When hydraulic fracturing operations are conducted in thick reservoir sections, it is common for the perforated interval to be long but yet still significantly shorter than the distance between reliable barriers to fracture propagation. Under these circumstances the fracture shape will change continuously as it evolves from the perforated interval, thus complicating the interpretation of pressure decline data measured during prestimulation mini-frac tests.

This paper presents a pressure decline analysis which assumes the fracture to have evolved as a family of confocal ellipses, which thereby ensures a smooth transition between the simpler fixed geometries which correspond to the injection of either very small or very large volumes of fluid (KGD and penny, respectively). The analysis enables the fracture shape and dimensions to be estimated, together with the fracture fluid-loss coefficient. An example is given of the application of this method, and a comparison is made with values determined assuming simpler, fixed shape models. The influence of injected fluid volume is considered. A rapid method for determining the Nolte "match pressure", P*, is also described.

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