The sub-surface department  is the budget holder and customer. The drilling requirements may be a prospective area or a contractual requirement to drill one or more wells under an exploration contract. There may also be a time constraint dictated by relinquishment provisions.

It is most important that a good working relationship exists between Operations and Exploration. Drilling requirements should be balanced against resources and commitments. Day-to-day contacts and regular meetings should be held. Location/ reporting structure of the exploration staff needs to be addressed at an early stage.

1 Well proposal

The well proposal is presented to partners and government agencies for approval. It is only on the basis of an approved proposal that the drilling programme can be finalised.

It will summarize the geological prognosis, evaluation requirements, trajectory and casing scheme plus other relevant data.

On the Drilling Engineering side the agreed summary should contain all the data required to design the well, including prognosticated depths of formation tops (with estimated accuracy), a definition of which formations are principal targets and which are secondary, and a realistic tolerance to reach the targets.

2 Well planning information

Well planning must begin before the well proposal is finalised. It is essential that all the relevant data are centralised and approved. For this purpose it is recommended to use the “well planning information sheet”.

The exploration and Drilling Managers will sign to indicate their technical concurrence. Changes should be documented and approved.

3 Mode of operation

It should be one of the first subjects to address, and need to be defined before tendering for transport/ construction services. Below are examples of decisions to be made:

• Timing of the operation in connection with infrastructure and seasonal weather variations.
• For an offshore campaign, whether the drilling unit should be a semi-submersible, a drillship or a Jackup. This decision will depend on water depth, bottom conditions, rig availability, typhoon evacuations, etc.
• For a land campaign, how the rig will be moved from its existing location to the wellsite. This decision will dependent on the existing road network and facilities available. Various option should be evaluated. Transport by land, river or air may be required. If a combination of methods is required, decision must be made on where to transfer from one to the other.
• Whether a field/offshore base is required, and if so where it should be.
• How materials (mainly casing, mud chemicals and cement, and most importantly fuel) will be taken into the country/operating area.
• The mode of operation should remain flexible until the major contracts are finalised, as discussion with tenderers may result in changes to the original plan.
• Prototype techniques should be questioned, as remote operations do not have back up facilities available in case of unforeseen difficulties. The main principles of running an operation in a remote area are to keep it simple and flexible.

4 Project initiation

Generally, the project has three distinct phases - the seismic acquisition, the evaluation of seismic results, and the drilling of one or more of the identified prospects. Only towards the end of the evaluation phase will it be possible to identify these prospects and do any planning based on firm data. However, due to time constraints in the Concession agreement and the lead time required to set up the drilling operation, it may be necessary to initiate some activities of the drilling phase while there is still a large amount of uncertainty about the requirements.

Following the exploration phase, and before drilling starts, the operations team should start working on the following:

• development of an outline drilling programme, including casing requirements;
• ordering of materials, equipment and stationery, including relevant reports and manuals.
• selection of contractors, preparing contracts, and arranging deliveries of equipment;
• establishing all aspects of personnel administration.
• establishing working and courtesy relationships with Government and local officials.
• selection of the office and base, and making any necessary arrangements arising out of this selection;
• hiring of local staff;
• obtaining permits and licences;
• establishing procedures for importation of all relevant material, including radioactives and explosives;
• making arrangements for the local transport, handling and storage of materials;
• sea bed investigation and weather forecasting (for offshore operations);
• arranging for an Environmental Impact Assessment.
• setting up a telecommunications network;

5 Budget estimate

As a result of the reconnaissance trip the team have a good idea of how the operation will be carried out, and what will be the cost of it. However confident cost estimate can only be made when the tenders for the high-cost items have been received.

6 Rig selection

The choice of rig type for an offshore operation depends on the water depth. The practical depth limits for the various types are:

- Jack-up: 5-100 metres

- Anchored MODU: 50-600 metres

- DP MODU: more than 100 metres

The choice between different types within the same group may also depend on the expected weather conditions, costs and availability in the operating area.

