Acoustic, mechanical, and microstructure data used in: Coda-Wave Based Monitoring of Pore-Pressure Depletion-driven Compaction of Slochteren Sandstone Samples from the Groningen Gas Field

Pore-pressure depletion in sandstone reservoirs is well known to cause both elastic and inelastic compaction, often resulting in notable surface subsidence and induced seismicity. Recent studies indicate that in such cases inelastic strain, which is often neglected in geomechanical models, represents a significant proportion of the total strain throughout reservoir production. While there has been considerable effort to quantify the proportion of continuous inelastic deformation from the mechanical response of laboratory samples, there has been little focus to date on the associated acoustic response throughout compaction. With this in mind, we employ three coda-wave based processing methods for the active source monitoring of ultrasonic velocity, scattering power, and intrinsic/scattering attenuation during the pore-pressure depletion of core samples from the Slochteren sandstone reservoir in the Groningen gas field (the Netherlands). Our results corroborate previous studies suggesting that initially, inelastic deformation occurs primarily along intergranular boundaries, with intergranular cracking developing towards the end of depletion and particularly for the highest porosity samples. Furthermore, analysis of Biot type intrinsic attenuation indicates that this compaction occurs in several stages of predominately intergranular closure, transitioning into primarily intergranular slip/cracking, and eventually porosity-dependent intragranular cracking. We demonstrate how this segmentation of pore-pressure driven compaction can be used to characterise differences in sample properties, and monitor the evolution of microstructural inelastic deformation throughout depletion. We further discuss the feasibility of in/cross-borehole monitoring of reservoir compaction, for both improved geo-mechanical modelling and early warning detection of induced seismicity.

砂岩储层中的孔隙压力衰竭（pore-pressure depletion）众所周知会引发弹性与非弹性压实作用，通常会造成显著的地面沉降与诱发地震（induced seismicity）。近期研究显示，在这类工况中，岩土力学模型（geomechanical models）中常被忽略的非弹性应变，在整个油藏开发周期内占总应变的可观份额。尽管学界已投入大量精力，通过实验室试样的力学响应来量化连续非弹性变形的占比，但迄今鲜有研究关注压实过程中的相关声学响应（acoustic response）。鉴于此，我们采用三种基于尾波（coda-wave）的处理方法，对荷兰格罗宁根气田（Groningen gas field）斯洛克特伦砂岩储层（Slochteren sandstone reservoir）的岩心样品开展孔隙压力衰竭过程中的主动源监测，获取超声波速度（ultrasonic velocity）、散射功率（scattering power）以及本征/散射衰减（intrinsic/scattering attenuation）相关数据。我们的研究结果佐证了此前的研究结论：压实初始阶段的非弹性变形主要沿晶间边界（intergranular boundaries）发生，而晶间开裂（intergranular cracking）会在衰竭末期逐渐发展，在孔隙度最高的样品中尤为显著。此外，对比奥型本征衰减（Biot type intrinsic attenuation）的分析表明，该压实过程可划分为多个阶段：初始阶段以晶间闭合为主，随后转变为以晶间滑移/开裂为主，最终进入孔隙度依赖型的晶内开裂（intragranular cracking）阶段。我们展示了如何借助孔隙压力驱动的压实阶段划分，来表征不同样品的性质差异，并监测整个衰竭过程中微观结构非弹性变形的演化历程。此外，我们还探讨了井内/跨井储层压实监测的可行性，以期为优化岩土力学建模以及诱发地震的早期预警提供支撑。