Typical construction of an oil or gas well includes the operations of assembling a casing string, inserting the casing string into a wellbore, and cementing the casing in place in the wellbore. Casing assembly involves connecting multiple individual lengths of pipe (or “joints”) to form an elongate casing string. Threaded connections are usually used to join the individual lengths of pipe, requiring the application of torque to “make up” the connections, or to “break out” the connections should the string need to be disassembled.
After a wellbore has been drilled to a desired depth into a subsurface formation, by means of a rotating drill bit mounted to the end of a drill string, the drill string is withdrawn and the casing string is then inserted essentially coaxially within the wellbore. In the alternative method known as casing drilling (or “drilling with casing”), the wellbore is drilled with a drill bit mounted to the bottom of the casing string, eliminating the need for a separate drill string. After the well is drilled, the casing remains in the wellbore. As used in this patent document, the term “drill string” is to be understood, in the context of the drilling phase, as referring to the casing string for purposes of well construction operations using casing drilling methods.
During the drilling phase of well construction, a selected drilling fluid (commonly called “drilling mud”) is pumped under pressure downward from the surface through the drill string, out through ports in the drill bit into the wellbore, and then upward back to the surface through the annular space that forms between the drill string and the wellbore (due to the fact that the drill bit diameter is larger than the drill string diameter). The drilling fluid, which may be water-based or oil-based, carries wellbore cuttings to the surface, and can serve other beneficial functions including drill bit cooling, and formation of a protective cake to stabilize and seal the wellbore wall.
Once the well has been drilled to a desired depth and the casing is in place within the wellbore, the casing is cemented into place by introducing a cement slurry (commonly referred to simply as “cement”) into the wellbore annulus. This is typically done by introducing an appropriate volume of cement into the casing string (i.e., a volume corresponding to the volume of the wellbore annulus), and then introducing a second and lighter fluid (such as drilling mud or water) into the casing under pressure, such that the second fluid will displace the cement downward and force it out and around the bottom of the casing, and up into the wellbore annulus. In the typical case, this operation is continued until the cement has risen within the wellbore annulus up to the top of the casing. Once thus cemented, the casing acts to structurally line the wellbore and provide hydraulic isolation of formation fluids from each other and from wellbore fluids.
It is increasingly common in the drilling industry to use top-drive-equipped drilling rigs instead of traditional rotary table rigs, and to install casing (an operation commonly referred to as “casing running”) and/or to drill with casing directly using the top drive. Casing running tools, such as the “Gripping Tool” described in U.S. patent application Ser. No. 11/912,665 (Publication No. US 2008/0210063), connect to the top drive quill and support these well construction operations by engaging the upper end of the tubular string (i.e., drill string or casing string, as the case may be) so as to allow transfer of axial and torsional loads between the tubular string and the top drive, and to allow the flow of fluids (such as drilling mud and cement) into or out of the casing string through a central passage or bore in the tool. Such tools thus enable the top drive to be used for make-up and break-out of connections between joints of pipe, hoisting and rotation of tubular strings, casing fill-up, circulation of drilling mud, and cementing of casing.
Whenever a casing running tool (or “CRT”) is disengaged and removed from the casing after flowing liquids into a drill string or casing string, liquids such as drilling mud tend to drain from the tool bore, resulting in undesirable spillage onto the drill floor of the drilling rig and/or elsewhere.
Additionally, when a CRT is used to add liquids such as drilling mud or cement to a partially-filled casing string (i.e., casing fill-up and cementing operations, respectively), the liquid displaces air which through gravity separation tends to accumulate or become trapped at the upper end of the casing string below the CRT. In situations where the CRT is in sealing engagement with the casing, this results in an increase of air pressure within the casing. When the CRT is then removed from the upper end of the casing string, the pressurized air abruptly vents to atmosphere, which is typically undesirable even for relatively low levels of trapped pressure.
During cementing operations, the cement is frequently denser than the liquids being displaced, leading to conditions where the cement continues to fall within the wellbore after pumping is stopped, tending to induce suction pressure in the casing and hence to draw air into the casing, which may then interfere with subsequent fluid displacement operations.
For the foregoing reasons, there is a need for apparatus and methods for improving the management of fluids in conjunction with the use of casing running tools, to prevent or minimize spillage of drilling mud or cement, to mitigate the effects of trapped air during casing fill-up, and to prevent air entry into the casing due to suction.
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