Aticollision Schlumberger

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Drilling Of fice X (DOX) Technical Manual / Manual / Anti-Collision

6

Anti-Collision This section contains the following topics: 6.1: Introductio Introduction n 6.2: Anti-Collision Analysis Analysis 6.4: Drill Ahead Rules and Alert Zone 6.5: Graphical Outputs Outputs 6.6: Repo Reports rts rence 6.8: Refe Reference

Private Copyright © 2012 Schlumberger, Unpublished Work. All rights reserved. Copyright

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6.1

166

Introduction Collision with neighboring wells must be avoided, especially when adjacent wells are producing. Any unplanned well to well collision is a D&M Zero Tolerance rule. To protect safety of people at the rig site and the environment, every well design and execution follows the Anti-Collision analysis performed in Drilling Of fice software. The results of these computations shall be included into Well Design File (WDF) and a nd rigorously checked during the well design process. To ensure a good understanding of the wellbore objectives and Anti-Collision concerns at the planning phase, it is important for Directional Driller to participate in pre-job meeting. pre-job meeting. While drilling the Directional Driller must follow Anti-Collision monitoring plan and report any issues before the violation takes place. Anti-Collision planning begins with accurate surveys of the position of the subject well and all existing wells in the vicinity, as well as a complete set of proposed well plans for the vicinity. vicinity. The surveys and well plans are used to carefully map the relationship of the proposed new well to all existing wells and any proposed future wells. Drilling Of fice performs an Anti-Collision proximity analysis of a proposed/planned well (subject well) against the surrounding (offset) well(s). In addition to the proximity analysis, Drilling Of fice allows the user to output output proximity maps and reports.




6.2

167

Anti-Collision Analysis Anti-Collision analysis consists of the following three steps: Step 1 – Definitive database database Anti-Collision planning begins from collection of the de finitive directional database, that represents the most accurate and current description of all well paths paths within within the working working area. In addition addition to de finitive directional surveys, Anti-Collision Anti-Collision analysis also has consideration for future well plans and still empty slots. That is why the Drilling Of fice allows to perform Anti-Collision analysis against proposed future well plans along with the existing offset surveys. Based on the proximity calculations, the engineer prepares the Anti-Collision reports and plots that are used to analyze collision risks.

Note Drilling Of fice flags the close approach situation for the wells that contain surveys within the database only. Anti-Collision analysis is not complete if any of the existing wellbores contain incorrect, incomplete or missing surveys. This is because according to D&M wellbore surveying and Anti-Collision standard, the Directional Driller has a special responsibility to ensure the count of the well in vicinity matches the Drilling Of fice well count.

Figure Figure 6-1: Drilling Drilling Of fice Anti-Collision calculations

Drilling Of fice differentiates between de finitive and non-de finitive surveys. While many surveys might be available in the same borehole (e.g. MWD and Gyro), only one survey is selected to describe the wellbore pro file. More accurate one is usually selected as de finitive. Non-de finitive surveys usually are not used for Anti-Collision analysis. To account for ongoing operations, the Drilling Of fice differentiate between Final De finitive and Working De finitive surveys - a final definitive survey is the most accurate description of the entire well path, while the "working" de finitive surveys are the most accurate description of the well path to the present TD position. Step 2 – Perform Global Scan




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Global Global scan is the initial initial scan made to search the entire database. database. During During the global scan sca n the Drilling Of fice identifies the wells that can be reached considering the technologies technologies of the current days. days. That way the Drilling Of fice filters out the wells that are impossible to collide with. Global scan is performed at the surface location; subsurface survey data is not used during this step. The area of 12,500m + MDs* radius is selected around the subject well. All the wells within this area are called “nearby”. All the rest wells a classi fied as single. Only nearby wells are wells are participated in the next step of Anti-Collision calculations.

Figure 6-2: Global Scan. The DOX Scan radius is automaticall automatically y set to [12,500 m + measured depth of the subject well]

The dummy survey created for all empty slots during the previous step (De finitive Database) and future well plans can also be identi fied as nearby if their surface location fall into selected area. Particular care needs to be taken that all recently completed or still drilled wells are updated with the latest Directional Data and included into Anti-Collision analysis. analysis. The nature of the global scan makes makes it imperative that field data is stored in the logical order in the database projects. Nearby wells that have been stored in different database projects cannot be scanned against each other. Step 3 – Proximity Calculations

