Solids Control Equipment

Drilling solids control equipment capability may affect the drilling fluids program. Inadequacies in pumps, mixing equipment, or solids-control facilities will likely increase consumption of materials, and sometimes the preferred program must be modified to compensate for deficiencies in the equipment. The importance of the drilling solids control equipment to the success of the mud program deserves a more extensive treatment than can be given here.

Table: Mud System Equipment Requirements      
EquipmentWater/Light
Treated Clay
Dispersed
Weighted
Non-dispersedOil MudsPreformed Stable FoamGas, Air,and
Unweighted Mist
Un-weightedWeighted
Well head
BOPsAs required for well controlAs requiredfor kick controlAs required for kick controlAs required for well controlGenerally 1 positive, 1 pipe ram and HydrilAs requiredfor
control
Rotating heador stripperMay be used for under bal. drig.May be used for under bal. drig.May be used for underbal. drig.Not usedEssential to divert
foam. Use rotating
head with Kelly and a stripper with power swivel
Essential to divert returns to waste sump
Variable chokeMay be used for back
pressure control
Essential for kick controlEssential for kick control. May be used for back pressure controlEssential for kick
control
Essential for back
pressure control
Not used
Surge chamber and mud separatorNot usedEssential for kick
control to save gas cut mud
Essential for kick control to reclaim gas cut mudEssential to reclaim expensivemud when gas cutSurge chamber or
cyclone type foam
suppressor when
foaming into a tank
Not used
Discharge linesFlow line to shakersFlow line to shakers, choke line
to surge tank and waste sump
Flow line to shakers, choke line to surge tank and to waste sumpFlow line to
shakers, choke
line to surge tank
and/or separator
Blooie line to waste
or surge tank
Blooie line to waste sump
Solids Control
Shaker screenHigh G-force shaker with the smallest screens possibleHigh G-force shaker with the smallest screens possibleHigh G-force shaker with the smallest screens possibleHigh G-force shaker with the smallest screens possibleHigh G-force shaker with the smallest screens possibleNo solids control equipment needed.No solids control equipment needed.
Sand trap20-30 bbl, with 45°
bottom-large diam.
dump
Be careful not to dump liquid mudImportant to settle coarse material ahead of desander-desilter unitsImportant to settle sand. Be careful of mud lossNo solids control
equipment needed
No solids control equipment used.
DesanderImportant-run ahead
of desilters
May be used to
remove coarse
material ahead
of desilting equipment
Important to prevent overloading desilters or centrifugeCan be used by dumping into tank of solventNormally,foam is a
one-pass system,
foam and solids go to waste sump
Air and solids to waste sump
DesilterImportant to remove
fine silts for low weight
Not usedEssential for low-solid mudsNot recommendedNot usedNo solids control
equipment needed.
No solids control
equipment needed.
Mud cleanerImportant to remove
fine silts for low weight
Excludes light solids on medium weight mudEssential for drilled
solids control
Useful on medium
weight muds
Not usedNo solids control equipment needed.No solids control equipment needed.
Decanting centrifugeNot usedEssential for eco-nomic control of
high-weight muds
May be used to reclaim liquid sand
dump drilled solids
Essential for high-weight mud
control
Can beused to
reduce weight
No solids control equipment needed.No solids control equipment needed.
DegasserMay be used ahead
of treatment if gas
encountered
Essential in kick control for true mud weightsEssential for good kick control practiceCan be used if gas cutting a problemCan use gas trap to
separate gas and liquids
May use low pressure trap to reclaim gas
Treatment
Mixing hopperMinimum required
for mixing clay, gel, chemicals
Maximum for rapid weight increase on kicksMaximum required to mix polymers;
located after solids control
Maximum required for mixing new mudNot required unless
additives used
Not needed
Bulk bariteNot usedEssential in high-
weight systems and kick control
Not usedEssential in kick controlMay be used on high-weight systemsNot usedNot needed
Stirring and agitation ( Mud Agitaors, Mud Gun )Adequate for lost
circ. material, top
guns best
Essential to prevent settlingImportant to maintain uniform systemEssential to prevent settling and maintain viscosityNeeded if additive
used but not after
foamer added
Not needed
Waste Pit Size
NormalMay be small to large depending on depth and if used for settling large amount of solids and liquidsMedium, will have smaller amount of solids and more liquidsMedium, will have smaller amount of solids and more liquidsSmall, will have
