Seismic attenuation imaging of free gas distribution reveals a structural uplift-controlled methane migration system in the Qiongdongnan Basin, South China Sea

This repository contains (i) the pre-stack seismic reflection data from the Qiongdongnan Basin of the South China Sea, (ii) the code for attenuation estimation (spectral ratio method), (iii) theoretical attenuation calculated by the proposed rock physics model, (iv) spatial distribution of free gas saturation along the inline and xline profiles in the Qiongdongnan Basin, and (v) well logging data (i.e., porosity well logs) used in this study. Below are the detailed descriptions. Two SEG-Y files correspond to two orthogonal seismic lines in this area. For each CMP, only the nearest trace is retained. The data were acquired in 2019 by China National Offshore Oil Corporation. The dominant frequency of the data is 40 Hz and the sampling rate is 2 ms. The data have inline and crossline spacings of 25 and 12.5 m, respectively. Further technical details are provided in the paper. The code used to estimate the attenuation from waveforms needs an open-source MATLAB toolbox CREWES by Gary F. Margrave. Since we do not have the right to redistribute this toolbox, we put the download link here: https://www.crewes.org/ResearchLinks/FreeSoftware/index.php The data "modeling results.txt" are arranged vertically in order of increasing frequency, with a 1‑Hz sampling interval from 1 to 9,999 Hz and a 1,000‑Hz interval from 10,000 to 30,000 Hz. Two files, "gas_saturation_distribution_inline.txt" and "gas_saturation_distribution_xline.txt", contain the spatial distribution of free gas saturation values along the inline and crossline profiles in the Qiongdongnan Basin used in our study. Null values indicate the absence of free gas at those locations. The rows and columns of each file correspond to depth and CMP position, respectively. The file "porosity_well_log.csv" is the porosity well logs at site GMGS5-W08. The first column is the measured porosity value (in %) and the second column is the corresponding depth (in m).