Dual gradient drilling - simulations during connection operations

Abstract

As oilfields are ageing and depleting, operators are forced to start searching for oil in more hostile environments. These new environments can introduce new drilling challenges. Prospects like ultra deep water reservoirs and depleted offshore reservoirs are difficult to drill with conventional drilling. This has lead the industry to developing the Dual Gradient Drilling (DGD) system. DGD is an unconventional drilling method and it is classified as a Managed Pressure Drilling (MPD) technique. By using fluids of varying density, DGD can provide the desired annular pressure profile in order to increase well performance, improve personnel safety and reduce Non Productive Time (NPT). Four major dual gradient drilling methods, along with the most important equipment, will be presented in this thesis. The various MPD technologies tries to compensate for the pressure variations experienced in the wellbore during connections. These pressure variations can cause formation fracturing, lost circulation, stuck pipe and more. By utilizing the DGD system the pressure variation related to connection operations can be significantly reduced. Although this new technology has several advantages over conventional drilling, it also has its challenges. To study the effects the DGD system has on downhole pressure during connection operations, the Kaasa model is used to simulate a DGD well and the results are compared to an MPD well.