# FREQUENCY AND TYPE OF SURVEYS Reference 1. Standard minimum survey programme for vertical exploration wells:

## PL2. GEOLOGICAL AND DRILLING WELL PROGRAMME

### 5. FREQUENCY AND TYPE OF SURVEYS Reference 1. Standard minimum survey programme for vertical exploration wells:

(Refer to Figure PL 2.3 )

P-1-M-6120 4.7

5.2. Standard minimum survey programme for directional wells:

(Refer to Table PL 2.4)

P-1-M-6120 4.8

6. ANTI-COLLISION Reference

6.1. Objectives

6.1.1. Anti-collision procedures will be implemented, in all cases where is a potential collision risk according to the policies outlined in this manual.

The prime reasons for specifying an anti-collision policy are to:

• Ensure a consistent method is used to evaluate and reduce collision risks between wells.

• Establish a common procedure for developing multi-well sites which takes into account actual well trajectory and trajectories of already existing wells.

• Establish a common procedure that discriminates between interference from completed/producing wells and plugged/abandoned/uncompleted wells.

P-1-M-6120 5.1

6.2. Definitions

6.2.1. Current Well (CW):

The well being planned or drilled.

P-1-M-6120 5.2.5

6.2.2. Target Well (TW):

Any well being considered for anti-collision purposes or proximity calculations.

P-1-M-6120 5.2.5

The ROU is the radius of a sphere, at a specific vertical depth, which has the probability of containing the well-path. It is a cumulative calculation based on the product of the Horizontal Uncertainty Factor of the survey instrument used to that point and the surveyed depth to that point.

P-1-M-6120 5.2.5

6.2.4. Uncertainty Factor (UF):

The UF is a coefficient, given in metres/thousand meters surveyed, that reflects the increase in radius of uncertainty of the well path with depth and depends only on the type of survey instrument and on the hole inclination.

P-1-M-6120 5.2.4

6.2.5. Separation ratio (SR):

• Separation Ratio > 1 = No interference between ROU’s.

• Separation Ratio < 1 = Interference between ROU’s.

SR = CCD/(CW ROU + TW ROU)

P-1-M-6120 5.2.8

6.2.6. Separation Distance (SD):

The SD is the distance, in the plane of the expected closest approach, between ROU of the CW and the TW at a given vertical depth.

SD = CCD -[ROU (CW) + ROW(TW) ]

P-1-M-6120 5.2.7

6.2.7. Centre To Centre Distance (CCD):

The CCD is the distance, in the plane of the expected closest approach, between the centres of CW and TW paths at a given vertical depth.

P-1-M-6120 5.2.8

6.2.8. Curve A - Threshold of separation:

Is the curve that, at any depth represent the condition SR = 1 At any depth define the distance of potential collision.

P-1-M-6120 5.2-F5.2

6.2.9. Curve B - Threshold of alert:

Is the curve where, at any depth, the condition SR = coefficient B.

Usually coefficient. B = 1.5

P-1-M-6120 5.2-F5.2

6.2.10. Curve C - Threshold of danger:

Is the curve where, at any depth, condition SR = coefficient C Usually coefficient. C = 2

P-1-M-6120 5.2-F5.2

6.2.11. Zone X - Field of danger:

The field between Curve C and Curve B

P-1-M-6120 5.2-F5.2

6.2.12. Zone Y - Field of alert:

The field between Curve B and Curve A

P-1-M-6120 5.2-F5.2

6.2.13. Zone Z - Field of Potential Collision:

The field delimited by Curve A

P-1-M-6120 5.2-F5.2

6.3. Proximity calculation

6.3.1. The values of coefficients B and C could be reduced on the basis of a probabilistic analysis of the occurrence of potential well collision situations. The Uncertainty Area Ratio (UAR) concept could be used to evaluate the probability of the occurrence of potential well collision situations. The UAR is the ratio of the sum of the two Uncertainty Area to the sum of the two hole sizes.

### ( )

CWOD = the outside diameter of the current well TWOD = the outside diameter of the target well

P-1-M-6120 5.2.10

6.4. Responsibilities (well planning stage)

6.4.1. The DM will have overall responsibility for the maintenance of safe operations while drilling in proximity to other wells.

P-1-M-6120 5.5.1-a P-1-M-6120 5.2.9

6.5. Planning wells with interference between existing producing/completed wells and new wells

6.5.1. Directional Well Plans in which trajectories fall into zone X is only allowed when the target well (TW) has been properly plugged.

