Geophysical Insights members Alvaro Chaveste and Rocky Roden will be presenting technical papers at the GSH 2024 Spring Symposium at the Houston Museum of Natural Sciencies on 19-20 April 2024.
Machine Learning for Lithofacies Prediction – a Fast, High-Resolution, and Economic Alternative to Seismic Inversion.
Alvaro Chaveste
Sr. Geophysical Advisor
Geophysical Insights
Abstract
A methodology for lithofacies prediction is presented. It is based on computing Self Organized Maps (SOM), an unsupervised form of Machine Learning (ML), and cross-referencing the results to lithofacies from petrophysical logs. The methodology defines the lithofacies of interest with improved resolution and significant time savings when compared to inversion-based reservoir characterization. The methodology outlined in this document is illustrated with a case study in the Niobrara formation and progress in an East Texas study.
Methodology
The methodology, unlike seismic and petrophysical inversions, is not deterministic. It computes SOM from a User defined number of seismic attributes. The process’ multi-dimensionality (each attribute is a dimension) reduces the non-uniqueness associated with seismic and petrophysical inversions. SOM classifies several attributes sample by sample (same sample for all attributes) and assigns a cluster (neuron) to each time/depth sample. This results in interpretable data below the wavelet’s limit of resolution. The assignment of geologically meaningful labels to SOM neurons is done by cross-referencing neurons from seismic to lithofacies computed from the wells’ petrophysical evaluation. The process counts the number of times each lithofacies matches, in time/depth, each of the neurons. In the end, the lithofacies with the largest occurrence for a neuron is considered the most probable lithofacies for that neuron.
Case histories
The methodology is illustrated with a case study in the Niobrara formation and progress in an East Texas study. The petrophysical evaluations in five wells are used to create four lithofacies in the Niobrara formation. The lithofacies, computed using K-Means, are cross-referenced with a 64 neuron SOM in which eight seismic attributes are input to the calculation. The result is a 3D volume of lithofacies that matches the analysis wells, has aerial continuity, and shows reliable data at a fraction of the wavelet’s limit of resolution. The results of an East Texas study, which is currently underway, are also presented.