08 Well Design Fundamentals (1)

Quartz School for Well Site Supervisors Module – 8 Directional Drilling

Section – 8 Well Design Fundamentals

Introduction •

Well Trajectory Design is one of the very first steps for Well Planning

•

This is a responsibility of the D&M Drilling Engineer who works together with Well Engineers, Geologist and Directional Driller

•

Normally the Oil Operator provides surface coordinates with vertical elevations and the coordinates for one or more objectives, including its shape

•

It is very important to involve the Drilling Engineer since the visualization and selection of geological objectives in order to optimize the well trajectory with regards to drilling hazards (Well Collision, Faults, Difficult formation to slide, etc.)

•

All dogleg severity limitations have to be specified at the very beginning of the well trajectory design (BHA Max Dogleg capability, Casing bending capacity, Completion Assembly specs, Electro-Sumersible pumps, etc)

•

Make sure that the Drilling Engineer is using previous experiences in the same field

Well Design Terminology •

There is a specific terminology that we need to understand for well trajectory design

•

This directional terminology define the main characteristics for the well trajectory

•

These terms describe how the well trajectory is built without the need of looking at the drawing

•

The Directional Driller will use these terms to give a verbal update for the current status of the well trajectory and he might ask for decisions to be taken based on the information given

Well Profile Concepts

Well Type “S”

Horizontal Well

Well Design Terminology 1. Surface Location or Surface Coordinates 2. Kick off Point 3. Build Section, Drop Section and Vertical Section 4. Well Profile (Vertical, J Type, S Type or Horizontal) 5. Target and Target Shape 6. Inclination and Direction (Azimuth) 7. Measured Depth 8. True Vertical Depth 9. Horizontal Displacement 10. Vertical Section 11. Build Rate 12. Turn Rate 13. Dogleg 14. Dogleg Severity 15. Closure 16. Closure Azimuth

Surface Location and Surface Coordinates

Well Origin or well reference point. Surface Coordinates represent the geographical location where the well is located. Surface coordinates can be given as local or geographical. Well profile is defined as the well trajectory from surface location to the well Total Depth. It is designed to avoid Torque & Drag issues by reducing the doglegs to the minimum allowable

Kick Off Point

The Kick off point is where the well is deviated to an specific direction (azimuth) to reach a given inclination with a determined build/turn rate. The kick off point is selected based on:

The

•

The well geometry profile

•

The Formation lithology

build/turn

rate

is

how

much

the

inclination and azimuth will change in a 30m interval

Kick off Point

Well Geological Target

This

is

an

area

defined

by

local

or

geographical coordinates at an specific true vertical depth or subsurface vertical depth. This target must to have a defined shape with tolerance lines. This area has to be well defined at the planning phase. It doesn’t matter how well the surface and intermediate sections are drilled if the target is not intersected. The actual well trajectory has to be projected to the target it doesn’t have to be right on the plan

Geological Target

Inclination and Direction (Azimuth)

Inclination: Angle between any point along the well trajectory and the vertical. Direction: Angle between any point along the well trajectory and the north. If the well is drilled towards north the direction is 0deg of azimuth. If the well is drilled towards east the direction is 90deg azimuth. True Vertical Depth: Well depth projected to the vertical plane

TVD

Measured Depth This is the real length of the well and it doesn’t require any projection. This is measured while the well is drilled by the

drowworks

sensor.

This

sensor

converts drowworks shaft rotation into drilled depth. The measured depth is allways referenced to the rotary table. Measured Depth is the same as the drillers depth which it is referenced to the drillpipe length.

Horizontal Plane Terminology

•

The vertical projection plane is normally defined by the direction of the well to the target at TD

on

t

ca lS ec ti

Vertical Section is the projection of the displacement to the vertical projection plane

em e n

•

sp l a c

Displacement or Closure is the hypotenuse of the latitude and departure. It is the distance from the WRP to any survey or Total Depth

Ve rti

•

Longitude

or D i

South and West negative

u re

•

Target

Clo s

North and East are positive

Latitude

•

Vertical Projection Plane

Surface Reference Point

Bottom Well Positioning: Vertical Section Vertical Section = Displacement X Cos (Target Azimuth – Closure Azimuth) Target

Survey Station

ec tio n

Ve rti ca lS

Dis pla cem ent

Vertical Section is the Projection of the Survey Station onto the Plane of Proposal

Latitude

Depart ure

Surface Reference Point

Bottom Well Positioning: Closure Azimuth T arge t

De pa rt ure

nt acem e Ve rtic al

Se c

tio n

Disp l

tan

Departure Latitude Latitude

CLOSURE AZIMUTH =

−1

Surface Reference Point

Purpose for calculating Vertical Section

PLANE OF PROPOSAL

Latitude

• Follow the progress of well trajectory on the Well Plan by plotting on it the “VS” vs. “TVD” for each survey station (bottom of well position)

Dis pla Ve cem rti ent ca lS ec tio n

Departure

• Project well onto the Plane of Proposal

Exercise - Well Plan Format What is the minimum information needed on a well plot to convey all the information a directional driller needs ? Note down all the items that are needed on a well plot (5 minutes).

