This paper presents a simple, practical approach to calculating postfrac productivity for indirect vertical fracture completion (IVFC) wells. The case envisioned is one where the main pay is not adjacent to perforations; with wellbore-to-pay communication being created via a wide propped vertical fracture. Such a fracture generally involves tip screenout type treatment designs, though that is not a subject of this paper.

Previous publications1,2  presented a case history of limiting perforations in a well to competent, lower permeability rock, and creating a propped fracture to communicate with weaker, higher permeability pay. An IVFC well in this formation served two goals: 1) to avoid need for gravel packing or other sand control measures required when the main pay is perforated, and 2) to maximize production from lower permeability pay sections, thus delaying water breakthrough (WBT) and increasing total reserve recovery. As part of that case history, a brief calculation scheme was proposed for predicting post-frac PI.

This paper discusses details of this calculation procedure, which is presented in a more general (partly dimension- less) form. Examples of predicted PI using these calculations are presented for several field cases where complex fracture completions of this type are being considered and implemented. In addition, accuracy of the simple, analytical calculations are tested against 3-D reservoir modeling. Results of the numerical modeling generally verify the simple procedure, but also place some limits on where / when analytical calculations should be used. The 3-D model is then used to consider possible impacts of turbulent flow and other parameters not included in the analytical calculation. Turbulent flow in the fracture was found to be a significant factor, even for single phase flow of oil.

Finally, predicted PI is compared to field measured post- frac results for several cases. Many field cases show unmistakable indications of turbulent flow, making it clear this factor must be considered in design of such completions.

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