Planning Methods
S- well Design
An S-well has three sections, Build-Hold-Build/Drop, and is defined by seven parameters. You can also add a hold for the kick-off.
The following graphic depicts 2D S-Well Design parameters:
To Enter a 2D S-well Profile:
1. Type in the coordinates of the point to aim for, or select a target.
2. Select two of the unknowns from the list of seven, shown below.
Example unknowns are 2nd Hold Length and Maximum Angle Held.
3. Enter the five remaining parameters:
• 1st Hold Length is the length of initial hold section before the kick-off. Enter zero for no length before the kick-off.
• 1st Build Rate is the build-up rate.
• Maximum Angle Held is the intermediate tangent angle of the profile.
• 2nd Hold Length is the length of the intermediate tangent section.
• 2nd Build Rate is the second build or drop rate, which is a positive (+) or negative (–) value.
• Final Inclination is the inclination you want to achieve at the target.
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• Final Hold Length is the distance from the end of the last build to the target. Enter zero if you do not want a straight section before the target.
The following graphic depicts an S-Well Plan example:
The preceding example displays a planned S-Well that is planned to target T9 with the kick-off point at 1500 ft, initial build rate of 2º/100 ft, second drop rate of 3º/100 ft, to a final inclination of 10º,with a final hold length to the target of 1450 ft. With these input parameters, the calculated inclination of the tangent section is 62.86 º, with an interim hold length of 3298.7 ft. The calculated plan is shown above in 3D (left) and Vertical Section (right), with each planned section highlighted with boundary lines.
3D Well Planning
3D planning methods assume that the well is drilled under some form of directional control, where the well can be turned to a given azimuth from a particular measured depth.
Chapter 5: Planning Module
Build/Turn Curves
The mathematics of Build/Turn curves assumes that the wellpath is wrapped around the surface of a cylinder. The shape of the wellpath is resolved into two planes: vertical (inclination) and horizontal
(direction). The build rate is the rate of change of inclination, and turn rate is the rate of change of direction or doglegs in the vertical and horizontal planes, respectively.
Build and Turn curves are constructed by assuming that the sections are drilled using a rotary drilling assembly. A number of submethods are available to plan different types of Build/Turn curves, utilizing different types of available information during the design.
The following graphic depicts the Build/Turn Curves planning models:
Build/Turn submethods are selected by clicking the appropriate icon at the bottom of the Plan Method window. Selecting different icons results in different parameter fields being active and inactive. Active fields require a value for the submethod to work. Inactive fields are calculated using the entered parameters.
For more detail, see the online help.
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The following graphic depicts a Build/Turn drop-down layout:
Dogleg/Toolface Curves
The mathematics of Dogleg/Toolface curves assumes that the wellpath is wrapped around the surface of a sphere—that is, a circular curve with orientation defined by toolface and radius defined by dogleg. Toolface is the direction from high-side of the hole. Toolface is 0º at high-side and 180º at low-side. Looking down the wellbore, toolface is positive clockwise and negative counterclockwise. If the wellbore has no inclination, toolface is referenced to local north.
Dogleg/Toolface curves are constructed by assuming that the sections are drilled using a steerable drilling assembly. A number of submethods are available to plan different types of Dogleg/Toolface curves that use different types of available information during the design.
Build/Turn submethod icons. These activate the required parameter entry fields when pressed.
Some Build/Turn methods enable a target TVD or location to be selected.
If a target is selected, the Target Adjust option is also available.
Required fields are active.
Calculated fields are grayed out.
Chapter 5: Planning Module
The following graphic depicts the Dogleg-Toolface Curve submethods:
Similarly to Build/Turn curves, Dogleg/Toolface curve submethods are selected by clicking the appropriate icon at the bottom of the
drop-down layout.
The following graphic depicts the Dogleg/Toolface drop-down layout:
Depending on the selected submethod, the appropriate parameter fields are activated.
After calculating, the grayed out fields display their calculated values.
Plan to tangent to a point generates two sections: either Hold-Curve or Curve-Hold.
