Preventing Mud Losses by Wellbore Strengthening

Abstract

Abstract Until recently, the drilling industry had an established range of options for dealing with lost circulation that included pre-treatment with lost circulation material (LCM) and/or remediation with LCM when losses occurred. This paper describes a fully engineered approach taken by BP and Halliburton to formulate a drilling fluid that can effectively strengthen the weak wellbore while drilling. The approach, called Stress Cage theory, is an extension of a lost circulation strategy that has been used for years in the drilling industry. However, it includes using log analysis to identify potential fracture location and determine its geometry, especially its width, and then identify a mixture of particulate materials to seal the calculated fracture width. The application of the appropriate mixture of materials can effectively increase fracture gradient (both in land and offshore), allowing the operator to drill through a weak formation pressured zone successfully with minimal to zero downhole losses. Case histories including drilling parameters, formation pressures, field and laboratory fluids testing, and some of the operational challenges are detailed. The estimated value of Stress Cage applications for BP in 2004 and 2005 has been calculated at $100MM.