What Does Straddle Packer Mean?
A straddle packer, in the context of fracture mechanics, is a cased hole packer system used for hydraulic fracturing tests to measure in-situ stress in rocks. It enables the isolation of two zones using a single packer system and allows the investigation of two zones with a single trip into the well with the downhole tools. The isolation created between the two zones also enables independent investigation of each zone. These packers are also used in well completion work to shut off zones.
Trenchlesspedia Explains Straddle Packer
The straddle packer system consists of an upper packer and a lower packer, which are spaced out such that the lower packer is set between the two zones of interest. The upper packer is set above the testing zone, isolating it from the annulus fluids above it. The isolation created between the two zones allows independent investigation of each zone.
Once the packer is set, fluid can flow through the inner diameter of the tool to stimulate the isolated zone between the packers. The fluid can also be allowed to flow through the tool to stimulate the zone below the lower packer.
Hydraulic fracturing uses vertically drilled holes — a short segment sealed with a straddle packer, set in a primary stress state and pressurized using water. For the packing system to work effectively, the seals must have a pressure 2 MPa higher than the test section. This increased pressure keeps the water from leaking around the seals during the test.