A DP drilling unit can possibly be used in water shallower than that quoted, down to say 50 m. the constraint is the allowable excursion, which for most vessels is around. 6% of water depth. At shallow depths much more fuel is used in to maintain station. Acceptable weather limits are lower which mean more time waiting-on-weather. Also as things happen more quickly there are more risk of damage due to drive-offs as reaction time has to be shortened.

For an offshore drilling unit it is necessary to check on regulations concerning the country of registration of the vessel. In non-traditional drilling areas a rig may be treated as a conventional ship, and foreign flagged vessels may not be allowed to operate in territorial waters. In this situation, dispensation will have to be initiated early. Also vessels of some nationalities may be banned for political reasons. Also, vessels may be granted permission to work, local regulation may restrict the selection and nationalities of the crews.

7 Heli-rigs

In remote areas surrounded by difficult terrain a heli-transportable rig may be required. In view of the need to breakdown the drilling rig, associated equipment and consumables into loads of between two and four tons (resulting in approximately 2,000 lifts to prepare for and drill a 4,000 m well).

Special consideration has to be given to the following:

- An Aircraft Supervisor must be provided.

- Civil engineering equipment (bulldozers, sawmills, etc.) and supplies for preparation of the location and staging areas will need to be transported.

- Large quantity of aviation fuel will be necessary to support the operation (400-500 litres/flying hour).

Two helicopters should be considered to support the operation (allow rig operations to continue while flying personnel and in case of breakdowns).

Depending on the number and sizes of the rig packages, and the temperature/elevation of the site, it may well be possible to use two different sized aircraft, with only one capable of lifting the heavier packages).

8 Land rig moves (including consumables)

If this is not included in the contracts, a rig-move on land should be undertaken by a professional international transport contractor. If a local transport contractors is capable of doing the move for a lower cost, remember that the vehicles are unlikely to be at an acceptable standard, leading to start-up delays, a higher breakdown rate and a slower move. It is also likely that additional supervision will be required. All these aspects should be included in the evaluation of the options.

An experienced "rig-move supervisor" can save a considerable amount of time. If the rig is being moved on a lump-sum basis it is to be hoped that the contractor will use such a man. If the move is on a day-rate basis the contract should include such supervisor at Company cost.

Unless the rig-move is over a very short distance, the procedure should include the use of convoys, with escort vehicles in front and behind and with radio communication both between the escort vehicles and between the convoy leader and the base.

Such convoys may be the exception to the general rule that no driving is done at night. If the route includes a section of public road which is busy during the day, or goes through villages, it may be advantageous to travel at night. In that case emphasis will have to be placed on the drivers being provided with accommodation suitable for sleeping during the day.

An attempt should be made to ensure that the transport supervisory staff are given the same conditions, with respect to accommodation and working cycles, as the drilling crew supervisors of equivalent status.

9 Deviated drilling/surveys

Deviated drilling

Although the majority of exploration wells are vertical it is necessary to be prepared to drill a technical sidetrack (which usually returns to vertical after kicking off, in order to reach the original target) or a geological sidetrack (which usually requires a high deviation angle, to reach a revised target).

In some geological conditions deviated drilling techniques may be required to achieve verticality. For these reasons it is always necessary to have the appropriate equipment either on site or on call.

Deviation surveys

The position of the well trajectory has to be known both for relief well drilling and for accuracy of geological data. The requirements of the latter will have to be decided in consultation with Exploration and will depend on the shape and structure of the objective.

With respect to relief well drilling, the maximum lateral position uncertainty for target wells should be 7.5 m (25 ft). This is to ensure that if a relief well has to be drilled, the combined positional uncertainty of both the blowing and relief well is 15 m (50 ft) or less, which is the order of magnitude of the range of homing-in tools in an average well.

Magnetised casing shoe or joint on the last casing string prior to entering the reservoir facilitates intersection of a relief well with a blowing or bridged-off well. In that case the positional tolerance (for relief well operations) can be relaxed. Equipment for magnetising casing can be obtained from companies such as Vetco Inspection Services GmbH.

The survey tool(s) chosen to survey the well must have an accuracy capable of defining the position of the well-bore to the required tolerance. Furthermore, they must be allowed to be able to perform to their stated specifications otherwise this tolerance limit may not be met.

Note that NMDCs can be checked qualitatively for hot spots on site by means of a hand compass.

