A drilling rig is used to create borehole or wells in the earth’s sub-surface, for example in order to extract natural resources such as gas or oil. During such drilling, data is acquired from the drilling rig sensors for a range of purposes such as: decision-support to monitor and manage the smooth operation of drilling; to make detailed records of the geologic formations penetrated by a borehole; to generate operations statistics and performance benchmarks such that improvements can be identified, and to provide well planners with accurate historical operations-performance data with which to perform statistical risk analysis for future well operations. The terms Measurement While Drilling, and Logging While Drilling are not used consistently throughout the industry. Although, these terms are related, within the context of this section, the term MWD refers to directional-drilling measurements, e.g., for decision support for the smooth operation of the drilling, while LWD refers to measurements concerning the geological formation made while drilling.
MWD typically concerns measurement taken of the wellbore inclination from vertical, and also magnetic direction from north. Using basic trigonometry, a three-dimensional plot of the path of the well can be produced. Essentially, a MWD Operator measures the trajectory of the hole as it is drilled. This information is then used to drill in a pre-planned direction into the formation which contains the oil, gas, water or condensate. Additional measurements can also be taken of natural gamma ray emissions from the rock; this helps broadly to determine what type of rock formation is being drilled, which in turn helps confirm the real-time location of the wellbore in relation to the presence of different types of known formations.
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