Well Planning

“The careful planning of a directional project prior to the commencement of actual operations is probably the single most important factor of a project”

Drilling a directional well basically involves drilling a hole from one point in space (the surface location) to another point in space (the target) in such a way that the hole can then be used for its intended purpose. To be able to do this we must first define the surface and target locations.

Well Planning

Well Planning Considerations

• Avoiding nearby wells is a major concern

• Depth of kick-off affects the profile

• Shape of trajectory : keep it simple

• Curvature, build-, drop-, turn rates should be at minimum

• Length and inclination of tangent section(s)

• Target intersection details

• Length and inclination of horizontal section

Well PlanningBasic Data

• Application Type

• Hole and Casing Sizes

• Casing Points

• Reservoir Conditions

• Well Profile (completion needs)

• Target Constraints

• Mud Data

• Surveying Requirements

Well PlanningSteps in Designing a Well Profile

• Selection of KOP depth

• Selection of BUR (or limits)

• Selection of tangent section(s) angle for …– Horizontal displacement– TVD uncertainty – adjustment– Directional performance uncertainty– Completion requirements

• Selection of 2nd BUR (if any)

• Considering the length of the lateral hole (if any)– Reservoir constraints– Torque and drag limitations– Hydraulic requirements and limitations (ECD, SPP)

Well Planning

Selection of Kick off Depth

• Consider at planned kick-off depth :– Formation properties (possible washouts)– Inclination and direction (use of gyro or single shot, MWD)– Directional assembly performance (bit selection, BUR)

• If cased hole sidetrack, the options are (casing survey, CBL, CCL are needed) :– Section milling– Whipstock + window milling

• Open hole sidetrack / kick-off :– Distance from casing shoe is important (rathole, magn. interference)– Cement plug might be necessary– Open hole whipstock is optional

Well Planning

Minimum Build up Rates

• Minimum BUR is defined by a circular arc from the KOP to the target entry point

• Minimum 15° inclination in the tangent section for stable direction

Well Planning

Maximum Build up Rates

• Casing / liner running should be possible

• Casing /liner bending stress must remain within pipe strength limits

• Mechanical loads imposed on drillstring elements (torque, drag, fatigue) or casing (wear, tensile strength reduction due to bending stress in doglegs)

• Rig power limits

• Max curvature for surveying and logging tools

• Completion requirements

• Risk of casing wear or keyseat in open hole

Well Planning

Well Profile Selection

• Selection is based on– Vertical depth between intended KOP and target– Horizontal displacement to target entry point– Completion design– Formation evaluation program– Hole size in reservoir

• Profile must provide tangent section(s) for– Completion equipment (packer, beam pump, ESP)– Adjustments if directional drilling difficulties arise

Well Planning

Why Large Direction Changes are Undesirable ?

• With increasing inclination it drastically increases the DLS

• Increases the torque and drag

• Increases the time when directional work is required

• Reduces the angle building capability of a given directional tool

Well Planning

Hole Inclination Ranges

Near vertical 0 - 10°

Low 10 - 30°

Intermediate 30 - 60°

High 60° <

Well Planning

Critical Angle for Hole Cleaning

• Critical range for hole cleaning can not be avoided, but it must be as short as possible

• Avoid planning a tangent section within the critical angle range

45 ° - 65°

Well Planning

Limitations

• Formation drillability

• Borehole stability

• Steerability, flexibility of drillstring

• Drillpipe strength

• Hole cleaning, cutting transport problems

• Standpipe / pump pressure, ECD

• Rig capacity (hook load, rotary torque, pumps, shakers)

Well Planning

Limitations

• Length of horizontal – reservoir engineering requirements– Well placement problems– ECD limits the length– Limitations due to drillstring strength

• Profile of the lateral hole – straight, curved or wavy trajectory

• Casing or liner to be run – buckling and lockup might be a problem

• Hole size selection – different bit sizes for the build and the lateral

• Drilling torque and overpull margin available

Well Planning

• Surface Location• Target Location• Target Considerations• Geological Considerations• Completion and Production• Drilling Considerations• Well Design• Nearby Wells

1. Well Plan Inputs

Well Planning

• Surface Location

Land LocationsPlanning a directional well assumes some limiting factors in the positioning of the surface location. With land wells, the surface location of the well will usually be determined by the factors originally prompting the decision to drill a deviated (as opposed to a vertical) well.

Offshore LocationsThe main difference between positioning a surface location on land and offshore is thenumber and proximity of wellbores. Many factors which directly affect installations including water depth, bottom slope, sandy bottom versus coral reef, local currents, etc.

1. Well Plan Inputs

Well Planning

• Target Location

The first step in planning any well is, of course, to define the objectives. A directional well can have one or more objectives. The most obvious of the objectives is the target. These can be geological structures, geological features such as faults or pinch-outs, other wellbores (as in relief well drilling) or a combination of these.

1. Well Plan Inputs

Well Planning

• Target Considerations

During the drilling phase of a directional well, the trajectory of the wellbore in relation to the target is constantly monitored. The technology available today allows us to drill extremely accurate wells. The cost of drilling the well is largely dependent on the accuracy required, so the acceptable limits of the target must be well-defined before the well is commenced.

