Design and Analysis of Pulse Tests With Unequal Pulse and Shut-In Periods

Abstract

Introduction Pulse testing is a relatively new well-testing procedure Pulse testing is a relatively new well-testing procedure in which a series of flow disturbances is generated at one well (the pulsing well) and the pressure is recorded in another well (the responding well), The flow disturbances at the pulsing well are generated by alternate periods of flow and shut in (or injection and shut in). At periods of flow and shut in (or injection and shut in). At the responding well, a sensitive differential pressure gauge records the pressure response and, consequently, the response amplitudes. The response amplitude (Fig. 1) is the pressure increment between the tangent to two consecutive valleys and the parallel tangent at the peak between them, or the pressure increment between the tangent to two consecutive peaks and the parallel tangent at the valley between them. The elapsed time between the end of a certain period and the point of tangency is called the time lag.The advantages of pulse tests are that the pressure response from a pulse test can be distinguished easily from other trends in the reservoir pressure and the pulse-test values are sensitive to the formation pulse-test values are sensitive to the formation properties between the two wells used in the test. properties between the two wells used in the test. The effects of different factors on the response of pulse tests have been reported. Studies have shown pulse tests have been reported. Studies have shown the response of pulse testing for a wide range of reservoir properties, when areal heterogeneities exist and for a two-zone reservoir. However, none of these papers supply enough information for an engineer to papers supply enough information for an engineer to design and analyze a pulse test. Only one paper shows how to design and analyze a pulse test; and even this paper is limited because it can be used only when the paper is limited because it can be used only when the pulse and the shut-in periods are equal, and it assumes pulse and the shut-in periods are equal, and it assumes that all the time lags are equal.In this paper, a graphical method and an analytical method that can be used to design and analyze pulse tests with unequal pulse and shut-in periods are presented. These methods allow the engineer to design presented. These methods allow the engineer to design and analyze pulse tests simply and accurately. These methods will enable the use of pulse tests without limitations on the length of the different periods. Thus, the optimum ratio between the pulse and shut-in periods that gives the maximum pulse-test response can be used. Theoretical Background To design and analyze any well test is simply to relate the test parameters to the reservoir and well properties. In the case of pulse testing, the test parameters are the pulse period, the shut-in period, the time lags, and pulse period, the shut-in period, the time lags, and the response amplitude. The reservoir properties are the formation permeability, porosity and thickness, the fluid viscosity, the total compressibility, and the distance between the pulsing and the responding wells.The reservoir properties and the test parameters can be used to define the following dimensionless groups. Pulse Ratio: Pulse Ratio:pulse periodR' =pulse period + shut-in period = = ..........(1) Dimensionless Cycle Period: = ....................(2) JPT P. 205