Vs measurements and rock-physics model

This repository contains: (i) shear wave velocity measurements from laboratory-synthesized methane hydrate-bearing sands and (ii) a modified friction-dependent effective medium model that can be used to properly interpret Vs data in hydrate-bearing unconsolidated sands. Descriptions of the experiments and code are provided below. Experiment Description: The experiments were conducted under excess-water conditions. Fifteen unconsolidated sand samples, each with a distinct grain-size distribution (particle diameters ranging from 117 to 870 μm), were prepared. The samples were placed into a cylindrical reaction chamber to measure compressional (VP) and shear (VS) wave velocities using an ultrasonic transducer system (100–600 kHz). Prior to hydrate synthesis, methane was injected to purge residual air from the pore space, and the chamber height was adjusted to ensure optimal contact between the sediment and the transducers. A constant confining pressure of 10 MPa was maintained throughout the experiments. The system was initially pressurized to a pore pressure of 5.0–5.5 MPa. Methane hydrate was formed by cooling the sample into the thermodynamic stability zone. At various stages of hydrate saturation, VP and VS were determined using the transmission method, based on the known sample length and measured wave travel times. Detailed descriptions of each file are provided in Readme.txt. Code DescriptionThis code calculate compressional (VP) and shear (VS) wave velocities in hydrate-bearing sands using a modified friction-dependent effective medium model. The model was developed because conventional effective medium theories fail to reproduce the low VS values observed in our experiments. It introduces a pressure-dependent coordination number to capture the reduced stiffness and incorporates a dimensionless friction coefficient (ranging from 0 to 1) to represent interparticle frictional behavior—from perfectly smooth (0) to fully rough (1) grain contacts. Detailed descriptions of each script are provided in Readme.txt.