Inclined Wellbore Stability in High Temperature Formations of Drilling

Abstract

In recent years, exploring and developing oil and gas continuously expands into high-temperature environments, such as the Gulf of Mexico, North Sea, South China Sea, etc. Development of a high-temperature oil field from a platform always requires directional wells or extended reach wells (ERWs) departing from a central cluster to their targets at different depth of water in various azimuth. When drilling wells in high temperature formations, there is commonly associated with a suite of wellbore instability problems that are not normally encountered in onshore and normal temperature formations drilling. These problems are usually related to the presence of typically weak overburden sediments, unconsolidated formations, a small sedimentary coverage above the reservoir, and a great temperature difference between the drilling fluid and formation at the bottom hole In the past decades, a number of studies have been conducted to study the wellbore stability. However, few of the models are specific for wellbore stability of the inclined high temperature wellbores. In this work, an inclined wellbore stability model for high temperature formations is developed. The numerical method of the model is also provided. The study shows that drilling along the direction of minimum horizontal in-situ stress is safer than drilling in other directions, and the wellbore with a high inclination poses more risk of wellbore instability than the wellbore with a low inclination. It also shows that both of the wellbore collapse pressure gradients and wellbore fracture pressure gradients will increase as the temperature of borehole rises, and the fracture pressure is more sensitive to temperature. The model provides a practical tool to predict the stability of inclined wellbores for high temperature formations.