Sustainable well integrity, for the life time of the well and long after abandonment, has always been a target for operators. However, unplanned stresses on the set-cement can cause severe damages to the cement sheath and may ultimately result in its failure. For that reason, a new generation of cementing system with optimized mechanical properties and self-sealing capabilities were designed.
The improved elastic constants and tensile strength value of the system make it more resistant to downhole stresses while the self-sealing feature provides an additional layer of assurance for long-term zonal isolation. The cement sheath’s ability to sustain stresses was confirmed using analytical and Finite Element Analysis (FEA) simulators. The mechanical properties and the expansion ratio were tested over several days, and the sealing ability was verified using a novel HPHT multi-function test cell simulating the well’s downhole conditions.
The system was successfully deployed in cementing a challenging gas-injector well with a dual hole size in the UAE. Novel fluid displacement software was used to assess effective laminar flow as the industry-recommended turbulent fluid flow was not achievable. The injector well is expected to be under an alternating pressure of 5,500 psi with two sets of perforations set 47 ft. apart. The cement placement operation was carried out successfully and a Cement Bond Log (CBL) run was conducted after 48 hours verifying good zonal isolation over the entire interval. An injectivity test was performed on the two perforated zones. No fluid communication was observed, eliminating the need for any cement remediation.
The successful implementation of the fit-for-purpose self-sealing resilient cement system from the slurry design and lab testing through the cement placement is described. Modelling simulation of the stress analysis, ECD and fluid displacement will be also shared. The review of this case history will provide useful lessons learned for successful cementing of critical wells.