HydraulicsIn mud engineering, hydraulics is defined as the branch of science which deals with drilling fluids in a static condition or in a dynamic condition.

Dynamic condition include:Circulation of the drilling fluid inside the casing or drill string and annulusMoving the casing or drill string up and down without circulation of drilling fluidOr combination of both

HYDRAULICSThe ability of the drilling fluid to effectively transport cuttings from the bottom of the hole depends upon the hydraulics of the system and the properties of the drilling fluid.The good hydraulic system provide adequate impingement to hydraulic power at the formation Insufficient hydraulic power will lead to regrinding the cuttings in the bottom instead of transporting them to surface.This hole cleaning deficiency can cause accumulation of cuttings in the bottom of the hole and consequently impede the rate of penetration.

FUNCTIONS OF DRILLING FLUIDThe primary function of drilling fluid are

to carry the drill cuttings to the surfaceto maintain the hydrostatic headto lubricate the drill string and bitto cool the bit while drillingto stop the loose formation from the caving-in

TYPES OF FLOWPlug FlowAt the start of circulation.Gelled mud. Circulation rate low. Pressure high.

Laminar FlowPressure losses lowerMostly laminar flow in annulus

Turbulent Flow Pressure losses higherNormally inside drill stringIn annulus as and when required

LAMINAR FLOWLess pr. LossesMax. vel. At center

Turbulent flowParticles moving randomly but moving forward

More pr. losses

Erosion is an issue

Recommended for cake removal etc

TYPE OF FLUIDSNewtonian FluidsWaterNon-Newtonian FluidsPseudo-plasticPlasticDrilling MudDilatantBlood

FLUID / VISCOSITYFLUIDSHEAR RATEVISCOSTY

Newtonian

Plastic

Pseudo-Plastic

Dilatant

Annular VelocityAnnular velocity: velocity of mud moving up in annulus

Slip velocity is velocity of cutting particles falling down to the bottom

Normally, annular velocity should be at least twice the slip velocity for proper hole cleaning

Annular VelocityAnnular velocity of mud

Slip velocity of particle

Annular VelocityMin value for proper bottom hole cleaning & avoiding poor ROPMax value to avoid hole erosion

17.50 hole : 18-30 meter/minute12.25 hole : 21-33 meter/minute8.5 hole : 36-54 meter/minute

CIRCULATION SYSTEMBasic hole circulation

The hole circulation is Equivalent to the circulation Through U-tube

Applying the Bernoulli's theorem:Energy in = Energy out(Neglecting friction)If friction is consideredEnergy in = Energy out + Friction EnergyReference line123456

CIRCULATION SYSTEM

U -Tube circulation equivalent of above figure123456Reference line

CIRCULATION SYSTEMFor practical calculations, energy is divide into three types:Pressure energyVelocity energyStatic energySumming up the energy components in the units of feet of fluid:Energy = P/+ c[V2/2g] + Z

Where, P = Pressure ( psi ) = Conversion of psi to ft of liquidV = Velocity( ft / min)g = Acceleration of gravity( ft/ sec)c = Conversion of ft/mi to ft of liquidZ = Static head(ft)

CIRCULATION SYSTEMApplying the energy equations to the circulation systembetween points 1(in) and 6(out) Energy1 = Energy6 + Friction energy 1-6 [P1/+ c[V12/2g] + Z1] = [P6/+ c[V62/2g] + Z6] + P1-6Where,P1-6 = Friction energy loss due to friction from points 1 to 6 of figureFollowing are considered negligible: c[V12/2g]=0Z1=0P6/=0c[V62/2g=0Z6=0

CIRCULATION SYSTEMEnergy equation can be simplified to :P1/= P1-6 P1-6 = P1-2 + P2-3 + P3-4 + P4-5 + P5-6 Where : P1=Rig pump pressure(psi) P1-2 =kelly hose and kelly pressure loss(psi) P2-3 =drill pipe inside pressure loss(psi) P3-4 =drill collar inside pressure loss(psi) P4-5=Jet nozzles pressure loss (psi) P5-6 =Total annular pressure loss(psi) Rig pump pressure consists of the sum of the pressure losses starting from the kelly upto the flowline.

Pressure LossesStandpipe pressure gauge gives total pressure lossTotal Pr Loss = Pr loss in bit + Circ. System Pr lossesCirc. System pr. losses = Loss in surface equipment + Loss in DP inside + Loss in DC inside + Loss in DP annulus + Loss in DC annulus PPUMP

CIRCULATION SYSTEM

CIRCULATION SYSTEM

Pressure Losses

PRESSURE LOSSIn shallow depths, circulating pressure loss is less as compared to bit pressure loss.In deeper depths circulating pressure loss increases significantly.Pressure loss is directly proportional to depth as string pressure loss increases with depth.So in deeper intervals, a compromise between minimum discharge and pressure loss has to be made.Pressure losses are directly proportional to mud weight. Thus in high- pressure wells, pressure losses increase

Surface Equipment Pressure LossesThis includes pr losses in Standpipe lines Rotary hose Swivel KellyDivided in four categories based on length and internal dia

Pressure loss in surface equipmentThis includes pressure loss in standpipe lines, rotary hoses, swivel and Kelley.Surface equipment is divided into four categories based on bore size and length of stand pipe, rotary hose, swivel and Kelly.

