A downhole method for preparing and/or providing isolation at a predetermined position in an existing well having a top and a first well tubular metal structure arranged in a wellbore, the first well tubular metal structure having a longitudinal extension, comprising inserting a downhole tool comprising a bit on a projection part in the first well tubular metal structure, positioning the downhole tool opposite the predetermined position, separating a first section being an upper part of the first well tubular metal structure from a second section being a lower part of the first well tubular metal structure by machining into and along a circumference of the first well tubular metal structure, moving the downhole tool a predetermined distance along the longitudinal extension in the first section of the first well tubular metal structure to a second position above the predetermined position, and separating a first part of the first section of the first well tubular metal structure from a second part of the first section of the first well tubular metal structure by machining into and along a circumference of the first well tubular metal structure, providing an uncased opening between the second part of the first section and the second section.

A plug system includes a lower plug, an upper plug, and a sleeve configured to be positioned at least partially within the lower plug, the upper plug, or both. The sleeve defines one or more channels in an outer surface thereof. The sleeve is configured to shift axially from a first position into a second position with respect to the lower plug. In the first position, fluid is prevented from flowing through the one or more channels. In the second position, the fluid is permitted to flow through the lower plug via the one or more channels.

A downhole well system can use a fiber optic cable that can be positioned downhole along a length of a wellbore. The well system may include a top plug, a bottom plug, or both that are used to contain a cement slurry during a cementing operation. The movement of the top plug and bottom plug may cause acoustic noise along the downhole portion of the casing. A reflectometer may detect the acoustic noise from strain in the fiber optic cable and determine a location of the top plug or bottom plug downhole.

A downhole well system can use a fiber optic cable that can be positioned downhole along a length of a wellbore. The well system may include a top plug, a bottom plug, or both that are used to contain a cement slurry during a cementing operation. The movement of the top plug and bottom plug may cause acoustic noise along the downhole portion of the casing. A reflectometer may detect the acoustic noise from strain in the fiber optic cable and determine a location of the top plug or bottom plug downhole.

A downhole tool for cleaning and sealing a wellbore includes a wash tool configured at a downhole end of the downhole tool to generate pulses of a first fluid at a first frequency and a first pressure for washing a target interval of a wellbore. The downhole tool further includes a plugging tool configured uphole or downhole from the wash tool to generate pulses of a second fluid at a second frequency and a second pressure for depositing a sealing plug at the target interval of the wellbore. The second fluid has a higher viscosity than the first fluid, the second frequency is lower than the first frequency, and the second pressure is higher than the first pressure.

A downhole tool for cleaning and sealing a wellbore includes a wash tool configured at a downhole end of the downhole tool to generate pulses of a first fluid at a first frequency and a first pressure for washing a target interval of a wellbore. The downhole tool further includes a plugging tool configured uphole or downhole from the wash tool to generate pulses of a second fluid at a second frequency and a second pressure for depositing a sealing plug at the target interval of the wellbore. The second fluid has a higher viscosity than the first fluid, the second frequency is lower than the first frequency, and the second pressure is higher than the first pressure.

A downhole tool for cleaning and sealing a wellbore includes a wash tool configured at a downhole end of the downhole tool to generate pulses of a first fluid at a first frequency and a first pressure for washing a target interval of a wellbore. The downhole tool further includes a plugging tool configured uphole or downhole from the wash tool to generate pulses of a second fluid at a second frequency and a second pressure for depositing a sealing plug at the target interval of the wellbore. The second fluid has a higher viscosity than the first fluid, the second frequency is lower than the first frequency, and the second pressure is higher than the first pressure.

A downhole tool for cleaning and sealing a wellbore includes a wash tool configured at a downhole end of the downhole tool to generate pulses of a first fluid at a first frequency and a first pressure for washing a target interval of a wellbore. The downhole tool further includes a plugging tool configured uphole or downhole from the wash tool to generate pulses of a second fluid at a second frequency and a second pressure for depositing a sealing plug at the target interval of the wellbore. The second fluid has a higher viscosity than the first fluid, the second frequency is lower than the first frequency, and the second pressure is higher than the first pressure.

A stage cementing tool has a mandrel defining a central flow passage and a plurality of fully open cement flow ports. A packer disposed about the mandrel is movable from an unset to a set position. An opening sleeve is movable in the mandrel from a closed position to an open position in which the flow ports are exposed to allow flow therethrough. The opening sleeve is operable to move the setting sleeve to set the packer against the wellbore as it moves in the mandrel from the closed to the open position.

A cementing tool and a method for cementing a casing string using the cementing tool is provided. The cementing tool comprises threaded top and bottom openings for attaching to a casing string, a plurality of ports, and a plurality of shear plugs shaped to fit within the ports. In the method, a casing string comprising the cementing tool is run into a well and the cementing process of the casing string is initiated. When the casing shoe of the casing string becomes plugged, the cementing tool is activated without removing the casing string from the well. Activation of the cementing tool releases pressure trapped in the cementing tool, thereby releasing the shear plugs from the ports and opening the ports to create alternative passages for the cement to complete the cementing process.