FLOW REGIME IDENTIFICATION METHODOLOGY WITH MCNP

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2009 International Nuclear Atlantic Conference - INAC 2009
Rio de Janeiro,RJ, Brazil, September27 to October 2, 2009
ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN
ISBN: 978-85-99141-03-8
FLOW REGIME IDENTIFICATION METHODOLOGY WITH MCNP-X CODE
AND ARTIFICIAL NEURAL NETWORK
César M. Salgado1,2, Roberto Schirru1, Luis E. B. Brandão2, Cláudio M. N. A. Pereira2
1
Nuclear Engineering Department (PEN-DNC), COPPE-POLI
Universidade Federal do Rio de Janeiro
21941-972 Rio de Janeiro, RJ
[email protected]
2
Instituto de Engenharia Nuclear, DIRA/IEN/CNEN
Caixa Postal 68550
21945-970 Rio de Janeiro, RJ
[email protected]; [email protected]; [email protected]
ABSTRACT
This paper presents flow regimes identification methodology in multiphase system in annular, stratified and
homogeneous oil-water-gas regimes. The principle is based on recognition of the pulse height distributions
(PHD) from gamma-ray with supervised artificial neural network (ANN) systems. The detection geometry
simulation comprises of two NaI(Tl) detectors and a dual-energy gamma-ray source. The measurement of
scattered radiation enables the dual modality densitometry (DMD) measurement principle to be explored. Its
basic principle is to combine the measurement of scattered and transmitted radiation in order to acquire
information about the different flow regimes. The PHDs obtained by the detectors were used as input to ANN.
The data sets required for training and testing the ANN were generated by the MCNP-X code from static and
ideal theoretical models of multiphase systems. The ANN correctly identified the three different flow regimes
for all data set evaluated. The results presented show that PHDs examined by ANN may be applied in the
successfully flow regime identification.
1. INTRODUCTION
Due to the exploration of oil wells in the sea, the measures of multiphase flows in offshore oil
industry are becoming increasingly important. Techniques of gamma-ray attenuation
[1,2,3,4,5] are often used in the petroleum industry because of its robustness and noninvasive
nature (character), and can perform these measurements without changing the operational
conditions in real time and allowing monitoring all the process. The meters are conventional
gamma-ray from a source with a detector installed diametrically opposite to the source; the
intention is to measure the attenuation of the beam that is influenced1 by changes in the
composition of the flow. These meters are highly dependent on the flow regime. Installing
other detectors around the tube, it significantly reduces the dependence on particular types of
regime.
The information flows in the liquid-gas system are usually obtained by subjective
interpretation from visual observations (graphic illustrations) which may lead to
misinterpretations [6,7]. Therefore, a noninvasive system that identifies the flow regime
without subjective evaluation is very important. To this end, artificial neural network (ANN)
1
The attenuation of the gamma-ray beam depends on the flow composition, the photon energy, the tube
diameter and the material and thickness of the tube wall; however, the photon energy and the diameter of the
tube are constant.
has been used [8] to interpret the PHDs obtained by detectors of gamma-ray radiation
[9,10,11]. The ANNs are mathematical models inspired by the human brain that have the
ability to extract knowledge from a finite set of information (patterns), and generalize2 it.
ANNs have been applied successfully in several classes of problems such as pattern
recognition and classification of images, voice and signals, and identification of behavior and
trends.
The data set (volume fraction and flow regime different) required for training and test the
ANN was obtained by static and ideal mathematical models of annular, stratified and
homogeneous regimes. These models were developed in the MCNP-X code [12] that is a
simulation tool widely used in radiation transport. These models consider the main effects of
the interaction of radiation with the materials involved and the PHDs obtained by NaI(Tl)
detectors. Energy resolution, dimension and characteristics of a real detector are also
considered [13].
The PHDs are used directly to feed an ANN without any parameterization of the signal,
which allows the use of a simplified detection scheme consisting of two NaI(Tl) detectors to
record the gamma-ray radiation. Thus, this work provides an intelligent system that identifies
the flow regime in multiphase flow (gas, water and oil) based on recognition of PHDs by
ANN.
2. METHOD APPLICATION AND RESULTS
2.1. Geometry proposal
The geometry simulation combines transmission (IT) and scattered (Is) radiation from
gamma-ray source (dual-mode densitometry) with a fan-beam; thus, it is possible to acquire
sufficient information about the flow regime and also to increase the measurement area on the
cross-section of the pipe [4,14] and make the material volume fraction (MVF) prediction less
dependent on the flow regime.
