Flow meter and fluid ratio tool

A robust basic flow meter

Fluid ratio water/oil or gas/oil

Flow meter

The flow meter device itself is a simple mechanical choke. The bore of the producing tubing is increased and then reduced. The choke, which reduces the bore, is instrumented and there is a force axially applied to this reduction choke which is proportional to flow.

The principle of operation of this meter is shown below here

The measurement is therefore made with a strain gauge device. This has been specially designed so that the wetted parts and the strain-gauged parts are separate allowing use in aggressive fluid environments without adverse affects on the sensing elements.

The tool is not particularly affected by turbulent flow regimes as the turbulence does not directly affect the measured force, unlike venturi meters where the pressure sensing ports are very sensitive to turbulence in the fluid.

Another benefit of this technique over a venturi meter is that the strain gauges are very sensitive and this unit will sense flow rates down to near zero.

The choke profile does not effect the reading of flow obtained. This means that any erosion of the choke will not alter the calibration of the meter. Again venturi meters are sensitive to choke erosion.

The device a fairly simple and creates minimal disruption to the flow. The maximum OD of the complete device is no greater than the maximum OD of the bulge section of the meter. The ratio of the ID to OD can be varied to suit the application. The only downside to reducing the bulge diameter to fit in tight spaces is that the resolution and sensitivity will be reduced. However since the strain gauges can be sized to any load range there is no major restriction on the annulus bulge size. Tools built to date have had a 3/5 ratio. This means 5 inch OD on a 3-inch nominal tool or 10 inch OD on a 6-inch nominal tool.

Fluid ratio tool

The ratio tool operates by making a measure of the electrical properties of the fluid. This is done on an array of sensor plates. In this way not only does the tool determine the overall characteristic of the fluid to determine the ratio of the two phases present but can also detect separated or mixed flow regimes. The basic principle is illustrated in the diagram shown here.

The actual ratio tool is a long device (10feet) with an array of sensor plates inside it.

Again this tool has a bulge or larger outside diameter than the nominal tubing bore into which it is inserted.

The tools designed to date have an increase in outside diameter of 1.25 inches.

The electronics system scans the array of sensor rods or plates and gathers information on the properties of the fluid. This is not a fast fluid tool and requires in the region of 10 minutes to develop a suitable average fluid ratio figure.

The tool not only scans a series of probe pair combinations but also performs spectral scanning of the electrical properties to further enhance the tools accuracy and sensitivity.

The complete system

A complete downhole system has both a ratio tool and a flow meter module. A single central electronics module would read these. This central module could be a retrievable cartridge, or be part of the tool assembly. The complete assembly including electronics will be in the region of 12-13 feet long.

The system has been designed to operate with a PC based software package and provide continuous monitoring of the fluid properties or any pipe line it is fitted to. The complete set of information that a complete tool assembly will measure is as follows

The software supplied with the tool allows visual display of this data and also graphical trending and review with printing of reports.

The complete downhole system is based on components taken form a library of parts built up over ten years, which are proven for use continuously in hostile environments. This platform ensures high temperature operation and long reliable life in a any situation.

The tool therefore while representing a new technology has been carefully designed to minimise the risk of failure.

To download a copy of the phase 1 test results click here.

To download a copy of the 2001 product specification click here.

To download a summary of recent tests in the Shell test in the Hague click here.