Pressure Transient Analysis and Simulation of Nonconventional Wells

Nowadays nonconventional wells (horizontal, multilateral, Rad Tech and others) are being extensively drilled throughout the world for the development of low-profit fields. Construction of these wells enables to reduce filtration resistivity resulting in productivity index increase and costs reduction. To select the optimal well design with regard to reservoir characteristics, effective well operation and determination of filtration characteristics one should possess calculation methods for steady and unsteady liquid flow in reservoir. Few related papers have been published so far. However analytical methods for steady flowing are suitable for homogeneous beds with simple geometry and equal length laterals. Available approaches for description of pressure build up allow to account for various lateral trajectories but FEA or semi-analytical decisions methods are too labor-intensive for practical application. Commercial program for interpretation of pressure build up is lacking. Therefore simple methods of productivity index determination and pressure transient test interpretation are suggested for nonconventional wells. These methods are suitable for low thickness beds. The basis of these methods is the superposition of filtration resistivity for two plane problems. Trajectory of laterals is simulated as a number of closely spaced vertical wells or nodes. The suggested method allows determining the field of application and regularities for nonconventional wells. Dimensionless fluid-movement profile calculated from steady fluid flow and a superposition method for pressure builds up in the nodes are used for determination of pressure build up. For description of build up in a node we recommend a diffusion equation in Laplace space and Stephest numerical algorithm. The problem is solved for porous and porous-fractured reservoirs. Numerical calculations show that cross-flows occur after the horizontal or multilateral well shut-down. Pressure derivative maximum testifies to low effective length of the borehole or positive skin-effect. Knowledge of effective intervals length is critical to pressure curve interpretation.