In all simulations, a fan-beam geometry simulation has been used for the source, as well as
two NaI(Tl) detectors. One of them is located aligned to the source (180°), and the other at
45°. Fig. 1 shows the measurement system. One collimated (angle beam 8.84°) gamma-ray
point source (59.45 keV: 241Am and 662 keV: 137Cs) has been simulated in the MCNP-X
code. In our studies, salt water was used (4% of NaCl to simulate the seawater) [14]. The
gaseous phase was substituted by air and petrol and assumed to be a hydrocarbon (molecular
formula C5H10) with a 0.896 g.cm-3 density [15]. The models for the different flow regimes
are shown in Fig. 1.
The mathematical model considered the NaI (Tl) scintillator detector as a homogeneous
cylinder [13,16,17,18,19,20] with 31 mm (diameter) x 19 mm (thickness). The information
(dimensions and materials) of a real NaI(Tl) detector was considered in the mathematical
model for calculating the MCNP-X code. A special treatment is provided in the MCNP-X
code: the Gaussian energy broadening3 (GEB) (card FTn) option has been used to better fit
2
3
They have the ability to appropriately respond to situations not included in the training data.
The energy peaks behave like a Gaussian function.
INAC 2009, Rio de Janeiro, RJ, Brazil.
the full energy peak shape of PHD; GEB parameters have been set taking into account4 the
resolution of the detector by means of the full width at half maximum (FWHM) provided by
radioactive sources [13], for the parameters must be inserted in the input file (INP) of the
detector’s mathematical model.
b) Annular
ro
a)
250 mm
αο
ra
αa
α g rg
c) Stra tified
5 mm
8.84º
5 mm
hg α g
Source
ho α ο
R
Energy:
59.45 keV
662.00 keV
Legend:
Detector 1
ha αa
d) Homogeneous
5 mm Detector 2
Al
NaI(Tl)
MgO
Oil
Water
Gas
PVC
Oil+water+gas
Figure 1. (a) Simulated system; Regime models; (b) annular; (c) stratified; (d)
homogeneous.
2.2. Generation of simulated data for training and test the ANN.
The first step in this investigation was the mathematical simulations by means of MCNP-X
code in order to generate the training set for the ANN. Data for testing the ANN have also
been generated to test the neural network in the working phase5. The models for the different
flow regimes (annular, stratified and homogeneous regimes) had been used to get a data set in
order to feed the ANN. The thickness values (rg, rw and ro - annular model, see Fig.1(b) and
hg, hw e ho - stratified model see Fig.1(c)) of each material varied in the MCNP-X code,
getting diverse combinations of MVF; while for the homogeneous regime, mass fraction of
each one of the materials varied. For each one of these combinations, which has varied from
0% to 100%, the relative counts from transmitted and scattered beams were calculated. It is
4
This step aims to validate the response of the detector quality through energy resolution while the order
quantity will be achieved by normalization of the full energy peak PHD obtained by MCNP-X.
5
The working phase (or the use of the ANN) in which the trained ANN is used to respond to new (real-world)
situations. This is an on-line phase and the ANN does not need the training set any more.
INAC 2009, Rio de Janeiro, RJ, Brazil.
important to emphasize that the MCNP-X code considers the material in a region (cell)
defined in the INP as uniform. The combinations of volume fractions which compose each of
data set were uniformly distributed throughout the ternary6.
Thus, a set of 354 (118x3) simulations for different combinations of MVFs and flow regimes
(annular, stratified and homogeneous) were made in order to generate the training set of the
ANN (195, (65x3) simulations), the test (84, (28x3) simulations) and the production (75,
(25x3) simulations). The test set was used to test the neural network in training phase7 (for
stopping criteria: cross validation, see Haykin, 1994) and to avoid overtraining. The
production set is used for a final test after ANN’s training in order to test the ANN in the
working phase.
2.3. Training of ANN
The methodology consists of using the PHDs to train the ANN to automatically identify the
flow regime of this system. The PHDs have a behaviors set that gathers the characteristics of
flow regime. From there, the system will enable other ANNs trained specifically for a
particular flow regime in order to predict more precisely the volume fraction [21]. A
schematic representation used for the training of ANN is shown in Fig. 2.
