THE UNIVERSI TY OF ADELAIDE COUPLED FLUID FLOW-GEOMECHANICS SIMULATIONS APPLIED TO COMPACTION AND SUBSIDENCE ESTIMATION IN STRESS SENSITIVE & HETEROGENEOUS RESERVOIRS A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY by Ta Quoc Dung Australian School of Petroleum, South Australia 2007 ii Acknowledgements First of all, I would like to express my deep sense of gratitude to Dr. Suzanne Hunt for her principle supervision and important support throughout the duration of this PhD research. I am grateful to her not only for encouragement and guidance during academic years, but also for patience and help with regard to my English as well as spending time to understand me personally. I am also highly indebted to Prof. Pete r Behrenbruch for his constant direction through petroleum courses in the Australian school of Petroleum (ASP) and giving me guidance. His industrial experience contributes to my professional development. I would like to thank my supervisor Prof. Carlo Sansour for his exceptional guidance and inspiration. He led me into the fascinating world of theory of continuum mechanics. In addition, he introduced me to the other beauty in my life: Argentinean Tango. I also would like to take this opportunity to express my gratitude to all colleagues and administrators. Particularly, I would like to thank Do Huu Minh Triet, Jacques Sayers, Dr. Hussam Goda, Dr. Mans oor Alharthy, Son Pham Ngoc, Pamela Eccles and Vanessa Ngoc who have always been warm-hearted and helpful during the most challenging times of PhD life. Thanks go to all friends in the ASP who shared many hours of exciting soccer after working hours. Financial support for both academic and life expenses was provided by the Chapter 6: Determination of new relative permeability curve due to compaction and its impacts on reservoir performance 147 -10.5 -10 -9.5 -9 -8.5 -8 -7.5 0 5000 10000 15000 20000 25000 30000 Distance (ft) Compaction (ft) Figure 6-13: Compaction profiles 6.5 Conclusions The research here suggests that when th e reservoir formation is compacted, the compaction process can be briefly divided in to 2 stages: rearrangement of sand grains and sand-crushing. Based on the Carmen-Kozeny’s equation, a new method has been introduced which is used to determine new values of irreducible water saturation (S wir ) due to compaction, calculated at each stage as the reservoir is developed. The new endpoint value is then applicable for creating new relative permeability curves. Applying this methodology to a case study of a compaction reservoir in a Venezuelan field, it is shown that this method has more accurate applicability for coupled reservoir simulation particularly in investigation of reservoir performance and compaction prediction. Further it is shown that accounting for changes in irreducible water saturation, residual oil saturation, effective porosity, altered Conventional model Model taking account change of relative permeability curve Chapter 6: Determination of new relative permeability curve due to compaction and its impacts on reservoir performance 148 permeability and changes in relative permeability, all as a result of compaction, may be significant. In this way it is possi ble to better describe overall reservoir performance and petroleum recovery. In addition, the approach can be used to evaluate the extent of formation compaction and reservoir performance resulting from the variation of stress sensitive porosity/permeability. This research also shows that compaction can have an advantage partic ularly in reducing water production. The theory and practical methodologies developed in this chapter can be extended by applying to other case studies, where compaction and stress sensitivity dominate the drive mechanism. New distributions of n o and n w are determined using Monte Carlo simulation. Values of n o and n w are not only a function of S w but depend on S wir , φ as well as S or . The new range of values of n o and n w are established. Minimum and maximum of n o are 2.14 and 3.37. Minimum and maximum of n w are 2.29 and 3.32. Consequently, the new range resulting from Monte Carlo simulation provides the decision maker with a better range of possible scenarios thus allowing for more accurate decision- making.