Drilling systems

Drilling system	Advantages	Disadvantages
Rotary	ü Most rock formations can be drilled ü Fast drilling process ü Operation is possible above and below the water-table ü Unstable formations are supported by mud and water ü Drilling can be made to depths of over 40m	ü Expensive equipment ü Water is required for pumping ü Problems with boulders can be encountered ü Careful operation and maintenance is required
Steerable mud motor	ü Borehole is better controlled due to reasonable flexibility ü Very hard rock formations can be drilled using diamond bits and PDC ü Desired direction of drilling bit orientation ü Borehole circulation is independent to torque and horsepower	ü Efficiency of motor operation is maintained by special pumps ü Bit speed is very high, therefore drilling bit selection is limited ü Economically not valuable and very adulterate because of preference to oil based mud
Rotary steerable	ü ROP is high due to drilling string sliding ü Less time is used to drill to target ü Unimportant well paths are reduced ü Directional control in 3D is improved ü Complex wells can be drilled	ü In deviated boreholes, drag on drill string can prevent surface generation of torque to rotate the drill bit ü When drilling highly deviated wells, drag and torque can be excessive

Which, in your opinion will deliver the smoothest wellbore and why?

Directional control in 3D is improved in rotary steerable as mentioned before, that’s why it can deliver the smoothest wellbore. So, non-essential uncertainties and inclinations are minimized.

Wellbore surveying

What can influence the magnetic azimuth readings of the MWD magnetometers?

Drilling cuttings, weight mineral and clay can deteriorate the reading on magnetometer. Magnetic property of the drilling fluid can also affect the azimuth readings. Loss of the azimuth symmetry makes the reading unforeseeable.

What can cause the inclinometers of the MWD to give wrong inclination measurements?

Inclinometers of the MWD can be caused by sag. Mismatch of the directional sensor with the borehole direction under gravity and borehole curvature is the source of this problem. Basically, it is BHA sag. ISCWSA model can be used to solve this problem partially. Uncertainty might reduce up to 50%.

Дата добавления: 2015-11-14