Development and application of ZM-2 drilling fluid density adjustment mixing device

High-pressure shallow (gas/water) flow is often hidden in the deepwater seabed, so penetrating shallow flow in drilling without BOP will be highly risky. In this case, the conventional well killing method to balance the formation pressure with back pressure generated by well head equipment is no longer suitable. Based on the analysis of structural characteristics of domestic and foreign multi-phase mixing systems, a ZM-2 drilling fluid density adjustment mixing device with independent intellectual property right was developed according to the principles of dynamic well killing. The device is mainly composed of a throttle valve, a high-precision electromagnetic flowmeter, a mixer, dumbbell-shaped nozzles, connecting pipes and other components. Fixed on the mixer are three inlets to fill heavy mud, seawater and additives. Opposed jetting is adopted to realize rapid and uniform mixing of fluids with different densities. A laboratory test was conducted to work out the relationship between throttle opening and injection flow rate and establish a linear relationship between killing fluid density and heavy mud flow. The results of field test conducted in the Nanhai No.8 drill ship showed that the mixing device was stable in operation and excellent in mixing performance. The density difference of ingredient mixture could be controlled within 0.05 g/cm3 after the mixture flowed out of the mixing chamber of the mixer of about 0.3 m long, so such high precision can meet the requirement of dynamic well killing.