Lecture Well control

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Lecture Well control present the content: well control principles, warning signs of kicks, secondary control, primary control, lost circulation, solids removal, excessive dilution of the mud (due to watering-back), gas cutting of the mud, reduced height of mud column, primary indicators of a kick, secondary indicators,...

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Nội dung Text: Lecture Well control

WELL CONTROL Trình bày: ĐỖ QUANG KHÁNH Bộ môn Khoan – Khai thác Dầu khí Khoa Kỹ thuật Địa chất và Dầu khí Đại học Bách Khoa TP. HCM Email: dqkhanh@hcmut.edu.vn
CONTENT 1. INTRODUCTION 2. WELL CONTROL PRINCIPLES 3. WARNING SIGNS OF KICKS 4. SECONDARY CONTROL Well Control  2 GEOPET
CONTENT 5. WELL KILLING PROCEDURES 6. BOP EQUIPMENT 7. BOP STACK ARRANGEMENTS 8. EXERCISES Well Control  3 GEOPET
1. INTRODUCTION Well Control  4 GEOPET
Well Control  5 GEOPET
INTRODUCTION Ensure that fluid (oil, gas or water) does not flow in an uncontrolled way from the formations being drilled, into the borehole and eventually to surface.  This flow will occur if the pressure in the pore space of the formations being drilled (pf) >= the hydrostatic pressure exerted by the column of mud in the wellbore (pbh).  It is essential that pf, due to the column of fluid, exceeds the formation pressure at all times during drilling. Well Control  6 GEOPET
Well Control  7 GEOPET
INTRODUCTION  If, for some reason, pf >= pbh an influx of fluid into the borehole (known as a kick) will occur.  If no action is taken to stop the influx of fluid once it begins, then all of the drilling mud will be pushed out of the borehole and the formation fluids will be flowing in an uncontrolled manner at surface. This would be known as a Blowout.  This flow of the formation fluid to surface is prevented by the secondary control system.  Secondary control is achieved by closing off the well at surface with valves, known as Blowout Preventers – BOPs. Well Control  8 GEOPET
Well Control  9 GEOPET
Well Control  10 GEOPET
INTRODUCTION The control of the formation pressure,  either by ensuring that the borehole pressure is greater than the formation pressure (known as Primary Control)  or by closing off the BOP valves at surface (known as Secondary Control) is generally referred to as keeping the pressures in the well under control or simply well control. Well Control  11 GEOPET
INTRODUCTION When pressure control over the well is lost, swift action must be taken to avert the severe consequences of a blow-out. These consequences may include:  Loss of human life  Loss of rig and equipment  Loss of reservoir fluids  Damage to the environment  Huge cost of bringing the well under control again. Well Control  12 GEOPET
INTRODUCTION For these reasons it is important to understand the principles of well control and the procedures and equipment used to prevent blowouts.  Every operating company will have a policy to deal with pressure control problems.  This policy will include • training for rig crews, • regular testing of BOP equipment, • BOP test drills and standard procedures to deal with a kick and a blow-out. Well Control  13 GEOPET
INTRODUCTION One of the basic skills in well control is to recognise when a kick has occurred.  Since the kick occurs at the bottom of the borehole its occurrence can only be inferred from signs at the surface.  The rig crew must be alert at all times to recognise the signs of a kick and take immediate action to bring the well back under control. Well Control  14 GEOPET
INTRODUCTION The severity of a kick (amount of fluid which enters the wellbore) depends on several factors including • the type of formation; • pressure; • and the nature of the influx.  The higher the permeability and porosity of the formation, the greater the potential for a severe kick (e.g. sand is considered to be more dangerous than a shale).  The greater the negative pressure differential (pf to pw) the easier it is for formation fluids to enter the wellbore, especially if this is coupled with high permeability and porosity.  Gas will flow into the wellbore much faster than oil or water. Well Control  15 GEOPET
2. WELL CONTROL PRINCIPLES  Two basic ways in which fluids can be prevented from flowing, from the formation, into the borehole:  Primary Control (PC)  Secondary Control (SC) Well Control  16 GEOPET
WELL CONTROL PRINCIPLES  Primary Control: is maintained by ensuring that the pressure due to the column of mud in the borehole is greater than the pressure in the formations being drilled i.e. maintaining a positive differential pressure or overbalance on the formation pressures. Well Control  17 GEOPET
WELL CONTROL PRINCIPLES  Secondary Control: is required when PC has failed and formation fluids are flowing into the wellbore. The aim: is to stop the flow of fluids into the wellbore and eventually allow the influx to be circulated to surface and safely discharged, while preventing further influx downhole. Fig. Secondary Control -Influx Controlled by Closing BOP's Well Control  18 GEOPET
WELL CONTROL PRINCIPLES  First step: close the annulus space off at surface, with the BOP valves, to prevent further influx of formation fluids  Next step: circulate heavy mud down the drillstring and up the annulus, to displace the influx and replace the original mud (which allowed the influx in the first place). • The second step will require flow the annulus but this is done in a controlled way so that no further influx occurs at the bottom of the borehole. • The heavier mud should prevent a further influx of formation fluid when drilling ahead.  The well will now be back under primary control. Well Control  19 GEOPET
WELL CONTROL PRINCIPLES PC of the well may be lost (i.e. pbh < pf) in two ways.  The first is if the formation pressure in a zone which is penetrated is higher than that predicted by the reservoir engineers or geologist. In this case the drilling engineer would have programmed a mud weight that was too low and therefore pbh would be less than pf. Fig. PC - Pressure due to mud column exceeds Pore Pressure Well Control  20 GEOPET