Typical Inflatable Packer Applications
Inflatable packers have been used in the oil and gas industry since the 1940s. Until recently, however, their use was restricted by prohibitive costs and limited availability. Now, several disciplines (e.g. ground water development, contamination studies, dewatering, geothermal, mining, coal bed methane, and geotechnical studies) use a wide selection of reasonably priced packers.
The selection of a packer for a particular job application is very important for success at a reasonable cost. The differential pressure and hole size are primary considerations. Next, the materials of construction should be considered, especially when adverse chemical and physical conditions could exist.
First, we will discuss the hole diameter size and borehole differential pressure in a packer application. For example, to pump a 2-inch diameter by 50-foot deep monitor well that is full of water, the maximum borehole differential pressure (maximum drawdown) would be 50 feet of water times 0.433 psi/foot of water equals 22 psi. Therefore, a 1-3/4 inch O.D. packer with a 22 psi differential pressure rating would do the job. In addition, the packer should be constructed of stainless steel and have an element gland covered with Viton* to reduce sample contamination. A Baski Purge PackerTM would be ideal.
Another packer application might be in a mud-filled pilot drill hole at a potential water well site. If there is nonpotable water at an unknown depth, packer testing can define where the "poor" water is located. A straddle packer configuration is attached to the drill pipe and lowered into the open borehole. Water is then pumped from a specific zone between the straddle packers by using airlift pumping methods inside the drill pipe. The testing would normally start from the bottom of the hole and progress upward. After locating the poor water, it can be cased off and a potable water well completed.
As an example, let us examine a straddle packer arrangement for the above application with a 7-7/8 inch I.D. by 1,000-foot deep hole. For a competent rock hole, a 5-1/2 inch O.D. packer with a 2-1/2 inch (Sch. 80) mandrel would be an economical choice. However, if unstable hole conditions are possible, then a better choice would be a 6-1/2 inch O.D. packer with a 3-inch (Sch. 160) mandrel. API round threads for a higher joint strength are also recommended in case the hole collapses. If the hole were completely pumped dry, there would be a 433 psi differential pressure. Therefore, a packer with a 500 psi differential pressure rating is recommended. Standard construction materials (aluminum, stainless steel and steel components, and a reinforced, natural rubber element) should be sufficient. All stainless steel construction with Viton* and a longer than standard element length are available options.
A third packer application could be hydrofracturing a low-yielding, 6-inch diameter, domestic well with an installed pitless adapter. A good selection would be the fracture packer (Fracker™) with a 4.9 inch O.D. to clear the pitless adapter which may protrude inside the well casing. A 3,000 psi differential pressure rating would be sufficient for most fracking jobs up to a 3,000 psi injection pressure. The life of the FrackerTM (i.e., the number of packer settings with high pressure injection) is a direct function of the inflatable packer specifications, the hole conditions and the proper procedures used by the contractor.
Hydrofracturing between two packers can develop an extremely high force on the connecting pipe between the packers. In a 10-inch hole at 3,000 psi, the tension force is close to a quarter of a million pounds! Proper selection of pipe and thread pattern between the packers prevents failure that can result in the loss of the lower packer and damage to both packer elements from sliding in the hole.