A proximity scan must be performed on all wells that have been identi fied as nearby. At this step, the subsurface offset directional data is used to calculate the distance between subject and each nearby well, called center-to-center distance. There is a number of ways to calculate the center-to-center distance; however, not all of them are accepted for use in Anti-Collision calculations. The Drilling Of fice uses two methods to calculate proximity to the offset well: • Normal Normal Plane Plane method method • 3D Least Least Distance Distance Method Method

Figure 6-3: 3D Least Distance Distance and Normal plane



Drilling Of fice X (DOX) Technical Manual / Anti-Collision

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The center-to-center is used to analyze the risks during an Anti-Collision analysis. Dif ferent directional companies and some operators have come to different conditions that would dictate stop the job point, a point where the risks of collision are considered signi ficant to stop drilling, assess the risks and make a new plan of actions that would allow to drill a well safe for the rig personnel and the environment. These conditions are usually referred to as “Rules”. Schlumberger Drill Ahead rules are covered in the following topics and based on D&M Wellbore Surveying and Anti-Collision Standard 002.

Private Copyright © 2012 Schlumberger, Unpublished Work. All rights reserved.



6.2.1

170

Normal Plane Method The normal plane method of computation calculates the close approach by stepping down each offset trajectory at the user-speci fied depth intervals. A measured depth (MD) interval is recommended for the normal plane analysis method because in horizontal wells, a true vertical depth (TVD) interval may have several positions within the offset trajectory, creating discontinuous results. The stepping is performed down the offset trajectory to ensure that the proximity of the entire offset trajectory is analyzed, and to ensure proper analysis of perpendicularly approaching wellbores. At each step (interval) down the offset trajectory, this method scans the subject trajectory to determine where a plane normal to the subject trajectory intersects the offset trajectory at the interval point. This scanning method can result in multiple planes that are all normal to the subject trajectory and all intersect the offset trajectory at the same point. Multiple solutions usually only occur in extremely tortuous well paths but are not limited to this type of trajectory. The minimum (least) distance of all will be reported by the Drilling Of fice as center-to-center distance for a given scan point. The proximity line, lying in the normal plane and connecting the intersection points of the subject trajectory and the offset trajectory, de fines the center-to-center (ct-ct) distance between the trajectories. The azimuth of the proximity line will reference either north or the high side of the well. If a north reference is used, the azimuth is computed as the angle between the proximity line (which lies on the normal plane) and the projection of north onto the normal plane. If high side is used, the azimuth is computed as the angle between the proximity line and the projection of high side onto the normal plane at that point in the subject trajectory (see Figure 6-4).




Figure 6-4: Azimuth proximity

Note The normal plane proximity analysis method is the only method that provides undistorted close approach results on a travelling cylinder diagram (referenced to the subject well) for all possible well pro file geometries.


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6.2.2

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Horizontal Plane Method The horizontal plane method steps down the subject trajectory at the user-speci fied depth interval. A true vertical depth (TVD) interval is recommended for the horizontal plane analysis method because in highly deviated wells (with inclinations at or exceeding 90° inclination) it is possible to have multiple penetrations with the horizontal plane and multiple distances from the same point in the subject trajectory. Multiple penetrations are also possible within the subject trajectory. A measured depth interval can also be selected for this analysis, in which case the corresponding TVD at that MD in the subject trajectory is used as the depth of interest. A measured depth interval analysis is subject to the same defects as the TVD interval but, in some instances, can provide smoother results (due to a consistent interval). However, a given TVD interval in a highly deviated well can result in rapidly changing proximity distances. If no depth interval is selected, Anti-Collision Analysis will calculate the proximity at each survey or planning station in the subject trajectory. At each step down the subject trajectory, the horizontal line that intersects the subject trajectory and the offset trajectory defines the ct-ct distance between the trajectories. In the horizontal plane analysis, the azimuth of the proximity line can reference either north or the high side of the well. If the north reference is used, the azimuth is a true north referenced azimuth. If high side is used, the azimuth is computed as the angle between the proximity line and the projection of high side onto the horizontal plane.

Note Horizontal plane method is NOT to be used as an Anti-Collision Analysis tool.




