NEW DATA PROCESSING WITH NEW GENERATION MAGNETIC RESONANCE WHILE DRILLING TOOL

摘要

Nuclear magnetic resonance (NMR) logging toolshave long proven their value to formationevaluation. Recently, new drilling tools have addedlow-gradient magnet configurations to help reducethe effects of axis motion. The primary challengeassociated with using low-gradient tools is therequirement of one preferred sensitive volume tobe tracked over temperature. The secondarychallenge is that the sensitive volume associatedwith low-gradient tools provides a vertically shortsensitive volume. As a result, the tools are moresensitive to vertical motion, and thus to rate ofpenetration (ROP) or pulling speed, opposed tohigh-gradient configuration tools, particularly forT_1 logging. Not only is porosity affected, but the T_1spectrum can also be distorted.A novel, low-gradient slim NMR tool used fordrilling in smaller holes (approximately 6.125-in.diameter) is presented and discussed, along with anew technique for data processing to achievereliable data while drilling or pulling. Thistechnique accounts for the effects of motion andimperfect RF magnetic field B_1 using simulation ofthe tool’s static magnetic field B_0 and B_1. Thetechnique is demonstrated using T1 data, but can bealso used with T_2. A vertical resolution of 23 in.can be achieved with an accuracy of 1PU, asdemonstrated by the example shown.