Abstract
Success and failure of hydraulic fracturing is driven by a number of factors including operational procedures, fluid dynamics and the geomechanical response of the reservoir. Thus, the complex nature of the hydraulic fracturing process makes it difficult to correlate its success or failure to one of the many factors alone. However, in this paperwe demonstrate – based on real experiences–some successes and failures that show strong evidence of being driven by geomechanics aspects alone.
The unsuccessful hydraulic fracturing of a well can be often interpreted as a failure in terms of operational procedures. However, there are cases where the unfavorable geomechanical setting plays the dominant role on the fracturing success. Modeling such complex processes can be very time consuming and costly, especially, if fluid dynamics of the pumped fluids is integrated into the calculations. One suggested way forward is to modestly simplify the world of (rock-) physics and hence focus on the problem down to the main contributors of the processes while still reaching the desired and representative result.
In this work we focused on stress and pressure changes around the wellbore and perforations, that have strong influence on the end result of fracturing. In four wells that were hydraulically fractured, we observed two wells experiencing successful breakdown (and propagation), whereas the other two wells could not be fractured. Optimal application of analyticalgeomechanical modeling was more than sufficient to prove that the major cause for the failure in formation breakdown was stress field changes around the well bore and perforations in coherence with the rockmechanical properties. Thus, the specific geomechanical setting has led to an elevated breakdown pressure that was too high to be achieved by the horse powerof the pressure pumping equipment. At the same time the model also explains the underlying reasons for the two successfully stimulated wells.
This experience not only leadsto a geomechanical explanation for hydraulic fracturing- (formation breakdown) failure and success, but also to more customized recommendations for avoiding loss in pump horse power. This is of importance when limitations in pump- and completion pressures are a concern. From this experience we learn also about the influence of geomechanical drivers on well placement, completion strategy, perforation schemes and injection point selection.
