1. Field of the Invention
The present invention relates to an assembly employed for sealing and isolating predetermined areas in a well bore, and more particularly, but not by way of limitation, to an improved sealing apparatus for repairing breaches in a portion of a casing in the well bore.
2. Description of Prior Art
During the drilling of a well in the exploration of fluid minerals, such as oil and gas, a casing is secured in a well bore by a cement slurry which is injected between the exterior of the casing and the well bore. The casing functions to provide a permanent well bore of known diameter through which drilling, production or injection operations may be conducted; and the casing also provides the structure for attaching surface equipment required to control and produce fluids from the well bore or for injecting fluids therein. In addition, the casing prevents the migration of fluids between subterranean formations through the well bore, i.e., the intrusion of water into oil or gas formations or the pollution of fresh water by oil, gas or salt water.
Testing the mechanical integrity of the casing and the ability of the casing to isolate subterranean formations may be required for producing wells, and is mandated by law for injection and disposal wells. Casing which has been cemented in an injection or disposal well bore is required to pass a mechanical integrity test to assure that no breaches in the casing exists. If the casing fails the mechanical integrity test, the casing must be repaired. Mechanical integrity failure can result from various means, such as corrosion, old perforations, or other breaches in the casing including joint leaks, split casing or parted casing.
Mechanical integrity failures are normally repaired by either replacing the defective casing, cementing a new casing inside the old casing, or injecting cement into the breach of the casing which is commonly known as "squeeze cementing". Replacement of defective casing is often not feasible because of the initial completion method used and the risk in damaging additional casing because of stress imparted on the casing during such an operation. Because the operation of inserting a new casing inside the old casing is expensive, this option may not be economically feasible. Additionally, squeeze cementing is not always economically feasible, and is inappropriate for certain types and depths of subterranean formations. Furthermore, when squeeze cementing is utilized, satisfactory results are not always obtained. Finally, because of the amount of time required for these operations, each of these remedies are costly in terms of time that the well is out of service.
To avoid the expense and time associated with the above-mentioned remedies, sealing apparatus have heretofore been utilized for sealing and isolating casing at the point of the mechanical integrity failure. However, when employing the sealing apparatus of the prior art, problems have been encountered. For example, when employing the sealing apparatus of the prior art, the annular flow of fluids about a tubing string, which is formed of a plurality of tubing sections and tubing collars and extends through the sealing apparatus, is often restricted by the upset of the tubing string located between the tubing section and the tubing collar, thus producing a hydraulic braking effect. Further, the annular flow may be restricted during mechanical integrity testing which requires an annulus between the tubing string and the casing. Lastly, the sealing apparatus of the prior art is often ineffective because the resilient sealing elements become worn or deteriorate due to rough or cement-coated interior casing walls when the sealing apparatus is inserted into the well bore.
Thus, a need has long existed for an improved sealing apparatus which can provide substantially unrestricted annular fluid flow about the tubing string and which has greater durability, while remaining inexpensive and time efficient. It is to such an improved sealing apparatus that the present invention is directed.