3.Well Profile Design

Instituto Superior TécnicoUniversidade de Lisboa

Masters in Petroleum Engineering 2014-2015

Drilling Engineering Course

José Pedro Santos Baptista

Mining and Geological Engineering Msc.Petroleum Engineering Msc.

Drilling Engineering Course

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3. Well Profile Design

Directional Drilling

Why and how do we do it?

Well Planning

Isn’t it just a line?

Uncertainty

A foot here, a foot there, what’s the point?

Drilling Engineering Course 2014-2015 Masters in Petroleum Engineering


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Directional Drilling – Concepts


To plan a well, mathematically, the drilling engineer only needs to obtain three variables:

Measured Depth (MD)

Length of the wellbore from the Reference point (tie-in point)

≠True Vertical Depth (TVD)

The vertical distance from a point in the well to a point atthe surface (reference point/tie-in)


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Measured DepthInclination

Deviation from vertical(0°), irrespective of compass direction

IInitially measured with a pendulum mechanism, and confirmedwith MWD accelerometers or gyroscopes

0°

90°


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Measured DepthInclinationAzimuth

Size of the angle measured from the north (0°)

The compass direction of a directional survey or of the wellbore asplanned or measured by a directional survey. The azimuth isusually specified in degrees with respect to the geographic ormagnetic north pole (Grid North or True North).


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Measured DepthInclinationAzimuth

Each Set is referred to as Survey Station

These three sets of data define the well path, allowing the calculation of the three local coordinates of every point in the

well – Northing, Easting and TVD


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In terms of terminology, there are specific points in the well profilewhich are important to mention due to their significance to thedirectional driller.

Kick Off Point (KOP) Depth at which the well is deviated fromthe vertical (or when a side-track begins, even if the

path is already deviated)

Build Section Part of the wellbore where the drift angle(inclination) is increasing

End Of Build (EOB) Point of the wellbore after which the driftangle (inclination variation) returns to zero


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Tangent section Part of the wellbore where the path is astraight line which is tangent to the buildsection, intersecting it in the EOB point

Drop off Section Part of the well’s trajectory where the driftangle is decreasing (decreasing inclination)

End Of Drop (EOD) Point of the wellbore, after the dropsection, after which the inclination remainsconstant (the path becomes a tangent)


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In 3D wells, there are a few other definitions that encompass thecomplexity of the design

Turn Section Part of the wellbore where the azimuth is changing,usually in a build or drop sections

Departure Distance measured perpendicularly to the North toa particular survey station

Horizontal Displacement Also called closure distance, is the shortesthorizontal distance from a particular surveystation back to the reference point

De part ure

Surface Reference Point

T a r g e t


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Dog Leg Severity (DLS) Parameter used to represent the change ofinclination and azimuth of the well path(degrees/100ft, degrees/30m)

≠Dog Leg Sharp localised bend in the wellbore

DLS = {cos-1 [(cos I1 x cos I2) + (sin I1 x sin I2) x cos (Az2 – Az1)]} x (100 ÷ MD)


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Well Planning


Iterative process – Problem with numerous solutions

Casing Design,

Completion & Reservoir Objectives

Lithology Review

Well Profile

Iteration

Anti-collision Analysis

Target Sizing

Torque & Drag

Analysis

Hydraulics Analysis

Well Plan


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Well Planning – Iteration Steps


Casing Design, Completion & Reservoir Objectives

Casing Design (company policy for pore pressure and kick margin)Completion RequirementsReservoir ObjectivesGeological Targets (description based on requirements)

The hole sizes, any tangents required for completions and maximum attainable/allowable DLSranges (due to casing, completion and tool specification limitations ,etc.) will be determined

Entry point into and profile in the reservoir is also established


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Lithology Review

Revision of the expected lithology the well is to intersect

Soft/Unconsolidated Formations

Formations prone to drilling problemsShalesChalkSaltDepleted Zones

SwellingMobility

Time dependency (compaction)

Stuck Pipe Prevention

DLS Capability and hole washout


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Lithology Review (cont.)

Revision of the expected lithology the well is to intersect

Hard Streaks

Formations with history of high ROP’s

Clear Formation MarkersAid in well placement and structural uncertainty (casing setting depths)

Drill Bit Strategy , Rate of penetration, etc.

At the end of this stage the bulk of the well profile can be established


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Well Profile Iteration

Preliminary Well Design is made to meet the established criteria from the previous steps

General Guide Lines

DLS as low as possibleTangent inclinations as low as possible (<45°, if more, as short as possible)Use gradually Build/Turn rates (1,5°/30m > 2°/30m > 3°/30m > …)Avoid drop sections (if required increase DLS)Keep inclination as low as possible and directional work at a minimum in:

Soft/Unconsolidated formationsHard StreaksFormations with past drilling Problems

In high ROP formations plan as long interval as possibleHit the targets as initially required (subject to optimisation)


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Anti-collision Iteration

Using the previous profile design, a thorough study of theoretical (planned) surveyuncertainty, resulting in the identification of possible collision problems

If necessary adjust the trajectory to cope with the new inputs

If the risk is too high go back to the previous step!

More details on survey uncertainty and anti-collision will be presented in the end of the lecture


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Target sizing Iteration

After the theoretical survey uncertainty is calculated and the ellipsoid of Uncertainty(EOU) at target is known (with no less that 95% confidence level), answer:

Does it fall in an acceptable range?

