Method and apparatus for the evaluation of formation pressure

摘要

Early evaluation testing of a subsurface formation (16) by monitoring pressure fall-off in the formation in accomplished by providing a column of fluid in the well (10) having an overbalanced, hydrostatic pressure at the subsurface formation greater than a natural formation pressure of the subsurface formation. A testing string (18) of the invention is run into the well (10), the testing string including a packer (24), a pressure monitor (26) and a closure tool (22) arranged to close a bore of the testing string. The formation is shut in by setting the packer (24) and closing the bore of the testing string with the closure tool (22), thereby initially trapping the overbalanced hydrostatic pressure of the column of fluid in the well below the packer (24). The pressure in the well below the packer (24) is then monitored as it falls off toward the natural formation pressure. The data can be extrapolated to estimate the natural formation pressure based upon a relatively short actual test interval on the order of ten to fifteen minutes. $$