Master of Science (MS)
Microannular gas flow in the wellbore is known to be one of the major reasons for Sustained Casing Pressure (SCP). Low success rate (under 50%) of costly remedial cementing operations and increasing difficulty in sealing off problematic areas motivated the industry to look for more practical remediation solutions. Expandable casing technology is one of those new proposed techniques. A bench-scale physical model tested the potential of expandable casing technology for remediation of microannular gas migration. The composite samples with pipe-inside-pipe cemented annulus were designed to simulate a wellbore system including a pre-manufactured microannulus on the inner pipe/cement interface. Multi-rate flow-through tests with nitrogen gas first evaluated the permeability and the size of the pre-manufactured microannulus. The post-expansion flow-through experiments tested the ability of pipe expansion in sealing the microannular gas flow. The effects of expansion on properties and structure of the cement were investigated by microindentation, optical microscopy, thermogravimetric analysis (TGA) and inductively coupled plasma (ICP) mass spectrometry. As observed with optical microscopy, the dissolution of unhydrated clinker grains during expansion is coupled with pore collapse within the cement sheath. Information obtained by microindentation showed that the cement sheath loses the integrity initially after expansion but regains most of the mechanical properties after a period of rehydration. Most important, multi-rate gas flow-through experiments showed that all three expansion ratios of 2%, 4% and 8% were successful in sealing the microannular gas flow. The seal was confirmed immediately and then 24 hours and 60 days after expansion. The findings in this research give solid support to the potential of expandable casing technology for remediation of microannular gas migration. Cement pore water propagation is the most likely driving force behind a successful expansion, one that is not an obstacle in subsurface conditions and also makes an ideal environment for cement rehydration post-expansion. Cement integrity should not be compromised by pipe expansion after certain period of rehydration. Finally, the research showed that expansion technology could be used during all operations in vertical and horizontal wells, whether injection or production wells, to mitigate well leaks caused by gas migration.
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Kupresan, Darko, "Experimental assessment of expandable casing technology as a solution for microannular gas flow" (2014). LSU Master's Theses. 1265.