drilling problems and optimization

PROJECT TITLE

DRILLING OPTIMIZATION BY CONSIDERING DRILLING PROBLEMS

AND THEIR SOLUTIONS

PIPE STICKING

Pipe sticking is a situation when the drill string is not move or may be partially move and you may be able to circulate fully or it can be obstructed circulation with either the pipe rotation freedom available

Stuck Pipe Classification

Bridging or pack off Wellbore geometry Differential sticking

Pipe Sticking

Pack off and bridging

There are three possible cases referred to this kind of stuck pipe

Unconsolidated and fractured formations Cement block Junk

Pack off and Bridging

Unconsolidated and fractured formations

1- Low cohesive forces and less fracture pressure gradient

2- Drilling in Lime stone and Chalk (fractured formations)

3- More severity in bedding planes dipping at high angle

Unconsolidated and fractured formations

Increase in torque and drag and high pump pressure to lift the cuttings

Large and irregular cutting size at Shale shaker

Loss circulation will be observed at small scale

Indicators

Mud should provide good quality filter cake to help consolidate the formation

Avoid unnecessary reaming and Circulating with the BHA against unconsolidated formations

If drill string stuck in lime stone or chalk formations then spot “inhibited hydrochloric acid pills” around the stuck zone

Preventions

Cement block and soft cement Cement around casing shoe or open hole squeeze cement become unstable and fall into the well bore

Cement chunks are seen at Shale shaker

Drastically increase in torque

When soft cement flash set then there will be no circulation and no rotation (loss of bore hole)

Indicators

Wait for cement settling prior to drilling ahead

Stop at least 100ft above the calculated top of cement and establish circulation prior to tag top of cement (TOC)

Minimize tripping speed when drill string passes through casing shoe or cement squeeze depth

Preventions

Any foreigner object falls into the well bore it will cause pipe stucking

Junk can be wrenches, broken metals, spanners, broken packer elements etc.

Junk

Maintain good house keeping on the rig floor

Keep the hole covered when drill string is out of the hole

Prevention

Pipe sticking caused by well bore geometry

Well bore geometry can also cause mechanical sticking in following manners:

Key seating Ledges and micro ledges Under gauge hole Mobile formations

Stuck pipe caused by Well bore geometry

Key seat

Key seats occur when the drill string rubs against the formation The longer the interval below dogleg more, greater will be the side load and more rapidly the development of key seat

Long drilling hours without reaming back through high dogleg

High over pull seen when BHA got stuck while POOH

Tight hole position can be estimated with the large OD species of BHA assembly

Indicators

If key seat is expected use key seat reamer Run short trip or wiper trip to minimize key seat

Perform back ream while drilling through dogleg zone

Preventions

Ledges are formed when successive soft and hard inter bedded formations encounter

Soft formation may become unstable due to many reasons such as excessive hydraulics, lack of inhibition, drill string vibration etc.

Ledges and micro ledges

Hard and soft rocks streaks can easily be observed by observing ROP

Mud logging samples can also indicate hard and soft cuttings

Increase in drag

Indicators

Back reaming should be performed while carefully observing the over pull and drag

Minimize reaming speed in soft formations

Avoid prolong circulation in soft formations

Preventions

Under Gauge hole Drilling of abrasive formations will result in wear and tear of bit and stabilizer which will gradually decrease the well bore diameter and consequently an under gauge well bore will be drilled.

This will only happen when tripping in the hole

Settled weight will suddenly increase

The bit get jam off bottom

Indicators

Gauge the old bit and stabilizers as well as new bit on every trip

Use hard faced stabilizers and use PDC bits in abrasive formations

Proper reaming should be done

If under gauge bit/stabilizer is observed then ream at least 1-2 stands off bottom

Don’t impose too much weight otherwise it will be difficult to free the drill string

Preventions

The term mobile generally referred to halite (salt) and clay stone

These formations have the property to deform and flow under the applied stress and this is one of the major problem to be encountered during drilling

Mobile formations

When water base muds are used to drill the salt sections then water phase in the WBM has the ability to dissolve salts causing large wash outs in the hole

Factors affecting salt wash out

Salts generally have high solubility in water

Bischofite is ten times more soluble than any other of the mixed halite

Soft shale and plastic salts usually flow under the applied stress

Salt wash out

Sodium chloride saturated drilling fluid will dissolve potassium, magnesium and calcium ions. More these ions in the drilling fluid, the rate of dissolution of salt will decrease and salt wash out will be avoided

