DSpace at VNU: Response Surface Design for Estimating the Optimal Operating Conditions in the Polymer Flooding Process

Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 37:1012–1022, 2015 Copyright © Taylor & Francis Group, LLC ISSN: 1556-7036 print/1556-7230 online DOI: 10.1080/15567036.2011.580331 Response Surface Design for Estimating the Optimal Operating Conditions in the Polymer Flooding Process H X Nguyen,1,2 W Bae,1 X V Tran,2 A K Permadi,3 and C Taemoon1 Department of Energy and Mineral Resources Engineering, Sejong University, Gwangjin-gu, Seoul, Korea Faculty of Geology and Petroleum Engineering, Ho Chi Minh City University of Technology, Ho Chi Minh City, Vietnam Faculty of Mining and Petroleum Engineering, Bandung Institute of Technology, Bandung, Jawa Barat, Indonesia The objective of this study is to apply experimental design for sensitivity investigation and determination of the optimum condition of operating variables in enhanced oil recovery by polymer flooding These experiments were designed consisting of 14 cases by the D-optimal design The maximum net present value is obtained at $244.94 mm, in which an optimum operating variable is injected at a polymer concentration of 1,780 ppm and slug size of 2.6 mlb under reservoir conditions This study successfully applied optimal operating parameters in a polymer flood, which is an economical way of obtaining the maximum profit in a short period of time and with the fewest number of experiments Keywords: enhanced oil recovery, HPAM, net present value, optimization, polymer flooding, response surface methodology INTRODUCTION Using innovation technologies to enhance hydrocarbon production are necessary due to an increased consumption demand in the world Chemical flooding is one of the most technically successful enhanced oil recovery methods used to produce additional oil recovery after primary and secondary recovery processes Among several methods of chemical flooding, polymer flooding plays an important role and holds a bright future for improving the oil recovery factor in mature fields After secondary recovery of the water-flooding process, residual oil remaining within porous media is difficult to be displaced or recovered There is an interest in polymers to increase the viscosity of the displacing fluid, thus reducing its mobility and effectively suppressing viscous channeling in reservoirs Polymer flooding increases the volumetric sweep efficiency to improve recovery factor due to greater viscosity of the displacing fluid However, the operating process is associated with high costs and high uncertainty due to the high cost for a large amount of injected Address correspondence to Dr Wisup Bae, Sejong University, 98 Gunja-dong, Gwangjin-ku, Seoul 143-747, Korea E-mail: wsbae@sejong.ac.kr Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/ueso 1012 THE POLYMER FLOODING PROCESS 1013 polymer into a reservoir if the design of operating condition is unreasonable and the fluctuations of oil and polymer prices in the market The operation planning consists of determining polymer concentration in injection water for each injector, polymer injection time, and slug size as well These can be formulated based on an optimization algorithm whose objective function is the economical return of net present value (NPV) to compare with a traditional water-flooding process Previous literatures, such as Lu (2004) and Wang et al (2007), conducted polymer flood processes based on classical methods through their numerical simulations and experiments; however, some doubt about confidence level existed because they did not determine the significance level of operational parameters and ignored interaction effects between considered parameters leading to a low efficiency of optimization issues These limitations can be avoided by applying D-optimal design and response surface methodology (RSM) that related to the statistical design of experiments, in which all different factors were used together in test runs In addition, economic models in previous studies were not enough, usually only considering technical aspect as oil recovery factor and slug size That approach could significantly reduce the accuracy of economics evaluation and it is very difficult to control operation conditions Integrating reservoir simulators and an economic model based on experimental design are used to identify optimum operating design under uncertain operating conditions The technique incorporates the following two steps: ● ● Conducting D-optimal design to find the most influential design and uncertain factors Simulation model runs for the design points included polymer concentration and injection water, whereas polymer slug size response is to calculate the amount of oil recovery and NPV Using RSM over those most influential factors to fit a response surface map, and then searching for an optimal design based on uncertainty of the NPV Field-scale polymer flooding using a CMG simulator is applied to define optimal operating values to maximize the NPV RESPONSE SURFACE METHODOLOGY AND D-OPTIMAL DESIGN Response surface methodology was developed by Box and Wilson (1951) to aid in improvement of manufacturing processes in the chemical industry The RSM technique could evaluate the variation on the objective function, and compute the correlation between the objective function and the control variables When the test for lack of fit of the first-order model indicates the vicinity of the maximum (or minimum) of the response surface, a second-order model should be fitted For p factors, the standard second-order model is used as: Yx;t ẳ ỵ p X i xi ỵ iẳ1 p X ii x2i ỵ p X ii xi xj ỵ x;t ; (1) i