Pressure limiter for a downhole pump and testing apparatus

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.

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.