2-well control & directional drilling

7/27/2019 2-Well Control & Directional Drilling

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FORMATION PRESSURE,

WELL CONTROL &DIRECTIONAL DRILLING



Pressure Relations• Overburden Pressure

– Total weight of the rock and fluid above the depth of material (total weight of material)

– Assume overburden pressure is 1psi/ft

• Formation Pressure

- The pressure of the fluid (Oil/gas/water) existing within thepore space of a rock formation. Also called Rock orReservoir pressure

Formation Pressure Classification

• Normal pressure

• Subnormal pressure

• Abnormal pressure



Formation Pressure Classification

• Normal Pressure

– Hydrostatic pressure exerted by all fluids in the formation

above a depth of interest.• Gulf of Mexico = 0.465 psi/ft

• Niger Delta = 0.442 psi/ft

• Subnormal Pressure

– Pressure that is lower than the actual pressure expected inthe area

Problems of subnormal pressure

– Lost Circulation

– Pipe stickingReasons for Subnormal Pressure

– Tectonic Movement

– Depletion Reservoir



Formation Pressure Classification• Abnormal Pressure

–

Pressure gradient is greater than expected/actualpressure in that area

Problems of Abnormal Pressure

– Kick

– Blowout

Reasons For Abnormal Pressure

– Earthquakes

–

Tectonic movements – Stresses in the subsurface

– Casing leakage in nearby area



Importance of Formation Pressure

determination

• Essential for proper well planning and drillingpractises

• Lessens the frequency and severity of kicks

and blowouts• Reduces differential pipe sticking

• Maximizes Penetration rate

• Reduces formation damage

• Minimizes drilling cost



Formation Fracture Gradient• The pressure at which an increase in the mud

will fracture the formation.

Reasons for Determining Formation Fracture Pressure

• Minimizes or avoids lost circulation problem

• Proper selection of casing seat depth (casing shoe)

* Field Determination – Leak-off test or Pressure

Integrity Test

* Leakoff Pressure – The point at which an increase inpressure pump into the well will tear and there will a

decrease in pressure



WELL CONTROL

•

Kick : It is an flux of formation fluids into theborehole that causes an unequal volume of

drilling fluids to be displaced from the drilling

hole.

• Blow out: It is an uncontrolled flow of

formation fluid from the borehole



STAGES OF WELL CONTROL• Primary control

– The pressure exerted by drilling fluid to hold backformation fluid from entering the borehole beforecasing

• Secondary control

– It arises from the failure from primary control – Surface equipment is closed to stop further entry

of formation fluids. Use BOP

• Tertiary control

– Techniques to control blow-out when it hasoccurred



CAUSES OF KICK• Reduction on the mud hydrostatics which could arise as

failure to fill hole during pull-out

•

Drop in level of mud weight in the hole• Low density of formation fluids being swabbed in during

tripping

SWABBING FACTORS• Pulling too fast

• High viscosity mud

• Small collar to hole clearance

• Balling up of bit

• Increased in formation pressure



KICK WARNING SIGNS• Improper fillup or displacement during trips

• Connection gas (gas caught mud)

• Increased drill rate

• Flowline mud temperature increase

•

Increased drillstring torque&drag• Increased number and quantity of cutting

• Decreasing shale density

• Lost circulation



SURFACE KICK INDICATOR• Excess flow from the well when tripping

• Return flow rate increase when pumping

• Pit gain

• Drilling break

• Flow from the well when pumps are shutoff



KILL METHODS

• Driller’s method

• Wait and weight method• Concurrent method

• Volumetric method

SHUTTING THE WELL

– Any further influx of formation fluid into the well

to be stopped

– To determine the pressure of the formation fluidso that the well can be killed with a heavier mud.

– This is done using BOP



DIRECTIONAL DRILLING

•This is the process of directing the wellborealong a specific trajectory to reach a specific

depth.

• Deviation control is the process of keeping the

wellbore contained within prescribed limit

relative to inclination angle and the horizontalextension from the vertical.



