A Laboratory Study of Two Straddle-Packer Systems Under Simulated Hydrofrac Stress-Measurement Conditions

Abstract

The mechanical behavior of two straddle-packer systems subjected to pressure histories which replicated hydrofracture stress-measurement procedures has been investigated. The systems were pressurized in borehole simulators consisting of lengths of steel casing instrumented with strain gages. From the strain histories, the stresses applied to the casing by the packer elements could be calculated. The systems studied differed in the manner in which the packer elements were coupled; in one system the packers were rigidly coupled end-to-end (rigid coupling), whereas in the other, the tops of the two packers were rigidly coupled leaving the bottom of the upper packer free to slide on the mandrel (sliding coupling). The elements that featured in the two systems were also greatly different. The results indicate that the sliding coupling system tested exhibited nearly ideal behavior up to the maximum interval pressure attained in the tests of 25 MPa. This is accredited to intrinsic superiority of the sliding coupling design.