Method for testing oil wells

Claim 1

A method of sampling an underground formation which is intersected by a fluid bore hole extending from the surface to the formation with a test string containing a bias-closing means within an annulus pressure operated power actuating means which is operable to open and close a sampler attached to said power actuating means, comprising the steps of: placing said test string in said fluid filled borehole; providing an open flow channel between said bias-closing means in said annulus pressure operated power actuating means and the annulus surrounding said test string when said test string is positioned in an upper portion of said borehole; lowering said test string into said borehole downwardly from said upper portion until said power actuating means and said attached sampler is in the vicinity of the formation to be tested; concurrent with said lowering step, utilizing the pressure of fluid in the annulus adjacent said annulus pressure operated power actuating means to supplement said bias-closing means thereby preventing operation of said sampler; isolating said formation from the annulus area surrounding said power actuating means whereby pressure increases in the fluid in said annulus area will not affect the pressure in said formation; closing said flow channel between said bias-closing means and said annulus; increasing the pressure of said fluid in said annulus area to a first predetermined level sufficient to overcome said supplemented bias-closing means, thereby opening said sampler and allowing formation fluid to flow through said test string; additionally increasing the pressure of said fluid in said annulus area above a second predetermined level sufficient to further overcome said supplemented bias-closing means, and to close said sampler thereby trapping a fluid sample; and locking said sampler in the closed position in response to said additional pressure increase.

Claim 2

A method of sampling an underground formation which is intersected by a fluid bore hole extending from the surface to the formation with a test string containing a bias-closing means within an annulus pressure operated power actuating means which is operable to open and close a sampler attached to said power actuating means, comprising the steps of: placing said test string in said fluid filled borehole; providing an open flow channel between said bias-closing means in said annulus pressure operated power actuating means and the annulus surrounding said test string when said test string is positioned in an upper portion of said borehole; lowering said test string into said borehole downwardly from said upper portion until said power actuating means and said attached sampler is in the vicinity of the formation to be tested; concurrent with said lowering step, utilizing the pressure of fluid in the annulus adjacent said annulus pressure operated power actuating means to supplement said bias-closing means thereby preventing operation of said sampler; isolating said formation from the annulus area surrounding said power actuating means whereby pressure increases in the fluid in said annulus area will not affect the pressure in said formation; closing said flow channel between said bias-closing means and said annulus; increasing the pressure of said fluid in said annulus area to a first predetermined level sufficient to overcome said supplemented bias-closing means, thereby opening said sampler and allowing formation fluid to flow through said test string; additionally increasing the pressure of said fluid in said annulus area above a second predetermined level sufficient to further overcome said supplemented bias-closing means, and to close said sampler thereby trapping a fluid sample; and locking said sampler in the closed position in response to said additional pressure increase.