Uncertainties in design considerations are usually attributed to unknown data in new wells, or unknown conditions from using the wrong model of calculation. This issue is exacerbated in extended, undulated horizontal wells, drilled in high productivity formations, with multiphase flow and experiencing transient flow, where the drilled wellbore is assumed fully contributing to flow while it is not. In addition, well productivity along the producing section will change with the onset of water or gas production. Additionally, multiphase flow through artificial lift systems, like ESP's, have been a challenge.

This paper presents analytical solutions for calculating the productivity index of extended reach wells lifted with electric submersible pumps. In addition, it presents examples of design tolerance calculations of artificial lifting in high productivity horizontal wells with lower productivity indices than expected. In furthermore, it manifests the compounded effect of inherent errors in classical pressure traverse calculations typically used to design artificial lifting. More importantly, it quantity the amount of performance degradation attributed to the wrong design attributes/calculations, and shows how much tolerance available before premature failures occur. Calculations show that inaccurate well productivity data for wells, that are assumed highly productive, could make pumps fail to design incompatibility and make pumps run beyond efficient envelope.

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