A. Dahi Taleghani

Emergence of Delamination Fractures Around the Casing and Its Stability

Casing support and zonal isolation are principal objectives in cementing the wells; however the later objective always raises the most concern particularly when there is a potential for formation fluid migration into the cement sheath. Wellbore integrity is highly dependent upon the integrity of the interfacial bond between the cement and the formation as well as the bonding between casing and cement. A closer look at the common cement strength test data, performed routinely in the labs, reveals complicated behavior that cannot be simply modeled using a single parameter (i.e. the interfacial strength).In this work we used a cohesive interface constitutive equation to model the behavior of cement interfaces. Comprehensive analysis of microannulus formation is presented by utilizing an axisymmetric poroelastic finite element model enriched with cohesive interfaces to simulate initiation of the failure zone and possible broaching of the failure zone along the wellbore to shallower zones. Using this model, we demonstrated that it is possible to use data from routine tests, such as the push-out test, to determine not only the shear strength but also normal fracture energy and the stiffness of the cement-formation interface. Cohesive interface properties are calibrated such that simulated test results match with the measured response of the specimens. In the next step, we used these parameters to anticipate well-cement behavior for the field-scale problem. A sensitivity analysis is provided at the end of the part to show the role of each parameter in initiation and development of the failure zone. Interestingly, the shear strength, which is commonly measured from push-out tests are not the only parameter determining the size of the fracture. Other parameters derived in this approach such as normal strength show equal influence on initiation and propagation of the failure zone. The proposed approach provides a tool for a more accurate prediction of cement integrity in the subsurface conditions to quantify the risk of wellbore integrity issues.

The State of the Art and Challenges in Geomechanical Modeling of Injector Wells: A Review Paper

Fluid injection is a common practice in the Oil and Gas industry found in many applications such as waterflooding and disposal of produced fluids. Maintaining high injection rates is crucial to guarantee the economic success of these projects; however, there are geomechanical risks and difficulties involved in this process that may threat the viability of fluid injection projects. Near wellbore reduction of permeability due to pore plugging, formation failure, out of zone injection, sand production, and local compaction are challenging the effectiveness of the injection process. Due to these complications, modeling and simulation has been used as an effective tool to assess injectors’ performance, however, different problems have yet be addressed. In this paper, we review some of these challenges and the solutions that have been proposed as a primary step to understand mechanisms affecting well performance.Copyright