Predicting CO2Minimum Miscibility Pressure (MMP) Using Alternating Conditional Expectation (ACE) Algorithm

O Alomair,M Iqbal,A Malallah,A Elsharkawy

doi:10.2516/ogst/2012097

Abstract

Miscible gas injection is one of the most important enhanced oil recovery (EOR) approaches for increasing oil recovery. Due to the massive cost associated with this approach a high degree of accuracy is required for predicting the outcome of the process. Such accuracy includes, the preliminary screening parameters for gas miscible displacement; the “Minimum Miscibility Pressure” (MMP) and the availability of the gas.All conventional and stat-of-art MMP measurement methods are either time consuming or decidedly cost demanding processes. Therefore, in order to address the immediate industry demands a nonparametric approach, Alternating Conditional Expectation (ACE), is used in this study to estimate MMP. This algorithm Breiman and Friedman [Brieman L., Friedman J.H. (1985) J. Am. Stat. Assoc. 80, 391, 580-619]estimates the transformations of a set of predictors (here C1 , C2 , C3 , C4 , C5 , C6 , C7+ , CO2 , H2 S, N2 , Mw5+ , Mw7+ and T) and a response (here MMP) that produce the maximum linear effect between these transformed variables. One hundred thirteen MMP data points are considered both from the relevant published literature and the experimental work. Five MMP measurements for Kuwaiti Oil are included as part of the testing data. The proposed model is validated using detailed statistical analysis; a reasonably good value of correlation coefficient 0.956 is obtained as compare to the existing correlations. Similarly, standard deviation and average absolute error values are at the lowest as 139 psia (8.55 bar) and 4.68% respectively. Hence, it reveals that the results are more reliable than the existing correlations for pure CO2 injection to enhance oil recovery. In addition to its accuracy, the ACE approach is more powerful, quick and can handle a huge data.

Highlights

The injection gases most commonly used for enhanced oil recovery processes are generally not miscible upon first contact with the reservoir fluids that they are displacing
Two important concepts associated with the description of miscible gas injection processes are the Minimum Miscibility Pressure (MMP) and Minimum Miscibility Enrichment (MME)
Equation of State (EOS)’s reliability depends on the quality of the data used and the oil composition. It is demonstrated by Wang and Peck (2000) that among the various available numerical MMP calculation approaches, one-dimensional compositional simulation MMP predictions are very consistent and agree with the slim-tube test data, provided an appropriate fluid phase behaviour characterization is available and numerical dispersion has already been taken into considerations

Summary

Introduction

The injection gases most commonly used for enhanced oil recovery processes are generally not miscible upon first contact with the reservoir fluids that they are displacing. The MMP has typically been accepted as the pressure at which practical maximum recovery efficiency is observed In other words, it is the lowest pressure at which gas and oil become miscible at a fixed temperature and the displacement process becomes very efficient (Ayirala and Rao, 2006). It is the lowest pressure at which gas and oil become miscible at a fixed temperature and the displacement process becomes very efficient (Ayirala and Rao, 2006) It is considered as one of the most important factors in the selection of candidate reservoirs for gas injection at which miscible recovery takes place and it determines the efficiency of oil displacement by gas

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Conclusion