GB2161942A - Apparatus for permeability measurements - Google Patents

Abstract

An apparatus for the measurement of the permeability of core samples to air or other gases of the type wherein a core sample 12 contained within a permeability cell 10 is subjected to a measured pressure differential and the resulting gas flow therethrough is determined. In order to ensure that there is no gas flow in the lines 35, 37 leading to transducers 36, 38 and 48 which measure the pressure across the cell and the absolute downstream pressure, the flow path 20, 49 by which the gas enters and leaves the core sample is arranged to be entirely separate from pipework 35, 37 associated with the differential pressure measurement performed by the aforementioned transducers. <IMAGE>

Description

SPECIFICATION Apparatus for permeability measurement The present invention is concerned with an apparatus for the measurement of the permeability of core samples to air or other gases.

The traditional method of measuring air permeability of core samples is to subject the samble to a measured pressure differential and to measure the resulting gas flow therethrough. The permeability can then be calculated using a well-established formula. The apparatus traditionally used in this technique includes the so-called Hassler-type permeability cell wherein the sample under test is confined within a cylindrical sleeve and between opposed faces of two axially displaceable, cylindrical platens. Each platen has an axial bore connected to inflow and outflow connectors at two opposite ends of the cell, respectively. The inflow connector is coupled by piping to a source of pressurised air by way of a pressure regulator. The outflow connector is coupled by further piping to a bank of standard orifices which are connected in parallel.The pressure upstream of the cell is measured by water and mercury manometers connected to the upstream pimping. The pressure downstream of the cell is measured by a water manometer or draft gauge connected to the piping which interconnects the downstream end of the cell and the orifices.

This traditional apparatus is awkward and time consuming to use, and suffers from inaccuracies due to the venturi effects at the coupling points of the various manometers with the connecting pipes and the pressure drops resulting from the relative remoteness of these manometers from the locations at which the pressure measurements are theoretically required.

It is an object of the present invention to provide an apparatus for permeability measurement which is easier to use and of greater accuracy than the traditional apparatus.

In accordance with a principal aspect of the present invention, the connections made to the permeability cell for the purposes of pressure differential measurement are arranged to be independent of and separate from the gas flow lines to and from the cell.

Preferably, the cell has a pair of cylindrical platens between which the core sample under test is confined, a gas flow through the sample being established by way of a first bore in one of the platens connected to a source of gas and second bore in the other of the platens connected to an exhaust outlet by way of a selected one of a plurality of calibrated orifices, the pressure differential across the sample being established by one or more pressure transducers connected to third and fourth bores in the two platens, respectively.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, wherein: Figure 1 is a diagrammatic representation of one embodiment of an apparatus for measuring permeability in accordance with the present invention; Figure 2 is a diagrammatic sectional view through one embodiment of a cell for holding a sample under test; Figure 3 is a partial end view of the cell of Fig. 2; Figure 4 is a section on line 7-7 of Fig. 2; and Figure 5 is an enlarged detail view of part of the cell of Fig. 2.

With reference to Fig. 1, the apparatus comprises a permeability cell 10, described further hereinafter, which houses the core sample 1 2 under test. A line 14 in parallel with the cell 10 contains upstream and downstream solenoid valves 1 6,1 8 which are for the purposes of protection and also for calibration. The flow line 20 upstream of the cell contains a controllable vent valve 22, the parallel combination of first and second regulator valves 24,26 (each of which has a series-connected solenoid valve 28,30, and a further common regulator 32. The flow line 20 leads from a supply of pressurised gas, in this case a nitrogen cylinder 34.

Connected in parallel with the core sample cell 10 by way of lines 35,37 are a low differential pressure transducer 36 and a high differential pressure transducer 38. Two protection solenoid valves 40,42 are associated with the transducer 38 and two protection solenoid valves 44,46 are associated with the transducer 36. The absolute pressure on the downstream side of the core sample is measured by an absolute pressure transducer 48.

The downstream side of the cell 10 is connected via a line 49 to a manifold 50 which can be selectively connected to one or more of a plurality of calibrated orifices (not shown) via respective solenoid valves 52. The absolute pressure in the manifold 50 is measured by a pressure transducer 47.

A preferred form of cell is now described with reference to Figs. 2 to 5. A cylindrical rigid housing 60 contains an inner sleeve 62 of rubber into which a core sampe (not shown) can be inserted. The sample is confined between opposed, grooved, end faces 64,66 of upstream and downstream platens 68,70 which project into the rubber sleeve 62. The platen 70 can be removed by a quick-release mechanism (described below) to enable the sample to be inserted. The position of the platen 68 relative to the platen 70 can be adjusted by means of a screw-threaded rod 72 received in a cross-head 74. A cylindrical guide member 76 embraces the housing 60.

The cross-head 74 is interconnected with the platen 70 by means of tie-bars 78 which extend through the guide member 76.

The platen 64 contains a pair of parallel bores 80,82 leading from the surface 64 and terminating in radially directed screw-threaded union sockets 84,86 respectively. The platen 70 contains a pair of parallel bores 88,90 leading from its surface 66 and terminating in screw-threaded union sockets 92,94 respectively.

