Abstract: NMR T2 Relaxation of Oil Based Mud Filtrates at Elevated Temperatures

KUMAR, NITESH, Consultant

The T2 relaxation of bulk oils depends strongly on temperature. Determination of the relaxation response of reservoir fluids at reservoir temperatures is needed for optimal interpretation of log data. The drilling fluid will strongly influence the NMR response of the flushed zone. In this work, the NMR T2 response of nine oil base mud filtrates (OBMF) and base oil samples at different elevated temperatures was studied.

A Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence was used to measure the NMR T2 relaxation at 2 MHz. All the samples were degassed by a standard helium sparging technique before T2 measurement. Dissolved oxygen can greatly reduce the T2 of refined oil products. The OBMF and base oil samples were studied over the temperature range 30 - 100 C at a constant pressure of 300 psig. A single component exponential decay adequately described the data. The temperature dependences of the bulk viscosities were determined using a rolling ball viscometer.

The observed T2 varied directly with temperature and inversely with viscosity. Our earlier work had shown that the T2-viscosity data for crudes at elevated temperatures fit a published room temperature correlation published by Straley et al. The T2-viscosity data measured for the OBMF and base oils in this work did not fit this correlation. However, a single correlation could fit the T2-viscosity relationships for all the OBMF and base oil samples.

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California