large amount of
solids, very little
liquids
Small,will have large amount of solid sand small amount of liquidSmall,solids very fine, very small liquid
Town lotMost use small steel tanks and haul all solids and liquids to an approved disposal site. Volumes of
solids and liquids critical to both storage space and trucking costs
Can foam into 500
bbl tank and defoam
Not used due to
dust problem
OffshoreAll waste collected in small steel tanks (mud skips) for treatment before disposalCan use existing production facilitiesNot used normally
Solids Disposal
NormalSolids are left in bottom of sump after liquids are removed and buried.Deflocculation treatment of liquids may help settle more solids.Solids are very clean and can be buriedSolids very fine but clean, can bury
Town lotAll solids must be hauled to an approved disposal site. Disposal cost may be more than mud costs.Oil wet cuttings
may require different disposal
site
Solids collected in tank after defoaming and hauled to dumpNot used, severe
dust problem
OffshoreClean washed solids may be dumped over board, perlocal regulations, or hauled to shore on waste bargesOil-wet solids
must be washed
w/solvent and
detergent to dump
Solids carried by foam through prod. facilities towasteNot used normally
Liquid Disposal
NormalNonoily fresh water fluids may be spread on land. Oily or salty fluids must be hauled to approved disposal site. May treat liquids to neutralize and
deflocculate to clarity before spreading or pumping into lakes or streams.
Liquidsmaybesolidifiedandmixedwithsoil.
Methods of incinerating oily waste are being investigatedSmall amount of
liquids. May reclaim fluids after foam breaks on long time drilling jobs
Little to no fluids for disposal
Town lotAll liquids must be hauled to approved disposal site.Oil or oily waste may require a different disposal site ormethodSmall volumes of
liquids can be dis-
charged into existing prod. facilities
Little or no fluids to dispose of
OffshoreLiquid waste is collected and pumped ashore through waste lines or barged ashore for disposal
BiodegradabilityNot degradableLignosulfonates biodegradable at low pHMost polymers, starches, CMC are
biodegradable
Limited degradationFoamers, additives are biodegradableFoamers used in mist are biodegradable
Ecological effectsFresh-water clay muds can be very beneficial to soils, particularly sandy soils. Sodium polyphosphates used as thinners degrade to ortho phosphate fertilizer. Lignite, lignins and tannins
are humic acids.
Lignosulfonate muds should not be harmful pro -vided chromates
are not used.
Polymer muds should not be harmful as long as chromic compound sand
chlorophenate bacteriacides are excluded.
Oil mudsareno
morehazardous
than oiland
shouldpresent
no problems
with adequate
controlsagainst
spillage andan
adequatedispo-
sal system.
Foam drilling com-patible with ecology since relatively small volumes of liquids are used. Drilled cuttings are large and no dust is generated.Air drlg. can result inserious dust problem since cuttings are ground very fine and blown out with air. Addition of foamer helps, but does not cure
completely.
Liquid Storage
ActiveMay be small to very large, depends on depth and lost circulationMust be adequate to fill hole on trips; normally 300 to 700bbls.Must be adequate to fill hole on trips; normally 300 to 700bbls.Adequate to fill hole on trips.20 to 100 bbl divided tank needed so that foamable solution can be mixed and used alternately.10 to 20 bbl foamer tank for misting.
ReserveMay be small to very large if used for settling.Should be adequate to displace cement.Should be adequate to displace cement and for lost circulation.May require two tanks;one for new light-weight mud,one for heavier mud.Not needed if water supply adequate, may be used to recycle foam solution.None
WasteMust be adequate to contain drilled solids, and waste liquids.Adequate to contain smaller volumes of drilled solids and liquids.Must be adequate to contain large volume of hole solids and smaller volumes of waste liquids.Minimal since only solids dumped, expensive mud saved.Long pit desirable to contain surging foam returns.Dry dust difficult to contain
Dry storageAdequate for mud and chemicals.Proper height and size essential.Should be proper height, size and location for mud and chemical.Adequate for mud and chemicalNot normally neededNot needed

The Solids control equipment employed in the mechanical separation of cuttings from the active mud system vitally affects mud costs. The mud engineer usually is assigned the responsibility for this equipment.