The union 84 is coupled to the flow pipe 20 leading, via the pressure regulators 24,26 from the nitrogen cylinder. The union 92 is coupled to the flow pipe 49 leading to the manifold 50. The union 86 is coupled to the lines leading to the high pressure sides of the pressure transducers 36,38 and the union 94 is coupled to the lines leading to the low pressure sides of these transducers.

The guide release mechanism comprises an annular ring 96 containing a pair of apertures 100 which are dimensioned to pass over heads 98 on the ends of the tie rods 78. The apertures communicate with circumferentially extending slots 102 which enable partial rotation of the ring 96 so that the ring engages behind the heads 98 on the tie rods to thereby lock the platen 70 securely in its operative position. The ring has only to be rotated back to align the apertures 100 with the heads 98 to enable the platen 70 to be released and the core sample to be removed and replaced by a further sample.

An important feature of this apparatus is that the flow path by which the gas enters and leaves the core sample is separate from the pipework 35,37 associated with the differential pressure measurement performed by the transducers 36,38. This means that there is no gas flow in the lines 35,37 leading to the transducers 36,38 and 48 and therefore no measurement inaccuracy due to pressure drops in these lines. True differential and absolute pressures, as required by theory, can thus be measured without venturi effects.

As a direct outcome of the latter feature, the downstream pipes/lines can be of a smaller diameter than otherwise, without influencing the test results.

The pressure measuring transducers are preferably electronic devices which can be auto-zeroed to eliminate zero-offset errors.

All process lines such as 20, 49, 35, 37 can be collected in a common internally bored manifold to afford an elegant mounting of a plurality of electrically activated solenoid.

The pressure regulators 24,26 are preferably plunger-operated by means of manually operable hydraulic rams (not shown) which are safety interlocked for pressure limiting and re-setting of the process.

The orifices controlled by the solenoid valves 52 are housed in a manifold 61 which is fitted with a removable boat containing desiccant. The manifold is partially transparent to allow visual inspection of the state of the desiccant. The orifices are arranged to be automatically actuated by a microprocessor in an autoranged manner (from large aperture to small) as required by the pressure regime during gas flow through the core sample.

The manifold allows a rapid calibration of the flow orifices with a primary transfer standard flow device (not shown).

The operation, calibration and inputting of constants are achieved by a dedicated microprocessor which performs all the necessary valve operations and calculations.

The various solenoids of the system can be operated manually (individually) for the purposes of trouble-shooting, calibration and inputting of orifice flow constants which are stored in a non-volatile memory, via a key-pad (not shown) and selected function switches.

The status of essential solenoids is shown by small mimic lights to enable training of operators and identification and repair of faults.

The apparatus is fitted with independent/spare pressure transducers to calibrate the working tansducer from time to time and serve as replacement in case of failure.

Process lines are fitted with guide release connectors to enable rapid changing from one sample size to another (e.g. 1-1 /2"1").

Claims (9)

1. An apparatus for the measurement of the permeability of core samples to air or other gases of the type wherein a core sample contained in a permeability cell is subjected to a measured pressure differential and the resulting gas flow therethrough is determined, wherein, connections made to the permeability cell for the purposes of pressure differential measurement are arranged to be independent of and separate from gas flow lines to and from the cell.

2. An apparatus as claimed in claim 1 wherein the cell has a pair of cylindrical platens between which, in use, a core sample under test is confined, a gas flow through the sample being arranged to be established by way of a first bore in one of the platens connected to a source of gas and a second bore in the other of the platens connected to an exhaust outlet by way of a selected one of a plurality of calibrated orifices, the pressure differential across the sample being arranged to established by one or more pressure transducers connected to third and fourth bores in the two platens, respectively.

3. An apparatus as claimed in claim 2, including a pressure transducer coupled to said fourth bore for measuring the absolute pressure on the downstream side of the core sample.

4. An apparatus as claimed in claim 2 or 3, including a low differential pressure transducer and a high differential pressure transducer connected in parallel across the cell by way of said third and fourth bores.

5. An apparatus as claimed in any of claims 2 to 4 wherein the downstream side of the cell is connected to a manifold which can be selectively connected to one or more of a plurality of calibrated orifices via respective solenoid valves.

6. An apparatus as claimed in any of claims 1 to 5 wherein the permeability cell comprises a rigid cylindrical housing containing an inner sleeve of rubber into which a core sample can be iserted so as to be confined between opposed, end faces of upstream and downstream platens which project into the rubber sleeve.

7. An apparatus as claimed in claim 6 wherein the downstream platen can be removed from the cell by a quick-release mechanism to enable the sample to be inserted.

8. An apparatus as claimed in claim 6 or 7 wherein the position of one platen relative to the other can be adjusted by means of a screw-threaded rod received in a cross-head fixed relative to said other platen.

9. An apparatus as claimed in claim 6, 7 or 8 wherein the process lines leading to and from the permeability cell are formed in a common, internally bored manifold.

1 0. An apparatus for the measurement of the permeability of core samples to air or other gases, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.