Log Quality Assurance Of Formation Evaluation Measurement While Drilling Data

Quality assurance of formation evaluation Measurement While Drilling (MWD) data, similar to wireline data, begins with the quantitative accuracy of calibration parameters, and includes the consistency of sensor responses in a downhole environment Quality assurance also pertains to the reliability of equipment; and recognizing when a device is not operating within its specified design environment Although some MWD devices are similar to wireline technology, there are differences in both the shop calibration and rigsite operational procedures which require modified MWD quality assurance techniques. MWD data acquisition is different from wireline logging because of dynamic effects induced by the drilling environment The characteristics of measurements are influenced by variable drilling rates, mud properties that change during a bit run and the stabilization of the drill collars. The length of time that permeable zones are exposed to invasion, rotating or sliding (steering) the bottom hole assembly, different orientations of the sensors while sliding and a changing inclination of the borehole can also have a significant effects on the response of MWD sensors. The drilling environment also, therefore, influences interpretations made from MWD measurements. Data processing of sensor measurements acquired while drilling requires specific drilling related quality assurance techniques which establish whether data are suitable for their intended purpose. Correlation of MWD sensor measurements in the time domain can distinguish dynamic drilling effects from geological features. Depth processing of MWD measurements sampled at unevenly spaced intervals, arid their conversion onto a regularly spaced depth grid requires different filtering techniques than those applied to wireline data. Drilling vibration and changes in the rate of penetration result in highly variable nuclear sensor spatial resolutions and statistical precisions.