The Dogleg/Toolface submethods are the same as Build/Turn curves, except the calculated wellpath shape is different.
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Build/Turn vs. Dogleg/Toolface
As discussed in the last two plan method sections, Build/Turn and Dogleg/Toolface plan profiles have a significantly different geometry.
Build/Turn plans approximate to Radius of Curvature curves that follow the surface of a cylinder. These curves emulate rotary drilling where build and walk are predicted. Build/Turn can also design a flat turn where the inclination remains constant—for example, when
sidetracking to a different azimuth.
Dogleg/Toolface plans construct a Minimum Curvature geometry that follows a great circle route around the surface of a spheroid.
Dogleg/Toolface curves cannot be used to design a flat turn; the inclination changes through the turn. For short turns, dogleg and toolface orientation remain constant. For larger turns, Dogleg/Toolface curves cannot construct a path with constant dogleg and toolface orientation—they change over the turn. This effect can be considerable over a long distance.
Optimum Align
The Optimum Align planning method adds three sections: Curve, Hold, and Curve (also called Steer-Hold-Steer). You can specify a final inclination and direction for the end of the final curve, or, if you select two targets, the COMPASS software computes the inclination and direction between them for you. If you select a single target, the COMPASS software lines up on the target to plan the well down dip.
Chapter 5: Planning Module
The following graphic depicts Optimum Align Planning Methods:
To Build an Optimum Align Profile
1. Set restrictions on the curve shape in one of three ways:
• Doglegs – Specify the doglegs of both curves.
• TVDs – Enter the start and end TVD of the intermediate hold section (or TVD at end of first turn, TVD at start of second turn).
• Tangent Length – Enter the length of the intermediate hold section, the COMPASS software calculates the TVDs and Inc/Azi. If you enter 0 for the tangent length, the COMPASS software computes a Curve-Curve trajectory that has no tangent length.
2. Select the first target to land the wellpath. You can adjust the landing point vertically/laterally using the Target Adjust tool. You can add a short section before the first target by specifying Hold length with or without a build rate before hitting the first target.
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3. Determine the final inclination and azimuth using one of the following methods:
• Selecting a second target to follow on to:
— Pick a target—the target you want to hit
— Line up on target—the target you want the wellpath to line up on at the end of the second curve. This target is
remembered in the plan, and a hold is computed between the two targets.
• Defining the end vector at the target:
— Pick No Target (Freehand) – If Target 1 has a dip and strike, the COMPASS software assumes you want to plan down dip and calculates inclination and azimuth accordingly.
These values are defaults that can be changed. If you want to plot sensitivities in the Wellpath Optimiser based on N/S and E/W coordinates, you must enter a freehand target.
When doing so, these parameters appear in the profile grid for editing.
— Inc – Enter the final inclination required.
— Azi – Enter the final required direction.
Chapter 5: Planning Module
The following graphic depicts an Optimum Align plan example:
The preceding example displays an Optimum Align plan to target T8 defined using two doglegs. When the plan hits target T8, the wellpath trajectory lines up to point directly at T9 so the well can be held to hit T9. This type of method is very effective to plan a well with the directional drilling completed top hole to limit costs. Deeper in the well after hitting T8, the well can be drilled with a stiff assembly and held to the final TD.
You can enter a short section before the first target by specifying exit length and build rate on the tangent length line.
The project back feature can be used to achieve similar results. Project back is also used to create soft landings into a target.
Kick Off Point
T9
First Curve section from Kick Off Point to start of Tangent section, DLS = 2.5 deg/100ft
Tangent section from end of first turn to start of second turn
Second Curve section from Tangent section to target T8, DLS = 3.0deg/100ft
Simple hold section to hit second target T9 Plan to hit target T8 with wellpath orientation aligned with target T9.
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To create a locked section between two targets:
1. Use optimum align as previously described to design to the second target (that is, the final target).
2. Project back and select the first target.
Chapter 5: Planning Module
3. Create a soft landing into Target 1 by highlighting the row in the planning grid that contains Target 1, and then project back again.
