DEVELOPMENT OF AN EXPERT SYSTEM FOR RESERVOIR FLUID PVT PROPERTIES CORRELEATIONS

Transcription

1 DEVELOPMENT OF AN EXPERT SYSTEM FOR RESERVOIR FLUID PVT PROPERTIES CORRELEATIONS Presented By Ahmed Moustafa Abd El-Rahman Al-Zahaby B.Sc. in Petroleum Eng. Al-Azhar University (2007) A Thesis Submitted to the Department of Mining, Petroleum, and Metallurgical Engineering Faculty of Engineering, Cairo University In Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN PETROLEUM ENGINEERING FACULTY OF ENGINEERING, CAIRO UNIVERSITY GIZA, EGYPT 2012 I

2 DEVELOPMENT OF AN EXPERT SYSTEM FOR RESERVOIR FLUID PVT PROPERTIES CORRELEATIONS Presented By Ahmed Moustafa Abd El-Rahman Al-Zahaby B.Sc. in Petroleum Eng. Al-Azhar University (2007) A Thesis Submitted to the Department of Mining, petroleum, and Metallurgical Engineering Faculty of Engineering, Cairo University In Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN PETROLEUM ENGINEERING Under the Supervision of Prof. Dr. Mohamed Helmy Sayyouh Professor of Petroleum Engineering Cairo University Prof. Ahmed El-Banbi Professor of Petroleum Engineering Cairo University FACULTY OF ENGINEERING, CAIRO UNIVERSITY GIZA, EGYPT 2012 II

3 DEVELOPMENT OF AN EXPERT SYSTEM FOR RESERVOIR FLUID PVT PROPERTIES CORRELEATIONS Presented By Ahmed Moustafa Abd-El Rahman Al-Zahaby B.Sc. in Petroleum Eng. Al-Azhar University (2007) A Thesis Submitted to the Department of Mining, Petroleum, and Metallurgical Engineering Faculty of Engineering, Cairo University In Partial Fulfillment of the Requirements for the Degree of Approved by the Examining Committee MASTER OF SCIENCE IN PETROLEUM ENGINEERING Prof. Dr. Mohamed Helmy Sayyouh Faculty of Engineering, Cairo University, Thesis Main Advisor Prof. Dr. Ahmed El-Banbi Faculty of Engineering, Cairo University, Thesis Main Advisor Prof. Dr. M. Khairy Faculty of Engineering, Cairo University, Member Prof. Dr. Ismail Mahgoub Faculty of Engineering, Cairo University, Member FACULTY OF ENGINEERING, CAIRO UNIVERSITY GIZA, EGYPT 2012 III

4 ABSTRACT DEVELOPMENT OF AN EXPERT SYSTEM FOR RESERVOIR FLUID PVT PROPERTIES CORRELEATIONS Accurate determination of the crude oil PVT properties is essential for solving many reservoir engineering, production engineering, and surface production and operational problems. A large number of PVT correlations for oil exist in the petroleum literature and numerous studies are also present for with data favoring one correlation over the other. In the absence of PVT data from laboratory experiments, it is often difficult to choose which correlation to use to calculate different PVT properties. We approached this problem in two ways. First, we developed an expert system that checks the input parameters (e.g. reservoir parameters) against the valid ranges of input data for different correlations, and then recommends which correlations to use for specific input parameters. Second, we tested all available PVT correlations for black oil on a database of selected 35 Egyptian crudes to develop guidelines on which correlations to use for each PVT property for the specific range of input data. These specific crudes were selected to allow testing of those guidelines on a wide range of reservoir input data for black oils. Our database included oils with o API ranging from 17 to 51, gas-oil-ratios of 8 to 7,800 scf/stb, formation volume factor at bubble point of 1.04 to 4.47 bbl/stb, bubble point pressures of 60 to 4739psia, and reservoir temperatures of 40 to 270 F. The present work included 14 bubble points, 6 solution-gas-oil ratio, 15 formation volume factors, 13 oil compressibilities, 14 dead oil viscosities, 9 saturated oil viscosities, 10 under saturated oil viscosities,12 under-saturated densities, 2 total formation volume factors and 2 saturated density correlations. In addition to 6 dew point pressure correlations and 8 gas compressibility factors. IV

