Simulation of Modified Dual Gradient Drilling System to Drill Deepwater and Ultra-Deepwater Wells

Abstract

One of the main challenges in deepwater subsea drilling is the narrow operational mud weight window between pore pressure and fracture gradient; as water depth increases so does the complexity of maintaining this window. In addition to the imprecise nature of pore pressure and fracture values, deepwater operations are subject to well control issues and fluid losses due to fracture propagation. Technology such as Managed Pressure Drilling (MPD) facilitates tackling such challenges by allowing the maintenance of hydraulic pressure in the annulus between pore pressure and fracture gradient. One of the MPD solutions for deepwater drilling is Dual Gradient Drilling (DGD). According to the definition of the International Association of Drilling Contractors (IADC), DGD is the drilling technology that uses or simulates the effect of two fluids of different gradients in the annulus to create dual hydrostatic gradients to better manage the annular pressure profile. For this specific project, DGD refers to subsea drilling operations where the mud is not circulated through a large conventional drilling riser but circulated through a small return line by using a subsea pump. A new DGD version has been proposed named modified dual gradient drilling where operational capabilities, new equipment specs, and procedures have been adapted and improved.