GB2172630A

GB2172630A - Improvements in downhole tools

Info

Publication number: GB2172630A
Application number: GB08507252A
Authority: GB
Inventors: Frank Baxter Bardsley; David Easton Stoddart
Original assignee: TESEL PLC
Current assignee: TESEL PLC
Priority date: 1985-03-20
Filing date: 1985-03-20
Publication date: 1986-09-24

Abstract

A tool for collecting material samples, e.g. formation fluid, for use down hole has an inlet (24) for allowing material into the tool, storage means (not shown), for storing material to be brought to the surface, means (35) for controlling flow of material to the storage means and means, for example in the form of a resistivity cell (27) for measuring electrical properties of the material flowing in the tool. <IMAGE>

Description

SPECIFICATION Improvements in downhole tools The invention relates to tools for use in testing formation fluid surrounding a borehole.

Many tools are already known for testing and investigating the nature of formation fluid surrounding a borehole. There are tools which measure formation fluid characteristics by resistivity measurements (or capacitive or inductive measurements) and tools which actually take samples of the formation fluid for analysis when the tool is brought back to the surface.

Hitherto, because of the complexity of operation, sample taking tools have been used downholewith no other information providing tool other than a gamma ray source used to ascertain the tool location. Sample taking tools have generally included a "pretest" facility, which provides a pressure characteristic for formation fluid being drawn into the tool, and a decision on when to take samples has had to be based on that characteristic.

Hereinafter the term "material" will be used to refer to "formation fluid" in the appropriate context.

According to the invention there is provided a tool for collecting material samples for use downhole, which tool includes an inlet for allowing material into the tool, storage means for storing material to be brought to the surface, means for controlling flow of material to the storage means and means for measuring electrical properties of the material flowing in the tool.

The electrical properties measuring means may comprise a device for measuring resistivity of material flowing in the tool, or alternatively a device for measuring capacitance of material flowing in the tool, or alternatively, a device for measuring inductance of material flowing in the tool.

The device preferably comprises a passage through which the material flows and measuring means, such as electrodes, surrounding the passage.

The device preferably includes a plurality of spaced apart electrodes insulated from one another.

Each electrode preferably includes a ring portion to provide a cylindrical surface forming part of the surface of the passage through the device.

The means for controlling flow of material to the storage means preferably comprises passage means for by-passing the storage means such that material is able to flow into, through and out of the tool, and me-ans for switching the flow from by-passing and into the storage means. Material preferably flows through the measuring device whether on its way to the storage means or to the by-passing passage means.

By way of example, one embodiment of a tool according to the invention will now be described with reference to the accompanying drawings, in which Figure lisa schematic diagram of the tool layout; Figure 2 is a diagrammatic view of a formation flushing module; Figure 3 is a diagrammatic view of a packer module; Figure 4 is a sectional view of a partly completed resistivity cell; and Figure 5 is a sectional view of a completed resistivity cell.

Figure 1 shows schematically the layout of a tool 10 according to the invention. The tool 10 is of necessity long and of small enough diameter to be movable in a drilled hole.

At one end of the tool 10 is an electronics module 11 containing the necessary control circuitry for the tool, and which is connected by appropriate cabling to the surface in use. Next to the electronics module 11 is a formation flushing section 12 which will be described in more detail later. Next to the formation flushing module 12 is a hydraulic power module 13, then a packer module 14 then four separate sample chambers 15, 16, 17 and 18 and finally an end cap 19.

Figures 2 and 3 show diagrammatically details of the formation flushing module 12 and the packer module 14 respectively.

The packer module 14 is supplied with pressurised hydraulic fluid through a hydraulic line 20 from the hydraulic power module 13. The hydraulic line 20 leads to a valve block 21 from which three hydraulic lines lead to operate back-up jacks 22, packer 23 and a probe 24.

The probe when extended has an opening through which material from outside the tool 10 can enter the probe 24 and thereby the tool 10. Material enters through a material flow line 25 which leads to an equalising valve 26 and a resistivity cell 27.

The line 25 branches three ways downstream of the resistivity cell 27, one branch 28 leading to a pretest assembly including a pretest drive motor 29, a ball screw assembly 30, a pretest piston and cylinder assembly 31 and a pressuretransducer32 (ascertaining material characteristics by examining pressure characteristics as a pretest piston is drawn along a pretest cylinder is a known test), a second branch 33 leading to the formation flushing module 12 and a third branch 34 leading to a sample valve assembly 35.

It will thus be seen that material flows through the resistivity cell 27 whether ultimately bound for the sample chambers, the pretest cylinder or for the formation flushing module.

Figure 2 shows diagrammatically the formation flushing module.