A gyro survey should be taken after setting casing prior to entering any formation which can blow out. If high-accuracy, electronic, magnetic surveying instruments are used, it is possible to have an Electronic Multishot Survey run in place of the gyro, providing certain criteria are met. Ideally, two probes should be run in tandem, which reduces both gross error and misrun risk. This option benefits drilling economics since the wireline crew and depth charges traditionally associated with gyro surveys are eliminated, very little rig time is utilised in acquiring the survey (since the survey barrels are "go-devilled" inside the DP and the survey data is acquired whilst POOH as with standard multishots). Misrun risk is significant reduced if a tandem survey is run which is not the case with gyro surveys.

In general, for the average, vertical exploration well Single Shots - either magnetic or electronic - should be taken every 150 m and a Multishot - either gyro or electronic - at casing setting points. If MWD is used single shots are not required.

10 Fuel

Fuel is the most important consumable involved in the operation. The stock kept on the drilling location/offshore unit has to depend on the ease or difficulty of re-supply, but should not be less than 5 days consumption.

Storage facilities may vary from a small drum or bladder storage area in a remote jungle location to a properly designed storage and dispensing depot similar to a normal roadside fuel station. The fuels required are usually petrol and diesel oil for water and land transport and kerosene for helicopter and fixed wing aircraft. Aviation gasoline could also be required for fixed wing aircraft. The transport and storage of fuel in remote areas can be difficult, requiring strict safety/security precautions and supervision, sometimes not fully appreciated by local inhabitants.

In the design of a land location provision should be made for easy access on a hard surface, to the fuel tanks. It is not necessary to construct a wall round the tanks, as there is a very low probability of a catastrophic failure, but drainage should be arranged so that small spills run into the contaminated water drain system.

Depending on the local circumstances, consideration should be given to fitting locks to the valves, vents, etc., to prevent theft and/or sabotage.

11 Water

Drill water for land locations

A minimum peak requirement of 30 m3/hour should be available.

If the water supply is regular with full redundancy built-in there is no need for reserve pits. If water supply is irregular, a buffer storage will be required. Although a rate of 30 m3/hour should be planned, the average consumption will be lower. A reserve water pit capacity of 500 m3 should be adequate to allow for a one day interruption.

If there is no river within a reasonable distance it may be necessary to drill one or more water wells. This will be undertaken by a specialized water well Drilling Contractor. The contract should include provision of all casing, tubing, screens, pumps, etc. It should also cover the maintenance of the wells during their use by the Company, and possibly the provision of power for the pumps. The local residents and the water well drilling contractors may have information about the most prospective location to site the water well.

Even if one well is sufficient to provide the required capacity, water is so important that consideration should be given to drill and equip two wells in order to cope with a pump breakdown. If the supply is taken from surface water some redundancy in pumping equipment should be considered.

If a shallow river is to be used, or a stream, it may be necessary to construct a dam. In that case some thought should be given to the residents downstream, so that their supply is not completely cut off while the dam fills, and so that they are not inconvenienced when the dam is removed at the end of the operation.

The amount of "new" drill water required may be reduced by using water from the waste pit to top up the mud system, but care should obviously be taken over the effect of this on mud properties.

Potable water

Offshore, potable water is normally provided by water-maker units, although it is sometimes possible to provide it via the supply vessels from a source ashore. The best water-makers for offshore use are reverse-osmosis units, but some drilling units are equipped with distillation units.

Onshore the normal system is to use drill water which has been passed through a purification unit (chlorination plus a sand filtration unit). This can go into the domestic supply for washing, showering, toilets etc. Water used for drinking, or for preparing food should be boiled for at least ten minutes.

Reverse osmosis units do not work reliably with river water as they tend to clog up with vegetable matter.

12 Abandonment guidelines

The abandonment of a well, implying that no useful additional information is obtainable from it, is a major decision which can only be taken by the General Mamnager after consultation with shareholders and partners, and normally with the agreement of the government. Although all preparations can be made, and a cementing string run into the hole, the final step should not be taken until all concerned have given their approval.

In most areas there will be regulations setting minimum standards for the abandonment.