COMPARISON OF PROCESSING METHODS TO OBTAIN ACCURATEBULK DENSITY COMPENSATION AND AZIMUTHAL DENSITYIMAGE FROM DUAL-DETECTOR GAMMA DENSITYMEASUREMENTS IN HIGH ANGLE AND HORIZONTAL WELLS

摘要

LWD density tools have the source and the detectorspackaged inside the drill collar with an offset from thecenter of the collar in order to provide azimuthalmeasurement sensitivity. LWD density images in highangle and horizontal wells (HAlHZ) can revealimportant sedimentary structures of fannalian bedding.However, the effects of bedding and borehole geometryon density measurements have not been clearlyunderstood.Although numerous post-processing techniques havebeen developed for dual-detector densitymeasurements, such as the widely used Lipcompensation scheme, these techniques are devised tomeasure infinitely thick fonnations with ID radialfonnation density variation only. Traditional verticalresolution enhancement techniques are applicable invertical wells with horizontal beds. Significant errorcan result from applying standard compensationschemes in HAlHZ wells. Furthennore, benefits ofapplying resolution enhancement techniques decreaserapidly as the relative dip between the borehole and thefonnation increases. This also leads to significanterrors in bulk density estimation and bed boundarydetection. Source and detector eccentricity andazimuthal rotation of the LWD density tool make itmore complicated to correctly derive fonnationgeometry and azimuthal density, particularly in HAlHZwells.Monic Carlo 3D modeling studies were conducied byvarying fonnation dip and tool azimuth to understandproblems associated with post-processing. A variety oftechniques were employed to develop new methods ofeffectively combining short- and long-spaced densitymeasurements to improve vertical resolution, and toincrease bulk density measurement accuracy, and toconstruct higher resolution azimuthal density images.The results of these studies are particularly applicableto density logging in HAlHZ wells where many issueshave yet to be resolved.