Improvements solved the issue?

Yes! Is it practical? Yes! Next StepNo! Improve Survey Program/redesign

Yes! Next Step


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Torque & Drag Analysis, Hydraulics Analysis

These two steps are the ones related to the practice of drilling. By performing thesecalculations the drilling engineer will answer the most important question:

IS THE WELL DRILLABLE?

If yes Next Step

If no Redesign!

More on these two subjects on lecture 5 – Drilling Operations


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Well Planning


The well design is done and approved by all thestakeholders. The well plan is used during thedrilling operations, by the directional driller, toaccurately drill the wellbore and reach the target(s).

To achieve this, the directional driller will be usingtwo major types of graphical aids:

Horizontal Plot

Vertical Section Plot


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Directional Drilling – Well Planning


Plan View/Horizontal Plot/Projection

The path is projected onto the horizontal planeA bird's eye view (looking from above)

Every point on the well path is defined by its North-South (X-axis) andEast-West (Y-axis) distance from the surface location (0,0).

Example:The target is 3,400ft north and 800ft east of the surface location.Coordinates of the target location: 3400ft N 800ft E.


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Vertical Section View/Plot

The path is projected onto a vertical planeLateral View (looking from a side)

The plane of proposal is defined by its angle from north (VerticalSection Azimuth)represents a theoretical vertical slice (plane) through the earth.

Example:The azimuthal plane of proposal passes through the surface locationand the target at a 52° angle from north.


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Vertical Section View/Plot (cont.)

Every point on the well path is defined by its true vertical depth, onthe Y-axis (TVD) against its vertical section departure, on the X-axis(distance between the surface location (0,0) and a point on the wellpath projected onto the plane of proposal at 90 °)

On rare occasions, the vertical section may be referenced to anotherpoint, for example, the platform reference point.

Example:TVD of the target is 7,800ft and the vertical section departure is3,800ft.


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In 3D wells, both plots need to be viewed closelytogether and the DD may require more than oneVertical Section plot (view from different angles)

“There is nothing insignificant in the world. It alldepends on the point of view.“

-Johann Wolfgang Von Goethe


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Directional Drilling – Reasons to Deviate


First recorded deliberately deviated well was drilled in 1930 inHuntington Beach California to target offshore oil sands

Typical applications of directional wells

Multi-Well Platform Fault DrillingInaccessible Locations Side-Tracking and StraighteningSalt Dome Drilling Relief Wells


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Directional Drilling – Typical Well Trajectories


Almost all the well shapes fit into thesefour categories

Vertical

J Type Directional

S Type Directional

Horizontal


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Vertical Wells

Exploratory

Land wells

No special restrictions

Cheap

Low producers

Injectors


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J Type DirectionalCurve- Tangent (Build – Hold)

Unable to get directly over target

Increase reservoir exposure

Offshore

Fault Drilling


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S Type DirectionalCurve – Tangent –Curve – Tangent (Build – Hold – Drop)

As J type

For wells to be fracced

Instability issues in the reservoir

Relief Well


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Horizontal Type DirectionalCurve- Tangent (Build – Hold)Curve – Tangent –Curve – Tangent (Build – Hold – Build – Hold)

Increase reservoir exposure

Thin zones

Naturally fractured areas


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ExxonMobil Sakhalin Island 12,700m MD, 2,344m TVD11,732m departure, 73 days

Maersk Qatar 36,768ft (11,207m) departure, 36 days

BP UK 35,197ft departure, 5370ft TVD

Total Patagonia34,728ft departure, 5434ft TVD


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Uncertainty – Surveying


In the planning stage, the well planner is responsible for the definition of the Survey Program

Selection of Tools that measure the 3 components of the well trajectory

Depth, Inclination and Azimuth

The wellbore surveying tools can be divided into two broad categories

MWD and Gyro


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Uncertainty – Surveying


The measurements have errors that must be accounted for in order to reach the well’s objective(s)

Magnetic field uncertaintiesMagnetic compass errors

Gyrocompass errorsTool misalignment errorsAlong-hole depth errors

These errors are the cause positioning uncertainty that needs to be modelled


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Uncertainty – Error Models


Cone Model

Assumes that the error is the same in all directions

(horizontally)

Uncertainty is a circle that increases in diameter with

depth (cumulative effect)

Visually creates a cone shape around the planned

well path.


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Uncertainty – Error Models


Ellipsoid Model

Initially created by Wolff and de Wardt (Systematic Error Model)

Recognises that the error is different in the x, y and z axis

The uncertainty is then an ellipsoid of increasing size with depth

Currently the Industry Standard is set by ISCWSA (Industry

Steering Committee on Wellbore Survey Accuracy)


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Uncertainty – Applications


Anti-collision monitoring purposes

Separation Factor Centre to Centre separation from the generic well to the check well(s)

Position uncertainties of both generic and check well(s)

Target Intersection

Reservoir Targets

Relief Wells


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Conclusion – Good Well Design


Lowest possible DDI (Directional Difficulty Index)

Collision risk managed (application of standards and procedures)

Planned hole sections delivered (casing design and directional plan integrated)

Targets Intersected


37Drilling Engineering Course 2014-2015 Masters in Petroleum Engineering

End of Well Profile Design

Next Chapter: 4. Drilling Equipment

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3.Well Profile Design

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