Dynamic Casing Design has Arrived
Well Complete was approached by Conoco-Philips and Altus Well Experts to devise methods and software to enable casing design using dynamic methods.
“With today’s computer capabilities, dynamic analysis can finally be realized.”
PROBLEM:
Unconventional shale wells pose critical design challenges especially in regard to the long production casing strings run in extended horizontal or lateral sections. Compressive frictional loads accumulated during running are trapped in the string by cement, packers and the wellhead. Thus, the initial load state must fully account for the initial frictional state in order to be realistic and conservative. Hydraulic fracturing at high flow rates and significant pump pressures including the possibility of screen-out represents a critical design load on the casing which can also significantly alter the orientation and magnitude of tubular/wellbore frictional contact. The particular phenomenon of repeated re-fractures in a multi-stage stimulation compounds the design challenge. Cycles of cold stimulation followed by renewed hot production can lead to unexpected migration of axial loads and localization of critical stresses.
The cyclic nature of loading due to repeated sequences of multi-stage re-fractures and renewed production has not received industry attention due to the unavailability of appropriate models. Lack of adequate models has perhaps resulted in the problem being overlooked.
SOLUTION:
A dynamic model is ideally suited to the analysis of cyclic loads because of its inherent ability to account for a full history of friction loads. The dynamics of loading and unloading are also critical to this new ability to address the design problem. Previous static-based stress models have been unable to provide a comprehensive basis of design.
The model developed has recently been used to analyze a casing failure in an unconventional well, which occurred during a fracturing operation. Some of this text has been quoted from the following paper, “Dynamic Stress Analysis of Critical and Cyclic Loads for Production Casing in Horizontal Shale Wells,” SPE-194062-MS.