6.2.3

Strengths and Weaknesses of the Scanning Methods Below, compare two methods used by the Drilling Of fice to define the Center-to-center distance:

Figure 6-5: 3D Least Distance scanning method


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Figure 6-6: Normal Plane scanning method

Both, 3D Least Distance and Normal Plane methods suffer from different but distinct weaknesses, and therefore, both methods must be used during the Anti-Collision scanning process to investigate the potential of collision. As a result, today the Normal Plane method is used to produce the Traveling Cylinder plot (discussed later) for graphical visualization of the no-go areas that the bit shall not cross, while 3D least distance is used to monitor the Anti-Collision working with the numerical results. The visualization of the Anti-Collision situation using 3D Least Distance method might distort the scale, and that is why is not used. Below is the summary of strengths and weaknesses for each scanning method:




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Table 6-1: Normal Plane

Strengths

Weaknesses

Travelling cylinder plots are undistorted and depict the true 3-D relative position of surrounding wells; these plots are especially useful for forward projections. Scanning down the offset survey ensures that no portion of the offset well is missed. This ability is especially important for detecting close approaches between wells oriented perpendicularly.

Will not detect a close well that is passing just beyond the end of the subject wellbore.

Table 6-2: Horizontal Plane

Strengths

Useful for determining relative positions of formation penetrations that are essentially fl at.

Weaknesses Limited use as an anticollision tool with high-angle, designer wells. A spider plot provides more information for anticollision, while depicting a horizontal perspective. Extremely distorted travelling cylinder plots.

Table 6-3: 3-D Least Distance Strengths Provides the true closest distance between wellbores for a given position, which is useful in additional applications (well injection/ fluid flow analysis). Anticollision uses are for blowout intersection for well killing procedures and for active magnetic ranging anticollision procedures.

Weaknesses

Distorted travelling cylinder plots.

Example #1: In this example, the subject and offset wells are within 120ft away at the Subject well TD. While Normal plane does not show any indication of close approach situation, the 3D least distance method does. Compare results for both scanning methods below:




Figure 6-7: Offset Well Analysis using 3D Least Method

Figure 6-8: Offset Well Analysis using Plane Method


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6.3

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Scan Method The Anti-Collision analysis provides the following three standard methods for computing separation distances between the subject well and the offset well(s): • 3-D least distance • Normal plane • Horizontal plane The following illustration is provided to assist in understanding the three standard methods of computing separation distances (see Figure 6-9).

Figure 6-9: Three methods of computing separation distances




6.3.1

178

3-D Least Distance Method The 3-D least distance analysis method calculates the nearest distance to each offset well by stepping down the subject trajectory at user-speci fied depth intervals. A measured depth interval is recommended for this method because in horizontal wells, a true vertical depth (TVD) interval may have several positions within the subject trajectory, creating discontinuous results. Once the depth interval is selected, at each step (interval) down the subject trajectory, this method scans the offset trajectory to determine a plane that is perpendicular/normal to the offset trajectory and intersects the subject trajectory at the interval point. Perpendicular to this plane is a tangent point of a spherical radius, centered on the interval point in the subject trajectory. Mathematically, this distance is the shortest (least) distance between the subject trajectory and the offset trajectory. This process can be visualized as if, at each interval point, it computes the radius of a sphere centered on the subject trajectory that just touches the offset trajectory (see Figure 6-10), and defines the center-to-center (ct-ct) distance between the trajectories.




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Figure 6-10: 3-D least distance method of scanning

The scanning can result in multiple planes all normal to the offset trajectory, while intersecting the subject trajectory at the same point. In this case, DOX will report the minimum (least) as a center-to-center distance, as shown in below example.




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Also considered as a possible solution among the multiple solutions are the end-points of the offset trajectory - surface location and well total depth (TD). These points are considered solutions even though the end points may not necessarily fit the de finition of a plane normal to the offset trajectory. The proximity line connects the center of the sphere to the tangent point. The azimuth of the proximity line can reference either north or high side. If the north reference is used, the azimuth is computed as the angle between the proximity line and the projection of north onto the normal plane of the subject trajectory. If high side is used, the azimuth is computed as the angle between the proximity line and the projection of high side onto the normal plane of the subject trajectory.




6.4

181

Drill Ahead Rules and Alert Zone Schlumberger D&M Anti-Collision Standard follows Drill Ahead Rules as below. Each of them applies to the planned and drilled well trajectories at all times. • Rule 1: Surface rule • Rule 2: OSF (Oriented Separation Factor) rule To avoid hitting other wells, we apply a minimum allowable separation (MAS) from offset wells for the well path in both rules with the largest MAS value being dominant. At or near surface, OSF values are unrealistically high, because the EOUs are very small. The Surface Rule has been implemented to impose a minimum separation between wells until the OSF Rule MAS value becomes dominant. The MAS is applied along the offset well and de fines the edge of No-Go Zone as well. If the trajectory or any of the projection indicates center to center distance is less than MAS, an exemption must be raised. The Drill Ahead rules are based on minimum allowable separation (MAS) that must be maintained between subject and the offset well. The calculation of MAS depends on the service provider or operator and usually programmed into the directional software. Schlumberger Drilling Of fice contains a number of pre-defined sets of rules, including some that were developed by the clients. If client requires their Anti-Collision rules are used, they will be applied along with the Drill Ahead rules used by Schlumberger; the more conservative of the two will apply. The set of Anti-Collision rules is manually selected in Drilling Of fice by the Drilling Engineer (see below). If no Drill Ahead rules were selected, the Anti-Collision computation will not be possible.

