GB1378596A - Borehole close-off tool - Google Patents

Abstract

1378596 Boring earth &c SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ NV 28 Feb 1972 9006/72 Heading E1F A close-off tool for inclusion in a drill string comprises a mandrel M telescopic in a housing H, an inflatable packer P, a first channel 30, 31, 32, 35, 36, 37 between a pressure source 23 and the interior of the packer, a second channel formed by bores 28, 43, a third channel 17, 44 between the bore 28 and the space about the mandrel, a coupling 45 for the transmission of torque between mandrel and housing, and valves V1, V2, V3 in the respective channels and operable by relative displacement of the mandrel and housing. During drilling the tool is in the string above the drill collars, the coupling is engaged and mud is pumped down the string and through the open valve V2 (see Fig. 1). Sudden entry of formation fluid is controlled by lowering the mandrel to close valve V2 and open valve V1 so that mud flows through openings 29 to force a piston 27 down and cause oil in the chamber 23 below the piston to flow through the first channel into the packer to expand it into engagement with the borehole wall 54. The mud pumps are stopped and the mandrel is raised to close the valve V1 and open the valve V2 so that the increased pressure in the lower part of the borehole may be measured at the surface. Heavier mud of a density sufficient to control the increased pressure is mixed. The valve V2 is closed and the valve V1 is opened by lowering the mandrel and the pumps are restarted pumping the heavier mud. The mandrel is partially rotated and slightly raised, the valve V2 remaining closed but the valve V3 opening so that the denser mud may be pumped to replace the mud in the annulus about the string above the openings 17 (see Fig. 5). When the annulus mud is replaced the mandrel is lowered to open the valve V1 and the pumps are stopped so that the packer deflates. The mandrel is partially rotated and raised to reengage the coupling, the pumps are restarted pumping heavier mud and drilling is resumed.