This paper provides laboratory and field-test results of a thermally compensated fluid-inflated packer system. This system greatly reduces the chance of sealing-element failure when inflatable packers or plugs are used where the borehole fluid changes temperature more than 50°F (10°C). To date, a primary cause of failure in achieving zonal isolation while using inflatable packers and plugs is the change in temperature of the borehole and inflation fluids once the packer is set.
Thermally compensated inflatable packers are an innovation in inflatable packer technology. These packers act in a manner unlike conventional inflatables, which are susceptible to temperature changes as little as 50°F (10°C) between borehole and internal fluids. These temperature changes can cause the fluids inside conventional inflatable packers either to expand and rupture the element or to contract and cause the element to lose its seal on the casing wall. Qualification tests and resulting data will be presented as well as data acquired after a thermally compensated inflatable plug system was deployed in a water injection well.
Possible applications include those in which a fluid inflatable packer, straddle packer, or plug would be used and subjected to temperature changes in excess of 50°F (10°C).
The introduction of thermally compensated inflatable packers offers a more technically effective, economical means of zonal isolation in almost any cased-hole application. This technology is equally applicable for openhole applications.
With improved coiled tubing technology and reliability and, in an effort to minimize costs, operators are scheduling more workover operations to deploy coiled tubing equipment. When possible, wells can be reworked faster and at a lower cost when the production string is left in-place. Service companies are expanding product lines to provide more services and equipment in conjunction with coiled tubing deployment. An area that has seen unprecedented growth involves through-tubing stimulation and testing.
High-expansion inflatable packer technology was developed for stimulating and testing applications that require a small run-in diameter yet have the capability to expand to seal in larger casing bores. Specifically, a through-tubing stimulation operation may require running through 2-7/8-in. tubing and setting in a 7-in. casing. Once deployed, the inflatable packer isolates the zone of interest to allow stimulation fluids to be injected. As these types of services have developed, injection volumes pumped downhole have increased to levels that can "chill" the region at or near the inflatable packer. Sometimes this temperature excursion can be quite extensive, 122°F to 302°F (50°C to 150°C). A temperature drop of this magnitude would cause the inflation fluid in the inflatable packer to contract considerably, thus reducing the inflation pressure. If the inflation pressure drops significantly, the packer seal with the wellbore could be compromised allowing fluid to bypass.
In the 1980s, Los Alamos National Labratories developed a high-temperature high-pressure inflatable treating packer for stimulating geothermal wells. In this application, Dreesen and others experienced packer seal failure because of "cooling" when exposed to large volumes of treating fluids pumped from the surface. To overcome this problem, their device incorporated a volume compensating piston and choke to maintain packer pressure. If the packer fluid volume contracted to the point that the compensating piston stroked out, then the back-pressure created, by the choke during circulation, was sufficient to re-open the inflatable, to inject additional fluid volume, and re-pressure the inflatable packer. However, this device addressed only cooling aspects and was not bi-directional in compensation.1
An alternative approach incorporates a temperature compensating device that compensates for the expansion or contraction of the inflation fluid to maintain a relatively constant inflation pressure. This device is designed to compensate for large swings in temperature (increasing or decreasing) and would not require additional fluid injection into the inflatable packer/plug.