffusion in two-phase flow is one of the key topics, as are slippage and extension of gas in the liquid. The paper describes how an explicit numerical scheme (AUSMV) is used as a numerical solver with the application of the slope-limiter technique to handle numerical diffusion. This has not yet been done for unloading of gas in riser. A simulation case will be constructed considering gas migration and expansion in a long riser. A sensitivity analysis will be performed where both the kick volumes and the threshold for gas suspension will be varied to study when kicks will start to unload the well vs. situations where they will become fully suspended. The phenomena mentioned will be studied for water-base drilling fluids. The paper will review previous work on the subject and highlight how transient flow models can be useful for gaining more insight into how the gas behaves in risers and what can be done to mitigate the consequences.

A Simplified Two-Phase Flow Model for Riser Gas Management With Non-Aqueous Drilling Fluids

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Nnamdi Nwaka ◽  
Chen Wei ◽  
Yuanhang Chen
Keyword(s):  
Drilling Fluids ◽  
Gas Migration ◽  
Dissolved Gas ◽  
Two Phase ◽  
Simplified Approach ◽  
Drift Flux Model ◽  
Drift Flux ◽  
Gas Kick ◽  
Flux Model ◽  
Using Data

Abstract Gas-in-riser events can lead to rapid unloading if not timely controlled in a proper manner. When gas influx enters a wellbore with non-aqueous muds (NAMs), the ability of gas being dissolved in NAMs increases the difficulty in gas kick detection and significantly alters gas migration and unloading behavior from the predictions based on water-based muds (WBMs) assumptions. In this study, a new mathematical model for riser gas management in NAMs is developed. In this model, the desorption of dissolved gas influx from NAMs is accounted for as an instantaneous process using a solubility-based mass transfer submodel. The effects of surface backpressures and circulation rates on the unloading behavior in both WBMs and NAMs were studied. This model was validated using data obtained from a drift-flux model (DFM) based simulator. Results show that with the same amount of free gas in the risers at the mudline level, the severity of unloading is significantly more severe in the cases of NAMs. Applied backpressure can effectively control the desorption of the gas influx from the mud, and the unloading occurs later and at shallower depth with higher backpressure. The behavior of unloading tends to be independent on the time when backpressures are applied but highly dependent on the magnitude of the backpressure and the circulation rates. The new two-phase model can accurately simulate riser gas kick events utilizing a simplified approach with improved numerical stability, making it more applicable for real-time riser gas management.

Solid viscosity of fluid-saturated porous rock with squirt flows at seismic frequencies

Geophysics ◽  
2016 ◽  
Vol 81 (4) ◽  
pp. D395-D404 ◽  
Author(s):  
Wubing Deng ◽  
Igor B. Morozov
Keyword(s):  
Wave Attenuation ◽  
Pore Space ◽  
Numerical Algorithms ◽  
Heterogeneous Porous Media ◽  
Macroscopic Model ◽  
Porous Rock ◽  
Two Phase ◽  
Waveform Modeling ◽  
Flow Models ◽  
Porous Frame

We have developed a macroscopic model for a two-phase medium (solid porous rock frame plus saturating pore fluid) with squirt flows based on Lagrangian continuum mechanics. The model focuses on improved physics of rock deformation, including explicit differential equations in time domain, causality, linearity, frequency-independent parameters with clear physical meanings, and an absence of mathematical internal or memory variables. The approach shows that all existing squirt-flow models can be viewed as microscopic models of viscosity for solid rock. As in existing models, the pore space is differentiated into compliant and relatively stiff pores. At lower frequencies, the effects of fluid flows within compliant pores are described by bulk and shear solid viscosities of the effective porous frame. Squirt-flow effects are “Biot consistent,” which means that there exists a viscous coupling between the rock frame and the fluid in stiff pores. Biot’s poroelastic effects associated with stiff porosity and global flows are also fully included in the model. Comparisons with several squirt-flow models show good agreement in predicting wave attenuation to approximately 1 kHz frequencies. The squirt-flow viscosity for sandstone is estimated in the range of [Formula: see text], which is close to field observations. Because of its origins in rigorous mechanics, the model can be used to describe any wavelike and transient deformations of heterogeneous porous media or finite bodies encountered in many field and laboratory experiments. The model also leads to new numerical algorithms for wavefield modeling, which are illustrated by 1D finite-difference waveform modeling.

