Abstract

The before closure analysis (BCA) method describes the unsteady flow of fracturing fluid into a formation considering time-dependent fracture face resistance. It provides a methodology for calculating the permeability and fracture face resistance instead of calculating the conventional leakoff coefficient. The original BCA model developed by Mayerhofer et al. (1995) has been simplified by different authors, including Valkó and Economides (1999). It is found that their proposed simplified formulation has some inconsistencies, which results in erroneous analysis of data and interpretation of permeability.

In this paper, the inconsistencies in the formulation have been addressed and resolved. The formulation of the corrected model is presented in a complete fashion. A discussion on sensitivity of the analysis, effect of pressure-dependent permeability, height recession, tip extension, and the effect of the reservoir fluid type is also provided. To validate the approach, two field examples of conventional oil reservoirs are presented as well. In the second case, the results are compared to the after closure analysis (ACA), and the effect of normal leakoff and pressure- dependent leakoff (PDL) on the BCA plot is discussed. The importance of considering correct data points in a normal leakoff portion is shown and illustrated on a BCA plot.

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