The Effect of Water Chemistry on Thermochemical Sulfate Reduction: A Case Study from the Ordovician in the Tazhong Area, Northwest China

Table 1

Geochemical and sulfur isotopic composition of formation water, concentrations and sulfur isotopic composition of H₂S in the gas, and concentrations of TAs in the oil in Tazhong area.

Well	Depth (m)	Strata	pH	(mg/l)	Cl^− (mg/l)	(mg/l)	Ca^2+ (mg/l)	Mg^2+ (mg/l)	Na^+ (mg/l)	TDS (g/L)	()	()	H2S (%)	TAs (μg/g)
TZ44	4873		7.0	781	50861	654	7333	92	—	84	—	—	0.1	32.96^#
TZ82	5460		6.7^▯	778^▯	62400^▯	341^▯	10500^▯	374^▯	—	107^▯	24.7^▯	—	0.2	—
TZ83-1	5638		6.4^&	99^&	97900^&	156^&	8741^&	684^&	51530^&	164^&	—	—	0.7	—
ZG103	6191		6.3	371	54800	321	3122	341	31970	96	22.7	11.9	0.4	—
ZG11	6398		6.8	527	55340	224	3240	234	—	92	26.8^▯	16.3		46.63^#
ZG2	5880		7.1^▯	239^▯	58000^▯	353^▯	9840^▯	395^▯	24320^▯	129^▯	25.7^▯		1.3	—
ZG433C	6133		8.0^&	484^&	120000^&	73^&	13500^&	1070^&	62400^&	204^&	—	13.2		—
ZG44	5647		7.2^&	617^&	100200^&	450^&	9635^&	770^&	53510^&	170^&	—	—	—	—
ZG44C	5647		5.5^&	3080^&	109000^&	571^&	14000^&	698^&	56900^&	188^&	—	—	—	—
ZG44-H2C	6056		6.8^&	369^&	95990^&	343^&	11150^&	768^&	46340^&	159^&	24.2	15.5^※		—
ZG46	5148		7.0^▯	6358^▯	97300^▯	330^▯	1580^▯	1050^▯	—	166^▯	24.2^▯	13.4		—
ZG461	5560		6.0	1317	56990	891	19800	810	20140	104	—	13.4	0.1
ZG5	6406		6.3^&	—	84900^&	617^&	43110^&	474^&		138^&	27.8	15.5		104.19^#
ZG511-2	5238		6.5^&	88^&	112000^&	34^&	10630^&	1003^&	52770^&	182^&	—	—	—	—
ZG6	6053		6.4^&	127^&	126000^&	31^&	13770^&	918^&	59260^&	206^&	29.8			147.20^#
ZG7	5794		7.8^▯	871^▯	102000^▯	53^▯	8890^▯	532^▯	—	112^▯	27.8^▯	—		100.75^#
ZS1C	6520	∈1	6.0	274	164000	182	41300	25500		248				1936.6^#

Note that ※ is from Cai et al. [10], is from Cai et al. [21], # is Cai et al. [13], & is from Li and Cai [33], ▯ is from Zhang et al. [25], and “—” represents no data available.