Characterizing Flow Through a Perforation Using Ultrasonic Doppler
Authors: Razi Muhammad , Morriss Steven L. , Podio Augusto L. 
Published: December 2007

Muhammad Razi,* Steven L. Morriss,* and Augusto L. Podio*

The flow velocity of the one dimensional, single phase flow within an individual perforation is determined using an ultrasonic Doppler technique. This new technique takes advantage of the fact that flow in an individual perforation is often single phase even when flow in the wellbore is not. Existing techniques for determining multi-phase flow rates in a well bore have many limitations, due in large part to the complexity of the many possible flow regimes. An innovative approach which partially circumvents this problem has been investigated experimentally. Work has been done using an experimental set-up simulating a well bore, with water as the fluid. Since the diameter of perforations for a known gun type and casing can be reasonably estimated, flow rate within an individual perforation can be determined from velocity. Comparison of the calculated flow rates with actual flow rates are encouraging, both in turbulent and laminar flows. It is envisioned that a televiewer-like tool could be developed to scan the entire perforated interval while logging, providing a complete description of flow entries and exits.

Introduction

Most oil and gas wells are completed by cementing steel casing in the well and then perforating the casing in the zones of interest, Laboratory studies indicate that crushing and compaction of rock during perforating reduce the flow capacity of the perforation. Productivity of a perforated completion may range from 5% to 90% of undamaged, open hole productivity. This results in a significant loss of production of oil and gas, and hence revenue. In injector wells, whether used for enhanced recovery or for waste disposal, poorly performing perforations are likewise undesirable.

Locating the ineffective perforations requires a reliable method for determining the flow through individual perforations. Many shortcomings and operational complications are associated with the use of present production logging techniques such as spinners, and radioactive tracers. The use of ultrasound for this purpose may be a good alternative. Since the only contact between the tool and fluid is sound waves, the flow stream in a perforation or the wellbore is not disturbed during the measurement. Also shortcomings associated with the use of mechanical tools, such as threshold speeds of spinners, are not present. The research reported here proposes to measure the flow in individual perforations as suggested in Fig. 1, providing the operator with a quantitative measure of perforation performance. Since downhole ultrasonic logging tools are available commercially to scan the inner wall of the hole for imaging purpose, only additional signal processing would be required to implement Doppler velocimetry.

DOPPLER THEORY

The exploitation of the Doppler effect is as old as the history of bats and dolphins since they exploit this phenomenon as a basic survival skill. The early investigation of this phenomenon was done by Christian Andreas Doppler, hence the effect is named after him.

The Doppler effect is commonly exploited for medical purposes where it is used to measure blood flow. In the upstream petroleum industry, production logging applications based on Doppler ultrasound are still in the research stage, with the first reported work done in 1990.

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