Operators of cyclic steam stimulation (CSS) wells are required by Alberta’s Energy Resources Conservation Board to do periodic casing integrity pressure tests.
The idea is to ensure well casing hasn’t developed a leak during high-pressure steam injection over many years of thermal bitumen operations.
Each test costs about $50,000 — mainly because a service rig is used to remove the well production equipment and install a test string with an inflatable packer. The packer is inflated and the pressure test is done against the packer. Then the packer is deflated, the test string is pulled out, and the production equipment is put back into the well.
In the process about a day’s production time is lost. Service rigs are complex and have had their share of accidents over the years. In some areas thermally stimulated bitumen production projects are starting to encounter hydrogen sulphide, necessitating the use of self-contained breathing apparatus (SCBA). (In the case of CSS, exposure of bitumen to heat from high-temperature steam injected into the reservoir causes the breakout of H2S.)
Dale Kunz, a certified engineering technologist with several issued or pending patents to his name and a background in CSS, believes he has come up with a way to do the casing integrity pressure tests without using a service rig.
“We eliminate the need for a service rig by eliminating the need for an inflatable packer. We replace the inflatable packer with an annular eutectic salt plug,” Kunz explained at a Petroleum Technology Alliance Canada (PTAC) technology information session last week.
A eutectic system is a mixture of chemicals which, when two or more compounds are combined, will melt and solidify at a lower temperature than either chemical would do by itself.
In CSS wells, the plug would be placed by injection of a molten eutectic salt into the annulus through a permanently installed tubing string.
Kunz’s proposed design incorporates a heater, or melter, at the surface. When the system is pressurized with nitrogen and a rupture disc is broken, the melted salt is pushed down the injection tubing to a salt distribution nozzle located where a packer would currently be installed.
“A characteristic of eutectic salt is the larger the difference between the liquid temperature and the surrounding temperature, the faster