1. Chapter 2 – Drilling Fluids
Drilling Engineering – PE 311
Chapter 2 – Drilling Fluids
Solid Control

2. Solid Control in Drilling Operations
Introduction
Laboratory tests and practical field experience show that closely monitoring drilled solids in the mud and minimizing their concentration can result in large savings of both money and time. These savings manifest in three ways:
Improved drilling rate
Increased bit life
Reduced wear on mud pumps.

3. Solid Control in Drilling Operations
Introduction
Solids control methods are based on the average diameters of the particles being handled:
Coarse Particles: Greater than 2000 microns
Intermediate Particles: From 250 and 2000 microns
Medium Particles: from 75 to 249 microns
Fine Particles: from 45 to 74 microns
Ultra-fine Particles: from 2 to 44 microns
Collodial Particles: less than 2 microns

4. Solid Control in Drilling Operations
Introduction

5. Solid Control Methods Settling
Treatment of solids-related mud problems may involve one or more of the following mechanisms: settling, dilution, mechanical separation and chemical treatment.
Settling involves retaining mud in a nearly quiescent state long enough to allow the undissolved solids, which are heavier than water, to "fall out" of the fluid. The relative success of this method depends on several factors, including the size and shape of the particles, the density of the particles, the density of the fluid, and the overall retention (settling) time.
The settling time can be reduced by using a flocculant to increase the particle size, or by inducing centrifugal force to increase the gravitational effect.

6. Solid Control Methods Dilution
Dilution, unlike the other solids control methods, does not involve removing solid particles from the mud; rather, it is a means of decreasing the solids concentration by adding base fluid to the system. Dilution is most often used to correct mud properties that have been altered by the accumulation of drilled solids. The drawback to this method is that as drilling progresses, concentrations of drilled solids continue to increase, and undesirable mud properties eventually reappear. Also, dilution is often expensive for the following reasons:
The consumption of the products required to maintain desired mud properties is continually increasing.
Lack of storage space for the increased mud volume often leads to the discarding of hundreds of barrels of valuable drilling mud.
Extra cleanup and transportation costs are incurred in environmentally sensitive areas.

7. Mechanical Separation
Solid Control Methods
Mechanical Separation
Mechanical separation devices are available in two basic types: vibrating screening devices (shakers) and systems that use centrifugal force to increase settling rate. Mechanical treatment of solids buildup is often the most practical and cost effective of the four available methods—it does not alter essential mud properties and it decreases the need for dilution. Generally speaking, the greater the cost per barrel of a given mud, the greater the savings in using mechanical equipment to rectify mud properties.
The equipment used to mechanically remove solids from the mud must be designed to fit the requirements of a given drilling operation; not every piece of equipment is appropriate in every situation. Furthermore, the equipment specifically selected to aid in mechanical removal of solids must be rigged up and maintained to ensure that the units operate at peak performance.

8. Mechanical Separation – Shale Shaker
Solid Control Methods
Mechanical Separation – Shale Shaker
Shale Shakers: The double-decker shale shaker has two screens mounted on a flat-bed construction. The screens can range down to 100 mesh with the mesh cross section varying from square to an exaggerated rectangle. Drilled solids down to 177 microns are removed by 80-mesh screens, and micron size particles by 20-mesh screens.

9. Mechanical Separation – Desilters and Desanders
Solid Control Methods
Mechanical Separation – Desilters and Desanders
Desilters and DesandersThe desilters/desanders must be equipped with centrifugal pumps capable of providing sufficient pressure to the hydrocyclones to allow them to operate in the desired pressure range. When correctly installed and operating in the design range, desilters and desanders are capable of removing up to 95% of solid particles larger than 15 microns.

10. Mechanical Separation – Mud Cleaner
Solid Control Methods
Mechanical Separation – Mud Cleaner
Mud Cleaner: The mud cleaner is designed for intermediate mud weight ranges of 11.0 to ppg. It consists of an eight-cone desilter bank mounted over a small high-speed shaker. The mud cleaner combines the advantages of solids separation by means of centrifugal force and solids removal by screening.
The screen sizes vary, but the size most commonly used is 200 mesh, which can remove fines down to 75 microns in size. It is impractical to use screen sizes much below 200 mesh because of excessive loss of barite over the shaker screen.

11. Mechanical Separation - Centrifuge
Solid Control Methods
Mechanical Separation - Centrifuge
Centrifuge: In weighted mud systems it is often desirable to reduce mud maintenance costs by methods other than dilution. Since it is not practical to use desilting equipment in these systems, a centrifuge is often used.
Mud centrifuges work on the decanting principle. The mud flow enters a chamber rotating at a high speed, and centrifugal force separates the mud stream into three components: fluid phase, low-specific-gravity solids, and high-specific-gravity solids. Following separation of the low- gravity solids, the high-gravity solids are returned to the active mud system.
In unweighted mud systems, a high-volume decanting centrifuge removes low-specific-gravity drilled solids most efficiently and economically. The centrifuge can be operated on unweighted muds at speeds up to 2200 to 2400 rpm, creating centrifugal forces greater than 1500 G-force. The high-volume centrifuge can remove fine solids down to two microns (e.g., bentonite and clays) .