A motor 36 drives a drive wheel 37 via a centrifugal clutch 38 and gear box 39. The drive wheel 37 imparts a reciprocating motion to connecting rod 40 to reciprocate a piston 41 in a pumping cylinder 42.

Although only one connecting rod 40, piston 41 and pumping cylinder 42 is shown in Figure 2, the formation flushing module has two such assemblies arranged in parallel, both assemblies being driven by an associated drive wheel.

The piston 41 draws material from the line 33 through non-return valve 43 and into the cylinder 42.

Upon the return stroke, the material in the cylinder 42 is ejected through the transverse channel 44 out of the tool 10.

In initial operation, the sample valve 35 is maintained closed, and formation fluid is flushed through the tool by the formation flushing module 12. While flushing material through the tool, the material passes through the resistivity cell 27 which measures the resistivity of material flowing along the line 25, and thereby provides an indication of the nature of the material. the resistivity cell 27 provides measurements of resistivity which are fed back to the surface for analysis.

As has been stated before, the pretest is a well know preliminary in formation testing and provides an indication of the nature of the material about to be sampled. The pretest facility may be used before any flushing takes place to make use of known pretest, characteristics, or indeed, during or after flushing. Information from eitherthe resistivity cell or the pretest, or indeed from both, may be used to determine when to take a sample.

When it is decided that a sample isto be taken, the sample valve 35 is opened and material flows down the line 34 to a selected one of the sample chambers.

It will be appreciated that the resistivity cell could be substituted by other material characteristic measuring devices, such as capacitance or inductive measuring devices.

Because of the small diameter of the tool 10, the resistivity cell 27 must be compact.

Figure 4 shows partly completed a resistivity cell according to the invention, and Figure 5 shows a complete resistivity cell.

The resistivity cell 27 includes components which are first assembled on a mandrel 50 as shown in Figure 4. An end block 51 of suitable rigid material, for example metal, capable of withstanding high temperatures carries four terminals 52 (two only of which are shown). Each terminal 52 is connected to a respective one of four annular electrodes (of, for example, lead or brass) 53,54,55 and 56 by bolted connections (other types of connection could be used). Between the four electrodes spacer tubes 57, 58, 59, 60 and 61 are inserted and a second end block 62 of insulating material capable of withstanding high temperatures is mounted on the mandrel 50. An outer metal sleeve 63 is held in place by screws 64 engaging the second end block 62.

As can be seen in Figure 2, the second end block has passages 65 through it, and these passages are used to allow injection of a resin or a like insulating, settable substance into the space between the spacer tubes and the sleeve 63. An epoxy resin is suitable, and may advantageously include some small spherical glass particles. Once the resin (which must be capable of withstanding high temperatures) has set, the mandrel 50 is removed by unscrewing one or both nuts 70, and the remaining passage is drilled to leave the finished cell of Figure 3.

The spaced apart electrodes 53, 54, 55 and 56 allows measurement of resistance therebetween, and these measurements are fed to the surface for analysis and consideration. A promising measurementwill probably together with a promising pretest result, lead the surface operator to open the sample valve to coilect a sample for later analysis.

Claims

1. A tool for collecting material samples for use down hole, which tool includes an inlet for allowing material into the tool, storage means for storage material to be brought to the surface, means for controlling flow of material to the storage means and means for measuring electrical properties of the material flowing in the tool.

2. A tool as claimed in Claim 1 wherein the electrical properties measuring means comprises a device for measuring resistivity of material flowing in the tool.

3. A tool as claimed in Claim 1 wherein the electrical properties measuring means comprises a device for measuring capacitance of material flowing in the tool.

4. Atool as claimed in Claim 1 wherein the electrical properties measuring means comprises a device for measuring inductance of material flowing in the tool.

5. Atool as claimed in any one of Claims 2 to 4 wherein the device comprises a passage through which the material flows and measuring means surrounding the passage.

6. A tool as claimed in Claim 5 wherein the measuring means are electrodes.

7. Atool as claimed in Claim 6 wherein the device includes a plurality of spaced apart electrodes insulated from one another.

8. Atool as claimed in Claim 6 or Claim 7 wherein each electrode includes a ring portion to provide a cylindrical surface forming part of the surface of the passage through the device.

9. A tool as claimed in any preceding Claim wherein the means for controlling flow of material to the storage means comprises passage means for by-passing the storage means such that material is able to flow into, through and out of the tool, and means for switching the flow from by-passing and into the storage means.

10. Atool as claimed in Claim 9 wherein the measuring device lies upstream of the flow switching means such that material flows through the measuring means whether material is flowing to the storage means or through the by-passing passage means.

11. A tool substantially as hereinbefore described with reference to and as shown in the accompanying drawings.