5 Based on this study, guidelines for selecting an appropriate correlation for PVT properties are introduced.these guidelines are recommended in programming of PVT correlations regardless of their geographic origin. V

6 Dedication To my dear mother, I am not able to thank you, because whatever I did, you deserve more. VI

7 ACKNOWLEDGEMENT All praise to Allah, the Almighty, who gave me the confidence to carry out this work. I wish to express my great gratitude to professor Dr. Mohamed Helmy Sayyouh and Prof. Ahmed Hamdi El-Banbi, Mining Petroleum, and Metallurgical Department, Faculty of Engineering, Cairo University for selecting the study subject, supervising the work, and for valuable guidance during the preparation and for their continuous suggestions and encouragement. I am grateful to Dr Ismail Mahgoub who allowed me to use some industry resources and useful materials. Also my acknowledgments to all my friends and staff members who made my stay here at Cairo and the British University in Egypt. Last but not the least; I am grateful to my mother and my father for their understanding and affection throughout my life. Acknowledgements are also extended to my professor Dr. Selim Zeidan of Faculty of Engineering Al-Azhar University for his continuous support and careful review of the manuscript. VII

8 CONTENTS Page ABSTRACT... IV DEDICATION... VI ACKNOWLEDGEMENT... VII CONTENTS... VIII LIST OF TABLES... XI LIST OF FIGURES... XIII NOMENCLATURE... XIV 1.CHAPTER INTRODUCTION CHAPTER LITERATURE REVIEW OIL CORRELATIONS BUBBLE POINT PRESSURE Solution Gas Oil Ratio Under-saturated Isothermal Oil Compressibility Under-saturated Oil Formation Volume Factor Bubble point Oil Formation Volume Factor Oil Viscosity: Under-saturated Oil Viscosity Bubble Point (Saturated) Oil Viscosity Dead Oil Viscosity Under-Saturated Oil Density Saturated Oil Density Gas correlations Compressibility Factor of Gas Direct calculations Indirect calculations Dew point pressure Gas Viscosity µg Hydrate Temperature Critical properties (Tc & Pc) Water correlations Solution Gas Water Ratio (Rsw): Formation Water Volume Factor (B w ): Density of Formation Water (ρ w ): The Coefficient of Isothermal Compressibility of Brine (cw): Formation Water Viscosity (µw): Formation Water Content of Gas W fw CHAPTER VIII

9 OBJECTIVES AND STATEMENT OF THE PROBLEM THE PROBLEM OBJECTIVES OF THE STUDY CHAPTER RESERVOIR FLUID CORRELATIONS OIL CORRELATIONS INTRODUCTION PROGRAMMING OF PVT OIL PROPERTIES CORRELATIONS EVALUATION OF PVT OIL CORRELATIONS BUBBLE POINT PRESSURE SOLUTION GAS OIL RATIO UNDER-SATURATED ISOTHERMAL OIL COMPRESSIBILITY UNDER-SATURATED OIL FORMATION VOLUME FACTOR BUBBLE POINT OIL FORMATION VOLUME FACTOR OIL VISCOSITY UNDER-SATURATED OIL VISCOSITY BUBBLE POINT (SATURATED) OIL VISCOSITY DEAD OIL VISCOSITY UNDER-SATURATED OIL DENSITY TOTAL FORMATION VOLUME FACTOR GAS CORRELATIONS DATA DESCRIPTION WATER CORRELATIONS CHAPTER DEVELOPMENT OF AN EXPERT SYSTEM INTRODUCTION PVT EXPERT SYSTEM DEVELOPMENT KNOWLEDGE ACQUISITION SYSTEM FORMULATION PVT EXPERT SYSTEM UTILISATION APPLICATION OF EXPERT SYSTEM ON SOME OF THE EGYPTIAN OIL PVT SAMPLES CHAPTER RESULTS AND DISCUSSIONS GUIDELINES FOR SELECTING THE APPROPRIATE PVT PROPERTIES BASED ON THE RESULTS OF RELIABILITY ANALYSIS PERFORMED ON EGYPTIAN OIL SAMPLES COMPARISON OF BUBBLE POINT PRESSURE CORRELATIONS COMPARISON OF SOLUTION GAS OIL RATIO CORRELATIONS COMPARISON OF BUBBLE POINT OIL FORMATION VOLUME FACTOR CORRELATIONS COMPARISON OF UNDER-SATURATED OIL FORMATION VOLUME FACTOR CORRELATIONS IX

