Method and apparatus for obtaining subterranean fluid samples

Abstract

Improved methods and apparatus are provided for obtaining multiple fluid samples from subterranean formations of interest. The present invention is particularly well suited for testing nuclear migration in ground water utilizing test wells surrounding a nuclear test site. A plurality of flow ports are provided in the casing each at a depth of a formation of interest, and a sliding sleeve is positioned over each port. A wireline tool is lowered to the selective depth, and downhole electric motor energized to power a pump and pass pressurized fluid to move a first dog radially outward. The downhole tool may be axially moved until the first dog locks into a groove provided in the casing. Fluid entering the casing is sealed above and below the sliding sleeve. Fluid pressure may then be applied to move a second dog radially outward to engage the sliding sleeve, and a control valve regulated to apply fluid pressure to axially move the sleeve and open the port. Entering fluid may be tested by a downhole tester, and a signal transmitted to the surface. If the fluid is determined to be representative of the downhole fluid to be tested, fluid is then passed to a chamber within the downhole tool so that it may subsequently be retrieved to the surface. The release of hydraulic pressure allows the dogs to disengage from the casing and the sliding sleeve, and the tool may be moved to another depth. Using the procedures of the present invention, multiple fluid samples may be reliably obtained at selected depths with a single wireline run, thereby substantially reducing costs.