Enhancing drilling operations: prioritizing wellbore integrity, formation preservation, and effective mud waste control (case study)
Authors: Elrayah Ahmed Abdelaziz Ibrahim 
Published: April 2024

This study examined the issues of wellbore instability encountered during the drilling of the vertical exploration Al-Rateena-1 well, Block 25D, Al-Rawat Field, Sudan. Measurements of the wellbore diameter revealed significant damage to the formation interval between 2775 and 2925 m. This damage released approximately 800 barrels of drill cuttings from the affected zone and overlying formations. A comprehensive wellbore stability assessment was conducted to identify the root causes of instability and develop strategies to mitigate future occurrences. The assessment involved a thorough analysis of the pore, vertical, effective vertical, and minimum and maximum horizontal pressures. All of these parameters play a crucial role in maintaining wellbore integrity. This study also evaluated the potential impact of these parameters on groundwater and soil quality, leading to the development of an efficient waste management system. The safe mud weight range for the well was determined to be between 13.5 and 15.5 pounds per gallon (PPG). However, the drilling fluid used during the operation had a significantly lower density of only 10 PPG. This ultimately leads to the collapse of the wellbore wall. Examination of drilling cuttings revealed elevated levels of various heavy metals. These heavy metals included Lead (94.12 ppm), Mercury (62.87 ppm), Nickel (1403 ppm), Copper (343 ppm), Calcium (23132.72 ppm), Magnesium (3700 ppm), and Barium (16000 ppm). These elements pose a significant threat to both surface water and groundwater quality. It is possible that they also contributed to the wellbore wall collapse. It was hypothesized that the interaction between these elements and the water-based drilling fluid or its additives could have triggered the collapse event. The findings of this study highlight the importance of conducting comprehensive wellbore stability assessments before drilling. Such assessments should incorporate detailed investigations, modelling, calculations, and simulations of various parameters that influence wellbore stability. In addition, careful consideration must be given to the potential environmental impacts of drilling fluids and cuttings, particularly in areas with sensitive ecosystems. The wellbore instability in the vertical exploration Al-Rateena-1 well was primarily caused by the use of an underweight drilling fluid. This underweight drilling fluid results in the collapse of the wellbore wall. Elevated levels of heavy metals in drill cuttings suggest a potential impact on groundwater quality. It is also possible that they contributed to the wellbore instability. Comprehensive wellbore stability assessments are essential to prevent similar incidents in the future. This study provides a detailed account of wellbore instability. This includes the identification of root causes and the development of preventive measures. This study also highlights the potential environmental impact of drilling fluids and cuttings. The findings of this study can help improve drilling practices and environmental protection in the oil and gas industry.