NTNU – Norwegian University of Science and Technology Department of Petroleum Engineering and Applied Geophysics __________________________________ CO2 as Injection Gas for Enhanced Oil Recovery and Estimation of the Potential on the Norwegian Continental Shelf by Odd Magne Mathiassen Chief Reservoir Engineer Norwegian Petroleum Directorate Trondheim / Stavanger, May 2003 ________________________________ Part I of II CO2 injection for Enhanced Oil Recovery 2 ___________________________________________________________________________ ACKNOWLEDGEMENT I would like to thank my supervisor Professor Ole Torsæter at the Norwegian University of Science and Technology for excellent guiding and help in my work with this thesis. I would also like to thank my employer, the Norwegian Petroleum Directorate, for giving me the opportunity and time to complete the thesis. My thanks also go to my colleagues Mr. Gunnar Einang, Mr. Søren Davidsen and Mr. Jan Bygdevoll for valuable discussions while working with this thesis. Finally, I would like to thank Dr. Eric Lindeberg and senior researcher Idar Akervoll at the Sintef Research for valuable information on CO2 related issues. SUMMARY The main objective of this thesis is to investigate the possibility of using CO2 as injection gas for enhanced oil recovery and estimate the potential of additional oil recovery from mature oil fields on the Norwegian Continental Shelf (NCS). Because of the lack of CO2 data from offshore oil fields, a literature study on CO2 flood experience worldwide was undertaken. In addition, the physical properties of CO2 and CO2 as a solvent have been studied. The literature study makes it possible to conclude that CO2 has been an excellent solvent for enhanced oil recovery from onshore oil fields, especially in the USA and Canada. Almost 30 years of experience and more than 80 CO2 projects show that the additional recovery is in the region of 7 to 15 % of the oil initially in place. The estimation is based on specific field data for all fields and reservoirs included in the thesis. CO2 data are limited to studies and reservoir simulations from Forties, Ekofisk, Brage and Gullfaks. Since Forties is a UK oil field, most of the data used are from the three Norwegian oil fields. This thesis includes all oilfields currently in production. Fields under development, fields with approved plan for development and operation (PDO), or discoveries under evaluation are not included. However, they may have potential for use of CO2 in the future. The candidates are screened according to their capability of being CO2 flooded, based on current industry experience and miscibility calculations. Then a model based on the most critical parameters is developed. Finally, risk analysis and Monte Carlo simulations are run to estimate the total potential. Applying the model developed and compensating for uncertainties, the additional recovery is estimated between 240 and 320 million Sm3 of oil. This potential constitutes large increases in oil production from the Norwegian Continental Shelf if CO2 can be made available at competitive prices. For some of the time critical fields, immediate action is called upon, but for the majority of the fields dealt with in this thesis, CO2 injection can be postponed 5 years or more. CO2 injection for Enhanced Oil Recovery 3 ___________________________________________________________________________ TABLE OF CONTENTS ACKNOWLEDGEMENT ......................................................................................................... 2 SUMMARY ............................................................................................................................... 2 TABLE OF CONTENTS........................................................................................................... 3 1. INTRODUCTION.............................................................................................................. 5 2. THE PHYSICAL PROPERTIES OF CO2 ......................................................................... 6 2.1 Phase transitions and phase diagram for CO2 ........................................................ 9 2.1.1 Phase equilibrium............................................................................................... 9 2.1.2 The Clausius - Clapeyron equation .................................................................. 10 2.1.3 Solid - Liquid Equilibrium ............................................................................... 10 2.1.4 Solid – Vapour Equilibrium ............................................................................. 11 2.1.5 Liquid - Vapour Equilibrium............................................................................ 12 2.1.6 Phase diagram calculated from the derived equations ..................................... 12 2.2 CO2 - rock and fluid interactions.............................................................................. 13 2.2.1 PVT conditions................................................................................................. 13 2.2.2 CO2 hydrates..................................................................................................... 13 2.2.3 Wettability........................................................................................................ 13 2.2.4 Scale ................................................................................................................. 14 2.3 Injectivity abnormalities........................................................................................... 14 2.3.1 Injectivity increases.......................................................................................... 14 2.3.2 Injectivity reduction ......................................................................................... 15 2.3.3 Entrapment ....................................................................................................... 15 2.3.4 Relative permeability ....................................................................................... 15 2.3.5 Heterogeneity ................................................................................................... 16 2.3.6 Concluding remarks on injectivity abnormalities ............................................ 16 2.4 Advantages and disadvantages by using CO2 as a solvent in miscible floods......... 17 2.4.1 Advantages....................................................................................................... 17 2.4.2 Disadvantages................................................................................................... 17 3. ENHANCED OIL RECOVERY...................................................................................... 18 4. ENHANCED OIL RECOVERY BY MISCIBLE GAS/CO2 FLOODING..................... 20 4.1 Miscibility and drive mechanism ............................................................................. 20 4.2 First contact miscible flooding................................................................................. 20 4.3 Multiple contact miscible flooding .......................................................................... 21 4.3.1 Vaporizing gas drive ........................................................................................ 21 4.3.2 Condensing gas drive ....................................................................................... 22 4.3.3 Combined vaporizing and condensing mechanism.......................................... 23 4.4 Minimum miscible pressure from slimtube miscibility apparatus........................... 23 4.5 Some remarks on the MMP and the calculation of the MMP.................................. 25 5 SUMMARY OF CO2 FLOOD PROJECTS WORLDWIDE........................................... 26 5.1 The Permian Basin ................................................................................................... 27 5.1.1 The SACROC Unit in the Permian Basin ........................................................ 28 5.1.2 SACROC CO2 project, key parameters............................................................ 30 5.2 The Weyburn Oil field in Canada ............................................................................ 30 5.2.1 Weyburn oil field, key parameters ................................................................... 34 5.2.2 The Weyburn CO2 Monitoring Project ............................................................ 34 5.3 EOR projects in the US and the role of CO2 floods................................................. 35 5.4 CO2 availability and prices in US and Canada......................................................... 37 5.4.1 CO2 sources...................................................................................................... 37 CO2 injection for Enhanced Oil Recovery 4 ___________________________________________________________________________ 5.4.2 CO2 pipelines.................................................................................................... 38 5.4.3 CO2 prices ........................................................................................................ 39 5.5 US and Canadian CO2 screening criteria ................................................................. 40 5.6 Experience gained from CO2 floods in US and Canada........................................... 41 5.7 Discussing ................................................................................................................ 41 6. NORTH SEA CO2 STUDIES .........................................................................................