Use of a Transient Model for Studying Kick Migration Velocities and Build-Up Pressures in a Closed Well

2021 ◽  
Author(s):  
Thea Hang Ngoc Tat ◽  
Dalila Gomes ◽  
Kjell Kåre Fjelde
Keyword(s):  
Flow Model ◽  
Transient Flow ◽  
Flow Patterns ◽  
Drilling Fluids ◽  
Transient Model ◽  
Drift Flux Model ◽  
Drift Flux ◽  
Gas Kick ◽  
Flux Model ◽  
Migration Velocities

Abstract The objective of the paper is to show that using pressure build-up curves for estimating kick migration velocities can be unreliable. This will be demonstrated by using a transient flow model where different flow patterns including suspended gas are considered. Suspended gas will occur in Non-Newtonian drilling fluids. This can also be the reason why there is reported large discrepancies in literature about what the gas kick migration velocities can be. A transient flow model based on the drift flux model supplemented with a gas slip relation will be used. The model will be solved by an explicit numerical scheme where numerical diffusion has been reduced. Different flow patterns are included i.e. suspended gas, bubble flow, slug flow and transition to one-phase gas. Kick migration in a closed well will be studied to study how pressure build-ups evolve. A sensitivity analysis will be performed varying kick sizes, suspension limits and changing the transition intervals between the flow patterns. It is seen in literature that the slope of the pressure build-up for a migrating kick in a closed well has been used for estimating what the kick velocity is. It has been reported earlier that this can be an unreliable approach. In the simulation study, it is clearly demonstrated that the suspension effect will have a significant impact of reducing the slopes of the pressure build-ups from the start of the kick onset. In some severe cases, the pressure builds up but then it reaches a stable pressure quite early. In these cases, the kick has stopped migrating in the well. However, in the cases where the kicks are still migrating, it seems that the bulk of the kick moves at the same velocity even though the degree of suspension is varied and gives different slopes for the pressure build-up. Hence, it seems impossible to deduce a unique gas velocity from different pressure build-up slopes. However, abrupt changes in the slope of the pressure build-up indicate flow pattern transitions.

scholarly journals Port-Hamiltonian formulation of two-phase flow models

2021 ◽  
Vol 149 ◽  
pp. 104881
Author(s):  
H. Bansal ◽  
P. Schulze ◽  
M.H. Abbasi ◽  
H. Zwart ◽  
L. Iapichino ◽  
...  
Keyword(s):  
Two Phase Flow ◽  
Hamiltonian Formulation ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Models

scholarly journals Numerical Study on an Interface Compression Method for the Volume of Fluid Approach

Fluids ◽  
2021 ◽  
Vol 6 (2) ◽  
pp. 80
Author(s):  
Yuria Okagaki ◽  
Taisuke Yonomoto ◽  
Masahiro Ishigaki ◽  
Yoshiyasu Hirose
Keyword(s):  
Linear Theory ◽  
Volume Fraction ◽  
Numerical Study ◽  
Volume Of Fluid ◽  
Interfacial Wave ◽  
Validation Process ◽  
Two Phase ◽  
Numerical Diffusion ◽  
Mesh Resolution ◽  
Water Reactors

Many thermohydraulic issues about the safety of light water reactors are related to complicated two-phase flow phenomena. In these phenomena, computational fluid dynamics (CFD) analysis using the volume of fluid (VOF) method causes numerical diffusion generated by the first-order upwind scheme used in the convection term of the volume fraction equation. Thus, in this study, we focused on an interface compression (IC) method for such a VOF approach; this technique prevents numerical diffusion issues and maintains boundedness and conservation with negative diffusion. First, on a sufficiently high mesh resolution and without the IC method, the validation process was considered by comparing the amplitude growth of the interfacial wave between a two-dimensional gas sheet and a quiescent liquid using the linear theory. The disturbance growth rates were consistent with the linear theory, and the validation process was considered appropriate. Then, this validation process confirmed the effects of the IC method on numerical diffusion, and we derived the optimum value of the IC coefficient, which is the parameter that controls the numerical diffusion.

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