\u0414\u0440illing fluid serves multiple roles at once: transporting cuttings to the surface, preventing borehole wall collapse, maintaining overbalance against formation pressures, and cooling plus lubricating the bit. All these functions rely on a single property\u2014composition stability. Once stratification begins in the tank, actual density and rheology no longer match calculated values, rendering any design decision meaningless.<\/p>\n
The circulation system forms a closed loop where liquid constantly changes composition. Cuttings remain after exiting the well; reagents are added when preparing fresh batches; weighting material is introduced manually or via ejector.<\/p>\n
Solid phase density exceeds liquid by several times, so heavy particles settle without constant motion. This happens fastest in tank corners, near baffles, and bottom zones where flow is minimal. A paradox emerges: instruments record normal parameters at sampling points, while pumps draw denser or lighter layers.<\/p>\n
Properly organized mixing addresses not one but several technological tasks:<\/p>\n
The key word here is «regime.» Excessive mixing destroys thixotropic structure, promotes aeration and foaming; excessive foam disrupts pump operation and distorts flowmeter readings. Too weak leaves stagnant zones. Optimum depends on drive power combination, impeller geometry, submersion depth, and internal piping configuration.<\/p>\n
Typical circulation system scheme\u2014vertical mixer with electric drive mounted on frame at tank neck. Shaft with impeller descends into liquid; blades generate flow engaging entire volume. By drive type, devices split into mechanical and hydraulic; first are more common due to simple maintenance and predictable characteristics.<\/p>\n
Selection usually evaluates five parameters. Motor power determines medium volume engaged in circulation. Impeller diameter and profile define flow structure: turbine blades create directed axial movement with high efficiency.<\/p>\n
Rotation speed for viscous weighted compositions must be low\u2014preserves solution structure, reduces foaming. Working wheel submersion depth adjusts to tank height and liquid level. Finally, materials and coatings must withstand abrasive wear and chemical aggression, including hydrocarbon systems exposure.<\/p>\n
Gearbox deserves special attention. Output shaft operates in abrasive environment, vulnerable node. Using wave gearbox without output shaft seal eliminates lubricant leak risk into solution, simplifies maintenance.<\/p>\n
Calculation starts not with model choice but tank analysis: volume, height, baffles presence, internal communications. Then consider composition density and viscosity, required homogeneity degree, operation mode\u2014continuous or periodic.<\/p>\n
For large tanks, one device often insufficient: single mixer forms local circulation zone, doesn’t cover whole volume. Such cases install multiple units distributed across deck so flows overlap rather than cancel each other.<\/p>\n
Useful to pre-model placement scheme considering pump suction ports location. Operational factors equally important: available power supply capacity, site climate conditions, protective coatings presence for specific solution type.<\/p>\n