In the classic weighted mud application the solids discharge (containing the majority of the weighting material) is returned to the mud system. The liquid effluent (containing the majority of the colloidal size solids) is discarded. As part of a“closed loop”, larger high capacity (75–250 GPM) decanting centrifuges (and sometimes standard centrifuges) are used to maximize fine solids removal. The coarser solids fraction is discarded in dry form, while the liquid and colloidal solids fraction is returned to the mud system.

Decanting centrifuges are becoming more popular for processing unweighted oil mud, especially if
1) the mud has been brought in from another location and may contain a large amount of fine drilled solids,
2) slow, hard drilling with a gradual buildup of ultra-fine solids is anticipated or
3) the liquid mud phase is valuable.
GN offers Decanting Centrifuge for unweighted mud applications.

Decanting centrifuges for oilfield applications were first introduced in the early 1950s. These early units were adapted from existing industrial decanting centrifuges. In the mid-1960s, a perorated rotor type machine was developed which does not perform like a pure decanter. Commonly called “barite recovery” centrifuges, these early designs were limited in capacity and application.

Today, the decanting centrifuge is even more important part of solids control. In addition, the increased use of low-solids mud and environmental dewatering applications require higher process volumes, greater clarification and solids capacity, and additional fine solids removal. Equipment selection is decided by site specific requirements. Proper system selection is the first step to effective solids control.

GN decanting centrifuge is purpose-built for drilling mud solids control in oilfield applications.

Decanting centrifuge is an import ant piece of equipment in mud solids control. Because of the environment regulation and high cost of drilling waste disposal, many CBM and HDD operator now prefers decanting centrifuges in their mud recycling system.

Also, as fluid costs increase, centrifuge use is highly recommended for reducing costs. The Australian client requires two set of GNLW363G decanting centrifuge to remove the supper fine solids to control the drilling mud density for reuse.

You can learn more about this Water Based Mud (WBM) Recovery System at GN solids news center.

According to Stokes Law, particle setting velocity is proportional to G-force. Since G-force increases with the square of bowl RPM, it is an important parameter of decanting centrifuge performance. G-force also increases linearly with bowl diameter. Figure 1 shows how solids removal efficiency improves with increasing G-force. For a given particle size and fluid properties, there is a minimum G-force necessary to invoke settling. Although high G-force is desirable, the cost is proportional to the cube of the bowl rpm and there are similar economic limitations on bowl diameter as well. Thus, the required G- force must be obtained from a practical combination of speed and diameter. Most oilfield decanting centrifuges have bowl dimensions from 14 to 28 inches in diameter and lengths from 30 to 55 in. Rotational speeds range from 1000 rpm to 4000 rpm, depending on the application. The more expensive, high “G” machines can provide up to 3,000 G’s.

Effect of G-Force on Separation (Higher G's Improve Separation Performance)

Note: however, that increasing G-force eventually reduces solids conveyance capacity due to torque limitations. As G-force increases, more solids are settled in the bowl and they adhere more tightly. More conveyor or torque is required to move the solids out. Once the torque limitations of the machine are reached, conveyance ceases.
G-Force for a Decanting centrifuges:
G’s = RPM2 x .0000142 x Diameter of Bowl (in inches)

High G-force decanting centrifuges are available from GN Solids Control.