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Subsurface Storage in the Floridan Aquifer System in Southern Florida: Oil Field Brine

Since the discovery of oil in southern Florida in 1943 at a field in Collier County, 12 other oil fields have been discovered that have produced commercial amounts of crude oil (fig. 28). Oil is chiefly produced from the Lower Cretaceous limestone, called the Sunniland Zone by drillers, that underlies the region at depths ranging from 11,000 to 12,000 ft. Along with the crude oil produced are large quantities of saltwater, called brine. The brines are several times saltier than seawater, and small amounts spilled on the surface can render a potable water supply useless for many years. Analyses of selected oil field brine are shown in table 11. Chloride concentrations range from 108,000 to 164,570 mg/L, compared with about 19,200 mg/L for seawater.

Total oil production for the 13 fields during 1943-83 was 77.3 million barrels (bbl) (3.2 billion gallons (Ggal)), and brine production was 193.2 million bbl (8.1 Ggal). The largest producer of oil and brine (fig. 28, site 4) yielded 35 million bbl of oil and 73 million bbl of brine during 1966-83. The next largest producer (fig. 28, site 1) yielded 18 million bbl of oil and 52 million bbl of brine during 1943-83. During 1943-66, the ratio of brine to oil was relatively stable, as production was mostly from the field shown as site 1 in figure 28. Subsequent oil production at site 4 resulted in significantly greater amounts of brine, and in 1971 oil production leveled off while brine production continued to increase exponentially (fig. 29). Ultimately, oil production began to decline in 1977, and brine production continued to rise. The brine-to-oil ratio in 1983 was 6.4 to 1.0 compared with a 1 to 1 ratio in 1964.

Table 11. Selected analyses of oil field brine, southern Florida [Concentrations in milligrams per liter. Remarks: BM, U.S. Bureau of Mines; GS, U.S. Geological Survey; PL, private laboratory; SDS, saltwater disposal system. Site locations shown in fig. 28. Dashes indicate no data]
Site No.	Date	Calcium	Magnesium	Sodium	Potassium	Chloride
1	12/43	25,204	3,110	58,491	4,700	143,601
	12/77	31,700	4,070	65,600	--	164,570
	6/55	23,800	3,400	48,300	3,150	129,000
2	11/7/55	6,910	3,010	53,500	2,030	108,000
	6/19/59	27,730	4,080	50,980	350	140,000
	8/1/65	27,700	4,770	56,900	3,950	152,000
3	11/64	21,100	2,880	55,600	2,850	131,000
	11/13/64	21,600	2,970	51,500	2,920	129,000
4	2/1/78	23,165	3,699	65,154	--	152,000
	2/1/78	23,165	3,946	62,730	--	149,000
7	12/29/77	28,448	4,439	60,292	--	156,000
	12/29/77	27,635	5,425	57,445	--	153,000
9	12/29/77	26,010	4,192	62,896	--	155,000
Site No.	Date	Sulfate	Dissolved solids	Remarks
1	12/43	275	230,827	Specific gravity 1.162 at 60.1°F. Drill stem test for discovery well. Permit 42. Analysis by BM. References: Gunter (1945, p. 18); Babcock (1962, p. 20).
	12/77	215	--	Composite injection into SDS No. 1, well 2. Permit 102. Analysis by PL. Source: Exxon Co.
	6/55	139	>207,000	Density 1.16 g/cm3 (grams per cubic centimeter) at 68.0°F. Drill stem test for nonproducing wildcat. Permit 222. Analysis by GS, No. 8655.
2	11/7/55	1,380	>175,000	Density 1.134 g/cm3 at 68.0°F. Pumped sample. Permit 167. Analysis by GS, No. 8016.
	6/19/59	408	246,000	Drill stem test. Permit 278. Analysis by GS, No. 17682.
	8/1/65	665	>254,000	Density 1.204 g/cm3 at 68.0°F. Drill stem test. Permit 331. Analysis by GS, No. MSF-546.
3	11/64	1,030	271,000	Drill stem test. Permit 314. Analysis by GS, No. MSF-170.
	11/13/64	415	>209,000	Pumped sample. Permit 315. Analysis by GS, No. OKE-19.
4	2/1/78	140	>244,000	Specific gravity 1.171 at 68.0°F. Composite injected into SDS No. 1, well 1. Permit 491. Analysis by PL. Source: Exxon Co.
	2/1/78	140	>239,000	Specific gravity 1.170 at 68.0°F. Composite injected into SDS No. 2, well 1. Permit 748. Analysis by PL. Source: Exxon Co.
7	12/29/77	130	>249,600	Specific gravity 1.177 at 73.0°F. Composite injected into SDS No. 2, well 1. Permit 856. Analysis by PL. Source: Exxon Co.
	12/29/77	140	>244,000	Specific gravity 1.176 at 73.0°F. Composite injected into SDS No. 1, well 1. Permit 761. Analysis by PL. Source: Exxon Co.
9	12/29/77	140	>248,500	Specific gravity 1.176 at 73.0°F. Composite injected into SDS No. 1, well 1. Permit 812. Analysis by PL. Source: Exxon Co.

