Improving Wellbore Stability by Leveraging Real-Time Spectral Gamma Ray Logs

Abstract

The objective of this paper is to examine the quantification effect of clay content on wellbore stability. Clay Content is known to have direct impact on hydrocarbon petrophysical modeling. The major factor to quantify clay content is to acquire spectral gamma ray logs. Utility of standalone gamma ray readings provides only qualitative clay content model in a form of clean and clay filled fashion rather than a quantified clay content. Assessing spectral gamma ray logs in real-time can be a potential factor contributing optimized decisions during the drilling operation. Dealing with abrasive sand environment require extra formation knowledge to formulate a better drilling plan that will ultimately result in a good hole condition. Wellbore stability is directly related to the formation matrix type that is being drilled. Clay content can also contribute to the calculation of permeability in the dynamic phase. To quantify clay content, spectral gamma ray logs are vital. Once spectral gamma ray logs are available, a full petrophysical lithology model is calculated featuring quantified clay content by volumetrically identify illite, orthoclase, and kaolinite contents. It directly works as a wellbore stability indicator leading drilling engineers to formulate real-time drilling plans minimizing wellbore stability issues. These plans can involve a better formulation of a mud system, change of inclination/azimuth, change of a drilling parameter such as rate of penetration to accommodate the current quantified clay content that is being drilled. The use of a quantified real-time formation clay content indicator to minimize wellbore instability is vital to avoid operational complexities and non-productive operational time. A comparison of qualitative and quantitative methodologies of clay content types verses wellbore stability is investigated. This will ultimately showcase the importance of establishing a wellbore instability mitigation plan leveraging real-time spectral gamma ray logs. Formulations of mud systems, rate of penetration recommendations are made based on the results. A representation of potential mitigation of non-productive operation time is showcased highlighting the vitality of the proposed method. This paper examines the direct impact of the quantification of clay content on wellbore stability. The process can add value to reduce the costs associated with wellbore instability. It can also manage to lower the non-productive operational time caused by a changed bit due to an inefficient management of either drilling mud/rate of penetration due to an unquantified formation clay content.