1. Well Plan Inputs

Well Planning

• Target Location

When planning and drilling a well, it is simpler to use partial coordinates when referring to the target. This involves using the surface location as a reference point (surface reference point) and attributing this point with the value 0,0. All other coordinates can then be referred back to this point, thus simplifying calculation and plotting procedures. The Surface Reference Point (SRP) is usually the rotary kelly bushing, the wellhead or the platform reference point. Once the exact location of the surface reference point and the target are known, the partial coordinates can easily be determined. Normally, these are either rectangular or polar.

1. Well Plan Inputs

Well Planning

• Geological Considerations

Interaction with the geologists is of prime importance to understand any limitations in the particular zone of interest.

•Lithology being drilled through (sand, shales, sloughing tendencies, coals, salt, medium hard formations with hard or soft stringers, marker zones)

•Location of water or gas top

•Level of geological control

•Type of target the geologist is expecting (channel sand, pinnacle reef, a seismic irregularity, exploration or infill drill)

1. Well Plan Inputs

Well Planning

• Geological Considerations (Cont)

•Geological structures that will be drilled through or into (dip, faults, unconsolidated shales)

•Regulatory issues (oil or gas target boundaries, wellbore clearance from existing wells, location of final total depth)

•Type of Well (Oil or Gas)

•Future sidetrack or re-entry potentials

1. Well Plan Inputs

Well Planning

• Completion and Production Considerations

This group is often missed and may result in a costly error if their needs are not considered in the planning phase. They usually share some of the planning responsibility with the geology department.

• Location of surface facilities or ability to move existing when infill drilling on an existing pad • Type of completion required (frac, pump rods) • May specify maximum inclination and dogleg limits based upon log and production requirements • Enhanced recovery completion requirements • Wellbore positioning requirements for future drainage/production plans • Downhole temperature and pressure

1. Well Plan Inputs

Well Planning

• Drilling Considerations

This group usually has control over the main operation and tries to pull all parties together. The overall cost estimation and economic feasibility may also rest in their hands. Consequently, the directional representative usually spends most of their time consulting with the members in this group. Even though the other groups have just as important information, the drilling group typically controls how the well is drilled and will make the final decision on any operational issues that occur.

• Selection of surface location and well centre(s) layout • Casing size and depths • Hole size • Required drilling fluid • Drilling rig equipment and capability • Length of time directional services are utilized • Influences the type of survey equipment and wellpath • Previous area drilling knowledge and identifies particular problematic areas

1. Well Plan Inputs

Well Planning

• Well Design

Knowing the position of the surface location and given the location of the Target, its TVD and rectangular coordinates, it is possible to determine the best geometric well profile from surface to the bottom-hole target. In general, Directional wells can be either:

· Straight· Slant type· “S" type· Horizontal

The type of profile selected will depend upon the Geological objective and production mechanism of the well. Once the profile has been selected, the well can be planned.

1. Well Plan Inputs

Well Planning

Determining the Kick-off Point

The Kick-off point is defined as a point in the wellbore at a given vertical depth below the surface location where the well will be deviated away from vertical in a given direction up to a given inclination at a given build rate. The selection of the Kick-off point is made by considering the geometrical well-path and the geological characteristics. The optimum inclination of the well is a function of the maximum permissible build rate (and drop rate if applicable) and the location of the target.

• Well Design

1. Well Plan Inputs

Well Planning

Determining Build and Drop Rates

The maximum permissible build/drop rate is normally determined by one or more of thefollowing:

· The total depth of the well.· Maximum Torque and Drag limitations.· The formations through which the build section must pass. · Mechanical limitations of the drill string or casing.· Mechanical limitations of logging tools and production strings.· Formation of “Keyseats" in the Kick-off arc.

Once the desired build rate and inclination have been established, the kick-off point canbe determined.

• Well Design

1. Well Plan Inputs

Well Planning

Calculating the Trajectory

Type 1 Well (Build and Hold)

Given:

· Wellhead coordinates· Target coordinates· Target TVD, V3

• Well Design

1. Well Plan Inputs

Well Planning

Calculating the Trajectory

Type 1 Well (Build and Hold)

To determine:· KOP vertical depth, V1· Build up rate, BUR· KOP Kick-off point.· V1 TVD of straight section/surface to KOP.· V2 TVD of end of build up. V2 - V1 TVD of Build up section with BUR corresponding to radius of curvature R.· V3 - V2 TVD of Tangent section to total depth.· D1 Displacement at end of build up.· D2 Total horizontal displacement of target.· θ Maximum inclination of well.

• Well Design

1. Well Plan Inputs

Well Planning

Calculating the Trajectory

Type 2 Well (S Type, Build, Hold, and Drop)

Given:

· Wellhead coordinates· Target coordinates· Target TVD, V5

• Well Design

1. Well Plan Inputs

Well Planning

• Well Design

1. Well Plan Inputs

Well Planning

2. Well Plan Outputs

• Well Profile• BHA´s Design• Drill Bits Selection• Hydraulics • Torque & Drag• Anticollision Issues