Three-Dimensional Modeling of Geomechanical Units Using Seismic Data in One of the Southern Iran Gas Fields

The current study employs an efficient approach in construction of 3D reservoir geomechanical models based on the concept of GMUs. Rock strength estimation using indirect methods plays an important role in reservoir characterization. Indirect methods are more cost-effective and efficient than direct methods. The elastic-dynamic moduli can be used to obtain rock strength data. In this study, the amount of data was reduced through using multiresolution graph-based clustering and geomechanical units (GMUs) were established based on MRGC-derived clusters. Construction of a 3D geomechanical model using these GMU’s is a reliable approximation of reservoir characteristics from the rock strength point of view. The elastic-dynamic moduli such as Young’s modulus, bulk modulus, shear modulus, Poisson’s ratio and UCS of the formation were calculated using compressive and shear wave velocities which are provided by DSI logging tools in eight wells. In some of the wells, shear wave velocities are predicted through multivariable regressions. Results show that the correlation coefficient between measured and estimated shear velocity is approximately 90 percent. Afterward, the calculated dynamic moduli were calibrated to static values using empirical equations extracted from a neighboring field. All calculated static moduli were clustered by using multiresolution graph-based clustering (MRGC) method for all eight wells. Finally, a 3D geomechanical model of the reservoir was generated based on these geomechanical units and the reservoir acoustic impedance model as a secondary parameter of co-krigging. The reservoir acoustic impedance model was built by using a genetic algorithm and model based inversion. After establishing the GMUs by MRGC, the GMUs evaluated through correlating with the caliper, gamma ray and NPHI logs. There is a good correlation between the clusters and the log-derived properties in all wells. GMUs can be compared with lithology logs and core data as an alternative verification method. Results of this study show that mechanical properties of GMUs are strongly affected by the clay content and porosity of rocks. Also, the 3D geomechanical model has been generated from GMUs, and the reservoir acoustic impedance model shows a good degree of correlation confirming further confidence on the results of this study.