Digital rock physics (DRP) modeling is known as a powerful tool for evaluating porous media and rock pore systems involving fluids, rock, and pore types through modeling or simulation. It contributes significantly to better performance in further operations such as enhanced oil recovery (EOR), 4D seismic surveys, and gas storage. However, it does not work in all situations due to various factors, not the least of which are porosity and lithology. This study utilizes well-logging data to examine the effects of these factors on DRP modeling across three zones with similar thicknesses (60 m) but varying petrophysical-mechanical properties. Zones A and B are carbonate zones (calcite, dolomite, and shale); however, in addition to their carbonate content, Zone C also includes a substantial amount of sandstone (approximately 75%). The difference in porosity percentage between Zones C and A is relatively small at 4%. However, when compared to Zone B, the difference increases significantly to approximately 15%. Firstly, the DRP modeling for all examined zones was developed based on Xu and Payne’s work. Then, fluids were added to the dry rock model (DRM) using Gassmann’s theory to build the saturated model. Finally, four parameters were calculated and examined: density (RHOB), P-wave velocity (VP), S-wave velocity (VS), and bulk modulus (K). Next, for validation model accuracy, all results were evaluated using a novel idea by the effective stress–velocity ratio technique. The results show that all estimated parameters in the carbonate zone (A – B) are much better than in the zone with an amount of sandstone (C). Additionally, in sandstone free zones, the value of VP and VS estimated in the low–porosity zone (B) are more satisfied with R2 = 0.8848 and R2 = 0.8886 compared to zone A with 16% porosity, whereas the density and K for low – shale zone (A) were responsible for much more acceptable results with R2 = 0.9601 and R2 = 0.8748, respectively. Moreover, the sandstone reservoir accounted for the highest amount of sandstone (75% on average) for the weakest results, especially for VS with R2 = 0.183; however, the best results for the C zone belong to K with R2 = 0.628. Therefore, it can be concluded that porosity significantly affected the estimation of seismic velocities, but lithology is more critical in predicting density and geomechanical parameters such as K.

Coupled effects of porosity and lithology on digital rock physics – mechanical investigations

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发表日期：

2025年10月31日

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Esmael Makarian,
Ayub Elyasi,
Dmitriy A. Martyushev,
Alireza Behinrad,
Maryam Mirhashemi

摘要

Digital rock physics (DRP) modeling is known as a powerful tool for evaluating porous media and rock pore systems involving fluids, rock, and pore types through modeling or simulation. It contributes significantly to better performance in further operations such as enhanced oil recovery (EOR), 4D seismic surveys, and gas storage. However, it does not work in all situations due to various factors, not the least of which are porosity and lithology. This study utilizes well-logging data to examine the effects of these factors on DRP modeling across three zones with similar thicknesses (60 m) but varying petrophysical-mechanical properties. Zones A and B are carbonate zones (calcite, dolomite, and shale); however, in addition to their carbonate content, Zone C also includes a substantial amount of sandstone (approximately 75%). The difference in porosity percentage between Zones C and A is relatively small at 4%. However, when compared to Zone B, the difference increases significantly to approximately 15%. Firstly, the DRP modeling for all examined zones was developed based on Xu and Payne’s work. Then, fluids were added to the dry rock model (DRM) using Gassmann’s theory to build the saturated model. Finally, four parameters were calculated and examined: density (RHOB), P-wave velocity (V_P), S-wave velocity (V_S), and bulk modulus (K). Next, for validation model accuracy, all results were evaluated using a novel idea by the effective stress–velocity ratio technique. The results show that all estimated parameters in the carbonate zone (A – B) are much better than in the zone with an amount of sandstone (C). Additionally, in sandstone free zones, the value of V_P and V_S estimated in the low–porosity zone (B) are more satisfied with R² = 0.8848 and R² = 0.8886 compared to zone A with 16% porosity, whereas the density and K for low – shale zone (A) were responsible for much more acceptable results with R² = 0.9601 and R² = 0.8748, respectively. Moreover, the sandstone reservoir accounted for the highest amount of sandstone (75% on average) for the weakest results, especially for V_S with R² = 0.183; however, the best results for the C zone belong to K with R² = 0.628. Therefore, it can be concluded that porosity significantly affected the estimation of seismic velocities, but lithology is more critical in predicting density and geomechanical parameters such as K.