Investigation of Factors for Strengthening a Wellbore by Propping Fractures

Abstract

Summary Wellbore strengthening or stress cage implementation has been recognized as an effective means of dealing with lost circulation during drilling operations. One of the mechanisms developed for strengthening a wellbore has been to prop induced and existing fractures with particulate lost circulation materials (LCM) to effectively increase hoop stress in the near wellbore region. However, a good understanding of this mechanism is necessary in order to avoid a potentially flawed design and implementation process which could adversely affect job success in the field. One of the main issues is fracture stability under the strengthening conditions. This paper will describe those factors which are important in designing wellbore strengthening jobs and address the conditions necessary to help ensure fracture stability, as determined through rock mechanics analysis. The strengthening of a wellbore by propping fractures has been discussed in a previous investigation (Wang et al. 2007a). In this paper, continuing the previous discussion, various parameters that affect the strengthening of the wellbore are addressed in detail. In-depth discussion of how each of those parameters affects the process of wellbore strengthening is presented. This study was accomplished using a boundary element numerical simulator to facilitate the analyses.