Pressure limiter for a downhole pump and testing apparatus

Claim 2

A pressure limiter apparatus for use in a well testing string having a positive displacement pump including a fluid displacement element, said apparatus comprising: enclosure means in said well testing string having a wall defining a pumping chamber adjacent said pump and in pressure transmitting communication with said fluid displacement element; inlet valve means associated with said enclosure means for controlling flow of fluid from a well annulus into said pumping chamber; outlet valve means associated with said enclosure means for controlling flow of fluid from said pumping chamber to a lower well testing string portion; and pressure limiting means in communication with said pumping chamber for increasing the volume of said pumping chamber when a positive fluid pressure differential between said pumping chamber and said well annulus exceeds a predetermined value and for preventing venting of said fluid in said pumping chamber to said well annulus when said volume is so increased.

Claim 3

The apparatus of claim 1 wherein said pressure limiting means is disposed substantially between said inlet and outlet valve means.

Claim 4

The apparatus of claim 1 wherein said enclosure means further includes a hole through the wall thereof providing communication between said pumping chamber and said lower testing string portion through bypass passage means defining a flow path bypassing said outlet valve means and said pressure limiter means comprises: a piston sealingly closing said hole to said bypass passage means when in a normal operating position and opening said hole to said bypass passage means when in an actuated position such that said pumping chamber and said lower testing string portion are in communication; and biasing means for biasing said piston toward said normal operating position.

Claim 5

The apparatus of claim 1 wherein said pressure limiting means comprises: piston means reciprocably disposed in said enclosure means and having a first portion and a second portion relatively smaller than said first portion such that an annular area is defined between said first and second portions, said piston means being movable in response to pumping action of said pump such that said volume of said pumping chamber is increased by an amount approximately equal to a displacement of said pump; first sealing means for sealingly separating said pumping chamber and said well annulus adjacent said first portion of said piston means; and second sealing means for sealingly separating said pumping chamber from said well annulus adjacent said second portion of said piston means.

Claim 6

The apparatus of claim 4 further comprising biasing means for biasing said piston means toward a position minimizing said volume of said pumping chamber.

Claim 7

The apparatus of claim 4 wherein: said piston means includes a third portion relatively smaller than said second portion such that another annular area is defined between said second and third portions in communication with said lower testing string portion; said second sealing means is further adapted for sealingly separating said well annulus and said lower testing string portion; and said pressure limiting means further comprises third sealing means for sealingly separating said pumping chamber and said lower testing string portion adjacent said third portion of said piston means.

Claim 8

The apparatus of claim 4 wherein said inlet valve means is mounted on said piston means.

Claim 9

The apparatus of claim 7 further comprising filtering means on said piston means for filtering said fluid in said well annulus flowing to said inlet valve means.

Claim 10

A pressure limiting apparatus comprising: a case having an upper end adapted for attachment to a pump in an upper testing string portion and a lower end adapted for attachment to a lower testing string portion, said case defining a transverse hole therethrough between said upper and lower ends; an inner mandrel having an upper end adapted for attachment to a mandrel in said upper testing string portion and a lower end adapted for attachment to a mandrel in said lower testing string portion, said case and mandrel defining an annulus therebetween; an inlet check valve disposed in said annulus and defining an inlet chamber portion of said annulus in communication with said hole in said case; an outlet check valve disposed in said annulus and defining an outlet chamber portion of said annulus in communication with said lower testing string portion, said inlet and outlet check valves defining a pumping chamber portion of said annulus therebetween, said pumping chamber opening adjacent said pump; a piston reciprocably disposed in said annulus between a normal position and an actuated position, said piston comprising: a first cylindrical portion; and a second cylindrical portion relatively smaller than said first cylindrical portion such that an annulus area is defined therebetween, said annular area being exposed to well hydrostatic pressure in said inlet chamber on an outer side of said piston and exposed to pumping chamber pressure on an inner side of said piston; and biasing means for biasing said piston toward said normal position; wherein, said piston is moved from said normal position to said actuated position when a differential pressure level between said pumping chamber and said inlet chamber acting on said annular area overcomes a force exerted by said biasing means, movement of said piston increasing a volume of said pumping chamber by an amount approximately equal to a displacement of a pump in said upper testing string portion such that said outlet check valve is rendered inoperative.

