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Application and Improvement of Ensemble Kalman Filter Method in Production Data Analysis

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Proceedings of the International Petroleum and Petrochemical Technology Conference 2019 (IPPTC 2019)

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Abstract

Production data analysis (PDA) is a subject to determine reservoir properties and predict future performance of single wells. It is normally conducted with either analytical methods or numerical history-matching methods. However, the analytical models normally have limited accuracy due to simplifying assumptions, while the history-match based on numerical simulations sacrifices computation load to increased accuracy. Therefore, in this study, the authors incorporated Ensemble Kalman Filter (EnKF) to improve PDA considering its superior efficiency in predicting system state and uncertainties. In this work, we applied the EnKF algorithm to single-well reservoir models to estimate permeability, skin factor, and drainage area. First, we tested the model accuracy after comparing the EnKF estimates to known reservoir properties. Next, we evaluated the cases with large estimation error and then adjusted the initial uncertainties and covariance of the static parameters. With confirmed improvements of property estimation in synthetic cases, the model is finally applied in a field study for further verifications. The results from this study confirmed that EnKF method could be an efficient solution for the modern PDA. They also indicate that accuracy issues are sometimes present when estimating skin factor and reservoir permeability simultaneously: large error exists in the property estimates, their uncertainties are overly reduced, and thus analysis and predicts are affected. By increasing the initial uncertainty bounds and adding minimum threshold values for the covariance, the property estimates could be improved, and reasonable uncertainty bounds are preserved. The methodology from this study is applicable for full-field evaluations.

Copyright 2019, IPPTC Organizing Committee.

This paper was prepared for presentation at the 2019 International Petroleum and Petrochemical Technology Conference in Beijing, China, 27–29, March, 2019.

This paper was selected for presentation by the IPPTC Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the IPPTC Technical Committee and are subject to correction by the author(s). The material does not necessarily reflect any position of the IPPTC Technical Committee, its members. Papers presented at the Conference are subject to publication review by Professional Team of Petroleum Engineering of the IPPTC Technical Committee. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of Shaanxi Petroleum Society is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words illustrations may not be copied. The abstract must contain conspicuous acknowledgment of IPPTC. Contact email: paper@ipptc.org.

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Abbreviations

\( A_{x} \) :

Cross-sectional area normal to x direction, ft2

\( A_{y} \) :

Cross-sectional area normal to y direction, ft2

\( B_{g} \) :

Gas formation volume factor, RB/scf

\( B_{o} \) :

Oil formation volume factor, RB/stb

\( B_{w} \) :

Water formation volume factor, RB/stb

c :

Component

B:

Formation volume factor, reservoir volume/volume at standard conditions

\( \varvec{C}_{D} \) :

Covariance matrix of the measured data

\( \varvec{C}_{Y}^{f} \) :

The prior covariance matrix for the state variables

\( \varvec{d}_{m}^{o} \) :

Measurement data used for assimilation

\( \varvec{d}_{m} \) :

Simulation model output at each assimilation time step

k:

Reservoir permeability, md (in the context of governing equation)

\( k_{r} \) :

Relative permeability, fraction

\( k_{rl} \) :

Relative permeability to phase l, dimensionless

\( k_{rg} \) :

Relative permeability to gas, dimensionless

\( k_{ro} \) :

Relative permeability to oil, dimensionless

\( k_{rw} \) :

Relative permeability to water, dimensionless

\( k_{s} \) :

Permeability of the damaged/stimulated area, md

\( k_{x} \) :

Permeability in the direction of the x axis, md

\( k_{y} \) :

Permeability in the direction of the y axis, md

\( \varvec{K} \) :

Kalman Gain

\( \overrightarrow {{\dot{m}}}_{c} \) :

Mass flux for component c, lbm/(D-ft2)

\( \dot{m}_{cx} \) :

c component of mass flux in x direction, lbm/(D-ft2)

\( \dot{m}_{cy} \) :

c component of mass flux in y direction, lbm/(D-ft2)

\( m_{{V_{c} }} \) :

Mass of component c per unit volume of rock, lbm/ft3

\( N_{d} \) :

Number of observations

\( N_{k} \) :

Ensemble size

\( N_{x} \) :

The number of the state variables

\( N_{y} \) :

\( N_{y} = N_{\theta } + N_{x} + N_{d} \)

\( N_{\theta } \) :

The number of poorly known parameters

\( \varvec{O} \) :

\( N_{d} \times \left( {N_{\theta } + N_{x} } \right) \) null matrix

\( P_{cgo} \) :

Gas/oil capillary pressure, psi

\( P_{cow} \) :

Oil/water capillary pressure, psi

\( P_{g} \) :

