WATER ROCK INTERACTION IN TERTIARY SANDSTONES, SAN-JOAQUIN BASIN, CALIFORNIA, USA - DIAGENETIC CONTROLS ON WATER COMPOSITION

Three water types are recognized among petroleum-associated waters of the southern San Joaquin basin: (1) meteoric water; (2) diagenetically modified connate water; and (3) mixed meteoric-modified connate water. The diagenetically modified connate marine water can be further subdivided into three types: (1) fully Mg depleted (Mg < 1 mole% of the sum of Na, K, Ca and Mg); (2) partially Mg depleted; and (3) Ca enriched. Enrichment in Ca, which is the sharpest chemical divide found for the diagenetically modified connate water, is the result of feldspar albitization. The Ca-enriched waters are also rich in total dissolved Al (up to ∼6 mg l-1 and exhibit lighter δ18O-values than other diagenetically modified connate waters. The total dissolved Al abundance in these waters may be due to the presence of organic complexing agents (simple and aromatic organic acids and phenolics). The lighter δ18O-values are probably due to both albitization and the lack of substantial clay diagenesis (illitization of smectite). © 1990.