A numerical study of the pressure behavior of a vertical well in a dry gas reservoir

Predicting production performance of a dry gas reservoir for reservoir management acquires understanding the behavior of pressure transients and fluid distribution over both space and time. In recent years, reservoir simulators have been extensively used to build various reservoir and well models to investigate and visualize the process under a series of potential scenarios, such as drilling new wells and injecting fluids. The objective of this study is to develop and present applications of a general purpose two-dimensional (2D) r-z, fully implicit, single-phase, real gas simulation model with a single well located at the center of a cylindrical reservoir. The simulation model includes wellbore storage, skin and non-Darcy flow effects. As the problem is non-linear, solve pressures at each gridblock at a specific time may require more than one iteration. Since two different methods called as functional iteration and Newton’s methods are applicable to solve such systems, they are analyzed, verified using at least two different solvers with respect to accuracy and speed. The simulator is verified by a well-known well test analysis software to perform a number of real field applications such as standard and routine tests of natural gas industry (i.e., flow-afterflow, isochronal and modified isochronal tests) for both partially and fully penetrated wells either in a single or multilayered systems. The simulator is also capable of conducting a packer-probe test called as Mini-Drill Stem Test (MiniDST) for estimation of reservoir properties such as permeability, skin, etc. The effect of Non-Darcy flow on pressure solutions at the tested well as well as throughout the reservoir for the entire flow rate history is also investigated in a different manner than described in mathematical formulation such that the a non-Darcy flow area in radial direction is introduced and restricted to a region of a specific radius which is concentric with wellbore.