MWD is a technology that needs to measure the information near the precision drill bit without interruption and can transmit information to the surface during normal drilling operations. There are several types of information.
1. Orientation data: well inclination, azimuth, and tool face angle (magnetism and gravity) guide drilling.
2. Drilling parameters: downhole pressure on drilling, rotational speed per minute of torque, etc.
LWD logging-while-drilling system is an upgrade and development on the basis of MWD. It has a more complete function and a more complex tilt-while-drilling system while drilling. The information transmitted by the LWD-while-drilling while measuring instrument increases compared with MWD: formation evaluation Parameter sensors, double lateral resistivity, natural gamma data, azimuth neutron density, acoustic information, compensated neutron density, etc.
LWD logging-while-drilling system: downhole high-temperature probes measure the orientation, well deflection, and tool surface of the well, as well as resistivity, natural gamma, well pressure, porosity, density, etc., which can replace the current wireline logging well.
There are currently two types of signal transmission systems commonly used in downhole high temperature, one is pulse type and the other is continuous wave type. Pulse type is divided into positive pressure and negative pressure pulse. The positive pressure pulse system uses a plunger to block the drilling fluid channel momentarily, causing a sudden rise in the riser pressure to a peak;
The negative pressure pulse system uses a relief valve to open instantly to allow the drilling fluid to flow to the annular space, causing a sudden drop in the riser pressure and a negative peak. The continuous wave system uses a set of slotted stator, rotor, and drilling fluid to generate a low-frequency wave of a certain frequency when the signal passes, and the signal is transmitted to the ground using this wave as a carrier.
When using a pulsed MWD tool to measure, generally stop the pump and stop the turntable.
The continuous wave type MWD tool can be used for continuous measurement while drilling without stopping the drilling operation.
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