Development of 3D-Geomechanical Model for Buzurgan Oil Field Using Actual and ANN-developed Synthetic Logs

ABSTRACT: Knowing the distributions of the rock mechanical properties along the whole reservoir is an important task for many applications related to reservoir geomechanics. A major challenge with determining the rock mechanical properties is that they are not directly measured at the wellbore. This study presents a methodology for generating synthetic-geomechanical well logs for the production section of the Buzurgan oil field, located in the southern part of Iraq, using artificial intelligence techniques. The Mishrif reservoir is the most critical hydrocarbon reservoir in Buzurqan oil field where the rock mechanical properties are not profoundly studied. This reservoir, which is mainly composed of carbonate (limestone), has been divided into six subsequent reservoir units: MA, MB11, MB12, MB21, MC1and MC2. An issue with the area of study is that shear wave velocities and pore pressure measurements in some wells are missing or incomplete, possibly for cost and time-saving purposes. To overcome these challenges, this study presented two developed models for estimating the shear wave velocity and pore pressure using the neural network (ANNs). A calibration was then performed to check the new models' performance. Geomechanical parameters are then measured at well locations, and for each well, a one-dimensional mechanical earth model (1DMEM) is constructed. A 3D distribution for each geomechanical property for the production section of Buzurgan oil field is presented using datasets of 10 wells to accurately visualize the mechanical properties of rocks, in-situ stress, and pore pressure. The obtained results revealed that the 3D MEM showed a huge variance in the rock properties and field stresses, even within a small distance. This heterogeneity can be attributed to the carbonate depositional environments and diagenetic processes. The shale layer (Tanuma formation) has low Young’s modulus, low rock strength, and high Poisson’s ratio, therefore it tends to fail more than limestone layers (Sadi, Khasib and Mishrif formayions). Both the MA and MB12 Mishrif’s units appear to have more stiffness than other Mishrif reservoir units. High rock stiffness is an indicator of small deformation exposed through drilling these units. In contrast, MB21 and MC2 units have the lowest Young’s modulus values among other units (less stiffness). This means that more attention related to the selection of rheological mud properties is required when drilling these units in future wells.