Modeling of Well Productivity in Perforated Completions

Abstract

Abstract 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 communication with the formation is re-established through perforations, usually 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 in perforated completions 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. This paper describes an improved numerical model to estimate the productivity of a perforated completion as a function of these perforating parameters. Unequal penetration depth, arbitrary phasing angle and shot density can be specified using a flexible algebraic grid generation technique. The near-wellbore grid is also coupled to a coarse-block reservoir simulator which allows different perforating designs to be exercised depending on the relative location of the wellbore (horizontal or vertical) with respect to the reservoir boundaries. The model demonstrated a good agreement with the existing models for equal penetration cases. Not a significant difference was observed in the productivity results of unequal penetration cases compared to equal penetration productivity results. Anisotropic runs showed lower productivity ratios compared to the existing models. The near-wellbore productivity model coupled with a reservoir simulator is a very useful tool for designing perforating jobs in thin formations with horizontal and slanted wells. P. 109