Effect of Temperature on Stiffness of Sandstones from the Deep North Sea Basin

Tobias Orlander*, Katrine Alling Andreassen, Ida Lykke Fabricius

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Abstract

Development of high-pressure, high-temperature (HPHT) petroleum reservoirs situated at depths exceeding 5 km and in situ temperature of 170 °C increases the demand for theories and supporting experimental data capable of describing temperature effects on rock stiffness. With the intention of experimentally investigating temperature effects on stiffness properties, we investigated three sandstones from the deep North Sea Basin. As the North Sea Basin is presently undergoing substantial subsidence, we assumed that studied reservoir sandstones have never experienced higher temperature than in situ. We measured ultrasonic velocities in a low- and high-stress regime, and used mass density and stress–strain curves to derive, respectively, dynamic and static elastic moduli. We found that in both regimes, the dry sandstones stiffens with increasing testing temperature and assign expansion of minerals as a controlling mechanism. In the low-stress regime with only partial microcrack closure, we propose closure of microcracks as the stiffening mechanism. In the high-stress regime, we propose that thermal expansion of constituting minerals increases stress in grain contacts when the applied stress is high enough for conversion of thermal strain to thermal stress, thus leading to higher stiffness at in situ temperature. We then applied an extension of Biot’s effective stress equation including a non-isothermal term from thermoelastic theory and explain test results by adding boundary conditions to the equations.
Original languageEnglish
JournalRock Mechanics and Rock Engineering
Number of pages34
ISSN0723-2632
DOIs
Publication statusAccepted/In press - 2021

Keywords

  • Sandstones
  • Rock stiffness
  • Temperature
  • Effective stress

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