--> ABSTRACT: Comparison of Formation Water Composition in the San Joaquin and Los Angeles Basin: Implications for Types of Water-Rock Interaction and Fluid Transfer, by Boles, James; Garven, Grant ; Camacho-Fernandez, Miguel A.; #90142 (2012)

Datapages, Inc.Print this page

Comparison of Formation Water Composition in the San Joaquin and Los Angeles Basin: Implications for Types of Water-Rock Interaction and Fluid Transfer

Boles, James *1; Garven, Grant 2; Camacho-Fernandez, Miguel A.3
(1) Earth Science, Univ Calif at Santa Barbara, Santa Barbara, CA.
(2) Dept Geology, Tufts University, Boston, MA.
(3) Signal Hill Petroleum, Signal Hill, CA.

New major element, 87/86Sr, 18/16O, and D isotopic analyses of formation waters in the Los Angeles (LA) Basin indicate that they have different compositions than those in the San Joaquin Basin to the north, even though both are derived from interaction of marine pore water with late Tertiary arkosic sediment. One major cause of the difference between the sample sets is that the San Joaquin samples have been buried more deeply (i.e., hotter) than those in the LA Basin and this difference is reflected in the type of water-rock interaction. Although the initial connate water trapped in these reservoirs was presumably sea water, the present day waters are generally less saline (up to 30%) than sea water salinity. Dilution of the initial sea water is presumably due to dewatering of smectite during conversion to illite, although we are evaluating possible meteoric contribution from basin flank uplift. Low Sr ratios (less than Plio-Miocene marine pore water) and high Ca/Na ratios in deeper reservoirs in the San Joaquin and LA Basins indicate plagioclase-pore water reactions (e.g., albitization). High Sr ratios in the shallow LA Basin reservoirs suggest dominantly clay-water and K-feldspar-water interaction due to weathering and/or shallow burial reactions.

Formation waters in the LA basin have distinct differences between shallow and deeper levels, including decreasing salinity, decreasing magnesium, and increasing alkalinity and boron content with depth. Overall, this unique data set has implications for fluid transfer in fault zones and types of fluid-rock interaction. Results to date indicate that formation waters from the deep basin can be distinguished from those at shallow levels, allowing detection of upward fluid movement along pathways, such as faults.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California