Figure 6-11: Proximity calculations require a set of Drill Ahead rules selected. Ensure the correct revision of Drill Ahead rules is used

D&M Anti-Collision Standard S002 de fines two rules for MAS calculation: Rule #1 – Surface Rule and Rule #2 – OSF Rule. Both rules are applied at all times, with largest MAs being dominant. Two rules have been used due limitation of




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the OSF near the surface when the EOUs are very small. The Surface Rule has been implemented to impose a minimum separation between wells until the OSF MAS becomes dominant. While drilling the deviations from the plan are possible, the Anti-Collision analysis identifies the area (drilling tunnel) where the chances of collision are low. The Drilling Of fice calculates the distance, called allowable deviation from the plan (ADP) that represents a safe zone of deviations in the direction to the offset well.

ADP = CtCt − MAS where CtCt is a center-to-center distance. Negative or zero ADP means a violation of the Anti-Collision rules. The results of MAS calculation may vary depending on the proximity scan method:

Figure 6-12: Anti-Collision calculations using 3D least distance method

Figure 6-13: Anti-Collision calculations using Normal Plane method




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Where the Anti-Collision analysis indicates a violation of the drill-ahead conditions, the well trajectory must be redesigned and additional analysis performed. If no other design options are reasonably available, an expert approver may approve an exemption, depending on speci fic circumstances and the risk assessment. Please refer to D&M Anti-Collision Standard 002 and D&M Appendix to SLB-QHSE-S010 Management of Change and Exemption Standard for more details.




6.4.1

Surface Rule Surface Rule stipulates a single distance value that represents the Minimum Allowable Separation (MAS) between two wells. MAS for Surface Rule is always calculated at Well Reference Point (WRP) which is located at the trajectory position at its point of ground penetration. This will be ground-level (GL) or mud-line (ML) as appropriate.


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6.4.1.1

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MAS Definition Based on Surface Rule The surface rule applies to all offset wells and allows drilling tunnel or ADP equal 20% of the well-to-well clearance. The surface rule MAs is capped at 10 meters. For all offset wells with a MAS@WRP > 10 m, a maximum MAS value of 10 m is to be used (see Figure 6-14).

Figure 6-14: MAS calculated from a subject well (grey)

Mathematically it can be represented through the following equations:

ADP = 0.2 × CtCtWRP − (R1 + R 2 

)

where

1 = largest hole radius of the offset well

2 = subject well radius




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CtCt WRP = center-to-center distance at the well reference point

Figure 6-15: Surface MAS

In this case, the following is true:

MAS = CtCtWRP − 0.2 × [CtCtWRP − (R1 + R 2)] = 0.8 × CtCtWRP + 0.2 × ( R1 + R2) This makes sure there is always separation between offset and subject wells. The effect is that the offset wells within 10 m of the subject well have a no drill zone / No-Go Zone of 80% of the initial clearance @WRP (see Figure 6-16). Thus, ADP = ct-to-ct – MAS ADP is short for Allowable Deviation from Plan. The MAS is individually calculated for each offset well. (For example, if there are 12 offset wells on a platform within 10 m ct-ct of the subject well, there will be 12 individual MAS values calculated.)




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Figure 6-16: Clearance @WRP and No-Go Zone based on Surface Rule

Below is the example of calculations performed by Drilling Of fice:

Figure 6-17: Example of the Drilling Of fice output

Well 1:

For 30” holes and CtCt

= 17.30(ft ) , MAS is calculated by the following way:

(

)

MAS = 0.8 × CtCtWRP + 0.2 × R1 + R 2 = 0.8 × 17.3′ + 0.2 × MAS = 13.84 + 0.2 *

15 + 15 12

()

= 13.84 + 0.5 = 14.34 ft

Compare this result to the results in Figure 6-15 above.


