In this paper authors present pressure decline analysis after injection tests using diagnostic plots with focus on events that occur before the fracture closure (PCA). The main feature of used method is that analysis is performed by identifying mistakes during interpretation that can disrupt pressure decline curve. The essential instrument of interpretation in our method is Log-Log plot. Some effects which were earlier relating to "nonideal behavior" are removed from the analysis as they are not result of work of a reservoir – fracture system, but mistakenly interpreted factors. The last is made by standardizing of Log-Log plot to a "normal" form at the dominating in time period of the linear flow in a fracture. GdP/dG plot is referential instrument whereby fracture closure pressure can be determined in small point vicinities explicit in Log-Log plot.

This paper discusses the existing methods of fracturing parameters determination, the analysis of completeness and clarity of these methods is carried out. Approaches to interpretation of J-shaped curves of pressure decline and the most probable causes of such behavior of pressure were discussed in the context of "nonideal behavior" in many papers. According to our method, Interpretation of pressure decline should at first been carried out according to "ideal behavior". Interpretation of S-shaped curves of pressure decline can be also carried out in the context of "ideal behavior", and leads, according to this paper authors, to correct assessment of efficiency and net pressure in fracture.

Paper is aimed at presenting of practical actions of the engineer in pressure decline analysis in low-permeable reservoirs. In this case, fracture can have the sufficient sizes to observation allowing to identify on Log-Log plot the characteristic flow states. This factor causes limits of applicability of the offered method. Definition of application, requires carrying out the analysis of statistics on fields, including the analysis as behavior of pressure decline after injection tests, so and production performance.

Described method was applied on field in Western Siberia. Occurred production problems were the cause to start investigation of pressure decline analysis methods.

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