10 COMPARISON OF UNDER-SATURATED OIL VISCOSITY CORRELATIONS COMPARISON OF GAS SATURATED OIL VISCOSITY CORRELATIONS COMPARISON OF THE COEFFICIENT OF UNDER-SATURATED ISOTHERMAL OIL COMPRESSIBILITY CORRELATIONS COMPARISON OF GAS SATURATED OIL DENSITY CORRELATIONS COMPARISON OF UNDER-SATURATED OIL DENSITY CORRELATIONS GUIDELINES FOR SELECTING THE APPROPRIATE PVT PROPERTIES BASED ON RESULTS OF RELIABILITY ANALYSIS PERFORMED ON WORLDWIDE GAS CONDENSATE SAMPLES COMPARISON OF GAS COMPRESSIBILITY FACTOR CORRELATIONS COMPARISON OF DEW POINT PRESSURE CORRELATIONS CHAPTER CONCLUSIONS AND RECOMMENDATIONS CONCLUSIONS: RECOMMENDATIONS: REFERENCES APPENDIX A EMPIRICAL PVT CORRELATIONS USED FOR CORRELATIONS APPENDIX B... ERROR CALCULATIONS DETAILS FOR OIL DATA BASE X

11 Table No. LIST OF TABLES Page Table 4-1: Data Range for the Egyptian PVT Data Table 4-2: Reported Input Parameters Ranges for Bubble Point Pressure Correlations 53 Table 4-3: Reported Input Parameters Ranges for Solution Gas Oil Ratio Correlations. 54 Table 4-4: Reported Input Parameters Ranges for Under-Saturated Isothermal Oil Compressibility Correlations Table 4-5: Reported Input Parameters Ranges for Formation Volume Factor Correlations Table 4-6: Reported Input Parameters Ranges for Total Formation Volume factor Correlations Table 4-7: Reported Input Parameters Ranges for under-saturated Oil Viscosity Correlations Table 4-8: Reported Input Parameters Ranges for Bubble Point Oil Viscosity Correlations Table 4-9: Reported Input Parameters Ranges for Dead Oil Viscosity Correlations Table 4-10: Data Range for the World-Wide PVT Gas Condensate Samples Table 4-11: Reported Input Parameters Ranges for Dew Point Pressure Correlations.. 74 Table 4-12: Reported Input Parameters Ranges for Gas Viscosity µg Correlations Table 4-13: Reported Input Parameters Ranges for Gas Z Factor Correlations Table 4-14: Reported Input Parameters Ranges for Critical Properties Correlations Table 4-15: Reported Input Parameters Ranges for Isothermal compressibility of a gas, cg Correlation Table 4-16: Reported Input Parameters Ranges for Hydrate temperature Correlations 79 Table 4-17: Reported Input Parameters Ranges for Bw Correlations Table 4-18: Reported Input Parameters Ranges for cw Correlations XI

12 Table 4-19: Reported Input Parameters Ranges for Water density ρw Correlations Table 4-20: Reported Input Parameters Ranges for methane solubility in brine Correlations Table 4-21: Reported Input Parameters Ranges for Brine viscosity µw Correlations XII

13 Figure No. LIST of FIGURES Page Figure 4-1: Cross-plot between estimated and experimental bubble point pressure, psia Figure 4-2: Cross-plot between estimated and experimental solution gas-oil ratio, scf/stb for the range of scf/stb Figure 4-3: Cross-plot between estimated and experimental solution gas-oil ratio, scf/stb for the range of scf/STB Figure 4-4: Cross-plot between estimated and experimental bubble point oil formation volume factor (bbl/stb) Figure 4-5: Cross-plot between estimated and experimental the coefficient of undersaturated isothermal oil compressibility data, psia Figure 4-6: Cross-plot between estimated and experimental under-saturated oil viscosity data, cp Figure 4-7: Cross-plot between estimated and experimental saturated oil viscosity data, cp Figure 4-8: Cross-plot between estimated and experimental under saturated oil formation volume factor, bbl/stb Figure 4-9: Cross-plot between calculated and experimental Z-factor for Pappy method Figure 4-10: Cross-plot between calculated and experimental dew point pressure of gas condensate, psia Figure 4-11: Cross-plot between estimated and experimental dew point pressure of gas condensate, psia Figure 5-1: PVT expert system utilisation Figure 5-2: An extract of the PVT Expert System database used in selection Figure 5-3: An extract of the PVT Expert System output results XIII

