Regional variations in sup 87 Sr/ sup 86 Sr and Sr concentration of formation fluids, San Joaquin basin, California

Conference · Fri Feb 01 04:00:00 EST 1991 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:5171408

Feldman, M D; Boles, J R ^[1]

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1. Univ. of California, Santa, Barbara (United States)

Formation fluids from the San Joaquin basin can be divided into three geographic provinces based on {sup 87}Sr/{sup 86}Sr ratios and Sr concentrations. Connate marine fluids from the central basin have {sup 87}Sr/{sup 86}Sr ratios between 0.7070 and 0.7080, and Sr concentrations between 15 and 200 mg/L. These results are interpreted in terms of mixing of Tertiary seawater Sr with Sr derived from Sierra Nevada plagioclase by dissolution and albitization reactions. Fluids from albitized reservoirs can be further distinguished by both elevated Sr concentrations and strongly modified Ca/Na rations. Meteoric fluids from the eastern flank of the basin have {sup 87}Sr/{sup 86}Sr ratios between 0.7061 and 0.7077, and Sr concentrations < 2 mg/l. The isotopic ratios suggest that plagioclase dissolution is the dominant source of Sr in these fluids. Fluids from the southern basin have anomalously high {sup 87}Sr/{sup 86}Sr ratios (> 0.7080), although Sr concentrations are comparable to fluids from the central basin. stable isotopic and chemical data show that the southern basin fluids are of marine or mixed marine-meteoric origin. The elevated {sup 87}Sr/{sup 86}Sr ratios suggest that a Sr source more radiogenic than Sierran plagioclase is involved in the evolution of these waters to a much larger extent than elsewhere in the basin. Possible Sr sources include Tertiary marine Carbonate, detrital smectite, and K-feldspar. The fluid provinces outlines here limit the scale of lateral fluid communication to distance < 10 km. Isotopic variations also occur within individual fields; in these cases, the scale of fluid communication may be much smaller.

• OSTI ID: 5171408
• Report Number(s): CONF-9103128--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (United States) Journal Volume: 75:2
• Country of Publication: United States
• Language: English

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