Gas pressure, psi

\( P_{o} \) :

Oil pressure, psi

\( P_{w} \) :

Water pressure, psi

\( q_{gsc} \) :

Gas production rate at standard conditions, scf/D

\( q_{{m_{c} }} \) :

Rate of mass depletion for component \( c \) through wells/lbm/D

\( q_{{mt_{c} }} \) :

Rate of mass depletion for component c between phases, lbm/D

\( q_{osc} \) :

Oil production rate at standard conditions, STB/D

\( q_{wsc} \) :

Water production rate at standard conditions, STB/D

\( r_{s} \) :

Radius of the damage/stimulated area around a wellbore, ft

\( {\text{r}}_{\text{w}} \) :

Well radius, ft

\( R_{s} \) :

Solution gas oil ratio, scf/STB

\( S_{g} \) :

Gas saturation, fraction

\( S_{o} \) :

Oil saturation, fraction

\( S_{w} \) :

Water saturation, fraction

t :

Simulation time, days

\( \Delta t \) :

Simulation time step, days

u :

Superficial velocity, RB/(D-ft2)

\( \overrightarrow {{u_{c} }} \) :

Component c superficial velocity vector, RB/(D-ft2)

\( u_{cx} \) :

x component of component c superficial velocity, RB/(D-ft2)

\( u_{cy} \) :

y component of component c superficial velocity, RB/(D-ft2)

\( V_{b} \) :

Gridblock bulk volume, ft

\( \varvec{x} \) :

Reservoir state vector (including reservoir pressures and phase saturations), \( x = x\left( t \right) \in {\mathbb{R}}^{{N_{x} }} \)

\( \varvec{y}_{m}^{k} \) :

State vector of ensemble number k at time m

\( \varvec{Y}_{m} \) :

State vectors of the entire ensembles at time m

\( \overline{{\varvec{Y}_{m} }} \) :

Matrix containing ensemble mean in each column at time m

\( \overline{{y_{m}^{1} }} \) :

Ensemble mean of each member at time m

\( \varepsilon_{m}^{o} \) :

Measurement error, which is a zero-mean Gaussian noise \( \varepsilon_{m}^{o} \sim \mathcal{N}\left( {0,R} \right) \)

\( \alpha_{c} \) :

Volumetric conversion factor, 5.614583

\( \beta_{c} \) :

Transmissibility conversion factor, 1.127

\( \gamma_{g} \) :

Gas gravity, psi/ft

\( \gamma_{l} \) :

Gravity of phase l, psi/ft

\( \gamma_{o} \) :

Oil gravity, psi/ft

\( \gamma_{w} \) :

Water gravity, psi/ft

\( \varepsilon_{m} \) :

Model error

\( \varvec{\theta} \) :

Static reservoir parameters, \( \theta \in {\mathbb{R}}^{{N_{\theta } }} \)

\( \Delta \) :

Difference, difference operator

\( \mu_{g} \) :

Gas viscosity, cp

\( \mu_{o} \) :

Oil viscosity, cp

\( \mu_{w} \) :

Water viscosity, cp

\( \rho_{c} \) :

Density of component \( c \), lbm/ft3

\( \rho_{g} \) :

Gas phase density, lbm/ft3

\( \rho_{gsc} \) :

Gas phase density at standard condition, lbm/ft3

\( \rho_{w} \) :

Water phase density, lbm/ft3

\( \phi \) :

Porosity, fraction

\( \Delta {\text{x}} \) :

Difference along x direction, ft

\( \Delta {\text{y}} \) :

Difference along y direction, ft

b :

Grid bulk

c :

Component

fg :

Free gas

g :

Gas

k :

Ensemble member, \( k = 1,2,3 \ldots N_{k} \)

l :

Phase l or component l

m :

Assimilation time, \( m = 1, 2, \ldots , N_{m} \)

mt :

Mass transfer

o :

Oil

sc :

Standard condition

sg :

Solution gas

t :

Simulation time

w :

Water

f :

Forecasted

o:

Observed or measured

u :

Updated

T :

Transpose of

→:

Vector

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Acknowledgements

The authors would like to acknowledge Computer Modeling Group Ltd. for providing the CMG software for this study.

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Correspondence to Wen-ting Yue .

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Yue, Wt., Wang, J.Y. (2020). Application and Improvement of Ensemble Kalman Filter Method in Production Data Analysis. In: Lin, J. (eds) Proceedings of the International Petroleum and Petrochemical Technology Conference 2019. IPPTC 2019. Springer, Singapore. https://doi.org/10.1007/978-981-15-0860-8_36

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  • DOI: https://doi.org/10.1007/978-981-15-0860-8_36

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