Abstract

Most drilling-related incidents are caused by unstable boreholes, whether they are caused by lost circulation, packoff, or stuck BHA and/or casing. One of the main objectives of this study was reduction in drilling incidents and associated Non Productive time (NPT) while drilling wells in a particular area of Kuwait, where often extremely challenging environments were faced due to wellbore instability arising from tectonic stresses, associated faults, fractures, complex structures, and anomalous pore pressure. Additional challenges were presented by a complicated and highly deviated well design, where planes of weakness of the formation being drilled and their relative angle with respect to the well path become crucial factors in assessing stability of the borehole. Multiple failure mechanisms such as stress induced wellbore instability, invasion of drilling fluids into weak bedding / micro-fractures and osmotic sensitivity, were found to be the root cause of wellbore instability across reactive shale formations especially during drilling of highly deviated wells.

In lie of these challenges, a comprehensive study was conducted to overcome the wellbore stability issues and investigate feasibility of drilling Ahmadi wells of Kuwait at high deviation. Correct mud weight (MW) prediction was one key factor during the drilling stage to keep the wellbore stable and deliver good borehole geometry (Figure 1). The key objectives of the study were to define a safe MW program for the vertical and deviated sections of the planned well by conducting a wellbore stability study and to determine a real-time strategy to mitigate and-or manage wellbore instabiity problems as they arise.

The scope of work included root cause analysis of drilling events, development of mechanical earth models (MEM) for offset wells, integrating sections of the MEM from the offsets to the planned well trajectory, and a safe MW program for planned well.

The paper describes the process of optimizing the drilling practices based on geomechanical outputs, to overcome serious drilling hazards and application of real time geomechanical monitoring for successful drilling. This application promises to open the prospect of drilling similar wells without complications and reduce NPT in Kuwait.

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