Gas reservoir engineering is the branch of reservoir engineering that deals exclusively with reservoirs of non-associated gas. The prime purpose of reservoir engineering is the formulation of development and production plans that will result in maximum recovery for a given set of economic, environmental and technical constraints. This is not a one-time activity but needs continual updating throughout the production life of a reservoir. The objective of this book is to bring together the fundamentals of gas reservoir engineering in a coherent and systematic manner. It is intended both for students who are new to the subject and practitioners, who may use this book as a reference and refresher. Each chapter can be read independently of the others and includes several, completely worked exercises. These exercises are an integral part of the book; they not only illustrate the theory but also show how to apply the theory to practical problems. Chapters 2, 3 and 4 are concerned with the basic physical properties of reservoirs and natural gas fluids, insofar as of relevance to gas reservoir engineering.
1. Introduction. Natural gas. Gas reservoir engineering. Objective and organization. Units and symbols. 2. Reservoir properties. Introduction. Rock types. Porosity. Viscous flow resistance. Inertial flow resistance. Rock compressibility. Capillary pressure. Relative permeability. 3. Gas properties. Introduction. Composition. Phase behaviour. Real-gas law. Z-factor. Compressibility. Condensate/gas ratio. Formation-volume factor. Viscosity. 4. Phase behaviour. Introduction. K-value method. Equation-of-state method. Laboratory experiments. Multistage separation. 5. Recoverable reserves. Introduction. Bulk volume. Pore volume. Hydrocarbon pore volume. Gas and condensate initially-in-place. Recoverable reserves. Uncertainty. 6. Material balance. Introduction. Wet-gas reservoirs. Gas-condensate reservoirs. Non-volumetric depletion. Aquifer influx. 7. Single-phase gas flow. Introduction. Steady-state Darcy flow. Steady-state radial flow. Non-Darcy flow. Transient flow. Linear flow - constant terminal rate. Linear flow - constant terminal pressure. Radial flow - Constant terminal rate. Non-radial flow. 8. Gaswell testing. Introduction. Backpressure equations. Flow-after-flow tests. Isochronal and modified isochronal tests. Transient well-pressure equations. Drawdown tests. Buildup tests. Multiple-rate transient tests. Example of multiple-rate transient test analysis. 9. Wellbore flow mechanics. Introduction. Single-phase flow equations. Pressure distribution in shut-in wells. Rate-dependent pressure losses. Pressure distribution in producing wells. Multi-phase flow. Minimum unloading rate. 10. Water coning. Introduction. Dupuit critical production rate. Schols critical production rate. Cone breakthrough. Water/gas ratio. 11. Natural depletion. Introduction. Development chronology. Reservoir performance. Well-inflow performance. Tubing-flow performance. Well deliverability. Depletion simulator. 12. Gas injection. Introduction. Injection-well performance. Microscopic mixing. Viscous fingering. Gravity overlay. Stratification. Well Pattern. Pattern-flood model. Appendices. Units and conversion factors. Physical and mathematical constants. Physical properties natural-gas components. Author index. Subject index.