Pressure loss in drill pipe borePressure loss occurs in the drill pipe bore due to circulation

During drilling, drill pipe length keeps on increasing as drilling progresses.

Pressure loss keeps on increasing with depth in drill pipe

Pressure loss in drill collar borePressure losses inside drill collar bores are quite high as compared to drill pipe as drill collar ID is much less as compared to drill pipe IDDrill collar should be used as minimum as possible to avoid un-necessary high pressure losses.Drill collar bore pressure loss for the complete bit run will remain the same if discharge is not changed.

Pressure loss in drill pipe annulusPressure loss in drill pipe annulus is quite small and can be neglected in large size holes of 17-1/2 and 12-1/4.

But this can be considered in smaller hole sizes of 8-1/2 and 6 hole sizes.

Pressure loss in nozzlesPressure loss in bit nozzles is the major part of total pressure loss.

Nozzle size is changed to optimize hydraulics.

Smaller nozzle size give higher pressure loss.

Larger size nozzles give less pressure loss.

Hydraulics optimization leads to improvement in ROP.

Pressure Losses Vs DepthPressure losses increase with depth

At shallow depth bit pr loss is higher and string pr loss is less in comparison

At deeper depth string losses become higher and less pr loss available for bit loss

FLOWRATE CRITERIAIn holes that are being drilled with mud weight above 12ppg it is recommended that minimum flow rates be thestarting point in a hydraulics calculation. Hole size (inch) Minimum Q (GPM)6-1/21408-1/22709-7/83251139012-1/44851559017-1/2750261325

Circulation rateDepends on Hole size Drill string size Annular velocity

Proper Hydraulic ProgramWhat is needed ?Use of correct nozzle sizesUse of correct circulation rate

What are the advantages ?Better bottom hole cleaningAs a result of above, increase in ROP

Methodology of Hydraulic ProgramUtilize maximum available pump hydraulichorse power at bit

50 % to 65 % pressure loss in bit ( of standpipe pressure gauge )

Bit HHP/ sq. in. of hole size = 2 to 5

Jet velocity = 100 to 168 m/sec

Operational Pressure Limit This is max allowed pump operating pr.Pump may be rated 3000 or 5000 psiLiner rating depends on liner sizeA -1700-PT pump7.0 liner : 205 kg/sq. cm.6.5 liner : 237 kg/sq. cm.Surface equipment like rotary hose and hammer unions and mud pump condition may dictate lower pr. rating.

Operational Pressure Limit Max Operational pr = Liner rating safety margin

Normally safety margin is 250 psi or 18 kg/ sq.cm.

7 liner with rating of 205 kg/sq.. cm. Operational Pr limit = 205 - 18 = 187 kg/sq.. cm.

Pump Discharge : Triplex Pump Pump output in liter per stroke = 0.0386 * (Liner size in inch)2 * Piston stroke length in inch

Ex. Liner size 12 and stroke length 7 PO = 0.0386 * 12 * 12 * 7 = 22.7 l/strk

Effect of Mud Weight on Pump Pressure

New pressure = Old pressure X ( New MW / Old MW)Old standpipe pr = 120 kg/sq.cm.Old MW = 1.2New MW = 1.5New standpipe pressure = 120 * (1.5 / 1.2) = 150 kg/sq.cm.

Effect of SPM Increase on Pump Pressure

New pressure = Old pressure X ( New SPM / Old SPM)2 Old standpipe pr = 100 kg/sq.cm.Old SPM = 100New SPM = 120New standpipe pressure = 100 * (120 / 100)2 = 144 kg/sq.cm.

Effect of ID on Pump Pressure

New pressure = Old pressure X ( Old ID / New ID)5 Old standpipe pr = 100 kg/sq.cm.Old ID = 4.27New ID = 4.00New standpipe pressure = 100 * (4.27 / 4)2 = 139 kg/sq.cm.

For optimized hydraulics, above parameters should fall within the following ranges :

(1) BHHP = 50 -65%(2) BHHP/inch of hole dia = 2 to 5(3) V n = 100 -168 m/sec

NOZZLESNozzles are made of hard material like tungsten carbide to avoid erosion, as mud passing through nozzles possesses very high jet velocity.A bit may have 3 or more nozzles of same or different sizes. Nozzle size is normally given in hole numbers like 6,7,8,9,10,11,12,13,14,15,16,18,20,22,24etc.Size 20 means nozzle diameter of 20/32. A triangular nozzle gauge is inserted inside nozzle hole to measure its size.Normally wide variation in nozzle sizes in a bit is not preferred. For example, 13-13-14 nozzles (area 0.408 sq.in.) will be preferable to 12-12-16 (0.416 sq. in.)

Surge Pressure due to Pipe MovementWhen a string of pipe is being lowered into the wellbore, drilling fluid is being displaced and forced out of the wellbore.The pressure required to force the displaced fluid out of the wellbore is called the surge pressure.

Surge Pressure due to Pipe MovementAn excessively high surge pressure can result in breakdown of a formation.When pipe is being withdrawn a similar reduction is pressure is experienced. This is called a swab pressure, and may be high enough to suck fluids into the wellbore, resulting in a kick.

Liner and Piston

Piston and Liner