Claim 11

A pressure limiting apparatus comprising: a case having an upper end adapted for attachment to a pump in an upper testing string portion and a lower end adapted for attachment to a lower testing string portion, said case defining a transverse hole therethrough between said upper and lower ends; an inner mandrel having an upper end adapted for attachment to a mandrel in said upper testing string portion and a lower end adapted for attachment to a mandrel in said lower testing string portion, said case and mandrel defining an annulus therebetween; an inlet check valve disposed in said annulus and defining an inlet chamber portion of said annulus in communication with said hole in said case; an outlet check valve disposed in said annulus and defining an outlet chamber portion of said annulus in communication with said lower testing string portion, said inlet and outlet check valves defining a pumping chamber portion of said annulus therebetween, said pumping chamber opening adjacent said pump; a piston reciprocably disposed in said annulus between a normal position and an actuated position, said piston comprising: a first cylindrical portion; and a second cylindrical portion relatively smaller than said first cylindrical portion such that an annulus area is defined therebetween, said annular area being exposed to well hydrostatic pressure in said inlet chamber on an outer side of said piston and exposed to pumping chamber pressure on an inner side of said piston; and biasing means for biasing said piston toward said normal position; wherein, said piston is moved from said normal position to said actuated position when a differential pressure level between said pumping chamber and said inlet chamber acting on said annular area overcomes a force exerted by said biasing means, movement of said piston increasing a volume of said pumping chamber by an amount approximately equal to a displacement of a pump in said upper testing string portion such that said outlet check valve is rendered inoperative.

Claim 12

The apparatus of claim 9 wherein said inlet check valve is mounted on said piston.

Claim 13

The apparatus of claim 9 further comprising: first sealing means for sealing on said first cylindrical portion of said piston between said pumping chamber and said inlet chamber; and second sealing means for sealing on said second cylindrical portion of said piston between said pumping chamber and said inlet chamber.

Claim 14

The apparatus of claim 9 wherein: said case has a shoulder thereon in said inlet chamber; said piston has a shoulder thereon in said inlet chamber and generally facing said shoulder on said case; and said biasing means is characterized by at least one spring annularly positioned in said inlet chamber between said shoulders.

Claim 15

The apparatus of claim 12 further comprising a plurality of spacers between said spring and at least one of said shoulders for selectively increasing a preload of said spring.

Claim 16

The apparatus of claim 9 further comprising an inlet screen mounted on said piston for filtering fluid flowing from said inlet chamber to said inlet check valve.

Claim 17

The apparatus of claim 9 wherein said piston further includes a third cylindrical portion relatively smaller than said second cylindrical portion thereof.

Claim 18

The apparatus of claim 15 further comprising: first sealing means for sealing on said first cylindrical portion of said piston between said pumping chamber and said inlet chamber; second sealing means for sealing on said second cylindrical portion of said piston between said inlet chamber and said inlet chamber; and third sealing means for sealing on said third cylindrical portion of said piston between said pumping chamber and said outlet chamber.

Claim 19

The apparatus of claim 9 wherein: said inlet check valve comprises a resilient valve portion having an annular lip thereon sealingly engaged with a surface of said pumping chamber when in a closed position; and said outlet check valve comprises a resilient valve portion having an annular lip thereon sealingly engaged with a surface of said pumping chamber when in a closed position.

Claim 20

A downhole testing tool for use on a testing string in a well annulus and having a central flow passageway therethrough, said tool comprising: a tester valve; a positive displacement pump positioned below said tester valve; a packer disposed below said pump and positionable in said well annulus above a formation to be tested, said packer being inflatable by said pump into sealing engagement with said well annulus; a pressure limiter between said pump and said packer for limiting pressure in said pump and packer and preventing overinflation of said packer, said pressure limiter defining a pumping chamber therein adjacent and in pressure transmitting communication with said pump and comprising: an inlet valve for allowing fluid flow from said well annulus into said pumping chamber; an outlet valve for allowing fluid flow from said pumping chamber to said packer; and means for internally bypassing said outlet valve when a positive differential between pressure in said pump and pumping chamber and pressure in said well annulus adjacent thereto exceeds a predetermined level; and a porting sub positionable adjacent said formation for allowing well fluid flow therethrough into said central flow passageway in response to actuation of said tester valve during a testing operation.

Claim 21

A downhole testing tool for use on a testing string in a well annulus and having a central flow passageway therethrough, said tool comprising: a tester valve; a positive displacement pump positioned below said tester valve; a packer disposed below said pump and positionable in said well annulus above a formation to be tested, said packer being inflatable by said pump into sealing engagement with said well annulus; a pressure limiter between said pump and said packer for limiting pressure in said pump and packer and preventing overinflation of said packer, said pressure limiter defining a pumping chamber therein adjacent and in pressure transmitting communication with said pump and comprising: an inlet valve for allowing fluid flow from said well annulus into said pumping chamber; an outlet valve for allowing fluid flow from said pumping chamber to said packer; and means for internally bypassing said outlet valve when a positive differential between pressure in said pump and pumping chamber and pressure in said well annulus adjacent thereto exceeds a predetermined level; and a porting sub positionable adjacent said formation for allowing well fluid flow therethrough into said central flow passageway in response to actuation of said tester valve during a testing operation.

Claim 22

The testing tool of claim 18 wherein said fluid flows from said pumping chamber is continuously sealingly separated from said well annulus.

Claim 23

The testing tool of claim 18 wherein said means for bypassing is characterized by a reciprocable piston in said pumping chamber, said piston being movable such that said volume of said pumping chamber is increased by an amount approximately equal to a displacement of said pump.