GB2139766A - Measurement of water in crude oil - Google Patents

Abstract

A measurement cell for measuring the water content of crude oil comprises an elongated body 3 closed at either end by end pieces 7,8 and provided with inlet and outlet pipes 1,2 to enable an oil-water mixture to be monitored to flow through the body. Each end piece 7,8 carries an axially extending capacitance sensing electrode 9,10 whereby variations in water content of the oil causing a variation in the capacitance between the electrodes can be measured. The end pieces 7,8 may be detachable and can carry temperature sensors 11,12. <IMAGE>

Description

SPECIFICATION Measurement of water in crude oil The present invention is an electrical capacitance fluid flow cell which provides for duplicate measurement of the electrical capacitance (and fluid temperature when necessary), in a manner which is advantageous for manufacture and application.

In recent years, the accurate measurement of the water content of crude oils has become very important, in order that the proper valuation can be assigned to the oil/water mixture, for fiscal, accounting and oil loss purposes.

The most common approach to making this measurement is to use automatic apparatus to draw a representative quantity of the oil/water mixture, for subsequent analysis. This approach has many problems.

An alternative approach now being developed is to measure the property continuously 'on line', by allowing a representative sample of the oil/water mixture to flow through a 'measurement cell' which produces an electrical signal related to the water content. The measurement cell is designed and constructed to have an electrical capacitance, which changes in an predictable manner because of the large difference between the dielectric constant of dry oil and the dielectric constant of water (fresh or saline).

The application of this difference between the dielectric constants of oil and water as a (rough) indication of water content of oils (and other related applications) is well known. However, the technique has not before been applied for accurate measurements. In general, the earlier art has used measurement devices inserted as 'spool pieces' into the production pipeline - typically in the smaller sizes of pipelines, ranging from 2" to 10". The current requirement is to have the measurement cell separate from the pipeline, in a 'fast loop' configuration.

Avery important factor in all fiscal measurement systems is to provide a high degree of confidence and integrity in the measurement. This is commonly achieved by duplicating the measurement device and comparing the two readings so obtained - which for satisfactory operation should be the same within prescribed (close) limits. From the practical viewpoint - eg cost of equipment, cost and ease of installation, control of operations - any device which minimises these factors is clearly advantageous.

Accordingly, the present invention is a measurement cell for measuring water content of crude oil, which cell comprises an elongated body closed at either end and provided with an inlet and an outlet to allow an oil-water mixture to flow through the body, and a capacitance sensing electrode extending axialliy from each end of the body.

The body may be closed by detachable end pieces which carry the capacitance sensing electrodes.

The tube may be provided with temperature sensors, which may extend axially from each end of the body.

The invention is illustrated with reference to the accompanying drawing.

The drawing shows a side view of a measurement cell according to the present invention with internal arrangements shown by dotted lines. There are two inlet/outlet pipes 1 and 2 which enable the oil whose water content is to be measured to be passed through the cylindrical body 3 of the cell in either direction. Each end of cylindrical body 3 is provided with flanges 5 and 6. Bolted to these flanges are end pieces 7 and 8 which close the ends of body 3 to provide an oil tight seal. These end pieces are identical and each carries capacitance sensing electrodes 9 or 10 and a temperature sensor 11 or 12 which project axially into the cylindrical body 3. The capacitance sensing electrode and temperature sensor may be of conventional type. The body 3 may be provided with means (not shown) located within it for holding the projecting ends of the capacitor sensing electrodes in position.

The end pieces 7 and 8 are electrically connected by wires shown at 13 and 14to instruments (not shown) for recording and displaying the signals received from the capacitance sensing electrodes and the temperature sensors. In use oil is passed through the body 3 by way of pipes 1 and 2.

Variations in water content in the oil cause variations in the capacitance measured by the two capacitor sensing electrodes. The water content can be calculated from the capacitance by known methods. If the two capacitance sensing electrodes give different capacitance values this is an indication that there is a fault in one of the capacitance probes. The measurement cell can then be disconnected from the oil supply for checking. Because all the measurement devices are axially mounted on the end plates it is relatively easy to replace a capacitance probe. By using identical end plates, the stock of replacement parts required is reduced.

1. A measurement cell for measuring the water content of crude oil, which cell comprises an elongated body closed at either end and provided with an inlet and an outlet to allow an oil-water mixture to flow through the body, and a capacitance sensing electrode extending axially from each end of the body.