Solids control Equipment

The importance of controlling drilled solids has been emphasized several times in the preceding sections. The advantages of doing so may be summarized as follows:

  1. Less barite and mud additives are required.
  2. Better rheological properties exist because the reduction in plastic viscosity increases the YP/PV ratio, thereby promoting shear thinning.
  3. Lower plastic viscosity facilitates the removal of entrained gas, hence lower mud densities can safely be carried.
  4. It results in faster drilling rates, because of lower viscosity and drilled solids content.
  5. There is less risk of sticking the pipe, because of thinner filter cakes.
  6. There is less bit wear.

The results of a field study, shown in Figure. 1, illustrate the relationship between rig costs and solids content. Such savings are generally much greater than the cost of renting and running solids control equipment.

Solids control equipment

Solids control equipment categories

The various pieces of solids control equipment and their purpose are briefly, as follows:

  • Double deck shale shakers are used to remove cuttings and coarse aggregates. They have a coarse screen, say 40 mesh, on top and an 80 mesh below. Double deck shakers are particularly advantageous when drilling solids because the 80-mesh screen removes aggregates of shale that would otherwise become dispersed and much more difficult to remove. Some modern high-efficiency shakers are capable of removing almost all of the first time circulated solids from shale muds. Development of an improved vibratory motion enables a 150-mesh screen to be used on the lower deck.
  • Hydrocyclones are used to recover sand and silt. The mud is injected tangentially at the top of the bowl, and the sand and/or silt thrown to the sides by centrifugal force and discharged at the bottom, while the rest of the mud goes to the overflow. The size of the particles discharged depends on the diameter of the bowl and the specific gravity of the particles. Typically, 8-inch bowls (desanders) are used to remove coarse sand, and 4-inch bowls (desilters) to remove fine sand and silt. Some barite particles are discharged in the underflow of desilters because of their high specific gravity. Loss of this barite may be avoided by passing the underflow through a suitably sized screen that removes the larger low-gravity particles; the under- flow from the screen is returned to the system. Hydrocyclones with screens and desander cone and desilter cone are called mud cleaner.
  • Decanting centrifuges are used to recover barite from surplus mud when the mud system has been diluted to reduce the colloidal clay content. The surplus mud is passed through a rotating drum, the barite is thrown out as a sludge and returned to the system, and the overflow is discarded. Pure barite is never recovered because some silt particles have the same sedimentation rate as some barite particles.
  • Dewatering surplus mud. It is possible to remove clay colloids from the surplus mud by flocculating it with chemicals before centrifuging it. The process results in practically solids-free water and wet mud cake, which is much easier to dispose of than liquid mud.
  • Down-hole solids control. A sub, which is placed directly above the bit, contains a high-efficiency cone that separates the mud into two fractions: a heavy fraction containing the removed solids, which is directed through two up-jets into the annulus; and a lighter fraction that passes on to the bit. In two field tests, increases in penetration rate up to 58% and improved bit life were obtained when drilling in shale.

For effective removal of drilled solids, it is essential that the shakers and hydrocyclones have enough capacity to handle the whole mud stream. Often, it is necessary to have two units operating in parallel. Using sufficient numbers and types of separators, they were able to remove all the drilled solids from an un-weighted mud in a well in Wyoming. Obviously, the amount of drilled solids that can be removed depends on the dispersion of the formation being drilled and on the type of mud being used. For instance, use of a non-dispersing polymer-brine mud greatly assists in solids control.

The benefits of solids control will be much less if the system is not properly designed and efficiently maintained.

Solids content of drilling mud volume percent

Figure 1. Solids content of drilling mud volume percent

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