ABSTRACT
Downhole Measurement While Drilling (MWD) services, within the first decade of commercial use, evolved into an essential component of a cost-effective drilling program. The present generation of MWD tools performs these services, individually or collectively, in any combination. The majority of current commercial MWD systems require a moving mud stream to transmit data for surface evaluation. There are various advantages and disadvantages to each of these three methods in terms of data rate and transmission reliability under different drilling conditions. The sensors are controlled by a downhole processor which reads each sensor in a pre-configured sequence. Data are stored in downhole memory and encoded for transmission. Memory is being used with MWD today, as either an alternative to, or a complement to, data transmission. Memory data are stored downhole and retrieved later at the surface.
