Offshore drill stem testing

Claim 2

A drill stem testing apparatus comprising: tester means including a mandrel movable upwardly and downwardly within a housing, said tester means having valve means operated in response to upward and downward movement for opening and closing a fluid passageway through said housing and said mandrel; first piston and cylinder means coupled respectively to said mandrel and said housing with the upper face of said piston being subject to the pressure of fluids in said passageway and the lower face thereof being subject to the pressure of fluids in the well annulus; second piston and cylinder means coupled respectively to said mandrel and said housing and enclosing a low pressure chamber above said piston means, the lower face of said piston means being subject to the pressure of fluids in the well annulus to provide an upwardly directed bias force tending to cause upward movement of said mandrel; packer means for isolating a formation interval to be tested; and slip joint means for connecting said housing to said packer means so that said mandrel and said housing can be moved longitudinally in the well bore with respect to said packer means.

Claim 3

The drill stem testing apparatus of claim 1 wherein said slip joint means includes a mandrel telescopically disposed within a housing, said mandrel and housing respectively having third piston and cylinder means with the upper face of said third piston means being subject to the pressure of fluids within said mandrel and the lower face thereof being subject to the pressure of fluids in the well annulus.

Claim 4

The drill stem testing apparatus of claim 1 further including seal means for preventing fluid leakage between said mandrel and said housing, the transverse cross-sectional area of said first piston means being substantially equal to the transverse area circumscribed by said seal means, so that the pressure of fluids within said mandrel acts with equal force in opposite longitudinal directions thereon.

Claim 5

The apparatus of claim 1 wherein said valve means includes longitudinally spaced valve elements on said mandrel, said tester means further including an annular sample chamber between said mandrel and said housing, said valve elements closing the upper and lower ends of said sample chamber to trap a sample of formation fluids.

Claim 6

A drill stem testing apparatus comprising: tester means including a mandrel movable upwardly and downwardly within a housing, said tester means having valve means operated in response to upward and downward movement for opening and closing a fluid passageway through said housing and said mandrel; first piston means on said mandrel sealingly slidable within first cylinder means on said housing; ports through the wall of said mandrel above said piston means and through the wall of said cylinder means below said piston means to subject the upper face of said piston means to the pressure of fluids within said mandrel and the lower face thereof to the pressure of fluids in the well annulus surrounding said housing; second piston means on said mandrel sealingly slidable within second cylinder means on said housing, said second piston and cylinder means enclosing a low pressure chamber above said second piston means; a port through the wall of said second cylinder means below said second piston means to subject the lower face thereof to the pressure of fluids in the well annulus surrounding said housing; packer means for isolating a formation interval to be tested; and a connection including longitudinally slidable parts for coupling said housing to said packer so that said tester can be moved longitudinally in the well bore to a limited extent with respect to said packer means.

Claim 7

A drill stem testing apparatus comprising: tester means including a mandrel movable upwardly and downwardly within a housing, said tester means having valve means operated in response to upward and downward movement for opening and closing a fluid passageway through said housing and said mandrel; first piston means on said mandrel sealingly slidable within first cylinder means on said housing; ports through the wall of said mandrel above said piston means and through the wall of said cylinder means below said piston means to subject the upper face of said piston means to the pressure of fluids within said mandrel and the lower face thereof to the pressure of fluids in the well annulus surrounding said housing; second piston means on said mandrel sealingly slidable within second cylinder means on said housing, said second piston and cylinder means enclosing a low pressure chamber above said second piston means; a port through the wall of said second cylinder means below said second piston means to subject the lower face thereof to the pressure of fluids in the well annulus surrounding said housing; packer means for isolating a formation interval to be tested; and a connection including longitudinally slidable parts for coupling said housing to said packer so that said tester can be moved longitudinally in the well bore to a limited extent with respect to said packer means.

Claim 8

The drill stem testing apparatus of claim 5 further including seal means for preventing fluid leakage between said mandrel and said housing, the transverse cross-sectional area of said first piston means being substantially equal to the transverse area circumscribed by said seal means.

Claim 9

The drill stem testing apparatus of claim 6 wherein said longitudinally slidable parts are constituted by a mandrel telescopically disposed within a housing, said last-mentioned mandrel and housing respectively having third piston and cylinder means with the upper face of said third piston means being subject to the pressure of fluids within said mandrel and the lower face thereof being subject to the pressure of fluids in the well annulus.

Claim 10

The drill stem testing apparatus of claim 7 wherein said third piston means is sized with respect to said mandrel so that vertically directed forces on said mandrel due to fluid pressure within said mandrel are balanced.

Claim 11

A drill stem testing apparatus for use in offshore testing from a floating vessel, comprising: a first string of pipe extending from the vessel into the well bore; a second string of pipe having a predetermined weight; first slip joint means including concentrically disposed members that are freely slidable relative to one another between longitudinally spaced positions for connecting the lower end of said first string to the upper end of said second string; tester means including a mandrel coupled to the lower end of said second string and movable upwardly and downwardly within a housing, said tester means having valve means operated in response to said upward and downward movement for closing and opening a fluid passageway through said housing and mandrel; piston and cylinder means operatively associated with said tester means and adapted to balance out and cancel the effect on said tester means of fluid pressure changes inside said tester means during a drill stem test; packer means for isolating a formation interval to be tested; and second slip joint means including concentrically disposed members that are freely slidable relative to one another between longitudinally spaced positions for connecting said tester means to said packer; said mandrel being moved upwardly by lifting said first and second pipe strings jointly, said mandrel being forced downwardly by lowering said first string to close said first slip joint means, so that the weight of said second string is applied to said mandrel; said second slip joint means isolating said packer means from the lifting forces applied to said tester means.

Claim 12

A drill stem testing apparatus for use in offshore testing from a floating vessel, comprising: a first string of pipe extending from the vessel into the well bore; a second string of pipe having a predetermined weight; first slip joint means including concentrically disposed members that are freely slidable relative to one another between longitudinally spaced positions for connecting the lower end of said first string to the upper end of said second string; tester means including a mandrel coupled to the lower end of said second string and movable upwardly and downwardly within a housing, said tester means having valve means operated in response to said upward and downward movement for closing and opening a fluid passageway through said housing and mandrel; piston and cylinder means operatively associated with said tester means and adapted to balance out and cancel the effect on said tester means of fluid pressure changes inside said tester means during a drill stem test; packer means for isolating a formation interval to be tested; and second slip joint means including concentrically disposed members that are freely slidable relative to one another between longitudinally spaced positions for connecting said tester means to said packer; said mandrel being moved upwardly by lifting said first and second pipe strings jointly, said mandrel being forced downwardly by lowering said first string to close said first slip joint means, so that the weight of said second string is applied to said mandrel; said second slip joint means isolating said packer means from the lifting forces applied to said tester means.

Claim 13

The testing apparatus of claim 9 further including bias means responsive to the hydrostatic head of fluids in the well bore for applying a lifting force to said mandrel when said mandrel is moved downwardly with respect to said housing.

Claim 14

The testing apparatus of claim 9 wherein said first and second slip joints each include piston and cylinder means for cancelling the effect thereon of changes in fluid pressures within said pipe strings.