Browsing by Author "Mostafavi Toroqi, Seyyed Vahidreza"

Now showing 1 - 1 of 1
  • Thumbnail Image
    ItemOpen Access
    Experimental Analysis and Mechanistic Modeling of Wellbore Strengthening
    (2012-10-04) Mostafavi Toroqi, Seyyed Vahidreza; Hareland, Geir; Aadnoy, Bernt; Husein, Maen
    Wellbore strengthening refers to the science and technology of increasing the pressure level at which circulation loss to the formation occurs. Although a fairly wide range of technologies have been proposed and tested, the application of engineered drilling fluids has proven to be the most promising approach. Circulation loss, which is one of the most troublesome issues occurring in drilling operations, is experienced at varying levels of severity. It is most expected in highly permeable formations, fractures and caverns. Lost circulation may have several consequences including fluid inflow, wellbore collapse, formation damage, non-productive rig time and environmental contamination. In order to mitigate the risks of circulation loss, a broad range of treatments and preventive methods have been practiced such as application of Lost Circulation Materials (LCM), cement plugs, squeeze gunk, gels and technologies like aerated drilling and stress caging. It has been observed that lost circulation occurs at varying pressure levels dependent on drilling fluid properties. This observation builds the foundation for drilling fluid based wellbore strengthening. Wellbore strengthening has been described previously but a general model to take into account the effects of fluid properties and its constituents does not exist. In addition, the governing mechanisms of this process are not well understood and explained in the literature. In this study a comprehensive literature survey and an extensive experimental analysis was completed to determine the mechanism of and contributing factors to wellbore strengthening. Next, a mechanistic model was developed and verified to predict the formation resistance prior to allowing drilling fluid loss. A field case of wellbore strengthening was also studied where the developed model exhibited a very good agreement. Results from this research are mostly directed towards circulation loss prevention via tensile fractures. However, they might be applicable for pore scale seepage loss through gravels and natural fractures. In the first chapter, an introduction to the circulation loss issue and its consequences is presented. Chapter two is dedicated to a brief review on wellbore stability analysis and a thorough survey on wellbore strengthening. In chapter three, the experimental part of this research is explained and its results are discussed. In chapter four, the experimental results are applied to build a mechanistic model. The model is analyzed and verified using a field case of wellbore strengthening. Conclusions of this research and some recommendation for future studies are presented in Chapter five.