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All Journal Statistika Jurnal Matematika & Sains JOURNAL OF EARTH ENERGY ENGINEERING International Journal of Computing Science and Applied Mathematics-IJCSAM
Agus Yodi Gunawan
Industrial and Financial Mathematics Research Division,Faculty of Mathematics and Natural Sciences, ITB
Computer Science & IT Decision Sciences, Operations Research & Management Earth & Planetary Sciences Economics, Econometrics & Finance Energy Engineering Industrial & Manufacturing Engineering Materials Science & Nanotechnology Mathematics

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Estimating Hyperbolic Decline Curves Parameters Sri Wahyuningsih; Sutawanir Darwis; Agus Yodi Gunawan; Kurni Permadi
Jurnal Matematika & Sains Vol 13, No 4 (2008)
Publisher : Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar

Abstract

The decline curve analysis refers to the estimation of some measure of well performance. The linearization of Arps hyperbolic decline curves leads to the estimation of initial value of decline exponent. This work proposes a graphical method to estimate the initial value of decline exponent and a binomial expansion to estimate the decline rate and the initial production value. The graphical approach is used to determine the initial value of the decline exponent for binomial expansion of hyperbolic Arps equations. Experimental study from some small data sets shows that our proposed method is capable in reducing the number of iterations needed in binomial linearization of hyperbolic decline curves. The main contribution of this work is a development of initial decline exponent estimation using graphical approach where the traditional approach is based on trial and error. Bias in estimating the initial values can produce large number of iterations in estimating the decline exponent. The proposed method is successfully reduce the number of iterations in estimating the decline exponent. Experimentally, this study indicates the existence of lower bound of decline exponent b* for each iteration using hyperbolic binomial expansion.  
A Mathematical Model of Intermittent Gas Lift in Elevation-Production Operation with Line-Pack and Line-Drafting Phenomena in a Gas Line Silvya Dewi Rahmawati; Tasmi Tasmi; Pudjo Sukarno; Agus Yodi Gunawan; Edy Soewono; Septoratno Siregar; Edward L. Tobing
Journal of Earth Energy Engineering Vol. 9 No. 2 (2020): OCTOBER
Publisher : Universitas Islam Riau (UIR) Press

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.25299/jeee.2020.5264

Abstract

This paper discusses a transient model of the intermittent gas lift technique in an oil well. The model is developed in the gas line, in the tubing-casing annulus, and the tubing. The line-pack and line-drafting phenomena in the gas line are considered in the model. A numerical approach will be used to solve the mathematical model that represents fluid flow during intermittent gas lift injection. The dynamics of important variables in the intermittent gas lift are investigated and analyzed to determine the best production strategy for intermittent gas lift. The variables are film thickness and velocity, slug height and velocity, and gas height and velocity. The relationships between surface injection control parameters (gas injection pressure and gas injection rate) and the velocity and height of film, gas, and liquid are shown in one cycle of the gas lift intermittent process. The higher the gas injection pressure, the faster the gas injection velocity, and the thinner the film thickness in the tubing. In order to obtain clean tubing from film thickness, the gas injection pressure needs to be optimized, which will lead to maintaining compressor discharge pressure availability. Detailed observation of the dynamic performance inside the tubing production well will give the optimum oil production rate for oil wells under a gas lift intermittent production strategy for field application.
Updating Reservoir Models Using Ensemble Kalman Filter Sutawanir Darwis; AGUS YODI GUNAWAN; SRI WAHYUNINGSIH; NURTITI SUNUSI; ACENG KOMARUDIN MUTAQIN; NINA FITRIYATI
STATISTIKA: Forum Teori dan Aplikasi Statistika Vol 10, No 1 (2010)
Publisher : Program Studi Statistika Unisba

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.29313/jstat.v10i1.1007

Abstract

The Ensemble Kalman Filter (EnKF) has gain popularity as a methodology for real time updates ofreservoir models. A sample of models is updated whenever observation data available. Successfulapplication of EnKF to estimate reservoir properties has been reported. A flow modeling is missing inthis research area. This paper presents the applicability of EnKF in flow modeling for three cases:infinite reservoir, bounded reservoir and one dimensional composite reservoir. The solution of flowequation was derived and used as a modeling component of state space modeling of Kalman filterupdating formula. This three reservoir models shows that the EnKF methodology can be used forupdating the reservoir models.
A Probability Flux Approach for Binary Dynamics on Networks Mohamad Riyadi; Agus Yodi Gunawan; Dewi Handayani
(IJCSAM) International Journal of Computing Science and Applied Mathematics Vol. 11 No. 2 (2025)
Publisher : LPPM Institut Teknologi Sepuluh Nopember

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.12962/j24775401.ijcsam.v11i2.8848

Abstract

Binary-state dynamics on networks provide a powerfulframework for modeling epidemics and related spreading processes.Two main approaches are commonly used, namely exactcontinuous-time Markov chain (CTMC) formulations and meanfieldapproximations. The CTMC approach ensures stochastic accuracybut suffers from exponential state-space growth, whereasmean-field approximations lose reliability in heterogeneous orsmall networks. In this study, we formulate the master equationfor binary dynamics using a probability flux approach, yieldingan exact formulation for arbitrary networks. By integrating localtransition rules, network topology, and state-space partitioning,the framework captures microscopic dynamics while enablingmacroscopic analysis. Numerical simulations reveal that bothstate probabilities and expected infection levels are influencednot only by mean degree but also by structural heterogeneity.For instance, star and line topologies exhibit distinct behaviorsdespite having identical connectivity. Spectral analysis confirmsthe asymptotic stability of the disease-free equilibrium, whileinvariance under node relabeling emphasizes the role of graphsymmetries in reducing state-space complexity. This work extendsflux-based theory to network epidemics and provides a foundationfor future studies on adaptive or time-varying networks.Index Terms - Binary dynamics, probability flux, master equation,CTMC, ep
Co-Authors Aceng Komarudin Mutaqin Dewi Handayani Edward L. Tobing Edy Soewono Fachry Abda El Rahman Kurni Permadi Mohamad Riyadi Nina Fitriyati NURTITI SUNUSI Pudjo Sukarno Septoratno Siregar Silvya Dewi Rahmawati Sri Wahyuningsih Sutawanir Darwis Tasmi Tasmi, Tasmi