Download or read book Numerical Investigation of Lost Circulation and Fracture Resistance Enhancement Mechanism written by Peidong Zhao and published by . This book was released on 2016 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Drilling in complex geological settings often possesses significant risk for unplanned events that potentially intensify the economic problem of cost-demanding operations. Lost circulation, a major challenge in well construction operations, refers to the loss of drilling fluid into formation during drilling operations. Over years of research effort and field practices, wellbore strengthening techniques have been successfully applied in the field to mitigate lost circulation and have proved effective in extending the drilling mud weight margin to access undrillable formations. In fact, wellbore strengthening contributes additional resistance to fractures so that an equivalent circulating density higher than the conventionally estimated fracture gradient can be exerted on the wellbore. Therefore, wellbore strengthening techniques artificially elevate the upper limit of the mud weight window. Wellbore strengthening techniques have seen profound advancement in the last 20 years. Several proposed wellbore strengthening models have contributed considerable knowledge for the drilling community to mitigate lost circulation. However, in each of these models, wellbore strengthening is uniquely explained as a different concept, with supporting mathematical models, experimental validation, and field best practices. Due to simplifications of the mathematical models, the limited scale of experiments, and insufficient validation of field observations, investigating the fundamental mechanisms of wellbore strengthening has been an active and controversial topic within the industry. Nevertheless, lost circulation is undoubtedly induced by tensile failure or reopening of natural fractures when excessive wellbore pressure appears. In this thesis, a fully coupled hydraulic fracturing model is developed using Abaqus Standard. By implementing this numerical model, an extensive parametric study on lost circulation is performed to investigate mechanical behaviors of the wellbore and the induced fracture under various rock properties and bottomhole conditions. Based on the fracture analysis, a novel approach to simulate the fracture sealing effect of wellbore strengthening is developed, along with a workflow quantifying fracture gradient extension for drilling operations. A case study on fracture sealing is performed to investigate the role of sealing permeability and sealing length. The results described in this thesis indicate the feasibility of hoop stress enhancement, detail the mechanism of fracture resistance enhancement, and provide insights for lost circulation mitigation and wellbore strengthening treatment.