Well Control Intro Slides

7/30/2019 Well Control Intro Slides

1/40

The Robert Gordon University 2006 1

A n I n t r o d u c t i o n t o W e l l Co n t r o l


2/40


Pore Pressures

The theory behind pore pressure Why pore pressure anomalies occur

A brief overview


3/40


Pressure Gradient Theory


4/40


Normal & Overpressure


5/40


Effect of Hydrocarbon Column

At 2000 ft pressure is 1395psi less 100 psi (1000 ft gas

column hydrostatic presure),1295psi

At 3000 ft, the gaswater contact is

0.465 x 3000 =1395 psi

At 3000 ft MW = 8.9 ppg

At 2000 ft, MW = 12.45 ppg


6/40


Effect of Faulting on Pressure


7/40


Kicks

A kick is the term used to describe the inflow of formationfluid into the wellbore during drilling operation.

This arises due to the formation pressure being greater

than the hydrostatic pressure imposed by the mud column. This can happen in a normal or abnormally pressured

formations.

A kick may be primarily composed of salt water, oil, naturalgas or a combination of the fluids. The influx of formationfluid may arise for a variety of reasons

T h e s e in c l u d e :


8/40


Insufficient mud weight; Swabbing;

Not keeping the hole full;

Loss of circulation (partial and full);

Kicks generally occur during trips with the influx occurringfrom a combination of swabbing and failure to keep the

hole full. Swabbing is the result of the piston effect of thedrillpipe due to excessive trip speed resulting in

instantaneous vacuum being created below the bit. Kicksoccurring during drilling operations most often occur due to

insufficient mud weight.


9/40


Insufficient mud weight

.m a y o cc u r d u e t o :

Penetration of an abnormally pressured zone;

Accidental dilution of the mud by fluid addition atsurface

Dilution of mud by influx from an aquifer exposed toopen hole;

Gradual mud density reduction due to gas cut andfailure to degas the mud at surface;

Improper mud mixing and poor quality control inmeasurement.


10/40


Low Level of Drilling Fluid ColumnNot keeping the hole full

Two conditions may lowerthe fluid column in the

annulus. These are:

Failure to fill the holeduring a trip;

Lost circulation during

drilling


11/40


Swabbing

Sw a b b i n g i s t h e r e d u c t io n o f b o t t o m h o l e p r e s su r e c a u se d b y u p w a r d p i p e m o v e m e n t - r e su l t i s r e d u ce d b o t t o m h o l e p r e s su r e . H i g h t r i p sp e e d c an l e ad t o

i n s t a n t a n e o u s v a cu u m b e lo w t h e b i t . Th e sw a b p r e s su r e d e p e n d s o n :

Pipe velocity; Bit and/or BHA balling; Clearance between pipe and hole - the smaller the annular

cross section, the greater the swabbing action;

Mud rheology - the higher the viscosity, the greater theswabbing action.


12/40


Kick Detection

The single most important step to blowoutprevention is closing the blowout preventerswhen the well kicks. The decision to do so

may well be the most important of yourworking life. It ranks with keeping the holefull of fluid as a matter of extreme importancein drilling operations.(Chevron Well Control Manual)

Be prepared and maintain a kick control WorkSheet at all times.


13/40


Maximum Working Casing Pressure

The casing and blowout preventer (BOP)are designed for the different expectedpressures during each drilling phase.

This is determined during well planning.

The pressure requirements are based on

the maximum anticipated pressurescaused by a gas kick.


14/40


MAASP(Maximum Allowable Annular Surface Pressure)

This is the annular pressure at the surface that correspondsto the pressure at the weakest point of the hole. Thefracture gradient at the last casing shoe traditionallydefines the weakest point. The MAASP represents theannulus pressure which may be expected to result in loss ofcirculation while controlling a kick.

MAASP = 0.052 x (Frac ) x Dw

Frac = Fracture pressure at shoe equivalent mud wt in ppg = current mud weight in ppg / Dw = TVD of weakest point


15/40


Rig Capacity for Weighting Mud

Although this data does not appear in theworksheet, it is important as it defines the

number of circulation cycles necessary to regainprimary control with given change of mud. Therig capacity depends on total reserves ofweighting materials (Barites, etc) and themaximum rate of addition to system. Themaximum rate of addition is measured in Ib/min

or kg/min. Backup supply MUST always beavailable on rig.


