Zeolites are known to be pozzolanic materials and may be stabilized with alkali or Portland cement in the presence of sufficient water. In most cases, it is possible to accelerate or retard the setting time by using conventional cement additives. However, it is the final strength of the composition that is of industrial concern.
Conventionally, a wellbore is drilled using a drilling fluid that is continuously circulated down a drill pipe, through a drill bit, and upwardly through the wellbore to the surface. Typically, after a wellbore has been drilled to total depth, the drill bit is withdrawn from the wellbore, and circulation of the drilling fluid is stopped, thereby initiating a shutdown period. During the shutdown period, the drilling fluid is typically left in the wellbore, and a filter cake of solids from the drilling fluid, and additional dehydrated drilling fluid and gelled drilling fluid, typically forms on the walls of the wellbore.
The next operation in completing the wellbore usually involves running a pipe string, e.g., casing, into the wellbore. While the pipe is being run, the drilling fluid left in the wellbore remains relatively static. During that time, the stagnant drilling fluid progressively increases in gel strength, whereby portions of the drilling fluid in the wellbore can become increasingly difficult to displace during subsequent clean-up operations.
After the pipe is run in the wellbore, the next operation typically involves cleaning out the wellbore, which may be accomplished by re-initiating circulation of drilling fluid. The drilling fluid is circulated downwardly through the interior of the pipe and upwardly through the annulus between the exterior of the pipe and the walls of the wellbore, while removing drilling solids, gas, filter cake, dehydrated drilling fluid, gelled drilling fluid, and any other undesired substances needing to be removed from the wellbore.
After clean-up operations are performed in the wellbore, primary cementing operations are typically performed therein. Namely, the pipe is cemented in the wellbore by placing a cement slurry in the annulus between the pipe and the walls of the wellbore. The cement slurry sets into a hard impermeable mass, and is intended to bond the pipe to the walls of the wellbore whereby the annulus is sealed and fluid communication between subterranean zones or to the surface by way of the annulus is prevented.
During any of the above or other operations performed in the wellbore, a number of problems can occur, including difficulty in removing portions of the drilling fluid, or inability to achieve a satisfactory bond between the pipe and the walls of the wellbore because of drilling fluid that remained in the wellbore during primary cementing operations.
Difficulty in removing portions of the drilling fluid is often caused by an increase in the gel strength of the drilling fluid, which is often due to the amount of time the drilling fluid has been left stagnant in the wellbore. In addition, polymeric viscosifiers and additives in the drilling fluid contribute to the formation of a filter cake that is generally very stable and can be difficult to remove. If appreciable drilling fluid and/or filter cake remain in the wellbore or on the walls of the wellbore, a satisfactory bond between the pipe, primary cement and the walls of the wellbore will not be achieved, which can lead to fluid leakage through the annulus and other problems.
Removal of the drilling fluid and filter cake from the wellbore is often attempted by running flushes, washes or spacer fluids through the annulus between the pipe and the walls of the wellbore prior to cementing. Other methods for removing drilling fluid and preventing filter cake from interfering with subsequent primary cementing operations include at least partially displacing the drilling fluid with a settable spotting fluid composition (also referred to as a “settable spotting fluid”) before the drilling fluid in the wellbore has had a chance to gain significant gel strength. Conventional settable spotting fluids include a material that sets over time, such as blast furnace slag, fly ash, and similar hydraulic components. Still other methods for achieving satisfactory primary cementing operations when deposits of filter cake are an issue include laying down a filter cake including a settable material on the walls of the wellbore and activating the settable material to set.
The present embodiments provide zeolite compositions having enhanced strength and desirable setting times. In particular, such compositions are useful as wellbore treating fluids in the form of settable spotting fluids in drilling operations.
USPTO Backgrounds
USPTO Backgrounds