GB2166243A - An overpressure protector for pressure gauges - Google Patents

Abstract

A pressure transmitter 1 is connected to pressure source piping 2. A moveable seal 3 separates measured fluid A from gauge fluid B. The transmitter 1 is connected to a pressure gauge 8 and a gas filled accumulator 6 containing a piston 7. When gauge fluid B pressure exceeds the pressure of the gas C in the accumulator the piston 7 will move and gauge fluid B will enter accumulator C. This allows the seal 3 to expand and close valve 4 thus preventing any further pressure increase in medium A from reaching the gauge. <IMAGE>

Description

SPECIFICATION Overpressure protector for pressure gauges This invention relates to pressure reading or recording devices used on high pressure sources to indicate low pressure, used typically on drilling rigs, to read pressure of formation fluid influx into the wellbore.

When drilling wells for oil and gas, fluid (drilling mud) is circulated down the well at high pressures, as much as 3,000 PSI, through the drill pipe to keep well bore hydro-static pressure balanced with formation pressure. For various reasons, this balance may frequently be upset, and formation fluid in the form of oil, gas or water enters the welibore, this is called a "kick". If a kick happens, circulation of drilling mud is stopped and the static pressure of the drilling mud in the drillpipe is measured at the surface. This pressure indicates the magnitude of pressure entering the well and is used to calculate the new density of drilling mud required to balance the well. For this reason, the pressure reading must be very accurate.However, pressures to be read during a "well kick" are often only very low, as little as 200 PSI, but pressure gauges installed are of the 3,000 to 5,000 PSI range due to the high circulating pressures. Smaller range gauges may burst under high pressures. Naturally the accuracy of reading very low pressures on high pressure range gauges is very poor, and often low pressure gauges may have to be fitted temporarily to record pressure during a well kick.

According to the present invention there is provided an overpressure protector for gauges consisting of a load cell with flexible diaphragm separating the measured medium from the gauge fluid, a valve in the top of the load cell cavity which is closed by the diaphragm when this is completely expanded due to all gauge fluid being discharged from the load cell, the valve positively closing off the pressure in the load cell from the gauge fluid to the gauge.

The gauge fluid outlet of the load cell is connected to the appropriate gauge and an accumulator which is precharged with compressible gas to a pressure equal to, or less than the pressure gauge range.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which: Figure 1 shows a schematic section of the load cell and accumulator, with necessary piping and gauge.

Referring to the drawing, the overpressure protector comprises a load cell 1, connected to the pressure system 2, with a flexible diaphragm 3, gauge fluid cut-off valve 4, piping 5 connecting the load cell to an accumulator 6 with separating piston 7 and gauge 8.

The accumulator 6 is precharged with compressible gas C to a pressure equal to the desired gauge working range. System pressure A is transmitted through diaphragm 3 to engage fluid B and conducted through piping 5 to accumulator 6 and gauge 8. If the pressure rises above the precharge pressure in the accumulator at C, the gauge fluid will lift piston 7 and flow into accumulator 6, compressing gas C. As gauge fluid is displaced into the accumulator 6, diaphragm 3 expands and closes valve 4, isolating system pressure A from the gauge fluid and eliminating any further rise in gauge pressure.

As an alternative, accumulator 6 can be replaced by a cylinder with an adjustable spring compressing the piston, thus replacing the compressible force of gas C with an adjustable spring force. (Not shown).

As a further alternative, a pressure relief valve may be incorporated to release excessive gauge fluid pressure in case of faiiure of the valve and diaphragm.

1. An overpressure protector for pressure gauges comprising a load cell separating the measured medium from the gauge fluid by a moveable sealing means which positively seals off measured pressure from the gauge after a certain amount of gauge fluid has been displaced from the cell.

2. An overpressure protector for pressure gauges as claimed in Claim 1, wherein an accumulator means is provided into which the gauge fluid will escape once its pressure reaches and exceeds a predetermined precharge pressure of the compressible gas with which the accumulator is charged.

3. An overpressure protector for pressure gauges as claimed in Claim 1 wherein a cylinder with a spring loaded piston is provided into which gauge fluid can escape when the force exerted by the gauge fluid pressure on the piston reaches and exceeds the preset force exerted onto the other side of the piston by a spring.

