06 C Mud Systems

1

Copyright 2002, RigSmarts 1

Functions of the Mud

The mud has several functions:1. To cool and lubricate the bit and drill string.2. To flush drilled cuttings from the bottom of the hole3. To carry the cuttings out of the well4. To support the well bore wall5. To hold back formation fluids6. To prevent lost circulation7. To transmit data to the surface. (MWD, mud logging, etc.)


Mud system

The active surface system is used to treat the mud and to provide enough volume to fill the hole when the drill string is removed.

One of the key functions of the active system is solids removal.

2


Why solids controlThe drilled solids influence:

Drilling performance

Down hole problems

Drilling mud cost and performance

Equipment wear

The quality of the logging

The quality of the cementing

Production


Drillability

Drillability is influenced by rock strength. As a tooth penetrates the formation the rock must move out of its way. To move the rock must compress, just as our core sample in the laboratory. Just like our core sample the rock will break once the rock strength is exceeded.

Overbalance is a confining pressure that raises the apparent rock strength. With higher mud weight we will need more bit weight to get the same tooth penetration, or we suffer lower penetration rates.

This is why an increase in penetration rate is an indicator that we have less overbalance.

3



Hydraulic horsepower at the bit is reduced by excessive viscosity.

Solids provide a filtercake that allows a differential pressure to exist across the bottom of the well. This acts as a confining pressure which increases the apparent rock strength.

Affects static and dynamic chip hold down.

Increases bit balling



Torque and drag

Bit life and trip frequency

Surge and swab pressures

Down time due to equipment repair or hole trouble

Drilling rate

Dril

ling

rate

Solids content

4


ViscositySolids have a negative impact on rheology. They increase viscosity and thixotropy

Increased pressure losses in drill pipe and annulus.

Less hydraulic horsepower to the bit

Higher ECD

Higher surge and swab pressures

Reduced solids removal efficiency

Loss of mud at surface

Coarser screens, ineffective hydro cyclones - More solids in mud

Reduced degasser efficiency

Increased channeling while cementing

Pump cavitation and difficulty in priming.

Chemical addition becomes less efficient.

Negative impact of viscosity:


Fluid lossDrilled solids lead to thicker more permeable filter cakes

Negative impact of thick filter cake:Increased torque and drag

Higher surge and swab

Potentially stuck pipe

Difficulty logging and running casing

Poor cement bond between casing and formation

Negative impact of fluid loss:

Formation damage from solids and fluidsEmulsion blockInterstitial clay swelling

Reduced log interpretationMisinterpretation of hydrocarbon/ water zonesDistorted porosity/ density logs

5


Equipment wear

Pumps

Lines, fittings and valves

Valves, liners, valve seats, and impellers

Swivel and drill string

Bits, and bit nozzles

Turbines, motors, MWD’s, LWD’s etc..

Solids control equipment

Casing


Cutting Size and Classification

API Classification Size range (micron) Description

Coarse

Intermediate

Medium

Fine

Ultra-Fine

Colloidal (clay)

250

74

44

2

0

>

-

-

-

-

-

2000

2000

250

74

44

2

Sand

Silt

Clay

API Classification of Solids

Beach sand

Human hair

Cement dust

80

30

3

>

-

-

2000

200

100} Examples

6


1”

1”

1”

½”

1/4” 1/8”

The specific area of a cutting increases as its size decreases. Specific area is the total surface area divided by the weight of the cutting. The specific area doubles each time the diameter of the cutting is halved.

Specific Area


Mud system

Sand Trap

Degasser pit

Desilter pit

Desander pit

Suction pit

Mixing pit

Centrifuge pit

Shale shaker

Degasser

Desilter DesanderCentrifugeMixing Hopper

Agitator

Note the direction of flow through each treatment pit..

125% of the flow rate should pass through the hydro cyclones

The treatment pits must be kept full to operate properly. The last treatment pit will have an overflow or swing arm equalizer to keep these pits full.

7


Shale shakers

Mesh

Wire size

(inches)

Opening

(microns)10 x 10

20 x 20

40 x 40

60 x 60

80 x 80

100 x 100

120 x 120

150 x 150

200 x 200

250 x 250

325 x 325

.025

.017

.010

.0075

.0055

.0045

.0037

.0026

.0021

.0016

.0014

1905

838

381

234

178

140

117

105

75

63

44

First 2/3 of screen bed should be covered with mud.

The goal is to remove cuttings before they degrade. Not retain mud!

circular

linear


Degasser

8


Degasser (Swaco)


Swaco vacuum valve

9


Degasser Drilco


Degasser Pit

Overflow not underflow!

If the degasser and its pit are not plumbed correctly it will not work correctly.

The desander pump should never be used as a degasser pump!

If there is an underflow into the degasser pit then the degasser will only see heavy mud, not the light gassy mud that needs to be treated.

10


Hydro cyclones

Cone Size

(inches)

10 - 12

8 – 6

4 – 3

2

150

40

10

Cut point

(micron)

74

40

15

8

Hydro cyclone efficiency decreases as viscosity, weight, and solids content increases.

Capacity

(gpm)

500

100

50

20

Optimum performance occurs with 75 feet of head, or roughly 4 x mud wt. in psi.

Solids

(tons/day)


De-sanders

11


De-Silters


Mud Cleaners

% by volume

Particle size

12


Centrifuge


Centrifuge arrangement

13


Agitator

Agitators mix the mud to keep it homogeneous.

They also serve to keep drilled solids in suspension so they can be treated out of the system.


Agitators

Axial agitators drive flow downward to scour the bottom of the tank. This type of agitator is more efficient than radial flow agitators.

Radial agitators drive the flow outward. This type of agitator must be placed close to the bottom and is normally only used in slug pits.

14


Mud Mixing

Chemicals should be added upstream of the suction pit to give the mud time to mix before reaching the suction line.

The hopper outlet should also be far away from any suction lines to prevent air entrapment.

The solids treatment system is kept full of mud by the use of an overflow out of the last treatment pit. The main active system can be drawn down without affecting hydro cyclone performance.

Suction pit

Mixing pit

Mixing Hopper

Agitator


Mud system (un-weighted)

With un-weighted mud all of the solids removed by the hydro-cyclones and centrifuge are discarded.

15


Mud system (weighted)

With weighted mud the solids removed by the hydro-cyclones are passed over a screen to salvage the smaller barite particles. The centrifuge may also be used to recover this barite if the waste from the cones is directed into a collection pit instead.

The centrifuge will still be used to recover barite, (and undesirable drilled solids), while colloidal size particles and fluid is discarded.


Swing arm equalizer

16


Active volume

Useable volume

18 in

We need 18 inches of mud above suction inlet to avoid cavitation and air entrainment.

We also never fill the pit completely unless it has a closed top.

The useable volume is much smaller than the total volume. The total volume of mud must be treated.

Solids that accumulate on the bottom of the tank may tie up treatment chemicals.

Notes: __________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

Notes: __________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

06 C Mud Systems

Documents

viscosity solids

degasser swaco copyright

degasser drilco copyright

mud logging

drilling performance

mudthe mud

drilled solids influence

rigsmarts1 mud system