This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 199710, “The Unconventional Unconventionals: Tectonically Influenced Regions, Stress States, and Casing Failures,” by A. Casero, SPE, and M. Rylance, SPE, BP, prepared for the 2020 SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, 4-6 February. The paper has not been peer reviewed.
In tectonically influenced regions, potential hydrocarbon traps are subject to complex states of stress. This scenario often translates into severe strike/slip (SS) and thrust-fault or reverse-fault (TF/RF) stress states. The complete paper demonstrates that such complex stress states will affect well completions and hydraulic fracturing directly in a multitude of ways but that, often, some of the more influential consequences are severe casing failures, production-liner restrictions, and complex-fracture-initiation scenarios. Unconventional-resource development in such environments requires that a renewed focus be made in all phases of well design and construction.
Distinguishing clearly between the two separate issues of well-integrity loss and reservoir-accessibility loss is critical when the presence of casing deformation or failure is considered. When describing casing deformation or failure, it is important to understand that not all of these failures are associated with a loss of well integrity. This is particularly true of any casing failure or deformation within the productive target formation because the target formation is fully outside the primary well barrier envelope.
In the complete paper, the authors refer only to those casing deformations and failures across and within the target productive intervals. Therefore, even if casing deformation results in loss of pressure integrity or partial or complete casing separation as a result of the event itself or because of the remedial actions implemented, this will not compromise actual well integrity. Consider that if the casing deformation occurs in a section that would or could normally be completed with perforations or fracturing, then the casing deformation is outside the primary wellbore barrier.
When such casing deformation occurs in the target area, well accessibility will be affected with regard to time, economics, and production but without health, safety, or environmental consequences. The operational effect can be significant up to and including a total loss of the well and a need to redrill through abandonment or sidetracking and is, therefore, a probabilistic part of development economics. The occurrence of extreme casing deformation within the primary well barrier envelope is extremely rare. Regardless, occurrence of such an event is treated as a major incident and involves all necessary regulatory bodies.