Measurement while drilling MWD

Perhaps the greatest stimulus for the development of such tools has been the proliferation of high angle wells in which deviation surveys are difficult and wireline logging services are impossible (without some sort of pipe conveyance system), and where MWD logging can minimise formation damage by reducing openhole exposure times. 

Azimuthal resistivity (depth of investigation Gamma ray 12in. orless) detector 

Data transmission rate per foot is a function of both pulse frequency and rate of penetration. Sensors acquire and transmit data samples at fixed time intervals and therefore the sampling per foot is a function of rate of penetration. Current tools allow a real time sampling and transmission rate similar to wireline tools as long as the penetration rate does not exceed about 100 ft/h. If drilling progresses faster or if there are significant variations in penetration rate, resampling by depth as opposed to time intervals may be required. 

Electrical power is supplied to MWD tools either from batteries run in the downhole assembly or from an alternator coupled to a turbine set in the mudstream. 

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Intermediate and low-rate cells are employed in oil exploration measure-while-drilling (MWD) equipment since they are capable of operating at high temperature. 

MWD Measurement-While-Drilling, Inteq-Baker-Hughes, Brochure 602-003, August 1993. 

Unlit recently, these measurements could be taken only when the drill bit and string were removed from the borehole. However, in the mid-1980s, a new dimension was added, namely, measmement while drilling (MWD) instruments. These devices are mounted above the drill bit and around the drill string to provide a continuing source of data on downhole characteristics. This advancement reduces the drilling downtime previously required when measurements were taken. 

The -sonic log can also be used to detect overpressured zones. The sonic measurements until recently were available only on wireline. Now, MWD sonic tools have been developed adding one more parameter for overpressure detection while drilling. Two equations relating the formation porosity to the transit time are used ... 

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