Chevron’s new approach to reducing trapped annular pressure uses a water-based spacer fluid that shrinks by 20%, creating room for thermal expansion.
J. B. Bloys, M. E. Gonzalez, J. Lofton, R. Carpenter, S. Azar, J. McKenzie, J. Capo, Chevron, R. Hermes, Los Alamos National Lab, R. Bland, R. Foley, F. Harvey, Baker Hughes Drilling Fluids, J. Daniel, F. Billings, I. Robinson, Lucite International, M. Allison, Flow Process Technologies Inc.
In deepwater or other sub-sea completed wells, fluids, usually spacers or drilling fluid, are commonly trapped in casing annuli above the top of cement and below the wellhead. When these trapped fluids are heated by the passage of warm produced oil and gas, thermal expansion can create very high pressures (10,000-12,000 psi or more) and cause the collapse of casing and tubing strings.1,2,4,12,15 Mitigation methods such as Vacuum Insulated Tubing (VIT) to limit heat transfer,6,7,14 nitrogen foam spacers yield highly compressible trapped fluids,8,9,10,11 crushable urethane foam insulation,3 etc. are somewhat successful, but are either very expensive, logistically troublesome or have unacceptable failure rates. This paper continues the discussion of a new approach which has created a water-based spacer fluid that will be used just ahead of the cement. The spacer contains perhaps 20-40% of emulsified Methyl Methacrylate Monomer (MMA). Upon polymerization, the MMA phase shrinks by 20%, creating room for the remaining fluid to thermally expand without creating catastrophic pressure, Fig. 1. The polymerization is triggered by heat and the target temperature can be controlled by an appropriate type and concentration of chemical initiator. Premature polymerization during spacer placement can be prevented by an appropriate type, and amount, of inhibitor. The initial lab work and a mid-scale field trial of this technology were reported in detail in SPE/IADC 104698.1
This paper covers the development and field testing (land) of all the equipment and processes necessary to apply the technology in deep water.
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This article was adapted from a professional society paper for which World Oil was granted the right to print one time only. Therefore, to review the article, you should refer to the actual World Oil magazine in which it originally appeared.
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