ABSTRACT:

The conventional interpretation methods in determining fracture transmissivity always assume a certain flow geometry through the fracture. For a natural fracture, the actual flow path (and associated flow volume) is unknown. In this paper, we introduce a new interpretation technique for analysis of transient responses of a flow test. With this technique it is possible to derive fracture transmissivity as well as the change in flow geometry away from the well. No a priori assumption of flow geometry in a fracture is assumed, but the rate of growth of the flow volume is derived as an output of the analysis. Synthetic hydraulic tests on the computer generated fractures have been conducted to demonstrate the application of this novel technique.

RESUME:

Les methodes de l'interpretation conventionnelles à determiner transmissivite de la fracture suppose toujours ecoulement un sûr geometric à travers la fracture. Pour une fracture naturelle l'ecoulernent trajectoire actuele (et associe volume)est inconnu. Dans ce papier nous introduisons une nouvelle technique d'interpretation pour analyser les reponses transitoires d'un test d'ecoulernent. Avec cette technique il est possible d'etablir la transmissivite de la fracture ainsi que la geometrie d'ecoulement à distance du forage (puits). Sans une presomption d'ecoulement geometrie dans une fracture suppose, mais Ie taux d'augmentation du volume du courant est derive comme une production de l'anaIyse. Épreuves synthetiques hydrauliques sur l'ordinateur qui ont produit des fractures a ete conduit pour demontrer I'application de cette technique.

ZUSAMMENFASSUNG:

Die klassischen Analysemethoden zur Ermittlung von Klufttransmissivitaeten muessen vom Anfang an, die Fliessgeometrie durch die Kluft als bckannt annehmen. In dem Fall einer natuerlichen Kluft, der Fliessweg und der damit verbundene Fliessvolumen ist nicht bekannt. Die vorliegende Veroeffentlichung praesentiert eine neue Methode fuer die Analyse von Testdaten unter instationaeren Bedingungen. Die neue Analysemethode erlaubt die Bestimmung der Klufttransmissivitaet sowie der Änderung der Fliessgeometrie mit dem Abstand zur Bohrung. Die Fliessgeometrie durch die Kluft wird nicht als bekannt angenommen, sondem wird waehrend der Analyse als Vergroesserungsrate des Fliessvolumens ermittelt. Die Anwendungder Methode wird anhand einiger synthetischer Beispiele demonstriert.

1 INTRODUCTION

Flow through fractured rocks has been an active research area in hydrogeology, petroleum engineering, and rock mechanics, with wide applications such as civil engineering, hydrocarbon and geothermal reservoirs, and geological disposal of radioactive wastes. At the heart of this research is the numerical simulation of hydraulic or hydromechanical behaviour of fractured rocks, where fracture transmissivity is a crucial input parameter. Fracture transmissivity is usually derived from hydraulic tests conducted either in the laboratory or in the field. However, the uncertainties associated with the interpretation of the test data are seldom questioned. Flow in a natural fracture is controlled by the variation of aperture, which results in the complex flow paths. Researchers have concentrated attention on "equivalent hydraulic aperture" and quantifying transmissivity based on the "cubic law" for use in numerical models. Pyrak-Nolte et al. (1990) provided a review in this area. A numerical simulation for flow through fractures actually requires fracture transmissivity (T), which is the product of fracture permeability (K) and fracture aperture (b). Thus, we will use the term of fracture transmissivity in this paper. However, the distribution of apertures within a fracture determines the flow geometry and affects the determination of the inferred transmissivity. Conventional methods of interpretation assume either uniform radial flow or linear flow in order to determine transmissivity from a hydraulic test. Given the complex flow paths in a natural fracture, such simple assumptions of flow geometry may not be valid. In this paper, we introduce a new interpretation technique for analysis of transient responses of a flow test. With this technique it is possible to derive fracture transmissivity as well as the change in flow geometry with distance from the source signal. No a priori assumption of flow geometry in a fracture is assumed, but the rate of growth of the flow volume is derived as an output of the analysis. A theoretical background to the new interpretation technique is described and numerical examples of flow geometry are examined to demonstrate the application of this technique.

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