Petrophysical model-driven seismic inversion for physical property parameters of deep coalbed methane reservoirs

Authors

• CHEN Yang, School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, ChinaFollow
• GUO Qiang, School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, ChinaFollow
• BA Jing, School of Earth Sciences and Engineering, Hohai University, Nanjing 221110, China

Abstract

Objective Deep coalbed methane (CBM) reservoirs typically exhibit complex pore-fracture structures, as well as strong nonlinear and non-unique corresponding relationships between elastic and physical property parameters. In this context, this study develops a seismic petrophysical inversion method that accounts for pore structure variations. Methods This study investigated deep CBM reservoirs along the eastern margin of the Ordos Basin. First, a petrophysical model based on variable pore aspect ratios was established, and the corresponding linearized forward operator was derived. Then, the pore aspect ratios were estimated using near-borehole log data. Meanwhile, the multimodal prior distributions of reservoir physical property parameters were characterized using a Gaussian mixture model. Finally, the porosity, shale content, and pore aspect ratios of the CBM reservoirs were simultaneously inverted based on a Bayesian linear inversion framework. Results and Conclusions Compared to a petrophysical model based on a fixed pore aspect ratio, the P- and S-wave impedances predicted using the petrophysical model based on variable pore aspect ratios agreed better with log curves. The correlation coefficients between log data and the porosity and shale content inverted using the proposed inversion method were determined at 0.772 and 0.757, respectively, higher than those obtained through conventional empirical fitting (0.748 and 0.693) and those derived using the model based on a fixed pore aspect ratio (0.720 and 0.310). The porosity inversion exhibited stable resistance to noise in the elastic parameters, while the shale content inversion was more sensitive to such noise. The inversion results of reservoir physical properties were also affected by the regularization parameter for prior covariance. Specifically, ultra-low parameter values would enhance the constraints imposed by the initial model, further leading to a loss of vertical high-frequency information. In contrast, excessively high parameter values would increase the uncertainty and local anomalies of the inversion results. The minimum inversion errors were observed when the regularization parameter values were set at 2 and 1 for wells 1 and 2, respectively. Furthermore, seismic profile inversion in the survey area exhibited a good balance between inversion accuracy and vertical resolution when the regularization parameter was set at 1−2. The proposed method enables the stable joint inversion of the porosity, shale content, and pore aspect ratios of deep CBM reservoirs while also achieving a good balance among inversion accuracy, stable resistance to noise, and vertical resolution. This study provides an effective method for physical property prediction, pore structure characterization, and play fairway evaluation of deep CBM reservoirs.

Keywords

deep coalbed methane (CBM), petrophysical inversion, reservoir physical property, Bayesian linear inversion

DOI

10.12363/issn.1001-1986.26.06.0408

Recommended Citation

CHEN Yang, GUO Qiang, BA Jing, et al. (2026) "Petrophysical model-driven seismic inversion for physical property parameters of deep coalbed methane reservoirs," Coal Geology & Exploration: Vol. 54: Iss. 9, Article 14.
DOI: 10.12363/issn.1001-1986.26.06.0408
Available at: https://cge.researchcommons.org/journal/vol54/iss9/14

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