Interference And Pulse Testing In Uniformly Fractured Reservoirs
Authors: Najurieta Humberto L. 
Published: December 2007

Introduction

Interference tests are one of the most valuable techniques to analyze reservoirs. Due to its characteristics, it is the only procedure that can measure transmissivity (T = kh/mu) and storage values (S = phi ch) among wells and provide, moreover, information about the anisotropy of the productive formation.

The technique consists of the generation of pressure signals in the reservoir by opening and pressure signals in the reservoir by opening and closing a well. The signals spread through the field and are measured in other wells. The analysis of these pressure signals provides information about the dynamic and productive characteristics of the reservoir.

The disturbance produced by the production changes propagates through the reservoir and can be measured in other wells of the reservoir with highly sensitive instruments. The shape of the measured curve depends mainly on the transmissivity and on the reservoir storage in the area affected by the pressure pulse. pulse. Fig. 1 shows the pressure signal that is measured in the observation well due to the changes in flow rate produced in the pulsing well.

At a first approach, we can consider the field as homogeneous, isotropous, and of constant thickness in the tested area. We also can suppose that the reservoir limits are far enough that they do not affect the pulse propagation. Hence, the pressure pulse is described mathematically by the solution of pulse is described mathematically by the solution of the differential equation:

............…(1)

where Delta p is the pressure signal measured in the observation well, and eta is the diffusivity of the reservoir:

.............(2)

The simplest case presented is that of the signal produced by closing the pulsing well; in that case, produced by closing the pulsing well; in that case, the solution of Eq. 1 with the corresponding boundary and initial conditions is

.............(3)

The analysis of interference tests consists of finding a pair of values of T and q (or T and 3) so that Eq. describes in the most accurate way the experimentally measured curve. then the pressure pulses are generated by a succession of flow pulses are generated by a succession of flow changes, it is necessary to use more complex expressions than Eq. 3, obtained by applying the superposition principle. Different analysis techniques have been developed for the interpretation of interference tests in homogeneous and isotropous reservoirs. There also exist techniques that allow the determination of the anisotropy of the reservoir, thus enabling the detection of preferential orientations of transmissivity.

In the last years, successful applications have been carried out in secondary recovery projects to study waterflooding and to detect tight projects to study waterflooding and to detect tight barriers.

The availability of highly sensitive electronic pressure gauges has allowed the extension of the pressure gauges has allowed the extension of the application fields of interference tests, being these techniques in an increasing stage of application.

Some papers on the application of these techniques in naturally fractured reservoirs have been published. The Warren and Root theory was extended by Kazemi et al. to interference tests. Gringarten also has presented a set of carefully conducted field tests and proposes the use of the heterogeneous equivalent concept in interference tests interpretation.