An innovative seismo-petrophysical characterization of a turbidite sand in the Nam Con Son Basin, using permeability-linked adaptive rock physics template (K-ARPT) with reference to gas exploration and carbon storage

Abstract

The MMF30 turbidite sand in the Hai Thach-Moc Tinh (HT-MT) field, Nam Con Son basin (NCSB), Vietnam, is a significant gas condensate-producing reservoir. However, the variable and high cementation make its reservoir characterization particularly challenging. With the declining production observed in many fields in the NCSB since 2018 one needs to think not only of exploring more hydrocarbon reservoirs, but also how to make use of depleted reservoirs for carbon storage in the near future.

In this study, we successfully conducted a comprehensive seismo-petrophysical characterization of a deep-seated, highly-cemented sand (MMF30) by integrating core testing, well log analysis, rock physical modeling and prestack seismic inversion. The predominant types of cementation of the study sand are quartz-overgrowth, clayey, and calcite, which altogether make a high percentage of up to 10%. The sand porosity was found to be from 11 to 17% and gas saturation from 50% up. An innovative contribution of this study is the successful proposal and construction of a new type of rock physics template named the permeability-linked adaptive rock physics template (K-ARPT) to help identify more in details the permeable subzones within the depleted gas reservoir. To construct K-ARPT, different permeability prediction models were tried, both traditional and machine learning-based, among which the random forest (RF) method proved to be the best for the study sand based on cross-validation with the available core measurements. As results of seismo-petrophysical characterization, five lithological units of shale and gas sand were identified in the MMF30 reservoir interval with porosity from 11 to 17%, gas saturation from 50% up and permeability from less than 0.5 to 50 mD, among which the unit of 20–50 mD would be the most suitable for carbon injection and storage.