Abstract
Multi-stage hydraulic fracturing in horizontal wells drilled in tight carbonate reservoir has become one of the main techniques to effectively create communication between the reservoir and wellbore to enhance hydrocarbon production. The completion processes start by drilling a horizontal hole in the direction of the minimum horizontal stress (σmin) and placing multi-stage fractures along the lateral using different techniques.
The efficiency of hydraulic fractures depends mainly on reservoir and completion quality parameters. Geomechanical characterization of the magnitude and orientation of in-situ stresses and mechanical properties play a major role in understanding the growth and behavior of hydraulic fractures.
A 3D geomechanical model was constructed for a sector of carbonate gas reservoir in Saudi Arabia. Properties from the 3D model were used to populate a finite element model to determine changes in stresses and strain as reservoir pressure decreased due to production. With the complex geometry and depleted reservoir pressure, the magnitudes and directions of principal horizontal stresses change. The horizontal stress magnitude decreases in the depleted area but increases in adjacent layers compared to pre-depletion stress magnitudes. The orientation of the stresses also changes. The increase in magnitude of stress in adjoining layers and rotation of the stresses cannot be predicted correctly by 1D geomechanical model. The hydraulic fracture simulation using the 3D stress data has shown that the increase in stress magnitude in adjoining layers can act as stress barrier to the fracture propagation. Stress profile data from the 3D FEM developed in this study can be used in any future fracture design and to check the alignment of the preferred hydraulic fracture plane with the wellbore trajectory.
