Analytical Estimation of Pressure Delay Time in Observation Wells During Pulse Testing of Formations
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Journal of Engineering Physics and Thermophysics, Vol. 93, No. 5, September, 2020
ANALYTICAL ESTIMATION OF PRESSURE DELAY TIME IN OBSERVATION WELLS DURING PULSE TESTING OF FORMATIONS A. M. Svalov
UDC 622.276
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. Keywords: formation pulse testing, formation parameters, observation well, delay time, formation pressure. In hydrodynamic investigations of wells, wide use is made of the method of formation pulse testing under which the regime of fluid withdrawal and pump down in an active well is changed in a certain way, and in a listening (observation) well, either the level of the fluid in the well shaft or, which is equivalent, the change of pressure at its bottom is registered. A comparison of the registered pressure curves with the analytical dependences describing the process of propagation of the filtration disturbance from the active well across the formation makes it possible to determine the formation parameters. Furthermore, it is important to note that the pressure value in the observation well follows the variation of the formation pressure in the vicinity of this well with some delay due to the process of filtration mass transfer between its shaft and wellbore area. In this paper, we present an analytical estimation of the pressure delay time at the bottom hole of an observation well in the case of change in formation pressure, which makes it possible to restore more correctly the real dependence of formation pressure on time and, accordingly, to raise the accuracy of determining the formation parameters in its pulse testing. To distribute the formation pressure P0(r, t) while launching an active well at the moment of ti
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