Experimental Evaluation of Separation Methods for a Riser Dilution Approach to Dual Density Drilling

A dual gradient, deepwater drilling system based on dilution of riser mud requires economically separating the riser mud into a low density dilution fluid and a higher density drilling fluid. This study investigated the practicality of accomplishing this separation using hydrocyclones and centrifuges and examined the possible benefits and efficiency of each. The separation experiments were conducted using a laboratory centrifuge and 2 in. hydrocyclones. The laboratory centrifuge was able to separate the riser mud into near ideal densities for dilution and drilling fluid. However, the dense slurry retained in the centrifuge had lower electrical stability than the feed stream. The hydrocyclones achieved much less contrast in density between the low and high density discharges, but their use consistently resulted in a beneficial increase in the stability of the mud emulsion in all of the flow streams and gave more desirable rheological properties. A qualitative comparison indicates that the hydrocyclone separation system may offer a feasible and desirable alternative to a centrifuge separation system.