What is "Blow-Out" ?

The hydrocarbon reservoirs often contains oil and gas naturally in high pressure. A lots of precautions needs to be taken to contain the high pressure in designing a oil or gas well and similar precautions are taken during drilling and then producing the well.

However, due to equipment failure or human error, if the flow of reservoir fluids to the surface is becomes uncontrollable, it is called "blow-out". Inflammable fluid (oil+gas) often catches fire and damages rigs and other surface equipment.

During drilling, often gust of high pressured fluids enter the well. The phenomena is called "kick". Controlling the kicks are special skills the drillers are expected to learn and implement. 

BOP or "Blow Out Preventor"s are special equipment used during drilling and work-over to prevent such events.

What is MWD & LWD ?

MWD stands for Measurements While Drilling.
LWD stands for Logging While Drilling.

As a well is drilled to a subsurface target, some instruments are attached to drilling string just above the drilling bit. The MWD tools measure the well trajectory parameters like inclination, azimuth etc, while LWD tools measure rock properties like Gamma Ray, Neutron & Sonic Density etc.

In modern highly complicated reservoirs, these tools play vital roles in steering the well along the most favorable reservoir body. It also saves time and money eliminating need for wireline logs and round trips of the drilling bit. 

Another very interesting aspects of these tools is that they communicate with the engineer sitting on the surface via mud-telemetry, that is, they uses pulses in the mud or the fluid system present inside the drill string to send data to the surface and also to receive instructions from the surface.