March 2001 Supplement  Case Study

Pressure-activated sealant repairs casing leaks

Doug Torr,* CamWest and David Rusch,** Seal-Tite, LLC
* Dtorr@camwestlp.com
** drusch@seal-tite.net

Bottom line. Sustained casing pressure and fluid loss due to casing leaks are ongoing and expensive problems in older oil and gas fields. To more safely and economically repair casing leaks in two mature fields in Wyoming, CamWest, Inc. utilized Seal-Tite’s pressure-activated sealant technology in five wells. Mechanical integrity, confirmed by subsequent tests, was restored in four of the five wells, saving about $135,000 compared to conventional approaches. The sealant operations were performed without risky well interventions.

The problem. With age, the integrity of all wellbores can deteriorate from pressure and thermal fluctuations, corrosion, rod pumping, etc., which can cause casing leaks. These leaks result in sustained casing pressure or fluid loss. State and federal agencies have adopted regulations requiring that all injection wells must pass regular mechanical integrity tests (MITs). The conventional solution for injection well casing leaks has been an expensive and often risky well workover. When the pressure leak is not severe and suspected to be due to a joint leak and not widespread corrosion, Seal Tite’s pressure-activated sealant can be an option.

Pressure-activated sealant. A unique, pressure-activated sealant is specifically designed to seal leaks in wells and severe-environment hydraulic systems. The sealant is unique in that a pressure drop through a leak site causes the sealant fluid to polymerize into a flexible solid seal. Seal-Tite has performed sealant operations on the following systems: subsurface safety valves; wellhead pack-off and hanger seals; casing and tubing packers, sleeves and connections; wellhead valves; riser connectors; umbilical lines; and pressure due to microannular cement leaks.

The sealant reaction is analogous to blood coagulating at a cut. The sealants remain fluid until the sealant is released through a leak site. Only at the point of differential pressure, through the leak site, will the sealant reaction occur. The monomers and polymers in the formula are crosslinked by the polymerizing chemicals. As the reaction proceeds, the polymerized sealant plates out on the edges of the leak site and simultaneously links across the leak site to seal the leak. The resulting seal is a flexible bond across the leak. The remainder of the sealant will remain fluid and will not clog the hydraulic system or well. The sealants can be left in the system or flushed out.

Experience in two Wyoming fields. CamWest, is the operator of Winkleman Dome and Lander fields west of Casper, Wyoming. Winkleman Dome was discovered in 1944, Lander was discovered in 1910. Both have a total of 260 wells on 10-acre spacing and use waterflooding as a secondary recovery mechanism. Injection wells must pass a MIT every five years, per EPA guidelines. The MIT requires that the tubing-casing annulus must hold 1,000 psi for a period of 30 min. with less than 10% leak-off.

Due to the age of the wellbores, casing leaks are common and remedial workovers can be costly and frequently result in plugging and abandoning the well. In September 2000, CamWest identified six injection wells that required remedial actions to repair casing leaks prior to performing MITs on the wells. The CamWest wells had pressure test profiles as shown in the table below.

In an effort to identify a lower-cost, lower-risk alternative to conventional leak repair workovers, CamWest contracted Seal-Tite to utilize its pressure-activated sealant technology. To verify leak severity, fresh water was injected into the tubing-casing annulus, and pump-in rates, fluid volumes and injection pressures were monitored. Sonic fluid levels were shot on all wells to help determine depth of the leak site. Once leak severity was determined and qualified as a proper candidate, sealant pumping equipment was rigged up. All except the sixth well – which had a severe leak of 1 bpm at 100 psi – were considered candidates.

Sealant treatments. The sealant operation required only a mixing tank, a triplex pump and associated hoses, gauges and fittings necessary to tie into the annulus and pump the sealant down the annulus. Initially, the annulus was prepared by pumping a wetting agent gel. The gel was followed by the Seal-Tite sealant pill. Volume and concentration of the pill was adjusted based on depth and severity of the leak. The pill was displaced down the annulus using treated fresh water.

During the sealant injection process, the volume of material injected, injection pressure and flowrate were monitored to determine when the sealant reached the leak site and to control the sealing process. As the polymerization process occurred within the leak site, injection pressure and flow rate were adjusted to maximize the reaction rate and quickly establish a low-pressure seal.

Once the leak was sealed at low pressure, pressure was increased to break the weak links in the polymerized sealant and recreate the leak. As liquid sealant flowed through the new leak site, it polymerized and linked with the existing polymerized sealant. By this process, the leak was resealed and a stronger bond established. This new seal was allowed to cure for a few minutes, and additional sealant was injected in a repeat of the described sealing process.

This breaking and resealing of the leak was continued at higher pressures until a strong seal was created and the leak cured at the maximum casing working pressure. The pressure was maintained at maximum working pressure and monitored for 12 hr. If no leakage was detected, the MIT was performed.

With minor variations of the outlined procedure, leaks were repaired in four out of the five CamWest wells. The technician attempted to cure the more serious leak in Well 5, but was not successful. The combination of higher pressure and rapid leakoff prevented establishing a seal. Geometry of leaks is critical. Long narrow leaks can be sealed, while circular holes are difficult to seal.

Economic benefits. Typical expenditures for casing-leak workovers on similar wells in the field have been in the range of $35,000 – $55,000. For the five wells mentioned, conventional workover costs would have been $225,000, or an average of $45,000 per well. Using the pressure-activated sealant technology, total cost was $90,000, or an average of $22,500 per well – roughly a 50% reduction.

About 85% of treatment costs were sealant costs. Jobs are priced based on an estimate of the sealant to be used and the difficulty of the operation. The sealant process was performed using only two technicians and very little equipment, and intervention by a workover rig was not required. Thus, resumption of operations were expedited, and risks of damage to equipment or injury to personnel were reduced. PTD