Formation Evaluation and Remaining Oil Saturation Estimation With Pulse Neutron Logging Inside Tubing

摘要

Through-tubing carbon-oxygen (C/O) logging is a popularrnmeans for reservoir monitoring since a slim logging-insidecasingrntool was introduced. The tools are available in 2.5 inchrnand 1.6875 inch outer diameters. Both the tools log inside ofrncasing to quantitatively determine fluid saturation within thernformation. In the absence of any other external information,rnthe C/O technique has limitations when the survey is carriedrnout inside the tubing. However, at times this becomesrnnecessary when the reservoir to be evaluated is covered withrnboth tubing and casing.rnThere has been limited use of the slim logging-inside-casingrntool for completions with both tubing and casing. Thisrnapplication has augmented the C/O methods of saturationrnestimation for measurements made inside the tubing.rnThe present work documents the results of a pulse neutronrnlogging operation carried out for estimation of the remainingrnoil saturation of a reservoir covered with tubing and casing.rnBoth the inelastic capture and the sigma survey were recordedrnin this well. Careful planning was carried out for achieving anrnoil saturation precision of around 7 saturation units. Therninterpretation of the lithology from both the open and therncased hole logs is discussed. A new method was used forrnestimating the permeability from the cased hole spectroscopyrnlogs. The saturation profile estimated from the C/O log isrnintegrated with the estimated permeability results.rnThe saturation results are in agreement with field observationsrnand also demonstrate that bypassed reserves can be estimatedrnon the basis of pulse neutron logging carried out inside tubing.