4. An overpressure protector for pressure gauges as claimed in any preceding claim wherein a poppet valve actuated by the moveable seaiing means positively closed off the gauge fluid system from the load cell.

5. An overpressure protector for pressure gauges substantially as described herein with reference to Figure 1 of the accompanying drawing.

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

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Overpressure protector for pressure gauges This invention relates to pressure reading or recording devices used on high pressure sources to indicate low pressure, used typically on drilling rigs, to read pressure of formation fluid influx into the wellbore. When drilling wells for oil and gas, fluid (drilling mud) is circulated down the well at high pressures, as much as 3,000 PSI, through the drill pipe to keep well bore hydro-static pressure balanced with formation pressure. For various reasons, this balance may frequently be upset, and formation fluid in the form of oil, gas or water enters the welibore, this is called a "kick". If a kick happens, circulation of drilling mud is stopped and the static pressure of the drilling mud in the drillpipe is measured at the surface. This pressure indicates the magnitude of pressure entering the well and is used to calculate the new density of drilling mud required to balance the well. For this reason, the pressure reading must be very accurate.However, pressures to be read during a "well kick" are often only very low, as little as 200 PSI, but pressure gauges installed are of the 3,000 to 5,000 PSI range due to the high circulating pressures. Smaller range gauges may burst under high pressures. Naturally the accuracy of reading very low pressures on high pressure range gauges is very poor, and often low pressure gauges may have to be fitted temporarily to record pressure during a well kick. According to the present invention there is provided an overpressure protector for gauges consisting of a load cell with flexible diaphragm separating the measured medium from the gauge fluid, a valve in the top of the load cell cavity which is closed by the diaphragm when this is completely expanded due to all gauge fluid being discharged from the load cell, the valve positively closing off the pressure in the load cell from the gauge fluid to the gauge. The gauge fluid outlet of the load cell is connected to the appropriate gauge and an accumulator which is precharged with compressible gas to a pressure equal to, or less than the pressure gauge range. A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which: Figure 1 shows a schematic section of the load cell and accumulator, with necessary piping and gauge. Referring to the drawing, the overpressure protector comprises a load cell 1, connected to the pressure system 2, with a flexible diaphragm 3, gauge fluid cut-off valve 4, piping 5 connecting the load cell to an accumulator 6 with separating piston 7 and gauge 8. The accumulator 6 is precharged with compressible gas C to a pressure equal to the desired gauge working range. System pressure A is transmitted through diaphragm 3 to engage fluid B and conducted through piping 5 to accumulator 6 and gauge 8. If the pressure rises above the precharge pressure in the accumulator at C, the gauge fluid will lift piston 7 and flow into accumulator 6, compressing gas C. As gauge fluid is displaced into the accumulator 6, diaphragm 3 expands and closes valve 4, isolating system pressure A from the gauge fluid and eliminating any further rise in gauge pressure. As an alternative, accumulator 6 can be replaced by a cylinder with an adjustable spring compressing the piston, thus replacing the compressible force of gas C with an adjustable spring force. (Not shown). As a further alternative, a pressure relief valve may be incorporated to release excessive gauge fluid pressure in case of faiiure of the valve and diaphragm. CLAIMS

1. An overpressure protector for pressure gauges comprising a load cell separating the measured medium from the gauge fluid by a moveable sealing means which positively seals off measured pressure from the gauge after a certain amount of gauge fluid has been displaced from the cell.

2. An overpressure protector for pressure gauges as claimed in Claim 1, wherein an accumulator means is provided into which the gauge fluid will escape once its pressure reaches and exceeds a predetermined precharge pressure of the compressible gas with which the accumulator is charged.

3. An overpressure protector for pressure gauges as claimed in Claim 1 wherein a cylinder with a spring loaded piston is provided into which gauge fluid can escape when the force exerted by the gauge fluid pressure on the piston reaches and exceeds the preset force exerted onto the other side of the piston by a spring.

4. An overpressure protector for pressure gauges as claimed in any preceding claim wherein a poppet valve actuated by the moveable seaiing means positively closed off the gauge fluid system from the load cell.

5. An overpressure protector for pressure gauges substantially as described herein with reference to Figure 1 of the accompanying drawing.