14 List of abbreviations Scf Bbl STB PVT CVD CCE standard cubic feet barrels Stock Tank Barrel Pressure, Volume and Temperature constant volume depletion constant composition expansion Bo Rso Oil Formation Volume Factor Solution Gas-oil ratio Nomenclature bbl/stb scf/stb Pb Bubble point pressure API Gravity of stock tank oil degree Mc7plus C7 plus molecular weight lb/lb. mole B gi Gas formation volume factor bbl/mscf B oi Oil formation volume factor Bbl/STB γgr reservoir gas specific gravity xc7plus % of C7plus (C7+) - γg sp separator gas specific gravity in Rspd Separator producing gas condensate ratio above the dew point pressure ρc7 densityc7plus g/cc GCR G i γ STO Gas condensate ratio Original gas in-place The specific gravity of the stock tank oil psia scf/stb SCF/STB MMscf AGP The additional gas produced and related to the mass of the gas produced from the second separator and the stock tank. XIV

15 VEQ The equivalent volume; is the volume of second separator gas and stock-tank gas plus the volume in scf that would be occupied by a barrel of stock-tank liquid if it were gas. XV SCF/STB o API API stock tank oil gravity Mw o Molecular weight of the stock-tank liquid lb/lb. mole µ Viscosity co oil compressibility γg Gas specific gravity STB γo Oil specific gravity - ρr Reduced density - P System pressure psi P ci Critical pressure of component i, psi P d Dew point pressure psi P i Initial reservoir pressure psi P Pc Pseudo-critical pressure psi P Pr Pseudo-reduced pressure - cp psia -1 P wf Bottom hole flowing pressure psi Psp Separator Pressure, psia Mscf/D Tsp Separator temperature F R Instantaneous gas oil ratio scf/stb O oil density g/cc R s Solution gas oil ratio Mscf/STB R si Initial solution gas oil ratio Mscf/STB R v Vaporized oil gas ratio STB/Mscf R vi Initial vaporized oil gas ratio STB/Mscf viscosity of the gas at atmospheric pressure and cp 1: reservoir temperature a0-a15 coefficients of the equations are given in the tables - S o Oil saturation fraction S wi Initial water saturation fraction T System temperature R T b Boiling point temperature R T ci critical temperature of component i R

16 T f Formation temperature R T PC Pseudo-critical temperature R Ppr (Pr): pseudo-reduced pressure of the gas mixture - Mole fraction of carbon dioxide in reservoir fluid Fraction Z co 2 (gas plus liquid) phases Mole fraction of hydrogen sulfide in reservoir fluid Fraction Z H2S (gas plus liquid) phases Mole fraction of component i in reservoir fluid (gas Fraction Z i plus liquid) phases Mole fraction of component i in reservoir liquid Fraction X i phase Mole fraction of component i in reservoir liquid Fraction y i phase Z Single gas phase deviation factor - Z 2p Two phase Z factor - Z d gas deviation factor at dew point - Z i gas deviation factor at initial condition - γ g dry gas specific gravity γ w Wet gas specific gravity γ o Specific gravity of the stock-tank liquid Tpr (Tr): pseudo-reduced temperature of the gas mixture - μ g Gas viscosity cp ρ g Gas density lb/ft 3 IAWPS The International Association for The Properties of Water and Steam XVI