Figure 29. Brine and oil production for southern Florida oil fields, 1943-83. [larger version]

Some of the produced brine was used to repressure the oil-producing zone during 1966-83 to enhance oil recovery. This process is termed "water flooding" or "secondary recovery" and generally involves injection of the brine back into an abandoned oil well. About 23.6 million bbl (991 million gallons; Mgal) of brine were reinjected into the producing zone for water flooding.

A summary of brine production, by oil field, is presented in table 12. During 1943-83, about 193.2 million bbl (8.1 Ggal) of brine were produced, of which 169.6 million bbl (7.1 Ggal) were injected into the Boulder Zone (Lower Floridan aquifer) and 23.6 million bbl (1.0 Ggal) were injected back into the oil-producing zone.

Figure 30 shows the hydrogeology and construction details of typical oil field brine disposal wells at two oil fields (sites 12 and 1). The injection well at site 12 was constructed since establishment of the UIC regulations and incorporates current design criteria. The injection well at site 1 is a converted oil-production well with a cement plug in the lower confining unit of the Floridan aquifer system. Both wells, however, inject brine through perforations into the Boulder Zone (Lower Floridan aquifer), The main difference between the injection wells is that the injection well at site 12 has two strings of casing that extend from land surface to the middle confining unit of the Floridan aquifer system, whereas the well at site 1 has only one string of casing to protect brackish ground water in the Upper Floridan aquifer. Also, the injection well at site 12 has associated with it a separate monitoring well (not shown in fig. 30) used to provide an early warning for leaks and upward migration of saltwater.

Table 12. Summary of brine production and disposal for oil fields in southern Florida, 1943-83 [Volume of brine in barrels. Operator: B. Burns; C, Commonwealth; E, Exxon; G, Gulf; K, Kanaba; NRM, Natural Resources Management; S, Sun; W, Weiner. No. of injection wells: B, Boulder Zone; P, Paleocene or older rocks; S, Sunniland Zone in Lower Cretaceous limestone. Dashes indicate no data. Site locations shown in fig. 28]
Site No.	Operator	Period	Brine production	No. of injection wells	Brine disposal
					Boulder Zone	Sunniland Zone
1	E	1943-73	51,789,210	3B	51,879,210	0
2	C/G	1954-55	98,700	--	98,700	0
3	S	1964-83	29,963,400	1B, 9S	13,862,112	16,101,288
4	S/E	1966-83	72,722,755	3B, 1S	69,428,463	3,294,292
5	K1	1969-83	0	--	0	0
26	E	1970-75	1,118,625	--	1,118,625	0
7	E	1972-83	18,369,565	2B,8S	14,215,772	4,153,793
8	W/K	1973-78	289,106	--	289,106	0
9	E	1974-83	17,658, 580	2B	17,658,580	0
10	E	1977-78	19,458	--	19,485	0
11	B	1977-83	1,000,222	1B	1,000,222	0
12	E	1977-83	13,880	1B	13,880	0
13	NRM	1982-83	60,396	1P	0	360,396
Total4			193,193,924 (8,114)		169,584,155 (7,122)	23,609,769 (992)
1Formerly owned by Mobil. 2This site was included in site 4 in 1975. 3Injection occurs below the Boulder Zone in the open hole between 3,835 and 11,074 feet. 4Total in parentheses is shown in million gallons.

Figure 30. Hydrogeology and typical construction of oil field brine disposal wells. [larger version]

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