2. A measurement cell according to claim 1 wherein the ends of the elongated body are closed by detachable end pieces which carry the capacitance sensing electrodes.

3. A measurement cell according to claim 1 wherein the body is cylindrical and is provided with flanges at either end.

4. A measurement cell according to claim 1 provided with a temperature sensor extending axialliy from each end of the body.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Measurement of water in crude oil The present invention is an electrical capacitance fluid flow cell which provides for duplicate measurement of the electrical capacitance (and fluid temperature when necessary), in a manner which is advantageous for manufacture and application. In recent years, the accurate measurement of the water content of crude oils has become very important, in order that the proper valuation can be assigned to the oil/water mixture, for fiscal, accounting and oil loss purposes. The most common approach to making this measurement is to use automatic apparatus to draw a representative quantity of the oil/water mixture, for subsequent analysis. This approach has many problems. An alternative approach now being developed is to measure the property continuously 'on line', by allowing a representative sample of the oil/water mixture to flow through a 'measurement cell' which produces an electrical signal related to the water content. The measurement cell is designed and constructed to have an electrical capacitance, which changes in an predictable manner because of the large difference between the dielectric constant of dry oil and the dielectric constant of water (fresh or saline). The application of this difference between the dielectric constants of oil and water as a (rough) indication of water content of oils (and other related applications) is well known. However, the technique has not before been applied for accurate measurements. In general, the earlier art has used measurement devices inserted as 'spool pieces' into the production pipeline - typically in the smaller sizes of pipelines, ranging from 2" to 10". The current requirement is to have the measurement cell separate from the pipeline, in a 'fast loop' configuration. Avery important factor in all fiscal measurement systems is to provide a high degree of confidence and integrity in the measurement. This is commonly achieved by duplicating the measurement device and comparing the two readings so obtained - which for satisfactory operation should be the same within prescribed (close) limits. From the practical viewpoint - eg cost of equipment, cost and ease of installation, control of operations - any device which minimises these factors is clearly advantageous. Accordingly, the present invention is a measurement cell for measuring water content of crude oil, which cell comprises an elongated body closed at either end and provided with an inlet and an outlet to allow an oil-water mixture to flow through the body, and a capacitance sensing electrode extending axialliy from each end of the body. The body may be closed by detachable end pieces which carry the capacitance sensing electrodes. The tube may be provided with temperature sensors, which may extend axially from each end of the body. The invention is illustrated with reference to the accompanying drawing. The drawing shows a side view of a measurement cell according to the present invention with internal arrangements shown by dotted lines. There are two inlet/outlet pipes 1 and 2 which enable the oil whose water content is to be measured to be passed through the cylindrical body 3 of the cell in either direction. Each end of cylindrical body 3 is provided with flanges 5 and 6. Bolted to these flanges are end pieces 7 and 8 which close the ends of body 3 to provide an oil tight seal. These end pieces are identical and each carries capacitance sensing electrodes 9 or 10 and a temperature sensor 11 or 12 which project axially into the cylindrical body 3. The capacitance sensing electrode and temperature sensor may be of conventional type. The body 3 may be provided with means (not shown) located within it for holding the projecting ends of the capacitor sensing electrodes in position. The end pieces 7 and 8 are electrically connected by wires shown at 13 and 14to instruments (not shown) for recording and displaying the signals received from the capacitance sensing electrodes and the temperature sensors. In use oil is passed through the body 3 by way of pipes 1 and 2. Variations in water content in the oil cause variations in the capacitance measured by the two capacitor sensing electrodes. The water content can be calculated from the capacitance by known methods. If the two capacitance sensing electrodes give different capacitance values this is an indication that there is a fault in one of the capacitance probes. The measurement cell can then be disconnected from the oil supply for checking. Because all the measurement devices are axially mounted on the end plates it is relatively easy to replace a capacitance probe. By using identical end plates, the stock of replacement parts required is reduced. CLAIMS

1. A measurement cell for measuring the water content of crude oil, which cell comprises an elongated body closed at either end and provided with an inlet and an outlet to allow an oil-water mixture to flow through the body, and a capacitance sensing electrode extending axially from each end of the body.

2. A measurement cell according to claim 1 wherein the ends of the elongated body are closed by detachable end pieces which carry the capacitance sensing electrodes.

3. A measurement cell according to claim 1 wherein the body is cylindrical and is provided with flanges at either end.

4. A measurement cell according to claim 1 provided with a temperature sensor extending axialliy from each end of the body.