An Analyzing Model of Stress-Related Wellbore Strengthening Techniques
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One of the major causes of nonproductive time (NPT) and the resulting additional costs during drilling operations is lost circulation. The problem of lost circulation is an ever growing concern to the operators for several reasons, including the continuous depletion of reservoirs and the naturally occurring narrow drilling window due to an abnormally pressured interval or simply the low fracture pressure gradient of the formation rock. To deal with the issue of lost circulation, the concept of wellbore strengthening was introduced. The ultimate goal of this concept is to increase the drilling fluid pressure required to fracture the formation; thus, eliminating lost circulation and NPT and reducing the costs. Numerous wellbore strengthening techniques were created for this purpose over the years. Those techniques vary in their applicability to different scenarios and their effectiveness. Therefore, there is a clear need for a tool that will help to define the most suitable wellbore strengthening technique for a well-defined scenario. The model described in this study aims to provide a practical tool that evaluates and predicts the performance of wellbore strengthening techniques in practical situations. The wellbore strengthening techniques covered by the model use stress changes around the wellbore as the primary criteria for enhancing the fracture pressure and effectively enlarging the drilling window. The model uses geometric principles, basic rock mechanics data, linear elasticity plane stress theory, drilling fluid data, and geological data to evaluate and predict the performance of a wellbore strengthening technique. Another important objective of the model is the proper selection of candidates for wellbore strengthening. To achieve that goal, the model creates all of the possible scenarios in terms of well placement, surface location, and trajectory based on the input data to emphasize the scenario that will yield maximum results using a specific wellbore strengthening technique. The use of the model is illustrated through the use of a case study. The results of the case study show practical advantages of applying the model in the well planning phase. The analysis performed using the model will demonstrate the applicability of a certain wellbore strengthening technique, the effectiveness of the technique, and the best parameters for the technique. Therefore, the analysis shows not only the best case scenario for applying a wellbore strengthening technique, but it also illustrates the cases where applying the technique should be avoided due to an expected unsatisfactory performance.
Albahrani, Hussain (2015). An Analyzing Model of Stress-Related Wellbore Strengthening Techniques. Master's thesis, Texas A & M University. Available electronically from