Experiment Study of Mud Filtrate Salinity Effect from NMR T2 Data in Tight Clay Sandstone

Yuanzhong Zhang
China University of Petroleum, Beijing, China

Nuclear Magnetic Resonance (NMR) logging is an effective tool for formation evaluation, which is often used to estimate permeability, porosity, pore size distributaries, wettability, free fluid and bound volumes and so on. The limitation of NMR logging is shallow depth of investigation (DOI). Invasion of the drilling mud filtrate is representative for displacement of the original pore fluid as well as the development of a mud-cake on the borehole wall. For lower permeability tight rocks, invasion may be deeper due to the slow build up of mud cake. The mud invasion often has a strong effect on NMR logging response, but this is poorly understood. In the paper two groups of tight clay sand core samples, where one is low porosity / low permeability and the other is relative high porosity and low permeability, are used to investigate the mud filtrate salinity effect on NMR data in low field NMR measurement at lab. The transverse relaxation time (T2) measurements using CPMG sequence have been conducted with different interecho times (TE) in the different salinity to simulate downhole NMR tools. The analysis of experiment results, combined with the measurement of X-ray, SEM, magnetic susceptibility, porosity and permeability, show that the mud invasion effect on T2 data mainly depend on clay mineral type and porosity.

AAPG Search and Discovery Article #90092©2009 AAPG Rocky Mountain Section, July 9-11, 2008, Denver, Colorado