Biot Critical Frequency Applied as Common Friction Factor for Pore Collapse and Failure of Chalk With Different Pore Fluids and Temperatures

Summary A fluid effect toward higher strengths for oil-saturated chalk compared with water-saturated chalk has previously been identified and labeled the "water-weakening phenomenon," but has not been further characterized physically. The hypothesis of this paper is that the Biot critical frequency with a strain or stress-rate dependence can be used to explain this behavior on the pore scale and can be extrapolated to the macroscale failure and pore-collapse properties. A large set of previously published laboratory test results on chalk with different pore fluids was collected, and as a supplement we present a new test series on Stevns chalk with unconfined compression and Brazilian strength results.