17 1. CHAPTER 1 INTRODUCTION Ideally, PVT properties are experimentally measured in the laboratory. When such direct measurements are not available, PVT correlations from the literature are often used. Fundamentally, there are two different types of correlations in literature. The first group of correlations is developed using randomly selected datasets. We would like to call such correlations generic correlations. The second group of correlations is developed using a certain geographical area or a certain types of oil. Correlations using randomly selected datasets may not be suitable for certain type of oils, or certain geographical areas. Even though the authors of the generic correlations want to cover a wide range of data.such correlations still work better for certain types of oils. Specialized correlations represent the properties of a certain type of oil or geographical area (for which they are developed) better than the general purpose correlations. The best source of oil property data is the laboratory PVT (pressure-volumetemperature) analysis of a reservoir fluid sample. However, in the absence of experimentally measured properties of reservoir fluids, these physical properties must be estimated from correlations. Many correlations for estimating crude oil PVT properties have been published in the past 50 years. Most of these correlations yield reasonably accurate results when applied at the original limitations. Here our work presents the details of the error statistics for each correlation. For comparison, error analyses were carried out for this study and for some of the more frequently used published correlations in the industry. We believe that the results obtained by using these correlations will improve the use of material balance calculations as well as the recovery efficiency of a reservoir. 1

18 A computer simulation program for oil PVT correlations model was written in a programming language to predict all the properties over a wide range of input data and also to provide the most appropriate correlation to be used for any reservoir data range based on the limitations of each correlation which has been mentioned in the literature with all database of limitations as briefly explained in chapter 4. In our work Chapter 1 gives a brief introduction about our crude oil, gas and water properties determination and how the correlation is useful in the petroleum literature. Chapter 2 is a literature review about the published correlations of oil, gas and water properties. In order to get reliable results of this work a special care is given to the limitations of the input parameters of each correlation. Chapter 3 presents the statement of the problem and objectives of the current study. Chapter 4 gives an overview about oil correlations and data range for the Egyptian PVT data and data bank ranges for each published correlation. Also, there are cross-plots between estimated and experimental properties. Results of reliability analysis were performed on Egyptian oil samples. Chapter 4 also presents gas correlations and how it is preferred for the petroleum science, where data range for the world wide above 119 PVT gas condensate samples are tested. Also, there are cross-plots between estimated and experimental properties of gas condensate properties. In chapter 4 water correlations are considered and how understanding of the properties of the produced water is very important in reducing the cost of handling the produced water and increase added value of the produced oil in addition to cost reduction. Chapter 5 explains in details the development process of the Expert System. Chapter 6 summarizes the results of reliability analysis performed on Egyptian oil samples and worldwide gas condensate samples. 2

19 Chapter 7 summarizes conclusion and recommendation of the evaluation studies of correlations. As more correlations are developed, the researchers evaluate the previously published correlations with the new ones. Others carried out studies to select the most accurate correlation for a particular reservoir in a geographic area. 3

20 2. CHAPTER 2 LITERATURE REVIEW In this chapter we present the most popular black oil correlations developed during the period from 1947 to The chapter provides the essential background required for the comparison and listed all ranges of the inputs according to the original condition of each correlation as published in the original paper. There have been a number of empirical correlations developed for medium and light crude oils. However, their applicability is limited to specific oils due to the complex formulation of the crude oils. Moreover, their applicability to heavy oils is very much in question. Egbogh 1 used the pour point as an additional input parameter for dead oil viscosity correlations.de Ghetto et al. 2 first defined the heavy oils in terms of o API gravity. Later, he divided the heavy oil into two groups: heavy oil(10 < o API <22.3)and extra heavy oil ( o API <10).Hossain and Sarica 3 mentioned that Lohrenz and Bray also used the crude oil chemical composition to develop an empirical correlation for oil viscosity. Standing 4,in 1947 used a total of 105 data points on 22 different crude oils from California to develop his correlations. Lasater 5, in 1958 presented a bubble point correlation using 158 measured bubble point data on 137 crude oils from Canada, Western and Mid-Continental United States and South America. Vasquez and Beggs 6,in 1989 developed correlations for the solution gas to oil ratio and formation volume factor using 600 laboratory PVT analysis. Glasso 7, in 1980 used data from 45 oil samples mostly from the North Sea region to develop his correlations. Al-Marhoun 8,in 1988 used 160 bubble point data on 69 Middle Eastern crude samples to develop a bubble point pressure correlation. Ahmed 9 used the combined reported data of Glasso and Marhoun to develop a correlation for determining the oil formation volume factor. 4