: A discrete particle model (PFC3D) has been applied to simulate coring and core reloading of a cemented granular material formed under a 3D state of stress. By accounting properly for the stress release

taking place during coring, the simulations demonstrate the feasibility of using the Kaiser effect to determine the in situ horizontal stresses from a rock core.


Rocks exhibit stress memory. This was demonstrated already 50 years ago, when Joseph Kaiser (Kaiser, 1953) discovered that acoustic emissions (AE) in cyclic uniaxial loading occurred only after the maximum previously experienced stress was reestablished. This phenomenon, known as the Kaiser effect, shows a potential for core based stress determination. It has until now, however, not been possible to apply this in practice. A major obstacle has been the 3D nature of the in situ stress state: Onset of AE activity occurs on a 3D so-called damage surface (Holcomb, 1993), which only at one point coincides with the previous maximum experienced stress. It has furthermore been assumed that the cores will remember their native in situ stress state. The stress path followed during coring brings the rock sample through another critical stress state, given (for a vertical core) by the (effective) horizontal stresses and the (known) mud overbalance. Kenter et al. (1998) conceived the idea that a rock core actually will remember this critical stress state and that consequently the horizontal in situ stress state can be determined on core by probing the 3D dam-age surface; the validity of this concept has been experimentally demonstrated in a accompanying paper by Pestman et al. (2001). The technique will further be referred to as the Pestman - Kenter - van Munster (PKM) method.

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