drilling

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• Drilling Engineering PE 311
• Chapter 2 Drilling Fluids
• Solid Control

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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.

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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

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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.

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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.

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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 methodsit
  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.

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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
  840-micron size particles by 20-mesh screens.

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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.

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Solid Control Methods
Mechanical Separation Mud Cleaner

• Mud Cleaner The mud cleaner is designed for
  intermediate mud weight ranges of 11.0 to 14.0
  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.

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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) .

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Solid Control Methods
Separation Efficiency

• The separation efficiency of hydrocyclones
  depends on four general factors
• Fluid properties
• Particle properties
• Flow parameters
• Hydrocyclone parameters.

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Solid Control Methods
Mechanical Separation - Hydrocyclone
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Solid Control Methods
Mechanical Separation - Hydrocyclone
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Solid Control Methods
Mechanical Separation - Hydrocyclone
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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 5.1 have
  been introduced. Because of their hardness, there
  is a concern about the abrasive of these
  materials in the circulating system.

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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

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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

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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

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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.

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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

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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.

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Solid Control in Drilling Fluids
Density control
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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

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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

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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.

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Solid Control in Drilling Fluids
Density control

• For a final volume of 800 bbl. V1 is given
• Thus, 99.47 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 25.79 bbl.