16/40


System Pressure Losses at SlowPump Rate

To control circulating a kick out of the hole without the risk ofcausing a second influx or losses from breaking down theformation with excessive annular pressures slow a circulating rate

(SCR) is used. of the well. This is is dependent on the rig, but thisis usually about 20 or 30 strokes per minute. This slow rate mustbe taken:

At the start of each tour;

If the mud weight changes;

If bit arrangement changes;

After bit changes;

Every 500 ft drilled.


17/40


Well Kill

CirculatingSystem


18/40


Kick Detection Techniques

There are a number of indicators that provide early warningof kick occurrence - positive kick indicators are:

Mud pit level/flow Increase; Incorrect hole fill up during trip; Decrease in standpipe pressure/Increase in pump rate; Increase/decrease in drillstring weight

Potential indicators are:

Increase in penetration rate; Lost circulation; Changes in gas levels, mud density and conductivity


19/40


Parameters used for detecting abnormal pressurezones are also potential kick indicators andinclude:

Torque, overpull and drag; Shale caving increase

Shale density/shale factor changes

Flow line mud temperature changes

d Exponent changesI n d i ca t o r s o f o ccu r r e n c e o f a k i ck f o l l o w


20/40


Dc Exponent

The dc exponent has to betreated with caution. Originallydeveloped in the US Gulf ofMexico it works well in the long

clay sections drilled there.However, In areas where thereare continuous changes offormation it is difficult toestablish a trend to detect

changes.The increase in pore pressure isindicated by the shift to the leftof the plot.


21/40


Mud Pit Level / Flow Increase

These parameters are major positive indicators. Asthe influx of formation fluid displaces the mud in theannulus, the pit level would increase in the active mudtanks. There would also be evidence of increase inreturn flow rate if logged. The effectiveness of pit

gain/flow increase depends on:

Initial size and type of kick; Mud fluid base and rheology; Minimum sensitivity of the measuring systems

But remember Gas kicks are more difficult to detectthan oil /water due to its compressibility ...


22/40


Incorrect Fill-up During Trips

If the hole does not take the correct volume ofmud for the volume of pipe pulled from the holethen an influx has probably been swabbed into

the well bore

The driller and mud loggers should bemaintaining independent records of volume takento fill the hole for every 5 stands

If the hole fill is not correct go back to bottomand circulate bottoms up to check what is at thebottom of the hole


23/40


Decrease in Standpipe Pressure/Increase inPump Rate

The circulation system is a U-tube. An influx of

fluid into the annulus creates an imbalanceresulting in a decrease in hydrostatic pressure inthe annulus. In such an unbalanced system,gravity helps move drilling fluid down the hole,requiring less energy from the pump. This will

result in a decrease in the standpipe pressure


24/40


Increase/Decrease in Drillstring Weight

Any influx into the wellbore from the formationreduces the buoyancy of the annular drilling fluid.A sensitive weight indicator will register thischange in weight as an increase in drill stringweight. For very large kicks, fluid may enter the

annulus with enough force to cause a decrease inindicated string weight.


25/40


Increase in Penetration Rate (DrillingBreak)

A marked increase in rate of penetration (ROP) may indicateeither changes in the type of formation being drilled or areduction in the differential between the mud pressure and pore

pressure. Generally, the following parameters affect the ROP: Rock type; Formation bulk density/porosity; Differential pressure; Bit type/wear; Hydraulics;

Weight on bit; Rotary speed; Personnel/equipment.

Drilling breaks are generally evidence ofporosity change. Drilling rate tends to

decrease with depth. Thus when adrilling break occurs, it may be anevidence of transition to an abnormalzone. It is crucial at this point to stop

drilling and check for flows.


26/40


Lost Circulation

Loss of substantial quantity of mud intothe formation will result in reduction inhydrostatic column height in the annulus.If not checked, this can result in a kick.