Exercise - Well Plan Format What is the minimum information needed on a well plot to convey all the information a directional driller needs ? Note down all the items that are needed on a well plot. • • • • •

Titles, Client, Date, Well Paths (labelled) Scales for each axis noted, measurement units Plane of proposal Geomagnetic model used for plan, version, date etc. True north, grid,magnetic north corrections – reference for well • Technical Sign off (QC), approved by etc

Projection of Well Trajectory on Vertical Section Plane of Proposal 90 degrees

For a simple build hold profile, if the well was going due East, 90 deg, this would be as shown. However if the plane of proposal was stated as 180 degree, what would the well look like on a plan view?

1000ft

1250ft

Well is going 90 degrees

1500ft

2000ft

Plane of Proposal 180 degrees

It would be a straight line , shown in red. Be careful with 3D well plans

Impact of Kick off Depth on Well Trajectory For the same target and BUR: • The shallower the kick off depth, the lower the tangent angle and the shorter is the well length. Surface Reference Point

Examples: MD feet

For a TIE Shallow KOP KOP

0 1000 2000 10712

INCL deg

AZI deg

0 0 30 30

0 90 90 90

INCL deg

AZI deg

TVD feet 0 1000 1955 9500

NORTHING N/-S feet

EASTING E/-W feet 0 0 0 0

0 0 256 4612

KOP 1

KOP 2 MD feet

For a Deeper KOP

TIE KOP

0 5735 7735 11958

0 0 60 60

0 90 90 90

TVD feet 0 5735 7389 9500

NORTHING N/-S feet

EASTING E/-W feet 0 0 0 0

0 0 955 4612

Target

Shallow Kick off Point •

Shorter well length • Lower casing costs, smaller rig capacity

•

Lower tangent angles • Easier for hole cleaning • Maybe more difficult for directional work - holding low angle is not always easy

•

Essential for pad drilling or platforms to get away from other wells

•

Allows high displacement even if at a shallow TVD • ERD wells use very high kick off points and very high angle tangent section angles • Build up rate typically low to reduce overall torque and drag • Allowing high build up rates here will have large impact on torque values further down well

“J” Vs. “S” type Wells To hit the same target for the same KOP, BUR and DOR, profiles would be as follows: J type Well TIE KOP

S type Well TIE KOP Hold Drop

MD feet 0 1000 2000 10712 MD feet 0 1000 2500 7440 8940 11246

INCL AZI deg deg 0 0 0 0 30 90 30 90

TVD feet

INCL AZI deg deg 0 0 0 0 45 90 45 90 0 90 0 90

TVD feet

NORTHING N/-S feet

0 1000 1955 9500

0 1000 2350 5844 7194 9500

0 0 0 0

EASTING DISPL DLS E/-W feet feet deg 0 0 0 0 0.00 256 256 3.00 4612 4612 0.00

0 0 0 0 0 0

EASTING DISPL DLS E/-W feet feet deg 0 0 0 0 0.00 559 559 3.00 4052 4052 0.00 4612 4612 3.00 4612 4612 0.00

NORTHING N/-S feet

“J” type vs. “S” type discussion •

As can be seen for the same kick off point there is a large difference in the tangent angle and measured depth of the well

•

“S” type wells will tend to develop a lot more torque than an equivalent displacement “J” type, it also depends on the DD work

•

Usually “S” shaped wells drilled for “production reasons” have a small tolerance on the angle across reservoir (less than 5 or 10 degrees)

•

“S” type wells are unavoidable for low displacement wells or when directional drilling is complicated at deeper sections

•

“S” type wells allow to use cheaper BHAs at deeper sections

•

Low dogleg is highly recommended at the drop off curve

•

Directional drilling might be very difficult at the drop off curve due to high torque and BHA hanging

Summary • Every target potentially has 100’s of well plans to hit the centre. • Choose your plan based on reason – don’t just accept the 1st one you are given • Use geology to help with plans, if you know a formation naturally builds then use this to your advantage • Also find out if formations are stable drilled in all directions • Make plans as simple as possible • Remember big bends at top sections cause major torque issues later • Know what the completion mechanism is during design stage e.g. ESP’s need tangent sections, PCP’s have dogleg constraints