DIRECTIONAL WELL• Long radius well

–

Well achieves a large horizontal displacementbefore reaching the target.

– Inclination angle - 2o – 6o/100’

– Radius – 1000 – 3000’

• Medium radius well

- Well turns from vertical to horizontal at

- Inclination angle – 8o – 20o/100’

- Radius – 285 – 700’

- Most commonly used because most tools can pass throughit and very effective for horizontal drilling



DIRECTIONAL WELL

•

Short radius wells – Inclination angle – 1.5 – 3o/ft

– Can reach 90o in 20 – 60’ of hole

–

Horizontal length are limited to few hundred feet – There are difficulties to pass completion tools

through the tight radius



DEFINITIONS

• Measured depth (MD) :

– Actual drill string measurement

• Drift/inclination angle:

- Deviation from vertical in degrees

• Kick off point: – Well depth at which inclination is initiated

• Build Section:

- Deviated length of the well from the kick off point



DEFINITIONS

• Build up rate:

- Rate at which the well deviates

• Tangent

- Length of the straight section of the well after thebuild section

• True vertical depth – The true vertical depth as calculated from the directional

survey

• Azimuth

- Direction of the well with respect to the true north



APPLICATIONS OF DIRECTIONAL DRILLING

• Side tracking

• Inaccessible locations

• Fault control

• Multi Exploration wells from single wellbore

• Onshore drilling to offshore location

• Relief well

•

Extended reach wells• Offshore multi well drilling



DIRECTIONAL WELL PLANNING

• Factors consider

– Design trajectory

– Geology of the area

– Bottom hole assemblies

• Well Trajectories:

– Build and hold

– Build hold and drop (“S” type)

– Modified “S”

– Continous build



DEFECTION TOOLSDrill string device that causes the bit to drill at an

angle to the existing hole

• Badger Bit

– Technique uses the fluid power direct through an enlarged

bit nozzle

– Used in soft formation and requires close control

• Whip Stock

- Steel wedge which is run in hole and set at the kick off

point- Wedge makes the deflection in the required direction

- Once deflection is made, whipstock is retrieved and hole

reamed to full guage



DEFECTION TOOLS• Rebel Tool

– Designed to make lateral push to either left or right

ADVANTAGES

- Makes gradual change in direction

- Allows normal drilling to continue

- Cheaper than using down hole motor

- Bent Sub- Short length of collar size pipe specially designed so that the axis of

the lower connection is offset from the vertical

- Available in ranges 1 – 3o

• Navigation Sub (Steerable system)• Standard mud motor converted to steerable motor by tilting the bit

at a predetermined angle (Positive displacement motor)

• Ensures deflection forces are applied to the face of the bit.



HORIZONTAL DRILLING•

Refers to well at 90o

to the vertical (parallel tobedding plane)

• A special aspect of directional drilling

•

HD is a procedure for drilling and completingoil and gas well with improved productivity

MAJOR REASON FOR HORIZONTAL DRILLING

•

Increase rate of return on investment (bettereconomics)

• Productivity increase

C O /C S C O O



APPLICATION/CANDIDATE SELECTION OF

HORIZONTAL WELLS

• Gas or water coning

• Tight Reservoirs

• Inaccessible reservoirs

• Heavy oil recovery

• Thin reservoir

• Reduced number of platforms and wells

needed to develop a field and better coverageof the reservoir from existing platform

O S



LIMITATIONS

• Only one payzone can be drained perhorizontal section

• Cost 1.4 – 3 times vertical wells

• High production related problems

• Well spacing



DESIGN FACTORS

• Rig sizing

• Drill string capacity• Directional well planning

• Plan for drilling hydraulics (hole cleaning, flow rate,rheology)

• Tortuosity consideration

– Hole drag & torque• Solid control

• Casing consideration – Geology at the point of target

– Interference with other wells

– Torque and drag as it affects casing

– Wear consideration and bending stress

2-well control & directional drilling

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