Auxiliary flow line filter for sampling probe

1. An apparatus, comprising:

a downhole tool for conveyance in a wellbore extending into a subterranean formation, wherein the downhole tool comprises a focused sampling probe that comprises:

an outer packer;

a set piston;

an inner packer carried with the set piston and comprising a central fluid inlet, wherein an annulus defined between the inner and outer packers comprises a peripheral fluid inlet;

a main flow line;

a primary filter carried with the set piston;

a filter piston slidable relative to the set piston between:

a first position, in which the filter piston prevents fluid, received from the formation in the central fluid inlet, from flowing through the primary filter to the main flow line; and

a second position, in which the filter piston permits fluid, received from the formation in the central fluid inlet, to flow through the primary filter to the main flow line;

an auxiliary flow line;

a scraper positionally fixed relative to the outer packer; and

an auxiliary filter carried externally with the set piston and in selective fluid communication between the peripheral fluid inlet and the auxiliary flow line based on an axial position of the set piston relative to the scraper, wherein the scraper scrapes against the auxiliary filter in response to axial movement of the set piston relative to the scraper.

2. The apparatus of claim 1 wherein the outer packer is extendable from the downhole tool.

3. The apparatus of claim 1 wherein the outer packer is extendable from the downhole tool via operation of a plurality of probe extension pistons.

4. The apparatus of claim 1 wherein the set piston is operable to translate relative to the outer packer in response to hydraulic pressure applied to the set piston by the downhole tool.

5. The apparatus of claim 1 wherein the filter piston scrapes against the primary filter in response to axial movement between the first and second positions.

6. The apparatus of claim 1 wherein the peripheral fluid inlet is annulus-shaped.

7. The apparatus of claim 1 wherein debris blocked by the primary filter while carried by fluid flowing from the central fluid inlet to the main flow line through the primary filter is scraped away from the primary filter by the filter piston during movement of the filter piston from the second position towards the first position.

8. The apparatus of claim 1 wherein debris blocked by the auxiliary filter while carried by fluid flowing from the peripheral fluid inlet to the auxiliary flow line through the auxiliary filter is scraped away from the auxiliary filter by the scraper during movement of the set piston inward relative to the outer packer.

9. The apparatus of claim 1 wherein:

first debris blocked by the primary filter while carried by fluid flowing from the central fluid inlet to the main flow line through the primary filter is scraped away from the primary filter by the filter piston during movement of the filter piston from the second position towards the first position; and

second debris blocked by the auxiliary filter while carried by fluid flowing from the peripheral fluid inlet to the auxiliary flow line through the auxiliary filter is scraped away from the auxiliary filter by the scraper during movement of the set piston inward relative to the outer packer.

10. An apparatus, comprising:

a downhole tool for conveyance in a wellbore extending into a subterranean formation, wherein the downhole tool comprises a focused sampling probe that comprises:

an outer packer;

a set piston;

an inner packer carried with the set piston and comprising a central fluid inlet, wherein an annulus defined between the inner and outer packers comprises a peripheral fluid inlet;

a main flow line;

a primary filter carried with the set piston;

a filter piston;

an auxiliary flow line;

a scraper positionally fixed relative to the outer packer; and

an auxiliary filter carried externally with the set piston;

wherein the focused sampling probe is configurable between:

a first configuration in which:

the filter piston blocks fluid, received in the central fluid inlet from the formation, from flowing through the primary filter to the main flow line; and

the scraper blocks fluid, received in the peripheral fluid inlet from the formation, from flowing through the auxiliary filter to the auxiliary flow line; and

a second configuration in which:

the filter piston permits fluid, received in the central fluid inlet from the formation, to flow through the primary filter to the main flow line; and

the scraper permits fluid, received in the peripheral fluid inlet from the formation, to flow through the auxiliary filter to the auxiliary flow line.

11. The apparatus of claim 10 wherein the outer packer is extendable from the downhole tool.

12. The apparatus of claim 10 wherein the outer packer is extendable from the downhole tool via operation of a plurality of probe extension pistons.

13. The apparatus of claim 10 wherein the focused sampling probe is configurable between the first and second configurations via hydraulic pressure changes applied by the downhole tool.

14. The apparatus of claim 10 wherein the filter piston scrapes against the primary filter in response to transition of the focused sampling probe between the first and second configurations.

15. The apparatus of claim 10 wherein the peripheral fluid inlet is annulus-shaped.

16. The apparatus of claim 10 wherein debris blocked by the primary filter while carried by fluid flowing from the central fluid inlet to the main flow line through the primary filter is scraped away from the primary filter by the filter piston during transition of the focused sampling probe from the second configuration towards the first configuration.

17. The apparatus of claim 10 wherein debris blocked by the auxiliary filter while carried by fluid flowing from the peripheral fluid inlet to the auxiliary flow line through the auxiliary filter is scraped away from the auxiliary filter by the scraper during transition of the focused sampling probe from the second configuration towards the first configuration.

18. A method, comprising:

conveying a downhole tool within a wellbore to a subterranean formation, wherein the downhole tool comprises a focused sampling probe that comprises:

an outer packer;

a set piston;

an inner packer carried with the set piston and comprising a central fluid inlet, wherein an annulus defined between the inner and outer packers comprises a peripheral fluid inlet;

a main flow line;

a primary filter carried with the set piston;

a filter piston;

an auxiliary flow line;

a scraper positionally fixed relative to the outer packer; and

an auxiliary filter carried externally with the set piston;

wherein the focused sampling probe in a first configuration in which:

the filter piston blocks fluid, received in the central fluid inlet from the formation, from flowing through the primary filter to the main flow line; and

the scraper blocks fluid, received in the peripheral fluid inlet from the formation, from flowing through the auxiliary filter to the auxiliary flow line; then

transitioning the focused sampling probe from the first configuration to a second configuration in which:

the filter piston permits fluid, received in the central fluid inlet from the formation, to flow through the primary filter to the main flow line; and

the scraper permits fluid, received in the peripheral fluid inlet from the formation, to flow through the auxiliary filter to the auxiliary flow line.

19. The method of claim 18 further comprising:

extending the outer packer from the downhole tool into contact with a wall of the wellbore after conveying the downhole tool within the wellbore to the subterranean formation and before transitioning the focused sampling probe into the second configuration;

pumping fluid from the subterranean formation into the downhole tool while the focused sampling probe is in the second configuration, including:

pumping a first fluid stream from the subterranean formation through the central fluid inlet, through the primary filter, and into the main flow line; and

pumping a second fluid stream from the subterranean formation through the peripheral fluid inlet, through the auxiliary filter, and into the auxiliary flow line;

ceasing pumping fluid from the subterranean formation into the downhole tool, and then transitioning the focused sampling probe from the second configuration to the first configuration;

after transitioning the focused sampling probe to the first configuration, retracting the outer packer from the wall of the wellbore, and then conveying the downhole tool to a new location within the wellbore.

20. The method of claim 19 wherein:

debris blocked by the primary filter while carried by fluid flowing from the central fluid inlet to the main flow line through the primary filter is scraped away from the primary filter by the filter piston during transition of the focused sampling probe from the second configuration towards the first configuration; and

debris blocked by the auxiliary filter while carried by fluid flowing from the peripheral fluid inlet to the auxiliary flow line through the auxiliary filter is scraped away from the auxiliary filter by the scraper during transition of the focused sampling probe from the second configuration towards the first configuration.