COMPARISON OF PROCESSING METHODS TO OBTAIN ACCURATE BULK DENSITY COMPENSATION AND AZIMUTHAL DENSITY IMAGE FROM DUAL-DETECTOR GAMMA DENSITY MEASUREMENTS IN HIGH ANGLE AND HORIZONTAL WELLS

摘要

LWD density tools have the source and the detectors packaged inside the drill collar with an offset from the center of the collar in order to provide azimuthal measurement sensitivity. LWD density images in high angle and horizontal wells (HAlHZ) can reveal important sedimentary structures of fannalian bedding. However, the effects of bedding and borehole geometry on density measurements have not been clearly understood. Although numerous post-processing techniques have been developed for dual-detector density measurements, such as the widely used Lip compensation scheme, these techniques are devised to measure infinitely thick fonnations with ID radial fonnation density variation only. Traditional vertical resolution enhancement techniques are applicable in vertical wells with horizontal beds. Significant error can result from applying standard compensation schemes in HAlHZ wells. Furthennore, benefits of applying resolution enhancement techniques decrease rapidly as the relative dip between the borehole and the fonnation increases. This also leads to significant errors in bulk density estimation and bed boundary detection. Source and detector eccentricity and azimuthal rotation of the LWD density tool make it more complicated to correctly derive fonnation geometry and azimuthal density, particularly in HAlHZ wells.Monic Carlo 3D modeling studies were conducied by varying fonnation dip and tool azimuth to understand problems associated with post-processing. A variety of techniques were employed to develop new methods of effectively combining short- and long-spaced density measurements to improve vertical resolution, and to increase bulk density measurement accuracy, and to construct higher resolution azimuthal density images. The results of these studies are particularly applicable to density logging in HAlHZ wells where many issues have yet to be resolved.