Mechanical properties of petroleum reservoirs can be determined via static techniques based on laboratory triaxial tests under reservoir conditions. Dynamic approaches represent an alternative in cases where such static laboratory data are unavailable. Dynamic elastic properties are calculated using ultrasonic wave measurements in the laboratory or in situ well logging. Different relationships have been proposed to estimate static properties from dynamic ones based on the available data from a particular reservoir. However, these relationships are often reservoir-specific, making them inadequate for general seismic inversion purposes. This research proposes a method for developing relationships between seismic parameters and static Young’s modulus in carbonate reservoirs by integrating ultrasonic measurements, well logging data, and rock mechanic tests. A multistage triaxial test simulating the reservoir conditions was used to fully control the stress and strain during the geomechanical experiments. Static Young’s modulus was cross-correlated with a broad spectrum of seismic parameters that can be extracted from seismic inversion (e.g., acoustic impedance, shear impedance, Lambda–rho, and mu–rho). Separate analytic relationships were proposed to convert dynamic Young’s modulus and seismic parameters into static Young’s modulus. Analysis of variance was used to evaluate the results and study the applicability and reliability of the obtained relationships. Furthermore, the reliability of the obtained relationships was successfully confirmed by well logging data and blind well analysis. The proposed methodology can be used to predict rock behavior for geomechanical and structural modeling.

We have evaluated an innovative application of extended elastic impedance (EEI) to integrate seismic and geomechanics for geomechanical interpretation of hydrocarbon reservoirs. EEI analysis is used to extract geomechanical parameters. To verify and assess the capabilities of EEI analysis for extracting geomechanical parameters, we selected a jointed, oil-bearing, shale carbonate reservoir in the southwest of Iran, and we used petrophysical data and core analysis to estimate static and dynamic moduli of the reservoir rock. We calculated the corresponding EEI curve to different intercept-gradient coordinate rotation angles (the chi angle, [Formula: see text]), and we selected the angles of the maximum correlation for the corresponding geomechanical parameters. Then, combining the intercept and gradient, we generated 3D reflectivity patterns of EEI at different angles. To obtain a cube of geomechanical parameters, we performed model-based inversion on the EEI reflectivity pattern. A comparison between the modeling results and well data indicated that the geomechanical parameters estimated by our method were well-correlated to the observed data. Accordingly, we extracted the geomechanical and rock-physical parameters from the EEI cube. We further found that EEI analysis was capable of giving a 3D mechanical earth model of the reservoir with the appropriate accuracy. Finally, we verified the proposed methodology on a blind well and compared the results with those of the simultaneous inversion, indicating comparable levels of accuracy. Therefore, application of this method in seismic geomechanics can bring about significant progress in the future.

Bulk modulus which relates seismic attributes to rock and fluid properties is considered as an important parameter for seismic reservoir characterisation workflows, and can provide useful information for such studies. However, its measurement and modelling approaches are yet to be sufficiently addressed and discussed especially for carbonate rocks. In this research, in order to provide more information about bulk modulus, nine samples from a carbonate oilfield were subjected to static and dynamic investigations under dry and saturated conditions. Then, the dynamic modulus was calculated using well log data and ultrasonic measurements. In order to obtain static data, multi-stage triaxial compression tests were performed on the vertical plugs extracted from conventional cores taken at different selected depths. The results showed that static and dynamic bulk moduli follow similar trends, although the value of dynamic modulus is usually higher. Furthermore, several empirical relationships based on simple linear regression and forward and backward stepwise multiple linear regressions were developed to relate measured static and dynamic bulk moduli for the given field, then proposed equations were evaluated by ANOVA analysis. Besides, dry and saturated bulk moduli were modelled using Xu and Payne rock physics model. Here, saturated bulk modulus was modelled using either dynamic or static dry bulk moduli within the Gassmann’s theory. It is observed that Gassmann’s equation gives a more accurate result using dynamic data rather than static ones. The poor Gassmann’s equation prediction under static condition could be attributed to microcracks in the samples and the uncertainty associated with this theory for complex pore geometry. The outcomes of this study can, furthermore, provide the necessary information and relationships for rock physics (e.g. shear wave estimating and fluid substitution modelling) and geomechanical (e.g. CO₂ injection and compaction forecast) studies for exploration and development programs.