12. Separation Efficiency
Solid Control Methods
Separation Efficiency
The separation efficiency of hydrocyclones depends on four general factors:
Fluid properties;
Particle properties;
Flow parameters;
Hydrocyclone parameters.

13. Mechanical Separation - Hydrocyclone
Solid Control Methods
Mechanical Separation - Hydrocyclone

14. Mechanical Separation - Hydrocyclone
Solid Control Methods
Mechanical Separation - Hydrocyclone

15. Mechanical Separation - Hydrocyclone
Solid Control Methods
Mechanical Separation - Hydrocyclone

16. Solid Control in Drilling Fluids
Density control
Barium sulfate (barite) is the primary additive used to increase the density of clay/water muds. Densities ranging from 9 – 19 lbm/gal can be obtained using mixtures of barium sulfate, clay, and water. The specific gravity of pure barium fulfate is 4.5, but the commercial grade used in drilling fluids (API barite) has an average specific gravity of about 4.2.
Recently, alternative density control agents such as hematite (Fe2O3) with specific gravity ranging from 4.9 to 5.3 and ilmenite (FeO.TiO2), with specific gravity ranging from 4.5 to have been introduced. Because of their hardness, there is a concern about the abrasive of these materials in the circulating system.

17. Solid Control in Drilling Fluids
Density control – Unlimited V2
The mixture density is given by
If the storage capacity is available, to increase the density of the drilling fluid, we simply add barite to the mud. Therefore, the known and unknown variables in this case are:
Known: V1, r1, rB, r2
Unknown: V2, mB
r1, V1
r2, V2
rB, VB

18. Solid Control in Drilling Fluids
Density control – Unlimited V2
For ideal mixing the volume of mud, V1 and weight material, VB, must sum to the desired new volume, V2
Likewise, the total mass of mud and weight material must sum to the desired density-volume product
Solving these equations simultaneously for unknowns V2 and mB yields

19. Solid Control in Drilling Fluids
Density control – Limited V2
When excess storage capacity is not available, the density increase will require discarding a portion of the mud. In this case the proper volume of old mud should be discarded before adding weight material.
Known: V2, r1, rB, r2
Unknown: V1, mB
r1, V1
r2, V2
rB, VB
Discarded mud

20. Solid Control in Drilling Fluids
Density control – Limited V2
When excess storage capacity is not available, the density increase will require discarding a portion of the mud. In this case the proper volume of old mud should be discarded before adding weight material.
Ideal mixing
Mass balance
Solving these two equations for V1 and mB gives
Then the volume of fluid need to discard: Vd = Vi – V1 ; With Vi is the initial mud volume.

21. Solid Control in Drilling Fluids
Density control – wetted barite
The addition of large amounts of API barite to the drilling fluid can cause the drilling fluid to become quite viscous. The finely divided API barite has an extremely large surface area and can absorb a significant amount of free water in the drilling fluid. This problem can be overcome by adding water with the weight material to make up for the water adsorbed on the surface of the finely divided particles. It is often desirable to add only the minimum water required to wet the surface of the weight material. The addition of approximately 1 gallon of water per 100 lbm of API barite is usually sufficient to prevent an unacceptable increase in fluid viscosity.
Mass balance

22. Solid Control in Drilling Fluids
Density control – wetted barite – limited V2
Solving these equations for unknowns V1 and mB gives
Note that VwB is the volume of water need to add with one pound of barite. VwB = 0.01
For mB pounds of barite, VwB = 0.01 mB.

23. Solid Control in Drilling Fluids
Density control

24. Solid Control in Drilling Fluids
Density control
Example: Compute the volume and density of a mud composed of 25 lbm of bentonite clay, 60 lbm of API barite, and 1 bbl of fresh water
Solution:
The total volume
Mixture density

25. Solid Control in Drilling Fluids
Density control
Example: is desired to increase the density of 200 bbl of 11-lbm/gal mud to 11.5 lbm/gal using API barite. The final volume is not limited. Compute the weight of API barite required.
Solution:
The final volume is given
The weight material barite required

26. Solid Control in Drilling Fluids
Density control
Example: it is desired to increase the density of 800 bbl of 12-lbm/gal mud to 14-lbm/gal. one gallon of water will be added with each 100-lbm sack of API barite to prevent excessive thickening of the mud. A final mud volume of 800 bbl is desired. Compute the volume of old mud that should be discarded and the mass of API barite to be added.

27. Solid Control in Drilling Fluids
Density control
For a final volume of 800 bbl. V1 is given
Thus, bbl of mud should be discarded before adding any API barite. The mass of API barite needed is given by
The volume of water to be added with the barite
0.01mB = 1,083 gal or bbl.