Simulation Analysis Of Multi - Phase Flow In Dynamic Drilling Of Deep Water

As the undiscovered resources are less and less on the land, the offshore oil and gas development is undoubtedly about to be a significant area of global energy development, in addition, deep-water oil and gas development is going to be the trend of global offshore oil and gas industry development. However, it is inevitable for deep-water drilling to encounter some difficulties which cannot be conquered by using conventional drilling technology and equipment. For instance, some shallow stream may emerge out during deep-water drilling, which can lead to complex problems, such as kick, blowout, or even ship sinking accident, nevertheless, deep research on riserless dynamic kill drilling(DKD) can effectively solve those problems.Based on deep research on DKD theory, this paper has established flowing physical models of DKD for study of total flowing path (well head-pipe inside-bottom hole-annulus-mud line). In consideration of variable flow rate, variable density during DKD, combining the basic theory of multiphase flow and the principle of integration, this paper established mixed fluid density model at different time and position within pipe and annulus by setting the relation between flow rate of seawater, base fluid and time, Considering the effect of borehole still temperature field, gas kick, ROP and other factors on the annulus pressure, the established models of annulus pressure and the pump pressure calculation on multiphase flowing conditions are solved by combining the boundary conditions and using the finite difference method. The annulus multiphase flow simulation software of deep-water dynamic kill drilling was coded. The effects of gas kick, seawater and base fluid flow rate, ROP, water depth and diameter and length of borehole under mud line on annulus pressure were discussed, and simulation of annulus loss, pump pressure, bottom hole pressure, annulus pressure, liquid holdup, mixed phase density and mixed phase velocity under the different flow rate model provided theoretical support for dynamic kill drilling parameter optimization.The calculation results show that greater rate of gas kick leads to less annulus pressure and bottom pressure, greater initial flow rate of base fluid and less initial flow rate of seawater always lead to bigger annulus pressure and bottom pressure; Moreover, deeper seawater depth and greater length of borehole under mud line also would result in larger bottom pressure, greater ROP would cause larger annulus pressure and bottom pressure, the effect of ROP on annulus loss is small. Additionally, annulus pressure loss is relatively sensitive to the flow rate, greater flow rate always leads to bigger annulus pressure loss, due to the big size of conductor diameter and short length of borehole under mud line, annulus pressure loss is usually small during DKD.According to the drilling practice of DKD in Mexico gulf, the flowing process on3well were stimulated, the bottom hole pressure and ECD were calculated, the theoretical results and field data were compared. The results have showed that the bottom pressure and annulus pressure of all of3wells are in the safe range, the operability of the dynamic kill drilling was proved. The paper has theoretical sense to parameter optimization and operation measurements during DKD.