Good cement bonds are required when cementing well bore casings into the wells. Poor cement bonds can result in formation pressures and fluids to breach to the surface, or to other formations within the cemented area. This will result in surface or underground blowouts, and a loss of well control.
Cement bonds are usually better in vertical wells, than those found in directional or horizontal wells. It is difficult to centralize casing in these build sections, but it is better when using rigid centralizer systems. The biggest problem is the circulation of the cement slurry to surface. The cement will usually find the easiest circulation path from the bottom of the well to surface. On directional wells, this path is usually the upper portion of the horizontal well, while the casing lies on the lower portion of the well. Movement of the casing during cement circulation is usually the best way to disrupt any type of cement channeling. The current type of cementing heads used, require piping that will not allow rotation of the cement head at surface, only reciprocation. Rotation can be achieved by use of a bearing assembly placed between the surface piping and the casing. As the casing weight rests in the casing slips in the rotary table, rotation of the table will rotate the casing without rotating the surface piping. Unfortunately, rotation and reciprocation of the casing string while cementing cannot be achieved simultaneously.
The newly designed Casing Cement Head (CMT) requires no piping tied to the cement head. This allows the CMT to rotate without the use of bearing assemblies and without the use of rotary tables. The top of the CMT is connected directly to the top drive, while the bottom of the CMT is connected directly to the casing. This CMT allows rotation and reciprocation of the casing simultaneously. This allows better casing movement down hole to eliminate cement channeling. Reciprocating the casing at the same time can cause alternating laminar and turbulent flows of the cement, breaking down even further, any forming of channels, and removal of trapped drilling fluids. Simultaneous movement also lowers the torsional loads to the casing and connections.
The top plug (located inside the CMT) has a through bore, and all circulations pass directly through the plug. Deployment of the top plug from the CMT is achieved by launching a ball that seats inside the through bore of the top plug. When the ball seats inside the top plug, the pressure above the plug forces the top plug down the casing, in the same manner that a typical solid top plug is moved. The launching of the top plug ball can be achieved manually or by remote control. The top plug ball can be launched on the fly (without stopping pumps) if required. This CMT does not have to be located at the rig floor when the top plug is launched, as remote activation can carry a distance of 500 feet.