(

30" 2

+

30" 2

)



188

Well 2:

For the holes radius, by the following way:

1

= R 2 = 30 " and CtCt = 79.29 ,′ MAS is calculated

(

)

MAS = 0.8 × CtCtWRP + 0.2 × R1 + R 2 = 0.8 × 79.29 ′ + 0.2 × MAS = 63.43 + 0.2 *

15 + 15 12

(

30" 2

+

()

= 63.43 + 0.5 = 63.93 ft

Due to capped surface rule MAS, the final MAS for the Well 2 equals to 10 meters or 32.81 feet. From above, it is clear that MAS is calculated separately for each of the offset wells. Calculated at the surface, Surface MAS of the same value is applied to sub-surface depths (see Figure 6-15) until OSF rule becomes dominant.


30" 2

)



6.4.2

189

OSF (Oriented Separation Factor) Rule The OSF rule uses a probabilistic approach for Anti-Collision analysis. Historically, the industry came to a number of different calculations that were based on the ratio between well-to-well clearance and the cumulative uncertainty between two wells:

Separation _ Factor =

Clearance Cumulative _Uncertaint y

For example, traditional separation factor (often SF) used the semi-major axes of two borehole EOUs to calculate the cumulative uncertainty:

SF =

Clearance

Semi _ Maj orwell1 + Semi_ Maj orwell 2

Unfortunately, this method of calculation did not provide the same probability of collision for the same separation factor used. Compare scenario below. On the right, we turned one of the EOU semi-major axis by 90º to be positioned away from us. Note the difference in EOU separation; the greater it is-the less chances of collision.

Figure 6-18: The probability of collision based on the same traditional separation factor may vary

To analyze the risks of a collision, Schlumberger uses an Oriented Separation Factor (OSF). Regardless, of situations, provided the same OSF, it guarantees the same probability of a collision. Instead of geometrical sum of EOUs, the OSF uses relative positional uncertainty between subject and the offset well:

OSF =

Clearance

Re lative_ Positional_Uncertainty




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While it is often believed that RELATIVE positional uncertainty above is a geometrical sun of two EOUs along the probability line, this is not true. OSF is a probabilistic analysis. De fining the boundaries of relative positional uncertainty, the calculation does not deal with the sizes of two ellipsoids of uncertainty. The Anti-Collision is concerned with the possible position of the subject and offset well RELATIVE to each other; that is why ABSOLUTE uncertainties are not used for Anti-Collision analysis. To comply with Wellbore Surveying and Anti-Collision Standard, Relative Positional Uncertainty in Drilling Of fice is calculated using 95% of con fidence level and 3D. These setting are default as long as set of latest Schlumberger drill ahead rules was selected. The boundary of the drill ahead rules are selected based on OSF=1.5 To comply with the standard, all offset wells must satisfy OSF greater, but not equal, a value of 1.5 at all analysis points. The MAS for OSF rule can further be calculated as follows:

OSF = 1.5 =

MAS − (R1 + R 2) Re lative_Positional_Uncertaint y

or

MAS = 1.5 × Relative_Uncertainty + (R 1 + R 2) where as previously well radius

1 = largest hole radius of the offset well ,

2 = subject

Since relative positional uncertainty is not a constant value, OSF based MAS also varies and represent an area that must not be entered unless approved during exemption process.




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Figure 6-19: Along red NO-GO line the OSF=1.5

Alert System

To warn the Directional Driller about the approaching risks, Drilling Of fice was built using an Alert system. Any well that entered Alert zone must be monitored while drilling. The Drill Ahead rules consist of Surface and OSF rules; both are implemented at all times, however only one is dominant. The dominating “Controlling rule” will define the “Alert Status” in Anti-Collision Analysis (shown in red below). Table Drill Ahead Rules are shown in red:

For example, if the Surface rule is dominant and MAS=8m, the drilling must cease before center-to-center distance ahead of the bit equals 8m.




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If the OSF rules is dominant and MAS = 25m for OSF=1.5, the drilling must cease before center-to-center distance ahead of the bit becomes equal 25m. However, if you were to monitor Anti-Collision based on MAS computations using DD Toolbox, you would find that MAS value, unlike Surface rule, would change from station to station. Instead, it is easier to monitor a threshold that is a constant value, like OSF=1.5. MAS and ADP for OSF rule is monitored graphically by use of TC plot.

The Anti-Collision monitoring plan is always tied to alert status: Under ALERT condition a details Anti-Collision report must be analyzed and included in the well design fi le (WDF). Traveling cylinder plot shall be used at the appropriate scale to identify the wells that are at the risk of the collision. A MINOR risk well is an offset well where the 1



operations. The well must be re-designed to attain a minor risk status. The exemption process must be repeated again and approval received before allowing a bit to cross that boundary.


