Spatial variation analysis of salinity to determine fluid flow pathways and reservoir compartmentalization in a deepwater Gulf of Mexico field

Abstract

Variations in salinity have been documented in previous studies onshore Louisiana in the Wilcox group (Funayama and Hanor 1995) as well as offshore Louisiana on the continental shelf (Bruno and Hanor 2003 and Steen et al. 2011). These studies were conducted using various methods to estimate pore water salinity and make inferences about possible fluid flow pathways and compartmentalization of reservoirs in order to better understand the complex hydrogeology of the Gulf of Mexico. Similar variations in salinity were documented in this study located in a deepwater salt withdrawal minibasin located on the upper slope of the Gulf of Mexico. Data that supported this study included digital well logs, 2D seismic lines and whole core analysis.Using a dual conductance model outlined in Revil et al. (1998) this study was able to calculate salinity from digital gamma ray, deep resistivity and density porosity well logs. This technique allowed for the estimation of salinity where there was well log coverage creating a salinity well log similar to standard well logs used in industry. Variations in salinity were documented between each section of the study area as well in each wellbore and correlated to structures such as salt and faults in order to make inferences about possible fluid flow pathways. Two hydrogeologic regimes, a hydropressured and overpressured regime, were described in each wellbore and illustrated the vertical and lateral variations in salinity across the study area. The hydropressured regime exhibited salinities that were approximately equal to normal marine salinity and the overpressured regime had multiple variations in salinities within each well. These hydrogeologic regimes and their associate salinity profiles are the result of complex fluid migration pathways associated with salt structures and faulting in the Gulf of Mexico.