Horizontal Well and Near-Well Region Simulation Using Coupled Axial-Radial Productivity Models
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Horizontal Well and Near-Well Region Simulation Using Coupled Axial-Radial Productivity Models by c Jie Cao A thesis submitted to the School of Graduate Studies in partial fulfillment of the requirements for the degree of Doctor of Philosophy Faculty of Engineering and Applied Science Memorial University of Newfoundland November 2016 St. John’s Newfoundland and Labrador Letter of Transmittal ii Abstract Directional drilling technologies have dramatically increased the application of advanced wells in reservoir development since the 1990s, including horizontal, deviated, multilateral and smart wells. The great demand for highly accurate and efficient well models arrives from the fact that drilling technology has outpaced simulation techniques. The well model, usu- ally coupled with the reservoir model, is crucial for productivity estimation and prediction. The main objectives of this research are to develop a well/near-well model and associated simulation techniques using coupled axial-radial productivity models for advanced wells. The analytical coupled axial-radial flow models were recently developed and described in research notes. These ideas originate from the observation that the axial reservoir pres- sure gradient cannot be ignored since pressure gradients exist in horizontal wellbores. The analytical models consider both axial reservoir flow and radial well inflow in the near-well reservoir, physically representing a two dimensional problem. These models were solved under both steady state and semi-steady state conditions, using external boundary pressure and average reservoir/grid block pressure, thereby generating the coupled axial-radial pro- ductivity (CARP) models. The main focus in this work is to apply the CARP models in the construction of a numerical scheme for horizontal well and near-well region simulation (i.e. the well/near-well model), in which wellbore hydraulics are included. In steady state and semi steady state flow, the pressure solutions are analytical in each grid block and result in curved surfaces of near-well iii reservoir pressure, contrary to the constant pressure distribution used in the finite differ- ence method. Hence, the new numerical scheme is demonstrated, and proved in the steady state case, to be a higher order method than the standard finite difference method. The simulation results show that the new method requires less grid block refinement to achieve the same accuracy compared to the finite difference method. The CPU time needed for the same grid blocks to achieve the same accuracy is greatly reduced using the new method compared to the finite difference method. This reduces the need for grid block refinement in the near-well region. Furthermore, the numerical well/near-well models are applied in heterogeneous reservoirs and special cases where cross flow occurs. Wide permeability ranges can be dealt with in these models in a stable manner without special treatment. Both the axial and radial flow directions are solved as unknowns in these models; hence the cross flow between the well and the near-well reservoir can be represented. Besides, the new well/near-well model can be coupled with standard finite difference reservoir simulators such that both the well completion effects and remote reservoir effects are taken into consideration. An iterative coupling scheme is used in this research, and calculated examples considering unevenly dis- tributed skin factors also demonstrate the application of the new well/near-well model and the stability of the coupling scheme. The well/near-well model is also developed for anisotropic reservoirs using average reservoir pressure. Based on previous research notes, this is achieved through a permeability tensor used for axial reservoir flow and well inflow equations. This permeability tensor is generated using a unique transformation that converts the anisotropic media into a virtually equivalent isotropic media in the axial and radial directions. This transformation is only applied in the near-well region without changing boundary conditions, and it preserves volume, flow rates and pressure. The cylindrical near-well region is transformed into elliptical cylinders; consequently, Dietz shape factors for ellipses are used in productivity models. iv Acknowledgements I feel that it is a great privilege to have pursued a Ph.D degree at Memorial University, as well as having been involved in a very interesting research topic. It is also a great city of St. John’s that I enjoyed living in just like in my hometown. I sincerely thank my research co-supervisors, Dr. Thormod Johansen and Dr. Lesley James for