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Fracture-calibration pressure decline has been used for determination of the leakoff coefficient, a bulk variable describing the process of fluid influx into the reservoir, normal to the created fracture face. In this work, the fluid loss is modeled in terms of the controlling mechanisms: flow through the filter cake, the invaded zone, and the reservoir. A rigorous model describes unsteady-state fluid flow from fractures of varying area into the formation, with the filter cake considered as a time-and rate-dependent skin effect. The injection history is superposed on the pressure decline. This work provides a straight-line technique for determination of reservoir permeability and fracture-face resistance. Log-log diagnostic plots provide the means to recognize visually whether the transient response is dominated by flow in the reservoir or at the fracture face. We found that the pressure transient very frequently is dominated by the flow in the reservoir rather than through the filter cake. The reservoir permeability (an essential value for fracture design that is usually not available) can be estimated, while the model captures all trends of the falloff-pressure variation.

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Evidence suggests that certain vibrations, generated either by natural seismic events or by artificial explosions, have altered the production behavior of oil wells at distances as much as 200 km from the epicenter. These changes have affected the produced water/oil ratio: the water production rate increased from a formation that was at approximately the interstitial water saturation, while the oil rate increased in watered-out reservoirs that were near the residual oil saturation.Theoretical and field investigations of the phenomena suggest that vibrations may influence substantially the water or oil relative permeability that appears to be partially reconstituted at saturations that ordinarily would prohibit the flow of a particular phase. The key role is played by ultrasound oscillations, generated by seismic waves within the stratum, and it has been confirmed by in-situ measurements during the vibrostimulation of reservoirs.This paper provides an interpretation of the process and describes wave requirements, wave generation, and propagation in oil-bearing porous media supported by laboratory experiments and field cases of vibrostimulation of oil production from water-flooded reservoirs.

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