NEW ADVANCES IN DEVELOPING A HIGH-TEMPERATURE LWD FORMATION EVALUATION SUITE

摘要

This paper describes the development effort to upgradea logging-while-drilling (LWD) neutron porosity anddensity measurement suite for 175°C capability. Newlithium-6 (Li-6) scintillation detectors have beendeveloped and tested to evaluate their performance atdifferent temperatures. Experimental tests show thelifetime of these new detectors at 175°C is comparableto that of present detectors at150°C. A mechanical study has also been focused onthe new detector package and shielding to predictpossible deformations at high pressure and hightemperature. Modeling results from finite-elementanalysis (FEA) show the tool can withstand 30,000 psiat 175°C and still maintain mechanical integrity. TheMonte Carlo N—Particle Transport Code System(MCNP) has been utilized to examine the impact ofdetector package on the tool response and on theneutron porosity measurement. Modeling results showthe new detector package has minimal effect on theneutron porosity measurement over the normal porositymeasurement range. Furthermore, based on theextensive modeling results at different temperatures, anew temperature-correction algorithm for the neutronporosity measurement has been developed. The newalgorithm is more precise than the present one,especially when logging at very high temperatures. Thebackground subtraction algorithm has been fine-tunedto account for higher noise levels at highertemperatures. The whole upgraded tool has beencalibrated and characterized in the laboratory usingwater-saturated limestone, sandstone, and dolomiteformations of different porosities and borehole sizes.Experimental results show that the tool readings are ingood agreement with the accepted lab formationporosity.