Switch to the OBM for preventing wash outs

Preventions

Differential sticking

Differentially sticking occurs when high contact forces caused by the differential pressure that is exerted over some area of the drill string

The force required to free the pipe is given by

Differential Pipe Sticking

Unnecessarily high differential pressure

Thick mud cake

Low-lubricity mud cake

Excessive embedded pipe length in mud cake

Increase in non-drilling time

Causes of differential sticking

RATE OF PENETRATION

It is the speed at which drill bit crush the rock under it to deepen the bore hole

Usually is measured in feet per hour (ft/hr)

Rate of Penetration (ROP)

Hydraulic Factors

Fluid Properties

Mechanical Factors

Factors affecting rate of penetration

The hydraulic factors means the factors related to the drilling fluid that affects the rate of penetration as

Borehole cleaning Rate of circulation

Hydraulic factors

The following are the fluid properties that affect the rate of penetration

Viscosity of drilling fluid Percentage of solid content Mud weight

Drilling fluid properties

The mechanical factors which affect ROP are:

Weight on bit Number of rotations

Mechanical Factors

HOLE DEVIATION

Hole deviation is the unintentional departure of the drill bit from a preselected borehole trajectory whether it involves drilling a straight or curved-hole section

Hole deviation

WELL CONTROL

The function of well control is divided into two main categories: Primary well control Secondary well control

WELL CONTROL

This relates to that technique which maintains hydrostatic pressure greater than the formation pressure but less than the formation fracture pressure.

The primary well controlling element is drilling mud

If hydrostatic pressure becomes less than the formation pressure then formation fluid will intrude into the well bore.

Primary well control

When pressure in the well bore fails to prevent formation fluid into the well bore, then well will flow own its own.

This process is stopped using Blow out preventer (BOP) for the containment of formation fluids into the well bore and this is the initial stage.

Secondary well control

Some key causes of “kick” to be occurred due to some imbalance such as:

Loss circulation Insufficient mud weight Swabbing Improper hole fill up during trips Cut mud

Causes of kick and influxes

Warning signs of kick

PRIMARY INDICATORS SECONDARY INDICATORSFlow rate increases Pump pressure decreases

Pit volume increases Drilling break

Well flows with pumps off Drill sting weight change

Improper hole fill up during tripping Cut mud weight

CASE STUDIES

CASE STUDY OF PIPE STUCKING

STUCK POINT IDENTIFICATION

STEP 1Calculate the depth of stuck point

Halliburton Free Point Tool

1. The Halliburton free point tool is based on the difference of difference on magnetic field.

2. Logged upward

3. The point where the change in magnetic field starts is the stuck point

STEP 1

Calculate the Differential Force

PIPE STUCKING CALCULATIONS

STEP 2

Calculate the buoyant weight of drill pipe


STEP 3

Calculate the hook load

STEP 4

Calculate the hook load


WELL DATA

PARAMETERS VALUES UNITSOuter diameter of drill pipe 5 inches

Thickness of drill pipe 0.45 inches

Inner diameter of drill pipe 4.1 inches

Length of drill sting 18000 ft

Mud density 13 ppg

Formation Pressure 10000 psia

Thickness of filter cake 0.5 ft

Length of permeable zone 40 ft

Friction factor 0.1

Weight of drill sting per ft 19.5 lb

Length of drill collars 500 ft

Weight of drill collars per ft 150 lb

TO FIND

Differential Force

Hook load

Margin of over pill

RESULTSPARAMETERS VALUES UNITSDifferential Force 52032 lb

Buoyancy Factor 0.8015

Buoyant Weight 281335.87 lb

Hook load 333367.87 lb

GRADE PIPE OD (inches)

Weight (lb/ft)

Drill Pipe Yield(lb)

MOP(lb)

E 5 19.5 311540 -21827

X95 5 19.5 394600 61232

G105 5 19.5 436150 102782

S135 5 19.5 560760 227392

SENSITIVITY ANALYSIS

OBSERATIONS ( h t f Differential Force1 400 30 0.4 0.1 4802 800 30 0.4 0.1 9603 1200 30 0.4 0.1 14404 1600 30 0.4 0.1 19205 2000 30 0.4 0.1 2400

200 400 600 800 1000 1200 1400 1600 1800 2000 22000

500

1000

1500

2000

2500

3000

f(x) = 1.2 x

Hs-Pf (psia)

Diff

eren

tial F

orce

(lb)



25 30 35 40 45 50 55 60 65 70 750

500

1000

1500

2000

2500

f(x) = 32 x

h (ft)

