This study presents a novel geophysical approach for estimating the level of thermal
maturity (LOM) in unconventional hydrocarbon reservoirs using well log data. LOM is
a crucial parameter for assessing the hydrocarbon generation potential of source rocks,
but it traditionally relies on laboratory measurements of core samples, which can
be time-consuming and costly. The proposed method combines two techniques: interval
inversion for estimating total organic carbon (TOC) content from well logs and simulated
annealing (SA) optimization for deriving LOM from the estimated TOC. The interval
inversion method enables accurate TOC estimation by jointly interpreting multiple
well logs over depth intervals, overcoming limitations of conventional point-by-point
inversion. Using the estimated TOC, the SA algorithm optimizes an energy function
related to Passey's empirical TOC-LOM relationship, iteratively finding the optimal
LOM value that best fits the well log data. This approach provides a continuous in
situ LOM profile along the borehole without requiring core measurements. The effectiveness
of the method is demonstrated through case studies on datasets from the North Sea
(Norway), the Pannonian Basin (Hungary), and the Kingak Formation (Alaska). The LOM
estimates show good agreement with reported maturity levels and allow reliable reservoir
characterization. Statistical analysis confirms the robustness and accuracy of the
results. By reducing dependence on core data, this integrated inversion-optimization
workflow streamlines the reservoir prospecting phase, enhancing operational efficiency.
The method holds promising applications across diverse geological settings for cost-effective
evaluation of unconventional hydrocarbon plays.
