OVERVIEW OF WELL PLANNING

Drilling of an oil/gas well plays a key role ‘m an overall field development the various aspects of which include:

Exploration to confirm the potential presence of hydrocarbons. This would
normally include seismic exploration among other techniques.
2. Drilling a number of wells to confirm the presence of and to exploit the
possible oil gas deposits.
3. Well completions involving the installation of necessary production tools, etc
4. Production operations include the processing of the produced fluids for
consumption or export., etc.

The drilling engineer is responsible for ‘making’ the hole.
There are three basic types of wells. These are
¨ Exploratory wells
¨ Appraisal Wells
¨ Development Wells

With exploratory and Appraisal wells, the objectives are to confirm the present of any hydrocarbon presence and to appraise the extent of the field in terms of geological information – stratigraphic features and lithological configurations, identification of likely problems and problem zones, reservoir characterisation with respect to actual reservoir/formation rock relationships, types of hydrocarbon, estimates of the reserves, production versus pressure relationships etc.
With these wells, there are little or no information about the particular block or field and it is the objective to set up a comprehensive information data bank for the field.

In development or infill wells, there is relatively good information about the environment.

Successful drilling of these wells therefore require careful planning.
The main objective of an effective well planning therefore is to ensure that the entire drilling programme is carried out as fast as possible at a relatively cheap rate and maximum safety standard. This requires that the Drilling engineer must have projections on anticipated potential problems and should develop appropriate preventive measures to eliminate or minimise the problem.

Taken further, he must develop appropriate strategies to cope with any potential problems.
Safety is the overriding criterion and safe drilling practices to prevent any
catastrophic problems requires effective planning prior to spudding the well to initiate the drilling programme.
For exploratory and appraisal wells, little or no Information is available prior to drilling. It is therefore essential to forecast the necessary information or data required for effective well planning. Thus the planning will be flexible and subject to modifications as drilling progresses in line with encountered facts.

For development drilling the planning is much simpler as there are data and experience of the particular environment.

The major areas that require well planning are essentially:

1. The sizing and trajectory of the hole
2.  Casing setting Depths, Casing Design and Cement programmes
3. Design of the Optimum Mud Weight, type and properties
4. Selection of the Drilling rig and rig equipment
5. Contingency planning against unknown eventualities.
6. Knowledge of formation/fracture pressure.

These programmes require a good knowledge of the formation pressure to be encountered and essentially the fracture gradient as these parameters drive the overall safe drilling programme.