their elaborate guidance, thoughtful help and financial support. You are my source of knowledge and power, without which I cannot make the progress enjoyable. I would also like to express my appreciation to my colleges in the Hibernia EOR group, whom I feel inspiring to work with. Thanks to Norah for helping me to revise all kinds of materials I wrote. Thanks also goes to the EOR lab engineers and researchers, and graduate office of Faculty of Engineering and Applied Science for the help of all kinds. I would also like to express my most appreciation to my wife Nan Zhang, for being on the roller coaster of my life no matter up or down. Thanks to my parents and older sister for their consistent love and support, which is beyond my word to express. v Table of Contents Letter of Transmittal ii Abstract iii Acknowledgments v Table of Contents ix List of Tables x List of Figures xv List of Nomenclature xvi 1 Introduction and Overview 1 1.1 Background . 1 1.2 Objectives and methodology outline . 4 1.3 Co-authorship Statement . 10 2 Literature Review 11 2.1 Horizontal/Advanced well modeling . 11 2.1.1 Horizontal well productivity models . 11 2.1.2 Pressure losses within the well . 15 2.1.3 Methods to couple the well model to the reservoir model . 18 2.2 Near-well region modeling . 22 vi 2.2.1 Grid system for the near-well region . 22 2.2.2 Flow performance in the near-well region . 25 3 Coupled Axial-Radial Productivity Model for Horizontal Wells in Steady State Flow 32 3.1 Overview . 32 3.2 Introduction . 33 3.3 Methodology . 34 3.3.1 Coupled axial-radial flow model . 34 3.3.2 Classical radial and axial flow models . 39 3.4 Results and analysis . 40 3.4.1 Calculated examples on axial and radial flow . 40 3.4.2 Pressure distribution in multi-segment wells . 42 3.4.3 Axial and radial flow ratio . 45 3.5 Conclusions . 51 4 High-Order Numerical Simulation Methods for Well/Near-Well Modeling using Coupled Axial-Radial Productivity Model 53 4.1 Overview . 53 4.2 Introduction . 54 4.3 Methodology of the well/near-well numerical model . 57 4.4 Cases study and analysis . 60 4.4.1 Real solution approximation . 61 4.4.2 Pressure and flow rates profiles . 62 4.4.3 Accuracy and efficiency . 63 4.5 Further applications . 70 4.5.1 Coupling Well/Near-Well Model and Reservoir Model . 70 4.5.2 Application to heterogeneous reservoirs . 75 4.5.3 Application to various external reservoir pressure distributions . 82 vii 4.5.4 Application to coupling with reservoir simulation . 87 4.6 Conclusion . 95 Appendix 4-A . 96 5 Semi-Steady State Flow Solution to Coupled Axial-Radial Productivity Model and Its Numerical Application 100 5.1 Overview . 100 5.2 Introduction . 101 5.3 Analytical solution to the coupled axial-radial productivity model . 106 5.3.1 General solution using external reservoir pressure . 106 5.3.2 General solution using average reservoir pressure . 110 5.3.3 Special cases: classical productivity models . 111 5.3.3.1 Pure radial flow . 111 5.3.3.2 Pure axial flow . 112 5.3.3.3 Radial flow with average reservoir pressure . 112 5.4 Solution to coupled axial-radial flow model in anisotropic media . 113 5.5 Application of coupled axial-radial productivity model . 115 5.5.1 Calculation example in single segment case . 115 5.5.2 Implementation in multi-segment case . 115 5.6 Numerical model for horizontal well and near-well region . 119 5.6.1 Flow performance in the near-well region . 119 5.6.2 Flow in the horizontal well . 120 5.7 Results and analysis . 121 5.7.1 Pressure distributions . 121 5.7.2 Flow rates . 123 5.7.3 Calculation efficiency . 124 5.8 Conclusions . 128 Appendix 5-A . 128 Appendix 5-B . 129 viii Appendix 5-C . 129 6 Modeling Horizontal Well and Near-Well Flow Performance in Anisotropic Media 134 6.1 Overview . 134 6.1.1 Preface . 134 6.1.2 Introduction . 135 6.2 Methodology of the near-well/well numerical model . 138 6.2.1 Coupled axial-radial Flow model in the near-well region . 138 6.2.2 Application of Dietz shape factor in near-well reservoir blocks . 141 6.2.3 The well/near-well numerical model . 144 6.3 Calculated Examples . 146 6.4 Conclusions . 149 Appendix 6-A . 156 7 Conclusions 163 7.1 Summary . 163 7.2 Further Work . 165 Bibliography 167 Appendixes 175 Appendix A . 175 Appendix B . 196 ix List of Tables 3.1 Parameters for calculation examples . 40 3.2 Basic parameters for multi-segment case . 44 3.3 Results from each iteration step . 45 4.1 Parameters for calculation examples . 61 4.2 Parameters used in the heterogeneous examples Ex. K-1, K-2 and K-3 . 75 4.3 Parameters used in the coupling examples, Ex. S-1 and S-2 . 88 5.1 Basic parameters for single segment case . 115 5.2 Basic parameters for multi-segment case . 117 5.3 Results from each iteration step at time t1 . 118 5.4 Basic parameters used in calculation .