Renan Martins Baptista

Estimating Mixing Volumes Between Batches in Multiproduct Pipelines

It is presented in this paper a new model for estimating mixing volumes which arises in batching transfers in multiproduct pipelines. The novel features of the model are the incorporation of the flow rate variation with time and the use of a more precise effective dispersion coefficient, which is considered to depend on the concentration. The governing equation of the model forms a non-linear initial-value problem that is solved by using a predictor-corrector finite difference method. A comparison among the theoretical predictions of the proposed model, a field test and other classical procedures show that it exhibits the best estimate over the whole range of admissible concentrations investigated.Copyright

PIPELINE LEAK LOCALIZATION USING PATTERN RECOGNITION AND A BAYES DETECTOR

A novel leak localization method for multi section pipelines is presented. Based on normal operation flowing thermodynamic pressure drop patterns along the pipeline, the system continuously compares with the measured pressure drops, and makes a decision based on the best fit finding the section where the leak occurs. A statistical approach is used accounting for noisy measured signals. The method uses steady state fluid equations, a recursive parameter estimation algorithm, and statistical decision and pattern recognition techniques. A modification is introduced to consider the cost of making a wrong leaky section choice in terms of the excess volume spilled due to gravitational flow after pipeline shut down. This leads to a Bayesian decision scheme minimizing a risk functional. The costs are the spill volumes, obtained from dynamical simulation of the pipeline, under the various possible decision scenarios. Finally, details are given of the successful implementation of the system on a 500km long oil pipeline, and real data from a simulated leak experiment are shown.© 2006 ASME

A Pipeline LDS Trial: Comparing Compensated Volume Balance Against SPRT Statistical Based LDS in a Brazilian Pipeline

This paper describes field trials for two different technologies (built in two commercial products) for leak detection, location and quantification systems (LDS). Modified Compensated Volumetric Balance was tested against SPRT Statistical Analysis, and the obtained results were analyzed/commented. The tests were carried out in a 43 km long 20 in. pipeline (PREPSP), carrying different batches of crude oils, located in the state of Bahia, Brazil. Actual leaks under shut in, steady state, pump transient startup and shutdown operational conditions were introduced, and the performance of both technologies analysed. For each of those conditions and technologies, a sensitivity curve was plotted, leak location and its quantification was tabled, compared and commented. Finally, reliability data for both technologies (essentially, number of false alarms and non-expected misbehavior) were gathered for a two weeks testing period.Copyright

Numerical Simulation of Non-Isothermal Two-Phase Flow in a Pipeline Using the Flux-Corrected Transport Method

Two phase flows occur in many engineering problems, especially in the nuclear, gas and petroleum industries. In oil and gas applications, specifically, a mixture of oil and natural gas is transported in pipelines from offshore platforms to the continent. The prediction of how the flow behaves in time as it moves along the pipe is extremely important, mainly during the pipeline design stage or regular operation. This paper presents simulations for stratified gas-liquid two-phase flow in a horizontal pipeline that is subject to the temperature gradients that exist in the bottom of the ocean, and the resulting heat transfer process that may lead to wax formation and deposition. A one-dimensional two-fluid mathematical model was employed that includes conservation equations of mass and momentum for each fluid and one energy equation for the mixture of liquid and gas. The problem was formulated as an initial-boundary value problem of the hyperbolic type and it was solved using the Flux Corrected Transport (FCT) numerical method, which is second-order accurate in space, coupled with an explicit discretization in time that is first-order accurate. The FCT method is appropriate to solve problems characterized by hyperbolic equations that may contain discontinuities and shock waves, and it presents small dispersive effects. The results showed excellent accuracy results when compared to commercial software widely used in the oil and gas industry.Copyright

Hyperbolicity Analysis of a One-Dimensional Two-Fluid Two-Phase Flow Model for Stratified-Flow Pattern

Two-phase flows in pipelines occur in a variety of processes in the nuclear, petroleum and gas industries. Because of the practical importance of accurately predicting steady and unsteady flows along the line, one-dimensional two-fluid flow models have been extensively employed in numerical simulations. These models are usually written as a system of non-linear hyperbolic partial-differential equations, but some of the available formulations are physically inconsistent due to a loss of the hyperbolicity property. In these cases, the associated eigenvalues become complex numbers and the model loses physical meaning locally. This paper presents a numerical study of a one-dimensional single-pressure four-equation two-fluid model for an isothermal stratified flow that occurs in a horizontal pipeline. The diameter, pressure and volume fraction are kept constant, whereas the liquid and gas velocities are varied to cover the entire range of superficial velocities in the stratified region. For each point, the eigenvalues are numerically computed to verify whether they are real numbers and to assess their signs. The results show that hyperbolicity is lost near the boundaries of the stratified pattern and in a vast area of the region itself. Moreover, the eigenvalue signs alternate, which has implications on the prescription of numerical boundary conditions.Copyright

Numerical Simulation of Stratified Two-Phase Flow in a Nearly Horizontal Gas-Liquid Pipeline With a Leak

