Ken E. Davis
The repair of small leaks detected in the casing annulus of wells frequently require special methodology. Although these leaks can be detected while the well is in service, they are extremely difficult to locate and repair using standard well maintenance techniques. Most well testing tools are designed for significantly higher pressures than those usually encountered in specialty well systems, such as those used in the Underground Injection Control (UIC) Program.
Historically, "Stop Leak" methods, such as those used to repair radiators and tires, have proved effective. However, this type of repair is normally effective in only one direction and the blockage across the leak is susceptible to being removed by tools moving across the leak area Micro-fine cement has also been used successfully. Unlike the "Stop-Leak" type repair, the micro-fine cement will frequently move into the leak matrix and stop the leak or restrict the flow path. Unfortunately, micro-fine cement has a very low compressive strength and cannot withstand very high pressure differentials or cyclic service.
A few teflon based sealants, similar to the thread dope used on threaded connections, have been used successfully. The teflon particles extrude into the leak matrix and seal off the leak. Unlike the micro-fine cement, teflon is pliable and conforms to the changing configuration of the leak path during cyclic or changing pressure differentials.
A special laboratory testing device was developed to evaluate various types of tubular failures as well as specific leak repair formulations. This article discusses the design of the test apparatus, presents the results of the initial laboratory investigation, and includes recommendations for field tests. The advantages of laboratory testing are outlined and recommendations made for equipment modifications.
AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995