TABLE 1.

Geochemical and biological characteristics of formation waters from three high-temperature California oil fields^a

Characteristic	Field, geological age, and formation
	South Elwood		Santa Clara			North Coles Levee	Yowlumne
	Upper Miocene	Lower Miocene	Upper Miocene	Lower Pliocene	Lower Pliocene	Middle Miocene	Middle Miocene
	Monterey	Rincon	Monterey	Upper Repetto	Lower Repetto	Stevens-Monterey	Stevens-Monterey
Physicochemical conditions
Depth (m)	1,500–1,700	1,524	2,316	1,759	2,392	2,700	3,940
Temperature (°C)	70–75	70–75	78	65	81	105	125
TDS (ppm)	44,340	21,803	24,500	23,000	24,500	21,986–30,400	9,966–15,974
pH	7.84	7.74	8.11	7.33	7.86	7.18	ND
H2S (mM)	11.2	0.94	2.4	0	0	0	ND
SO4 (mM)	0.47–0.9	0.71	0.29	0.6	BD	0.45	0.75
wt% sulfur oilb	∼4%	0.2%	4.5–5%	ND	ND	ND	ND
Direct counts (103 cells/ml)	54.5	1,420	2.55	18.5	529	372	145
Representative genera enrichment cultures	Thermococcus	Thermococcus	Thermococcus	Thermococcus	Petrotoga	Thermococcusc	Thermococcusc
	Petrotoga	Thermotogales	Methanococcus	Thermotogac	Anaerobaculum	Thermotogac	Thermotogac
	Thermoanaerobacter	Anaerobaculum	Methanobacterium	Methanococcus	Methanobacterium	Methanobacteriumc	Methanobacteriumc
	Deferribacter	Methanobacterium		Methanobacterium
	Thermotogac	Methanoculleus
	Methanococcus
	Methanoculleus

^aTDS, total dissolved solids; BD, below detection; ND, not determined. 

^bReference 6a. 

^cPutative identification based on phase microscopy and physiological characteristics.