Abstract
Effective stage-to-stage isolation is typically accomplished by setting a bridge plug in a properly cemented casing between stages. This isolation plays a vital role in a horizontal well multistage fracturing completion. Failure of isolation not only impacts the well productivity but also wastes fracturing materials.
The challenges isolation failure poses for stimulation effectiveness include both detection and remediation. First, there has been historically no reliable and cost-effective solution to detect stage-to-stage isolation onsite. One may only start to realize this problem when inconsistent production is observed. Second, existing remedial actions are seldom satisfying in case of an isolation failure. Most commonly, a new plug is set to replace the failed one. However, because the perforation clusters of an unstimulated stage may create irregularities in well inside diameter (ID) (e.g., casing deformation or burr), there is a risk that the plug will be damaged or become stuck when it passes the perforation area. Also, when the plug passes a perforation cluster, the perforations start to take in the pump-down fluid, which can increase the difficulty of the pump-down job.
A novel remedial action uses high-frequency pressure monitoring (HFPM) and diversion to solve both challenges. The stage isolation integrity is evaluated in quasi-real time by analyzing the water hammer after the pump shutdown. In the case of a plug failure, large-particle fracture diversion materials and techniques can establish temporary wellbore isolation through a quick and simple delivery process. To close the cycle, the effect of the diversion can be evaluated by HFPM, which can reveal the fluid entry point of the treatment fluid after diversion.
The technique was applied to two cases in Ordos basin in which wellbore isolation failure interrupted the operation. The problem identification, development of the solution workflow, and observation from treatment analysis are discussed. In both cases, the stage-to-stage isolation was recovered, and the drilled sand body was successfully stimulated without involving costly and time-consuming well intervention. The stimulation operation of the entire well was successfully resumed in a timely manner.
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