9 solids removal

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1Agip KCO Well Area OperationsDrilling Supervisors Training Course Drilling Muds RPW2021A

SOLIDS REMOVAL




INTRODUCTION

Solids control is a constant problem, every day on every well.

Solids control, allows the monitoring of undesired cuttings in a mud system since the

increasing of these solids can generate negative effects both to the well and drilling.

Solids influence mud cost due to dilution and additives but also well cost because of

potential problems for torque and drag, hole solubility, stuck pipe.

Excess of solids can also influence life of bits, pumps and other equipment.

Solids in drilling fluids are essentially of two kind. The first is referred to solids added to

achieve various desirable properties, and include chemicals (bentonite, polymers,

dispersant), weight materials (barite, calcium carbonate) and L.C.M. (myca, granulars).The second consists of drill solids, rocks and clays incorporated into the mud. These

solids affect some mud properties in undesirable way and it is necessary to remove them

from the system.




These are the methods ( and usually in the same sequence) for solids separation:

• Settling• Screening• Hydrociclones• Mud Centrifuges

Settling of particles is governed by the laws of physics (Stokes’s Law):

SOLIDS SEPARATION METHODS

Vs = Settling Velocity (ft/sec)gc = Gravity Constant (ft/sec 2)Ds = Diameter of the solid (ft)

= Solid Density (lb/ft 3)

= Liquid Density (lb/ft3)= Liquid Viscosity (cP)

For centrifugal motion (hydraulics and centrifuges) the separating force is proportional tothe diameter of circular motion times the square of the rotating speed (RPM) times the

mass of the particle.

µ

ρ ρ

3.46)(Dg

V2

cs

ls −+

=

s ρ

l ρ µ




SOLIDS CHARACTERISTICS

5.04.0 - 4.52.3 - 2.72.7 - 2.9

0.851.0

2.6 - 2.7

HematiteBarite

BentoniteLimestone

Gas-oilWater Sand

Density of the common drill ing fluids components





8415954102972501771491251058874442

203040506080

100120140170200325400

Opening sizesMicrons

SizesMesh

Standard mesh size





Size Particles Classification




METHODS FOR SOLIDS CONTROL

Dilution method

Dilution method is only a solid control, not a solid removal method.

Oil-based muds can be diluted with basic oils (or new oil-based mud) and the water-base

muds can be diluted with water (or with new water-based mud) to keep the concentration

and volume of the solids within the limits.





Gravity Settl ing Method

Settling pit or sand trap is usually the second step for solid control following the first arriveof mud on the shale shakers screens.The rate of solids settling depends on:

• The size, shape and S.G. of the particles.• The density of the mud.• The viscosity of the mud.• The type of fluid flow regime• The time involved in passing through the settling pit.

According to the Stokes’s Law, the solids settling can be achieved only in laminar flowregime. Settling rates can be improved by using low viscosities and gels.




Mechanical Separation Method

Shale-Shakers

These are the most important solids control devices. They are vibrating screen

separators used to remove drilling solids of different size from the circulating mud once

it’s returned on surface.

The shale shakers represent the first line of defence against solid accumulation. All the

circulating mud is processed from the shale shakers and most of the drilled solids can be

removed by an efficient shale shakers equipment.






In the picture below, a 200 mesh shale-shaker screen will remove 100% of the solids

greater than 74 microns

Screen mesh sizes vs.opening microns.




SHALE-SHAKERS

Types of Shale-Shakers:

• Circular-motion Shaker

It is considered the first type of shaker used and produces the lowest centrifugal forcecompared to the other models but at a fast transport.

• Elliptical-motion Shaker The centre of gravity is raised above the deck and the variation of both intensity and

throw is obtained as the solids move down the deck. Moderately G-force and slowtransport.It produces the greatest drying and is preferred to dry the underflow from desilter.

• Linear-motion shaker It is fitted with two circular-motion motors mounted on the same deck and set for opposite rotation. It is the best because it produces a high G-force and a fasttransport.




SHALE-SHAKERS

Many different shaker types can be combined in a “cascade” to improve their solid-

removal efficiency.

Sometimes, circular-motion shakers are used as “scalping” shakers to remove large

and sticky solids.




SHALE-SHAKERS

SHAKER SCREENS

Screen Mesh: it is the number of openings per linear inch. A 30 x 30 mesh square screen

has 30 openings along 1 inch. line, in both directions. A 70 x 30 mesh (oblong) screenhas 70 openings along a 1 inch line one way and 30 openings on a 1 inch line

perpendicular.

Cut Point: a D 50 cut point represents the particle size, where 50% of the particles of thatsize are removed by the solids control equipment. D 20 cut means that 20% of the stated

micron size particles are removed.

Open Area: the area not taken up by the wires.

Conductance: the relative flow-rate capacity or permeability per unit thickness of a

screen. Usually, it is relative to gallons per minute (GPM) per square foot of screen.




REMOVAL EQUIPMENT

3740050035

4432559030

5327071025

6223084020

74200100018

88170119016

105140141014

125120168012

149100200010

1778023808

2107028307

2506033606

2975040005

3504547604

420405,6603.5

Cut Point(µ)

D100

U.S. Sieve(mesh)

Cut Point(µ)

D100

U.S. Sieve(mesh)

Screens




36.037400400 x 400

30.544325325 x 325

36.061234250 x 250

33.674200200 x 200

37.9105140150 x 150

30.5117128120 x 120

30.3140108100 x 100

31.41778080 x 80

30.52346460 x 60

30.32795450 x 50

36.03814340 x 40

37.15164130 x 30

46.28642820 x 20

50.711302716 x 16

Open air (%)Cut Point (µ)D100

Equivalent U.S(mesh)

Filter definition

Types of screens on the market.

