ABSTRACT We examine the effect of poroelastic boundary conditions when determining elastic properties of fluid‐saturated porous rocks from forced‐oscillation laboratory experiments. One undesired yet often unavoidable complication in the estimation of the undrained bulk modulus is due to the presence of the so‐called dead volume. It implies that some fluid mass can escape the rock sample under applying a confining pressure perturbation. Thus, the dead volume compromises the undrained state required to unambiguously determine the undrained bulk modulus. In this paper, we model data of recently performed low‐frequency (0.1 Hz) measurements. Therein, the dead volume has been systematically varied from 10% to 1000% of the pore volume. For the smallest dead volume, the inferred bulk modulus is close to the Biot–Gassmann undrained bulk modulus. With increasing dead volume, the experimentally inferred bulk modulus approaches the drained bulk modulus. We show that the transition from undrained to drained state as a function of dead volume can be modelled with a 1D poroelastic model for the rock sample‐dead volume system with a boundary condition that honours the continuity of the fluid volume flux. We discuss the limitations of the 1D model when applied to data recorded at higher frequencies (up to 100 Hz).

中文翻译：

---

死体积变化引起的流体饱和多孔岩石中体积模量的排水向不排水转变

摘要 我们通过强制振荡实验室实验确定了流体饱和多孔岩石的弹性特性时，研究了多孔弹性边界条件的影响。在估算不排水体积模量时，一个不希望但通常不可避免的复杂情况是由于所谓的死体积的存在。这意味着在施加围压扰动的情况下，一些流体质量可以从岩石样品中逸出。因此，死体积损害了明确确定不排水体积模量所需的不排水状态。在本文中，我们对最近执行的低频 (0.1 Hz) 测量数据进行建模。其中，死体积已系统地从孔体积的 10% 到 1000% 变化。对于最小死体积，推断的体积模量接近 Biot-Gassmann 不排水体积模量。随着死体积的增加，实验推断的体积模量接近排水体积模量。我们表明，作为死体积的函数，从不排水状态到排水状态的转变可以用岩石样品 - 死体积系统的一维多孔弹性模型建模，其边界条件尊重流体体积通量的连续性。我们讨论了 1D 模型在应用于以更高频率（高达 100 Hz）记录的数据时的局限性。