Analytical Estimation of Pressure Delay Time in Observation Wells During Pulse Testing of Formations

In using the method of pulse testing of formations, a pressure pulse is generated in an active well by changing the regime of its operation; the pulse propagates across the formation and is registered in an observation well. Based on the results of processing the obtained dependence of pressure in the well shaft on time equated with formation pressure dependence on time at the point of location of the observation well, the formation parameters are determined by comparison with certain analytical relations. It is taken into consideration that the pressure in the well shaft of the observation well follows the variation of the formation pressure in the vicinity of the observation well with some delay due to the processes of filtration mass transfer of liquid between the well shaft and its wellbore area. Mathematical analysis of this mass transfer process presented in this paper shows that the delay time may be 4–5 h or more, depending on the parameters of the formation and formation fluid, which determines the marked difference between the curves of the pressure in the shaft of the observation well and the formation pressure. In this investigation, we obtained an analytical expression of delay time making it possible to correctly reproduce the dependence of formation pressure on time and, accordingly, to raise the reliability of data from the analysis of the results of formation pulse testing.