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6.4.3

The Drill ahead Rules The Surface Rule and OSF rule each apply a MAS for the well path. Surface Rule MAS is based on geometrical clearance between two wells. OSF Rule MAS is based on separation with relative positional uncertainty between two wells (see Figure 6-20).

Figure 6-20: Surface Rule MAS (Grey) and OSF Rule MAS(Red)


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At or near surface, OSF Rule is not suitable, as EOU sizes are very small. However, the most common well collision problems are found at surface. That is where Surface Rule is often dominant (see Figure 6-21).

Figure 6-21: Surface Rule is dominant

If the wellbore trajectory fails either the Surface or OSF Rules by entering the No-Go zone created by surface rule or OSF >1.5 rule is not allowed without an approved exemption. Drilling MUST STOP (see Figure 6-22).This is applied to the calculation at the survey point, projection to the bit and minimum 60m (180 ft) projection ahead.

Figur e 6-22: Violation of Drill ahead Rule MUST STOP




6.5

Graphical Outputs There are two types of graphical outputs from Anti-Collision Analysis results: • Traveling cylinder plot • Spider plot


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6.5.1

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Traveling Cylinder Plot Traveling cylinder plot is not unique to Schlumberger and used for Anti-Collision purposes by the oil industry since 1968. The main advantage of the traveling cylinder plot is its ability to clearly and accurately display drilling tolerances or “drilling tunnel”. Drilling Of fice Traveling Cylinder is produced using Normal plane scanning method. The azimuth of the proximity line on the traveling cylinder plot are referenced to the north. It is computed as an angle between proximity line and north direction projected onto normal plane.




198

All depths that appear on the traveling cylinder plot are the measured Depths of the PLANNED trajectory. While drilling, the real trajectory is plotted relative to the plan. The proximity to the offset wells is monitored by comparing the position of the projections against the NO-GO zones. The NO-GO circles are plotted for a particular depth around offset trajectories with the radius equal MAS that was calculated using Normal Plane method. That is why NO-GO circles for traveling cylinder are based on either Surface or OSF rule, whichever dominates at that point. The area between the center of the traveling cylinder plot and the NO-GO circle is a drilling tunnel or ADP . The tolerance lines can be drawn connecting the NO-GO circle edges for the same depths to form a NO-GO envelope. Refer to Anti-Collision Procedures for more information on traveling cylinder plot and tolerance lines.





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6.5.2

200

Spider Plot The spider plot is a horizontal projection that shows wells in a given area as if the earth were transparent (see ). The well paths can be shown with TVD depth markers, indicating the TVD depth at a particular location. The spider plot depicts the true relationship of wellbores to each other.

Figure 6-23: Spider Plot

Note Intersection of two wells is not necessarily the closest point.




201

The spider plot can be con figured to show both the surveys and the slot positions in a zoomed view (see Figure 6-24)

Figure 6-24: Surveys and slot positions on spider plot




6.6

202

Reports There are two numerical types of the Anti-Collision report produced using Drilling Of fice. Both of them can be produced using 3D least or Normal Plane scanning method: • AC Summary reports • AC Detailed reports The graphical visualization of the “drilling tunnel’ is available using travelling cylinder plot. The Drilling Of fice produces North referenced traveling cylinder plot that is based on the Normal Plan scan method. It is primary tool for monitoring Anti-Collision at the rig site. AC Summary Report

The Anti-Collision summary report is performed for every well and is a part of the well design fi le. It contains the depths of the subject well where the any of the alert lines is crossed as well as risk (status) associated with each offset well. This report is used to reduce the number of wells to be examined if the alert status was bridged. Refer to Appendix A for example of the AC summary report. AC Detailed Report

The detailed Anti-Collision report is required for any offset well , which was reported under ALERT during summary scan. The detailed report can be customized to include additional fields to aid the Anti-Collision analysis (e.g. MAS, ADP, Controlling Rule, Status). It contains a description of the offset survey including depths of the subject and the offset wells where the alert boundaries were crossed, the survey programs used for Anti-Collision analysis, Anti-Collision rules and corresponding alerts used. Refer to Appendix B for example of the AC details report.




6.7

Appendix Appendix B- Example of the Detailed Anti-Collision report


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Appendix B- Example of the Detailed Anti-Collision report


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Aticollision Schlumberger

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