Diff

eren

tial F

orce

(lb)



0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.850

500

1000

1500

2000

2500

f(x) = 2400 x

t (ft)

Diff

eren

tial F

orce

(lb)



0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.550

1000

2000

3000

4000

5000

6000

f(x) = 9600 x

f

Diff

eren

tial F

orce

(lb)

CASE STUDY OF LOSS CIRCULATION

WELL PROFILE

WELL DATA

PARAMETERS VALUES UNITSReservoir Pressure 4000 psia

Hydrostatic Pressure 4400 psia

Total Depth 4200 ft

Depth of conductor casing 700 ft

Depth of surface casing 1500 ft

Outer diameter of drill pipe (d) 0.5 ft

Open hole interval 2000 ft

Loss circulation zone depth 2700 ft

Loss circulation zone interval 20 ft

Diameter of conductor casing 20 inch

Inner diameter of surface casing 1.01 ft

Rate of volume loss 0.15 bbl/min

Density of drilling mud 12.5 ppg

TO FIND

Decrease in height due to loss circulation

Time for underbalance condition

CASE 1

DRILL STING INSIDE WELL BORE

Find the decrease in height due to loss circulation

SOLUTIONSTEP 1

Find the time to underbalance condition

= P =

• D

STEP 2

RESULTS

PARAMETERS VALUES UNITSAnnular Capacity 0.1094 bbl/ft

Decrease in height 1.371 ft

Decrease in pressure per unit time 0.891 psia/min

Time for underbalance condition 448 min

CASE 2

DRILL STING OUTSIDE WELL BORE

Find the decrease in height due to loss circulation

• D

SOLUTIONSTEP 1

Find the time to underbalance condition

= P =

STEP 2

RESULTS

PARAMETERS VALUES UNITSAnnular Capacity 0.144 bbl/ft

Decrease in height 1.038 ft

Decrease in pressure per unit time 0.675 psia/min

Time for underbalance condition 592 min

CASE STUDY OF RATE OF PENETRATION

WELL DATA

PARAMETERS VALUES UNITSReservoir Pressure 7500 psia

Depth 12000 ft

Density of drilling mud 12.5 ppg

Rate of penetration 25 ft/hr

Hydrostatic Head 7800 psia

TO FIND

Change in rate of penetration if density changes to ppg

SOLUTION

RESULTS

PARAMETERS VALUES UNITSSlope of line -0.000666 bbl/ft

Rate of penetration at ppg density 15.49 ft/hr


Density(ppg)

ROP(ft/hr)

slope ROP(ft/hr)

12 40.3 0.00011 23.08

13 15.4 0.00022 21.31

14 5.94 0.00033 19.68

15 2.28 0.00044 18.17

16 0.87 0.00055 16.77

17 0.36 0.00066 15.49

0 2 4 6 8 10 12 14 16 180

10

20

30

40

50

Density (ppg)

RO

P (f

t/hr)

0

0.000

1

0.000

2

0.000

3

0.000

4

0.000

5

0.000

6

0.000

70

5

10

15

20

25

Slope

RO

P (f

t/hr)

CASE STUDY OF WELL CONTROL

WELL DATA

PARAMETERS VALUES UNITSTotal vertical depth 10000 ft

Well bore size 9 inch

Diameter of bottom hole assembly 8 inch

Length of bottom hole assembly 420 inch

Shut in drill pipe pressure 750 psia

Shut in casing pressure 1250 psia

Pit gain 25 bbls

Mud weight 14 ppg

Diameter of drill pipe 6 inch

Slow circulating pressure 1600 psia

TO FIND

Influx Height

Type of influx

Kill mud weight

Find the height of influx

• =Diameter of well bore

SOLUTIONSTEP 1

• =Diameter of well bore

Cont.…

RESULTS

PARAMETERS VALUES UNITSAnnular Capacity b/w hole and BHA 0.0165 bbls/ft

Annular Volume 6.9360 bbls

Influx volume above BHA 18.063 bbls

Annular Capacity b/w hole and drill pipe 0.0437 bbls/ft

Total height of influx 413.22 ft

Find the type of influx

RESULTS

Cont.…STEP 2

PARAMETER VALUE UNITInflux density 2.46 ppg

The influx is a gas.

Find the kill mud weight

RESULTS

Cont..STEP 3

PARAMETER VALUE UNITKill mud weight 16.4 ppg

Find the final circulating pressure

RESULTS

Cont..STEP 4

PARAMETER VALUE UNITSlow circulating pressure 850 psia

Final circulating pressure 996 psia

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