The capability of producing accurate numerical simulations of transient gas-liquid flows in gas pipelines has long been a serious concern in the oil industry. In this paper we are particularly interested in simulating this type of flow during the occurrence of a leak in the pipe. We use the flux-corrected transport (FCT) finite-difference method, which is second-order in space, to solve a one-dimensional single-pressure four-equation two-fluid model. We consider this two-phase flow to occur in a nearly horizontal pipeline characterized by the stratified-flow pattern, and we assume that the flow is isothermal with a compressible gas phase and an incompressible liquid phase. We model the leak as a source term in the mass conservation equations. The results of the numerical simulations allow the model sensitivity to be studied by changing the leak diameter and the leak location. From this analysis, we may observe how these parameters affect the pressure gradients along the pipeline that develop upstream and downstream of the leak.© 2014 ASME

Featuring Pig Movement in Two-Phase Gas Pipelines

This paper presents a mechanical model, along with a numerical scheme for obtaining approximating solutions for the resulting initial-boundary-value problem, for describing the pig movement in transient two-phase gas pipelines. By taking advantage of the best features of the existing models presented in the literature so far, an idealized general purpose pig model is proposed, contemplating the possibility of representing, within a same context, different types of pigs or pig functions. Both mechanical and hydrodynamic friction forces at the interface of the pig and the pipe wall, as well as by-pass flow rates for the liquid and gaseous phases, are naturally incorporated in the modeling in a coherent mechanical context. The governing equations of the two-phase flow model are intentionally written in a general form, so that different existing models can be used within the framework presented herein. Following this same strategy, a detailed numerical scheme is presented in which the discretization of the flux terms are left open, so that different numerical strategies of first or higher orders can be accommodated without any additional difficulties.Copyright

Accuracy Study of the Flux-Corrected Transport Numerical Method Applied to Transient Two-Phase Flow Simulations in Gas Pipelines

The ability to produce accurate numerical simulations of transient two-phase flows in gas pipelines has long been an important issue in the oil industry. A reliable prediction of such flows is a difficult task to accomplish due to the numerous sources of uncertainties, such as the basic two-phase flow model, the flow-pattern models, the initial condition and the numerical method used to solve the system of partial differential equations. Several numerical methods, conservative or not, of first- and second-order accuracies may be used to discretize the problem. In this paper we use the flux-corrected transport (FCT) finite-difference method to solve a one-dimensional single-pressure four-equation two-fluid model for the two-phase flow that occurs in a nearly horizontal pipeline characterized by the stratified-flow pattern. Because the FCT algorithm is of indeterminate order, we use a test case to assess the spatial and time accuracies for the specific class of hyperbolic problem that we obtain with the modeling employed here. The results show that the method is first order in time and second order in space, which have important consequences on the choice of mesh spacing and time step for a desired accuracy.Copyright

On the Influence of the Fluid Dynamics Over the Valve Line Break Set Point in a Dual Phase Gas Pipeline

Shut down valves (SDV) actuated by a reaction against a pressure decay are an approach to face pipeline leakages, full ruptures, amidst several other important operational events. They are ordinarily employed at single phase pipelines throughout the world. Their usage at a dual phase gas pipeline is however subjected to specific scenarios in which their actuators (usually line breaks) are not impacted somehow by the presence of liquids, and other particular effects of fluid dynamics.This paper approaches a study based on dual phase numerical flow simulations, using a commercial flow simulator, performed for a Brazilian pipeline, in which a relevant amount of liquid is always present, as well as one or two pigs. The main focus is on the upper bound of the time derivative of pressure distributed along the developed length, aiming to produce a sensitivity analysis, describing situations in which this variable may falsely and appropriately trigger a SDV closure.As most of other important flow events, the critical moment is when the pig approaches the pipeline tail, when major variations on important variables such as flow, pressure and holdup are experienced. Those effects may be deeply augmented when worst case scenarios are imposed and coupled with pigs’ arrivals/withdrawals, such as a pipeline blockage at it’s head or flow rate relevant increase at the tail. These scenarios are simulated and analysed, and the way pressure may relate to the dimensioning of line brakes, is commented.Copyright

New Developments for the Description of Oil Leakages by Advective Migration From Submarine Pipelines

The significant growth in offshore operations increases the risk of a pipeline rupture, even considering the high standards of safety involved. Throughout a submarine leakage, four different amounts of oil may be accounted. The first one is the oil volume released until the leakage detection. The second one is the volume leaked throughout mitigation initiatives (e.g., pump shutdown and valve closure). The third parcel is the amount released by gravitational flow. Finally, the fourth and last amount of oil is released due to the water-oil entrainment, generally known as advective migration. Normally, a considerable amount of oil is released in this step. It begins just after the internal pipeline pressure becomes equal to the external one. The present work continues to introduce a mathematical alternative approach, based on the theories of perturbation and unstable immiscible displacement, to accurately estimate the leakage kinetics and the amount of oil released by the advective migration phenomenon. Situations considering different hole sizes and thicknesses were tested experimentally and through simulations. Additional experiments were accomplished using smooth and rough edge surfaces, besides different slopes (using the horizontal plane as reference). Those experiments permitted a preliminary evaluation of the importance of these factors. The results obtained with the model showed good agreement with the experimental data in many situations considered. DOI: 10.1115/1.3089499