PHD 1
1
2
3
S1
1
0
0
S2
0
1
0
S3
0
0
1
6
10
12000
PHD 1
PHD 2
10000
C20
C30
Count s
8000
C720
.
.
.
6000
5
10
4000
C20
C30
2000
0
C360
.
.
.
4
10
0
100
200
300
400
Energy (keV)
500
600
ANN
700
PHD 2
Annular
Str atified
Homogeneous
Figure 2. Schematic representation used for training of the ANN.
In this work, a 3-layer feed-forward multilayer perceptron (MLP) [8] has been used. The
learning/training algorithm was the well-known (supervised) back-propagation algorithm
[8,22,23,24].
6
A ternary graphically depicts the ratios of the three variables as positions in an equilateral triangle. It is used
in petrology and other physical sciences to show the proportions of systems composed of three species. In a
ternary plot, the proportions of the three variables gas, water and oil must sum to some constant which is
represented as 100%.
7
The training phase, in which, by using a learning (training) algorithm, the ANN is supposed to learn features
(behavior, patterns, etc) from a previously provided finite set of examples (the training set). This is often an offline phase and training set may be carefully generated.
INAC 2009, Rio de Janeiro, RJ, Brazil.
The ANN training patterns are composed of the following data:
- ANN inputs8 (106 neurons):
PHD1: 20 to 720 keV, with steps of 10 keV (C20, C30, ..., C720 – counts from channel 2 to 71);
PHD2: 20 to 360 keV, with steps of 10 keV (C20, C30, ..., C350 – counts from channel 2 to 35).
- ANN outputs (3 neurons): S3, S2 and S1.
The output data were classified considering three neurons in ANN output (S3, S2 and S1), so
that to obtain the identification of systems it is only necessary the neural network to set the
highest value among the network outputs to "1" corresponding to dominant flow regime and
to "0" to other. To illustrate, suppose that the flow regime is annular, then the network should
adjust the output for S3=0, S2=0 and S1=1.
2.4. Identification of regimes for ANN from PHDs
To evaluate the differences between the flow regimes, for illustration, some simulated
measurement of transmitted and scattered beam to the volume fraction of 30% air, 20% water
and 50% oil to annular, stratified and homogeneous regimes that supplied the PHDs are
presented in Fig. 3. It was possible from the differences (behavior) found between the PHDs
for each one of the flow regime to train a ANN that resulted in 100% accuracy, correctly
identifying all the regimes submitted for a total of 354 tests. The production set with 75
patterns was used in order to test successfully the ANN in working phase.
For the interpretation of results, it was identified correctly the flow regime related to ANN’s
output for response that produced the largest absolute value among the other outputs (S3, S2
and S1).
4
8.0x10
Counts (PHD1)
Annular
Stratified
Homogeneous
PHD1
4
6.0x10
5
10
4
4.0x10
PHD2
4
Counts (PHD2)
6
10
4
2.0x10
10
0
200
400
600
800
Figure 3. PHDs obtained by MCNP-X code for different flow regimes.
8
The energy range choice of each PHD used in the training took into account the value of relative error (R)
below 10% in the counts, percentage acceptable according to the MCNP-X manual.
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3. CONCLUSIONS
It was possible to correctly identify, without errors, all the flow regimes from the proposed
geometry simulation and with the interpretation of PHDs by ANN obtained by only two
NaI(Tl) detectors. In order to provide an ideal input to the training process of ANN, a data set
was simulated by MCNP-X code for annular, stratified and homogeneous models that proved
to be reliable for training and for the working phase of ANN.
The use of simulated data obtained by gamma-ray attenuation technique with supervised
neural networks adequately trained as a reliable tool can improve the accuracy of volume
fraction measures from the correct identification of the flow regime. The results are
encouraging and indicate that the methodology can be used in determining the volume
fraction independently of the knowledge, a priori, of the flow regime.
Acknowledgments
The authors would like to thank Dr. Ademir Xavier da Silva for allowing the use of the
MCNP-X code of the Universidade Federal do Rio de Janeiro (UFRJ), and Claudio M. N. A.
Pereira and Roberto Schirru, supported by Conselho Nacional de Desenvolvimento Científico
e Tecnológico (CNPq) and Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro
(FAPERJ).
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