Modeling of well productivity in perforated completions using near-wellbore grid generation

Well productivity is the major factor which determines the economic outcome of a well. It depends on the degree of communication between the wellbore and the producing formation. Most oil and gas wells in the petroleum industry today are completed with a steel casing and cement to control the water influx and production from different zones. In these wells the communication with the formation is re-established through perforations which are created by firing shaped charges.; The productivity of the resulting completion depends on design variables like shot density, penetration depth and phasing angle. Previous attempts to calculate productivity suffer from built in assumptions that require cylindrical symmetry in the reservoir and equal penetration depths for all perforations. This makes the models difficult to interpret in practical situations and inapplicable to horizontal wells in thin production intervals.; An improved numerical model has been developed in this study to estimate the productivity of a perforated completion as a function of various perforating parameters. The three-dimensional single phase transient flow simulator has been developed using the finite-difference technique. Unequal penetration depth, arbitrary phasing angle and shot density can be specified to form the perforated completion around the wellbore using the flexible algebraic grid generation technique. Equal penetration model results were confirmed for shot densities less than six shots per foot. Productivity ratio values for anisotropic cases resulted in much lower than the results of the existing model. The performance of unequally perforated completions revealed not a significant difference from equal penetration productivity ratio when plotted as a function of perforation length.; The generated near-wellbore grid was coupled to a coarse-block reservoir simulator to test different perforating designs depending on the relative location of the wellbore. The coupled model was also used as an improved well inflow modeling tool in reservoir simulation applications. Its performance was compared against the standard Peaceman's well modeling approach.