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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA minifrac test is usually performed before a fracture stimulation treatment to calculate formation and fracture properties. Recently the analysis techniques were extended to the after-closure period. The after-closure data are analyzed to calculate formation permeability and reservoir pressure.Technology developers have hypothesized the existence of either pseudo-radial or linear flow behavior during the afterclosure region. Identifying the presence of the flowing regime is an awkward process at best. The roots of the linear flow equations are different from those of the pseudo-radial flow equations. Many tests do not follow either flow regime.In this paper, we have created a general approach for analysis of after-closure pressure decline data. Because the determination of the flow regime and type of fracture depends only on time and monitored pressure, the analysis may even be performed in real time. The technique determines whether sufficient data have been obtained to perform a reliable analysis. The calculated parameters would be used to update the fracture design and, in turn, for performing the fracture treatment.The new technique is simpler and more generalized than what currently exists. The technique initially determines whether analyzable data exist. It shows that three flow regimes may dominate the after-closure region, depending on the reservoir properties and residual fracture conductivity. The technique presented not only determines the type of regime, and consequently, the type of residual fracture, it also determines the formation permeability and reservoir pressure.There is no reason to restrict the application of this test to minifrac test analysis. We believe the approach is also applicable to analysis of data after performing a fracture stimulation treatment. A numerical simulator was used to model the pumping and closure process and to validate the new approach.The paper also presents a detailed discussion and analysis of several field cases, demonstrating the various flow regimes and, ultimately, the validity of the developed technique.

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A magnetic float densimeter capable of measuring density over a wide range of values to within 5 ppm is described. The solenoid of the system consists of a few thousand turns of fine copper wire and the float has been provided with a quickfit joint to change its weight by the addition or subtraction of mercury from inside. There is a micrometer syringe assembly to vary the concentration of the solution. The whole densimetric assembly is placed in a thermostatic air bath. A fixed temperature of the air bath is maintained by a sensitive relay system and the exact temperature of the experimental liquid at the time of measurements can be checked and monitored with the help of a specially designed thermistor probe.