Enter the Course Length (CL) required and the build rate into the target. Click Calculate.
Hold Tool
The Hold tool is a very useful utility for defining planned kick-off points, or extending the trajectory beyond a target.
Thread Targets
Click the Thread Targets icon ( ) on the Plan Editor to access the Thread Targets dialog box.
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Thread targets plans curved profiles through a series of targets, with a number of plan methods available between each pair of targets. This tool is very useful for quickly generating rough plans through a number of targets to see what magnitude of doglegs are required to plan through them. It is also commonly used to plan wells up-dip, using decreasing TVD targets.
The following graphic depicts the Thread Targets Planning Options:
For each one of the Planning methods, the Thread Targets tool also enables you to select how the targets are sorted. The options are: by increased displacement from the slot origin, descending TVD,
ascending TVD, or by Name. The last option enables targets to be sorted in any order using the order in which the targets were placed in the thread list.
Chapter 5: Planning Module
The following graphic displays the Target Threading sort methods:
The Thread Target window enables you to select which targets you want to thread. The targets displayed are those selected by the
current wellpath.
Desc TVD
Target Sort Methods
Target Thread Methods:
• Curve Only
• Curve-Hold
• Optimum Align
• Straight
The COMPASS software tries to use this dogleg if possible; otherwise, it is incremented automatically until a solution is achieved through all targets.
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To Thread Targets:
For information, see online help.
Nudge
Nudge contains plan methods for horizontal or dipping formation targets. It is also useful for inserting nudge sections into a plan to assist with anticollision.
Simple Projection computes the trajectory to land at a vector at a specified TVD, MD, or dogleg.
1. Enter the required inclination and azimuth.
2. Enter one other parameter from MD, TVD, or DLS. The other parameters in the curve will be computed.
Chapter 5: Planning Module
Project Ahead
Click the Project Ahead icon ( ) to access the Project To dialog box.
Project Ahead is the process of looking forward from the current bit depth to see if the path is heading towards the target. If the wellbore is not on course, Project Ahead can be used to determine the correction necessary to get back on the plan or to go directly to the target. The projection is made from the last observation in the open survey, plus the initial-hold length. Should stations be added to the survey, the projection recalculates from the end of these stations. If anticollision is being used, then the projection will be included in the anticollision scan.The results are for information only, and are not added to the plan.
Select Project to Target, Plan, or Formation to specify the required location, and the COMPASS software computes the trajectory changes using one of the trajectory types. If the current wellbore has a principal plan, the actions required to return to the plan are indicated. This also works for dipping formations.
Select User Defined Projection, Curve Only to specify the projection distance to a MD or TVD as well as the curve rates, and the COMPASS software computes the new location.
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Applied Walk Rates
With noncontrollable rotary BHAs and rock bits, the hole azimuth tends to drift to the right (and sometimes to the left); this is known as “walk.”
After a few wells have been drilled in the area, you should know roughly how much correction or lead azimuth to apply to hit the target. Different amounts of walk are associated with different formations, which can be defined by vertical depth.
If the wellpath is properly led, steering should not be required, because the natural walk tendency brings the wellpath into the target. If walk is not included in the design—that is, if the wellpath is planned as tangent sections between targets—frequent steering could result as the well is corrected to counteract the natural walk tendency.
To apply walk rates to a plan with straight sections defined:
1. By using one of the 2D planning tools for Slant or S-Well, plan to one target that has been created in the Target Editor.
2. Click the Walk icon ( ) in the toolbar.
3. Enter a number of walk rates in the grid, and the TVDs at which you anticipate the drift begins. A positive walk is to the right; a negative walk is to the left.
4. Click OK or press Enter to apply the walk rates. The COMPASS software modifies the well plan by adding new sections at walk horizons and uses the first target in the plan as the walk target. It only applies walk to straight sections. If you modify a walked plan by using another planning method, you will not be able to restore the original unwalked plan.
Enter the TVD of the start of a known walk section. This value may correspond to a formation top, change in lithology, or entry into a geological structure.
Chapter 5: Planning Module