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Well planning report for the Molly field exploration well

Technischer Bericht 2011 31 Seiten

Ingenieurwissenschaften - Geotechnik



1.0 Executive Summary

2.0 Introduction

3.0 Assumptions

4.0 Basis of Well Planning and Design
4.1 Drilling Rig Selection
4.2 Pore and Fracture Pressure Gradient Estimation
4.3 Anticipated Drilling Problems / Lithological Characteristics
4.4 Casing Scheme
4.5 Mud Programme
4.6 Cement Programme
4.7 Derrick Capacity
4.8 Well Safety Considerations
4.9 Completion Design
4.10 Well Schematic

5.0 Conclusion

6.0 References

7.0 Appendices

1.0 Executive Summary:

The Kenmac Petroleum Corporation is planning to drill a new vertical exploratory well in their newly licensed Molly field. This report covers the detailed description of tasks that are required to be carried out for well planning.

- The Jack-up rig Trident II is selected. This selection is mainly based on the operability of the rig in the given conditions of the operating area i.e. water depth of the field, required derrick capacity, weather parameters etc.
- The casing scheme is based on the casing diameters those are minimum feasible given the formation evaluation requirements and drilling and production equipment sizes.
- The mud programme is selected after giving due consideration to the various formations to be drilled and the required hydrostatic pressure balance required to maintain the pore pressure of the reservoir.
- Cement design takes in to consideration the presence of “Zechstein” formation which is known mobile/plastic (salt) formation.
- Cased-hole Cemented Completion is proposed.

Overall the well design is to provide the maximum economic value of deliverability, serviceability and functionality for the target reservoir(s) to be penetrated. It meets the need for reliable pressure containment and well integrity over its life.


Molly is newly licensed field located in “Kenmac Petroleum Corporation’s” North Sea Block 14/ab and is planning to drill vertical exploratory well within the “Carboniferous Siltstone” reservoir at 10000ft true vertical depth (TVD), below rotary table (BRT).

In this well drilling programme, following topics are covered in detail:

- selection of appropriate rig,
- estimation of pore and fracture pressure gradients,
- potential drilling problems,
- casing scheme,
- mud program,
- cementing programme,
- design and estimation of derrick capacity,
- well safety
- completion design.

The objectives of this well drilling programme are to:

I. Drill, and complete the well without any safety or environmental incidents
II. Drill each section with one bit shoe to shoe.
III. Achieve good quality cement jobs on each size of casing strings.
IV. Drill the reservoir section without any problems and obtain good quality data.
V. Perforate and complete the well in “Carboniferous siltstone” reservoir with minimal formation damage.


The following general assumptions are made to complete the well planning process. However, some more specific technical assumptions are also required in relevant sections which are stated therein separately:

1. Permits and approvals from the regulatory agencies have been obtained prior to rig arrival on the location.
2. Seabed survey and shallow gas studies are carried out.
3. 30” Conductor casing pre-set at 300m TVD BRT.
4. Average drilling rate over the entire well is 6.25m/hr (20.5ft/hr), including trips.
5. Studies to determine the pore and fracture pressures of the formations are carried out.
6. Corrosive gases such as H2S and CO2 are absent in the reservoir.

4.0 Basis of Well Planning and Design:

The following individual programs are included in the well planning and design of the well to be drilled in the field.

4.1 Drilling Rig Selection:

The drilling rig is selected to suit specific well drilling requirements. Following considerations are taken in to account to select the drilling rig:

- Formation pressures.
- Proposed casing scheme.
- Drill string size and weight(s) to be used.
- Required derrick capacity
- Hydraulic requirements.
- Any auxiliary equipment requirements.

From Transocean’s website the suitable rig to drill this well is Jack-up rig “Trident-II”. Detailed specifications are at Appendix A. Options of using semi-submersible and platform rigs were considered. Ultimately those options were discounted due to semi-submersible will be limited by water depth of the field and an expensive option. Since there are no concrete plans as yet for production from this well, installation of platform will not be there, hence, no platform rig.

4.2 Pore and Fracture Pressure Gradient Estimation:

Pore and fracture pressure estimations play an important role in successful planning and drilling of a well. The impact on well safety and economics can be catastrophic if these two important down hole pressures are not correctly estimated in well planning stage.

The low side prediction is used for consideration of losses and sticking. The expected prediction is used for mud weight determination. The high side prediction is used for selecting casing setting depth, leak-off / limit test requirements, kick tolerance and well control etc.

Pore and fracture pressures can be predicted from the following:

1. Log data or d-exponent data from an offset well.
2. Density logs from offset wells.
3. Using Eaton’s equation.

Table 2 below shows the expected pore and fracture gradients in ppg and psi/ft:

illustration not visible in this excerpt

Table 2 –Molly Field Pressure Profile Plot

The pore and fracture pressure profiles are plotted in following graph acted nd the same plot is also used for estimation of casing setting depths by accounting for trip and kick margins of 0.5ppg respectively.

illustration not visible in this excerpt

4.3 Anticipated Drilling Problems / Lithological Characteristics:

The Molly field lithological column suggests carboniferous sedimentary depositions with each of the layers may pose its own peculiar drilling problems.

Table 3 below lists some of the anticipated drilling problems which can encounter while drilling the well through these formations.

illustration not visible in this excerpt

Table 3 – Anticipated Drilling Problems



ISBN (eBook)
ISBN (Buch)
599 KB
Institution / Hochschule
Robert Gordon University Aberdeen



Titel: Well planning report for the Molly field exploration well