The Role of Solids Control Centrifuges in Achieving Effective Mud Management

Effective mud management is essential to drilling operations. Mud dumping and excessive dilution are costly and environmentally harmful.

Rig operators are focusing on more efficient monitoring of mud solids control equipment. The equipment layout must be carefully designed, and the operating parameters must be defined according to Sedco Forex field test data.

Solids Removal

When drilling, solids build up in the mud system and are removed from the drill cuttings through shakers and solids control centrifuges. This process is known as dewatering the mud.

Shakers separate large particles from the mud while the desander and desilter segregate slightly smaller debris, leaving liquid and fine drill solids behind. Depending on the screen size, these two pieces of equipment can remove up to 70% of the debris that could cause problems downhole.

The first step in this process is a shale shaker, the rig’s “first line of defense.” This initial removal stage is necessary for downstream hydrocyclones and centrifuges to be overloaded beyond their design capacity.

Decanter centrifuges use high-speed rotation to generate centrifugal forces that separate heavy debris from the liquid and lighter components of the mud. This device consists of a conical steel bowl that rotates at high speed while another conveyor moves in the same direction as the bowl but at a lower speed. The separation process throws the heavier particles against the side of the bowl and down toward a discharge port while the lighter materials are carried into an overflow port.

Rheology Control

Using the appropriate rheology control additives to the drilling fluids allows for precise management of mud properties such as sag, resistance, and leveling. This is achieved by introducing compounds that provide suspension, stabilization, and thickening with a range of flow characteristics.

Most modern rigs operate their primary shakers with screens far too coarse to achieve the goals of their solids control program. The result is that the rigs are constantly generating more colloidal and ultra-fine solids through degradation than can be effectively removed by their centrifuge systems.

This results in the centrifuges having to work harder – which causes their performance to degrade over time. To counter this, a mud handling program must be established that involves the contractor Rig Engineer, Mud Engineer, and rig crew to monitor the equipment efficiently. This includes the development of an intermediate slurry tank that is well-sized and properly equipped for separating and discharging the cuttings to be processed by the centrifuges.

Fluid Recovery

In field tests, it was found that the centrifuge separation curve for a given screen mesh is not significantly affected by changes in mud type, mud weight, or plastic viscosity*. However, the centrifuge flow rate capacity decreases with increases in these characteristics.

Typical centrifuge systems return the overflow (“center” or light phase effluent) to the mud system, which always involves returning colloidal solids. This leads to progressive degradation of the average particle size and mud quality, increasing wall cake build-up, causing barite and low-gravity solids dilution and degrading rheological properties.

A properly designed and sized vertical cuttings dryer eliminates this problem by allowing centrifuges to operate at full treatment capacity, dramatically reducing waste disposal costs, significantly lowering whole mud losses within those wastes, and improving the overall quality of the mud. This is achieved by combining better equipment selection, careful monitoring of the equipment performance, and minimizing mud losses through improved process management.

Environmental Impact

In addition to minimizing operational costs through reduced dilution rates, complete solids control equipment reduces the amount of chemical reagents needed to maintain proper mud properties. This saves money on expensive mud products.

All mud systems should include mechanical solids removal equipment like the shale shaker that physically removes large debris. Adding a desander to take care of medium-sized debris and a desilter to remove the smaller silt particles left behind will improve the system’s effectiveness.

A decanter centrifuge, another hydrocyclone-like device, can effectively separate the heavier solids from the liquid and lighter mud components. This enables the mud to remain at an optimum weight for drilling while also improving the efficiency of the entire rig system.

With effective mud management, the usable life of the fluid is increased by up to two or thrice as much, which makes it extremely valuable to drilling companies. Mud dumping and dilution are no longer acceptable from an environmental perspective, but the same waste can be recycled and reused with solids control.


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