P-1-M-6120 5.5.1-b

6.5.2. The SDE will define any CWs falling within the zone X, during the well planning stage and will prepare necessary recommendation according to the following guideline:

• The TW directional data must be of reliable source and quality.

• Planning the CW, relevant anti-collision analysis are performed.

•••• Proximity calculation and projection are done regularly at the wellsite while drilling the CW in order to confirm the CW position within zone X.

• While drilling within zone X to assure adequate quality and frequency of the surveys, MWD will be used.

P-1-M-6120 5.5.1-c

6.5.3. The SDE will prepare a contingency plan for plugging appropriate TWs.

The contingency plan will specify procedures, timing and responsibilities of other Eni-Agip Division and Affiliates departments in suspending the appropriate TWs and will be included in the well programme for the CW.

P-1-M-6120 5.5.1-d P-1-M-6120 5.5.1-e

6.5.4. Planning directional wells in which trajectories fall into the zone Y are not allowed as a part of normal procedure.

Dispensation will require approval by the DM and must be clearly stated and documented.

P-1-M-6120 5.5.1-f P-1-M-6120 5.5.1-g

6.5.5. Planning and drilling with separation falling in the zone Z is unacceptable under any circumstance.

P-1-M-6120 5.5.1-n

6.6. Planning wells with interference between existing, non completed/plugged & abandoned wells and new wells

P-1-M-6120 5.5.2

6.6.1. Planning new wells within zone Y is allowed when the target well (TW) is a plugged and abandoned, suspended or not completed well.

P-1-M-6120 5.5.1-b

6.6.2. During the well planning stage, the SDE will define any CWs falling within the zone Y and will prepare necessary recommendation according to the following guidelines:

• The TW directional data must be of reliable source and quality.

• Planning the CW, relevant anti-collision analysis is performed.

• Proximity calculation and projection are done regularly at the wellsite while drilling the CW in order to confirm the CW position within zone Y.

• While drilling within zone Y to assure adequate quality and frequency of the surveys, MWD will be used.

P-1-M-6120 5.5.1-d

6.6.3. Planning and drilling with separation falling in the zone Z is unacceptable under any circumstance.

P-1-M-6120 5.5.1-c

6.7. Suspension of wells

6.7.1. Suspension of target wells (TW):

(Refer to Figure PL 2.3 )

P-1-M-6120 5.6 Figure. 5.6

6.7.2. Suspension of current well (CW):

(Refer to Figure PL 2.3 )

P-1-M-6120 5.7 Figure. 5.6

6.8. Projection technique

6.8.1. Additional hole uncertainty due to maximum dogleg potential of the assembly will be added to the ROU of the current well.

P-1-M-6120 5.3.4

6.9. Planning a multi-well site

6.9.1. Reduce potential well collision situations:

• The slot allocations will account for final target displacement and direction. Higher displacement wells will be drilled from the outer slots whenever possible.

• The kick-off points of wells will be spaced vertically depending on final target displacement. Larger displacement wells will be kicked off at shallower depths whenever possible.

• If crossing of trajectories is unavoidable, the tangent section on both wells should be achieved while drilling whenever possible.

• The drilling order of wells will be such that the eventual shut-in time requirement of adjacent wells is kept to a minimum.

P-1-M-6120 5.4

6.9.2. Spacing of wells for the surface vertical phases will not be subjected to SR < 1 limit, in case drilling is planned/performed from a multi-well site where all the surface phases have to be drilled subsequently at once time.

P-1-M-6120 5.4

6.9.3. Antic collision procedures will apply, for the surface vertical phase, in case drilling is planned/performed from a multi-well site where production from adjacent wells is on going or during any production while drilling activity.

P-1-M-6120 5.4

6.10. Well site procedure

6.10.1. Proximity calculations will be done at regular intervals depending on the risk of collision but, at least twice daily while drilling.

P-1-M-6120 5.8-5

6.10.2. Proximity calculations and projections are to be performed on each survey

P-1-M-6120 5.8-8

6.10.3. Unless required for directional control, the use of drilling motors will be avoided while drilling in this situation. If motor use is unavoidable then a low torque motor will be the preferred option

P-1-M-6120 5.8-15

6.10.4. Whenever possible use PDC bits instead of tricone bits P-1-M-6120 5.8-16

7. BHA ANALYSIS Reference

7.1. Bottom hole assembly response

7.1.1. Common holding assemblies. P-1-M-6140 9.4.4

7.1.2. Drop off assemblies. P-1-M-6140 9.4.4

8. REPORTING Reference

Outline

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