Abstract

The relatively conservative behaviour in the drilling industry with respect to implementation of new technology will not survive any longer. More and more difficult formations, extended reach drilling, extreme environmental conditions on the rig locations and increasingly smaller reservoirs need to be explored and are just calling for combined efforts of all parties involved in the drilling process. Experience and application of state of the art technology is the correct answer.

Whereas on Offshore installations, usually gaining higher day-rates, sophisticated technology has been widely accepted already, on movable land rigs it is very often just the opposite. Drilling contractors might not care as they are paid by dayrate. However, if the bore-hole quality is bad, down time has to be faced which is paid on lower rates if at all. Operators will just win since well quality and drilling performance improves. Offshore technology and safety standards will step by step find their way onto land drilling rigs.

So what is going on down there?

The drill bit, pushed downwards by heavy weight drill pipes, is rotated either via Top Drive or via Rotary Table, high pressure mud powers the downhole motors, carries the cuttings upwards and cools the bit down. Simple!

As it was that simple in the past, it will be much more difficult in the future, described above already. Mud needs to be available on higher volume and higher pressure. Deeper wells are calling for longer drill-strings putting higher stress to the materials used. Some formations can only be drilled with very low pressure, called under balanced drilling (UBD). Down hole data needs to be transferred to the surface whereas the drilling process itself has to be as smooth as possible to keep the bit lifetime high, subsequently to avoid unplanned round trips. Drill pipe is opposed to very high friction over almost the whole length since extended reach wells are far more drilled horizontally then vertically. The pipe is just laying on the bottom of the bore hole. The handling of the string on the surface asks for bigger set-back capacity on the rig floor, gear driven drawworks are nowadays the preferred selection for powerful and flexible operation.

The common way of drilling is to make use of the physical limits of the equipment. All over the world scientists and companies within the Oilfield are trying to find more efficient ways to drill.

Until these solutions are available to the field, it is a ‘must’ to optimise the drilling process as we know it today. Experienced staff is definitely as important as the application of improved technology. So every change can only be made step by step. Upgraded standard land rigs and new land rigs that are able to work according to future requirements are available today already.

Where are we now, where do we want to go to?

Common rigs are still equipped with chain driven draw works. They are reliable, known to all drillers and accepted in the Oilfield. The ‘weight on bit’ control (WOB) is done manually, just through opening and closing the mechanical brake, according to the information supplied through the hook-load indicator.

The torque and the RPM-value of the drill-string is set manually as well, not taking care enough of the responses from down hole. Mud volume / pressure, the third important factor for the quality of the bore process, is again just manually controlled.

As we face the limits of this way of operation for drilling rigs, some very important adaptations should be taken into consideration.

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