27/40


Changes in Gas Levels/MudDensity/Conductivity

Gas extracted from the mud comes from one ormore of the following sources: -

Liberated gas which is the measured gas from the return mudflow, released from the pore spaces of the drilled cuttings. It isthe so-called background gas during circulation. If there is

overbalance, and the ROP is constant with flow rate, this liberatedgas; Produced Gas enters the wellbore from adjacent permeable

formations when underbalance exists. A background gas increasewhen ROP is constant is evidence of produced gas;

Recycled gas is the gas recirculated into the hole. It appears ondetection equipment as an increase in background levels;

Contamination Gas results from chemical breakdown of mudadditives;

Connection gas and trip gas are short duration gas peaks causedby swabbing action.


28/40


Changes in Gas Levels/MudDensity/Conductivity

Gas extracted from the mud comes from one ormore of the following sources: -

Liberated gas which is the measured gas from the return mudflow, released from the pore spaces of the drilled cuttings. It isthe so-called background gas during circulation. If there is

overbalance, and the ROP is constant with flow rate, this liberatedgas; Produced Gas enters the wellbore from adjacent permeable

formations when underbalance exists. A background gas increasewhen ROP is constant is evidence of produced gas;

Recycled gas is the gas recirculated into the hole. It appears ondetection equipment as an increase in background levels;

Contamination Gas results from chemical breakdown of mudadditives;

Connection gas and trip gas are short duration gas peaks causedby swabbing action.

Depending on sensitivity level surface monitors should detect arelatively steady level of gas extracted from mud during normal

drilling. This background gas level may show occasional variationsdepending on penetration rate, mud pumping rate, hydrocarbon

content of section drilled. Under normal conditions, thebackground gas should remain within about 50% of local average.It is crucial that all gas values must be reported whether they aresignificant or not. Thorough inspection of gas monitoring systems

and calibration as part or routine maintenance exercise is essential

to preventing potential disasters


29/40


Connection and trip gas are most common whiledrilling. The connection gas peaks are a clear signthat pressures are near balance, making foroptimum ROP. Swabbing is the main cause ofconnection/trip gas as it creates negativedifferential pressure. . Effects of gas expansion atsurface are varied. Evidence includes:

Rapid fall in flow line mud density; Increase in return flow;

Mud pit level increase; Rapid increase in total gas or hydrocarbon levels.


30/40


Closing theWell In

The Blowout Preventer(BOP) Stack

Closes the annulus

Has multiple redundancies


31/40


Protecting theDrill Pipe Side

The top valve is a FULLOPENING SAFETY VALVE.Installed on the drill pipe whena kick is taken while tripping.

The lower valve is an INSIDEBOP - it is potentiallyDANGEROUS and its useshould be avoided!


32/40


Protecting the Drill Pipe Sidecontinued

To provide permanent protection in thedrill pipe when handling a kick a drillingfloat valve should be used.

This is a non-return valve installedimmediately above the bit.


33/40


Circulating out a Kick

Two basic techniques;

The Drillers method - 2 circulations; The Engineers or Waite and Weight

method - 1 circulation;

The Engineers method results in lower

annular pressure, particularly at the shoe.


34/40


DrillersMethod


35/40


Engineers orWait and

WeightMethod


36/40


Important Principles

A kick is NOT a blowout.

Most blowouts are due to human error inhandling a kick.

The fundamental principle in well control isCONSTANT BOTTOM HOLE PRESSURE

Shut the well in using the HARD or FASTSHUT IN using the annular BOP.


37/40


Important Principlescontinued

Control a kick with the bit on bottom.

Use True Vertical Depth (TVD) for calculating

pressures. Use Measured Depth (MD) for volumes and

displacements.

Establish pore pressure by recording the shut in

drill pipe pressure.


38/40


Important Principlescontinued

Maintain constant bottom hole pressure bycontrolling the drill pipe pressure - do not

us the casing pressure. Assume and design for a gas kick unless

the reservoir fluid is known.

Gas is more difficult to handle - primarilydue to large expansion during circulatingout a kick. (Boyles Law: P1V1 = P2V2)


39/40


If You Get it Wrong!


40/40

Th R b t G d U i it 2006 40

Further Reading

Campusmoodle: ENM201 notes Well Control

SPEs Applied Drilling Engineering (Red Book) :

Chapter 4 Drilling Hydraulics

Chapter 6 Formation Pore Pressure & Fracture Resistance

Documents

Well Control Intro Slides