Baroid OTF Mixer

Baroid OTF Mixer Offers Solutions to Riserless Drilling Challenges

When drilling offshore in deepwater, before the marine riser is used, seawater typically is used as a drilling fluid. The seawater is pumped down the drillstring, and the returns (fluid and drill cuttings) are discharged at the seafloor. This seawater is usually supplemented with high viscosity sweeps to clean out the hole. This drilling technique requires large volumes (as hole volumes are large and all returns are deposited at the sea floor), but as seawater is readily available offshore, this is not usually a problem and is also very economical.

However in certain applications, usually when concerns exist about shallow water flows, shallow salt drilling that requires salt saturated fluid with densities above 10 ppg to prevent salt leaching, or wellbore stability, the hydrostatic pressure seawater exerts is not sufficient. Higher density fluids can help prevent a flow or ensure the hole remains stable. But with no marine riser, these fluids and cuttings will also be lost to the seafloor. Because of the pump rates required to efficiently clean the hole in these intervals, very high volumes of weighted drilling fluid may be required to drill relatively short intervals of a few hundred feet. This creates significant logistical challenges associated with riserless drilling. Up to 15,000 bbl of weighted drilling fluid may be required. Many rigs simply do not have the storage facilities for these types of volumes and significant numbers of supply boats may also be required. The high rates also mean that standard rig mixing systems will not be quick enough to keep up with the drilling fluid demand.

One solution to this challenge has been to ship smaller volumes of high density fluids (perhaps as high as 16 – 17 lb/gal) and mix with seawater on the fly (OTF) to generate the required volumes of lower weight mud. This method significantly simplifies logistics and costs. A 3-inlet, high performance eductor is often used to blend riserless drilling fluids.

Baroid Surface Solutions™ service offers the simple-to-install Baroid OTF Mixer that can blend fluid and seawater at rates of up to 2000 gpm, yet provide consistent and even mixing and consistent fluid physical properties. The system is small, easy to install and simple to operate. In addition to the flow meter technology installed on all units to measure all input and output flow rates, the Baroid OTF Mixer also can be installed with online density measurement as well. The system is also adjustable, allowing the Baroid operators to get the exact blending required.