There are many reasons to drill a hole, For example, to:
- put something in for storage or disposal
- pass through something for access (e.g. shafts, tunnels)
- gain information from the drilling itself, from tests/ measurements made in the hole or from formation samples recovered from the hole
- produce oil, gas, steam, water, molten, or dissolved minerals.
The reason for making a hole is called the drilling objective. It consists of four important parts:
- Statements — tell the driller what to do and why
- Standards — tell the driller the measurement, drilling angle, and drill logging requirements
- Conditions — tell the driller how, when, and where the standards apply
- Checks — tell the driller the method to use to ensure that the standards are being met.
The Statements clearly set out the objective. It is important that statements are clearly worded so that the driller can understand them. After all, he cannot be expected to do a job unless he has a clear picture of what it is he is expected to do.
For example: Drill an exploratory hole to produce data on the nature and position of the formations; and produce chip samples for laboratory testing.
The Standards tell the driller the precise requirements for drilling. Certain standards will be required for every hole and they must be adhered to exactly. They are a measurement of the work to be performed.
- The hole to be drilled must be drilled within 0.5 metres (18 in) of the peg
- The hole must be drilled to a depth of 100 metres (300 ft)
- The minimum hole diameter is to be 125 mm (5 in)
- The hole must be within 3 degrees of vertical throughout
- The sample interval is to be every 1 metre (3 ft)
- Drilling logs must record changes of formation within 0.2 metres (8 in) of the correct position.
The Conditions provide a frame of reference for the work (i.e. how, when, and where the standards apply).
They may describe site access or weather conditions and their efect on the drill site or hours of work.
They could comprise the following:
- Drilling is to be conducted only during the dry season
- Drilling will be performed only during daylight hours
- The hole is to be stabilised and kept open for logging after drilling is completed
- Fireighting equipment will be carried and maintained in good working condition.
Examples of Checks made to ensure that the required standards are being, or have been, met include:
- Hole verticality may be checked using a wire line survey method
- The position of the changes in formation may be checked by electric logging
- Sample volume and variation will be randomly checked throughout the program.
The examples given above should help to understand how drilling objectives should be documented. If drilling contracts were writen with these guidelines in mind, there would be fewer problems, as all on-site personnel would have thorough knowledge of the requirements.
The driller is primarily concerned with the three objectives highlighted in Figure 1–2. He should recognise that other objectives have contributed to this, but must achieve his objectives while keeping the other objectives in mind. As the diagram shows, the drilling process conirms some of the contributing objectives and clearly they are critical ones.
With the advances in technology that have taken place in the drilling industry, it is now possible to drill a hole in any material, get the required information from it, and achieve the drilling objectives.
But each objective can be achieved only if it is matched with the appropriate skills, equipment, tools, and materials to do the job. To ensure that the driller satisies the job requirements, he must be able to select and use the most suitable drilling equipment, along with the best hole making and stabilising method.
If the driller has done this while recognising what is happening, he can be reasonably sure of completing the job successfully. However, all these considerations cost money. If a client asks for some particular result or information, a driller must be able to explain:
- what is involved in achieving the result or gaining the information
- how much the required skills and equipment will cost
- how long it will take.
Drilling objectives are only one of a number of objectives all contributing to a project objective.
Used in conjunction with the driller’s knowledge, skills, and equipment, almost any objective can be achieved, provided that the objective is clearly and concisely writen. This will ensure that all personnel have a thorough knowledge of the requirements. The driller can then use his equipment and skills to carry out an eicient and economical drilling operation.