Chapter 7: WELL CONTROL

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DRILLING ENGINEERING I (CGE577)

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Contents

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Definition of Kick and Blowout

Primary Control and Secondary Control

Origin of Kick

Kick Indicators and Precautions

BOP Assembly

Shut in Procedures

Determination of kick size, kicking formation pressure, kick type and kill mud weight

Well killing Procedures

INTRODUCTION

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The purpose of well control is to ensure that fluid (oil, gas and water) does not flow in an uncontrolled way from the formations being drilled, into the borehole and eventually to surface.

The uncontrolled flow will occur if the pressure in the pore space of the formation being drilled (the formation pressure) is higher than the hydrostatic pressure exerted by the column of mud in the wellbore.

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INTRODUCTION

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If formation pressure is greater than the borehole pressure an influx of fluid into the borehole will occur. Well taken a kick .

If no action is taken to stop the influx of fluid once it begins, then drilling mud will be pushed out of the borehole and the formation will be flowing in an uncontrolled manner at surface known as blowout .

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Blowout

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INTRODUCTION

Kick is an influx of fluid flowing into the borehole as a result from higher pore pressure compared to the mud pressure

This influx have to be stopped to avoid the fluid from flowing in an uncontrolled manner to the surface. If this happened, all the mud will be pushed out from the borehole and the phenomena is called blowout .

Blowout will cause severe damage to the rig and people injuries

The blowout could also lead to loss to reservoir fluid and environmental damage. High cost would involve to control the well and stop the blowout.

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INTRODUCTION

Well control involves controlling the borehole pressure so that it is higher than the formation pressure (overbalance) and closing the BOP at surface to prevent the blowout.

Closing the BOP take place if the drillers failed to control the borehole pressure in overbalance.

After BOP is closed the fluid influx will be safely discharged at surface and further downhole influx would be prevented.

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PRINCIPLES OF WELL CONTROL

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Primary Control

Pressure exerted by column of mud in the borehole is greater than the pressure in the formations being drilled

Primary control has failed

The aim of secondary control is to stop the flow of fluids into well bore and eventually allow the influx to be circulated to surface and safely discharge, while preventing further influx down hole

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Primary Control

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Secondary Control

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In order to avoid kicks, mudweight is designed about 200 to 300 psi overbalance

The kicks can be originated from two principles:

The formation pressure is higher than predicted

The mud density or the height of the mud colomn decreases.

The reduction in mud density normally due to:

Removal of solid contents (Barite) or Barite settling in the pits

Watering back/ excessive dilution of the mud (improve mud viscosity and evaporation in deep wells)

Gas cutting (background gas seeps into the mud).

Heavy rains in the pits

ORIGIN OF KICKS

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Height of mud column: Volume of mud pumped into the borehole = volume of mud returned When the mud stop circulating, the colom of mud should not fall below the mud flow line.

The height of the mud colom could reduce due to: Swabbing - happened when the formation fluid is sucked into the borehole as the drillstring is being pulled too fast out of the hole. Tripping reduced the height of mud colom and the volume of pipe removed must be replaced accordingly. Lost circulation can happened in a fractured or high permeability reservoirs due to excessive mud weights, excessive annular friction loss, excessive surge pressure during trips, excessive shut-in pressures.

Possum Belly Tank (trip tank) is used to accurately measured the volumes of mud needed to be replaced in the hole during tripping. As the pipe is pulled from the hole, mud from the trip tank is allowed to fill the hole as needed.

ORIGIN OF KICKS

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Causes of Kicks

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Causes of Kicks

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Causes of Kicks

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Primary indicators:

Increasing in flow rate and pit volume

In normal drilling operation, volume of mud pumped in is equal to the volume of return at surface. However, if the volume of returns exceeds the volume pumped in, it indicates that formation fluids have invaded the well

mud in the pits to watch for signs of kick.

Flowing well with pump shut off when circulation pressure decreased

When influx intermix with the existing drilling mud, a new fluid of reduced viscosity and density which in turn results in lower annular pressure losses. Then total pressure loses is reduced. When lighter fluids enter the wellbore, the circulation pressure is further reduced because of U-tubing effect resulting from density differences between the heavy mud inside the drillpipe and lighter fluids in the annulus. Decreased pump pressure, increase pump speed. Surface indication shows well flow with pump off.

INDICATORS OF A KICK

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Primary indicators:

Improper hole fill up during tripping

Improper fill on trip occurs when the volume of drilling fluid to keep the hole full on a Trip (complete operation of removing the drillstring from the wellbore and running it back in the hole) is less than that calculated or less than Trip Book Record. This condition is usually caused by formation fluid entering the wellbore due to the swabbing action of the drill string.

An increase in chloride content

Mud engineer routinely measures the quantity of chloride in mud to establish the datum level for Cl-. Most formation fluids contain high levels of salinity compared with those of the drilling mud. Indication that formation fluids have invaded the well is obtained when the measured Cl-

content of mud exceeds the datum level.

INDICATORS OF A KICK

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INDICATORS OF A KICK

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Secondary indicators (not confirmed of a kick sign and could be from something else):

Drilling break (abrupt increase in rate of penetration)

This indication must be used with other surface indications because frequent changes in penetration rate occur due to changes in formation type being drill. Increase penetration rate at the surface can be seen by the increased volume of cuttings on the shale shaker and by the large size of the individual chips.

Gas cut mud drilling in gas bearing zone or swabbing during trips

Changes in pump pressure washout in drillstring or twist -off

PRECAUTIONS OF A KICK

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During drilling - Flowcheck:

Pick up the Kelly until a tool joint appears above the rotary table

Shut down the mud pumps

Set the slips to support the drillstring

Observe flowline and check for flow from the annulus

If well is flowing, close the BOP

If the well is not flowing, resume drilling

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BOP Equipment

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The BOPs are a series of powerful sealing elements designed to close off the annular space between the pipe and hole

By closing off this route, the well can be "shut-in" and the mud and/or formation fluids forced to flow through a controllable choke/valve

This choke control the pressure that reaches the surface and followed by the necessary steps for "killing" the well

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BOP ASSEMBLY

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Annular Preventer

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Ram Preventers

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Shear Ram

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Drilling/ Casing Spool

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SHUT IN PROCEDURES

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Kick while drilling Raise Kelly above the rotary table until a tool joint appears Stop the mud pumps Close the annular preventer read shut in drill pipe pressure, annulus pressure and pit gain

Kick while tripping

Set the top tool joint on slips Install a safety valve (open) on top of the string Close the safety valve and annular preventer make up the Kelly open the safety valve read the shut in pressure and the pit gain

Start when primary control failed kick detected & pit gain on surface

Close (Shut-In) the well by activating BOPs seal off drillstring to wellhead annulus

at surface (not necessary to close off valves inside the drilpipe to allow mud circulation for pressure control)

Record the pit gain

Record the Shut-In Drill Pipe Pressure (SIDPP)

Record the Shut-In Casing Pressure (SICP)/ Annulus Pressure

Determine the type of influx (kick type - gas, oil, water, mixture), size and kill mudweight

SHUT IN PROCEDURE

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