REMOVAL EQUIPMENT




SOLIDS-EQUIPMENT SEQUENTIAL CONTROL

Flow line

Gas Mud cut

Smaltim.sabbia

RemovedSolids

(Cuttings)

Vacuum degasser

Screen underflow

Solids discharge

Mud Cleaner Return to thetanks

CentrifugeElimination

Baritereturn

LowEquiliser

LowEquiliser

LowEquiliser

LowEquiliser

LowEquiliser

Agitators

Return at thepumps

Highweir

Highweir

Fluids removal area




REMOVAL EQUIPMENT HYDROCLONES

Clean mud (overflow)Pressured mud inlet.

Vortex finder

ApexSolids discharge

The light liquid moves up andthe heavier moves down in arotary motion

The rotation of mud in theupper part of a cone genratesa centrifugal force separating

the cutting from mud

Solids removal with Hydrocyclone

(Wet Cuttings)




Wet Classif icationWet classification is the separation of solids from a slurry according to particle mass (sizeand density) by means other than screening. All wet classifiers separate solids based onthe variables described in Stokes’ law. Several factors govern wet classification:

1. Coarses particles have a faster settling rate than fine particles of the same specific

gravity.2. High-gravity solids have a faster settling rate than low-gravity solids of the same

size.3. Settling rate becomes progressively slower as the viscosity and/or density of the

mud increases.

The wet-solids classifiers most commonly used for solids removal from drilling muds arehydroclones and centrifuges.

HYDROCLONES




REMOVAL EQUIPMENT

Hydrocyclone – Types of d ischarge

Mud in

Mud andsolid out

Rope discharge. No air suction

Crowded apex

High wear Low efficiencyPlugs easily

Mud in

Clean mudout

Spray discharge and air suction

Open apex

Lowest wear Highest efficiency

Air suction




REMOVAL EQUIPMENT

Hydrocyclone characteristics




DESANDERS - DESILTERS

Desanders

A desander is needed to prevent overload on the desilters. Generally, a 6-in. ID or

larger hydroclone is used, with a unit made up of two 12-in. hydroclones, rated at 500

gpm per hydroclone, being common. Large desander hydroclones have theadvantage of a large volumetric capacity (flow rate) per hydroclone, but have the

disadvantage of making wide particle-size cuts in the 45- to 74- micron range.

Desilters

To achieve maximum efficiency and prevent overloading the desilter, the entire flow

should be desanded before being desilted. Generally, a 4-in. ID hydroclone is used for

desilting, with a unit containing 12 or more 4-in. hydroclones, rated at 75 gpm per

hydroclone, being common.

The proper volumetric capacity for desilter and desanders should be equal to 125 to

150% of the circulation rate.




DESANDERS - DESILTERS

Mud Cleaners

Basically, a mud cleaner is a desilter mounted over a vibrating-screen shaker. A mudcleaner will remove sand-size drill solids from the mud, yet retain the barite. It first

processes the mud through the desilter, then screens the discharge through a fine-

mesh shaker. The mud and solids that pass through the screen (cut size depending

on screen mesh) are saved; the larger solids retained on the screen are discarded.

By API specifications, 97% of barite particles are less than 74 microns in size;

therefore, most of the barite will be discharged by the hydroclones and will pass

through the screen and be returned to the system.




MUD CLEANER

Mud cleaner circuits




MUD CENTRIFUGES

Centrifuges

As with hydroclones, decanting-type centrifuges increase the forces causing separation of the solids by

increasing centrifugal force. The decanting centrifuge (see Figure) consists of a conical, horizontal steel

bowl rotating at a high speed, with a screw-shaped conveyor inside. This conveyor rotates in the same

direction as the outer bowl, but at a slightly slower speed. The high rotating speed forces the solids to

the inside wall of the bowl and the conveyor pushes them to the end for discharge.




CENTRIFUGE APPLICATIONS

• In weighted drilling fluids, a centrifuge is normally used for barite recovery. The

centrifuge is arranged to separate mostly barite, returning it to the system, while

discarding the liquid phase containing the detrimental fine and colloidal solids. The

discarded liquid volume is replaced with liquid dilution or new volume.

• In unweighted drilling fluids, a centrifuge is normally used for liquid recovery. The

centrifuge is arranged to separate and discard silt-size solids and return the liquid

phase to the system.

• Dual centrifuges are incorporated in closed-loop systems. The first centrifuge is

operated as a barite recovery unit; the second, operated at higher G-force (RPM),

processes the effluent from the barite recovery centrifuge, returning the liquid to the

mud system and discarding the solids. Dual centrifuges are used commonly with oil-

base mud systems.

SOLIDS CONTROL




SOLIDS CONTROL

Basic system unweighted mud

SOLIDS CONTROL




SOLIDS CONTROL

Unweighted mud with degasser

SOLIDS CONTROL




SOLIDS CONTROL

Unweighted mud with centrifuge

SOLIDS CONTROL




SOLIDS CONTROL

Weighted mud with mud cleaner and centri fuge

9 solids removal

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