Geomechanical Aspects of Cementing Casings in Exploration Wells: Significance of Fracture Gradient in Assuring Well Integrity

Borehole cementation is essential for achieving well objectives and ensuring the safe drilling of oil and gas wells, particularly during exploration. The primary aim of cementing operations is to uphold well integrity and ensure zonal isolation. A critical component of cement design involves accurately determining the cementing window, which is constrained by the lower limit of pore pressure and the upper limit of fracture pressure in an open hole. It is crucial to adhere to design standards that address subsurface hazards to prevent incidents similar to the Macondo well disaster in the Gulf of Mexico in 2010. A well-executed cement design can significantly mitigate the risk of losing well control and the potential release of hydrocarbons, events that can adversely affect both the environment and the bottom line of the business. Formation fracture pressure may be exceeded during cementing operations as a result of either static or dynamic cementing heads. Such formation failures typically occur when the equivalent circulating density of the cement fluid breaches the cementing window. Recent analyses of several exploration wells worldwide reveal that inadequate cementation at intermediate casings was often due to the cement slurry's density exceeding the formation's breakdown strength during the cementing process. In certain instances, the growth of fractures and the migration of subsurface fluids to the surface or seabed resulted in the early abandonment of these wells. Developing a cementing program for a well solely based on fracture gradient predictions derived from leak-off tests and formation integrity tests is insufficient. The implementation of real-time fracture gradient modeling is crucial as it offers a comprehensive range of fracture pressures that can be applied to enhance the cementing design, thereby reducing the risk of expensive cementing failures during operations. This paper highlights the importance of real-time fracture pressure modeling, supported by case studies from various locations worldwide.