OIL FIELD GEOTHERMAL WATERS OF WYOMING

Over 150 million gallons of water a day are brought to the surface in the oil fields of Wyoming. The temperature of this water is nearly always greater than 90/sup 0/F, and ranges as high as 230/sup 0/F. The location, volume, temperature, and present use status of co-produced oil field thermal waters are presented briefly.

OIL FIELD GEOTHERMAL WATERS OF WYOMI NG Bern S. Hinckley Wyoming Geothermal Resource Assessment Group Department of Geology and Geophysics University of Wyoming L ar ami e , Wyomi ng August, 1983 In t roduc t i on Over 150 million gallons of water a day are brought t o the surface i n the oil fields of Wyoming. T h i s water is produced for neither agriculture nor municipal use, b u t is a by-product accompanying the production of o i l and gas.
The temperature of this water i s nearly always greater than 900 F, and ranges as high as 2300 F. Approximately one half of the water is not reused by the o i l and gas industry, b u t is disposed of either by reinjection or, more commonly, by discharge t o the surface. The thermal energy of discharged water is simply dissipated, and the water either soaks into the ground or f i n d s its way into natural drainages .
Fifty-two of the largest water producing o i l fields i n the state (accounting f o r over 98% of the total o i l field water production) were inventoried i n 1982 as the basis f o r this report. Eighty-eight percent of the water produced i n these fields is warmer than 1000 F; 60% i s hotter than 1200 F. If the total water production of these 52 fields were cooled t o 700 F, approximat e l y 800 megawatts of thermal power would be released. -.
The purp-ose of this report is t o briefly present the location, volume, temperature, and present use status of co-produced o i l field thermal waters. I t i s hoped that making this information available will focus attention on development of applications for this substantial energy resource which, i n spite of ready availability, is virtually unused a t present. None of the agencies cited above gathers data on water temperature. (If the temperature of discharged waters were high enough to be a significant environmental concern, the Department of Environmental Quality is empowered to regulate such discharges,) Therefore, it has been necessary to contact oil field operators directly for the information of this report. Information on water production, temperature and disposition i s that provided by the operators unless otherwise noted, The essence of this report is assembled in Table 1. Table and  -Water Volume. Oil fields are generally defined on the basis of the geologic conditions creating a more or less continuous oil reservoir. Thus, field sizes will vary greatly as will the number of wells contributing to total production. Since the oil/water production of many wells is commonly collected at oil separation facilities, thermal waters will be concentrated at various locations within each field. The total production figures listed do not reflect in-field distribution; how much water is actually collected at any one point will vary widely depending on specific field characteristics. All volumes are listed in gallons per minute (gpm); 1 gpm = 1.6 acre-ft/yr. Water production values enclosed by parentheses in Table 1 are average 1981 values calculated from Petroleum Information Carp. Production Summaries (see References); no reports were received directly from field operators in these cases.

The discussion which follows is an explanation and discussion of the
Since the value of oil field geothermal resources is small relative to the petroleum resources, oil fields will continue to be managed for optimum oil and gas revenues. It is unlikely t h i s will generally lead to optimum geothermal production as well, so geothermal applications will be largely dependent upon petroleum production stategies. The range i n water production (based on monthly averages for a l l operators i n the field) has therefore been compiled from the published Production Summaries (see References). Fields w i t h relatively constant water production are certainly the most attractive candidates f o r geothermal development; development would have t o be carefully coordinated w i t h field operators t o establish a secure energy source i n any case.
Water Temperature. The temperature of produced water w i 11 generally decrease from the bottom-hole temperature to the point of final disposition.
Geothermal applications which follow oil-water separation processes and in-field water uses will have to depend on somewhat lower temperatures than will applications which can extract heat from produced waters before or d u r i n g separation processes.
produced waters is not an unused by-product.
I t should also be noted that a l l the thermal energy i n In some fields these waters are stock watering and irrigation. Where such uses have appropriated water r i g h t s they would take precedence over geothermal applications i n the event of a conf 1 i c t .
In many cases discharged oilfield waters are presently used for Question marks i n the "Discharge Water" column of Table 1 indicate the part i t i o n i n g of produced waters between the 3 options listed above is unclear. A question mark following a value indicates produced water was assumed t o be surface discharged because there were no injection projects reported f o r these fields. Values enclosed by parentheses are taken from the f i l e s of the Water Qual i t y Division of the Wyoming Department of Environmental Quality (DEQ). The number of discharge permits has also been extracted from these f i l e s . Numbers followed by an asterick denote permits which DEQ has noted as covering discharges greater than 1 million gallons per day (700 gallons/minute). Many discharge permits are filed against the contingency of possible discharge.
Discharge may rarely occur under there permits, so the number of permits listed for a f i e l d is a maximum number of discharge points.
-Second t o waters discharged t o the surface, the most available waters for geothermal applications are those destined for waste reinjection. These waters are presumably of no value to the oil and gas operations; examination of DEQ f i l e s reveals that i n many cases waste waters which were previously surface discharged have been converted t o reinjection due t o t i g h t e n i n g discharge water quality standards. Thus, geothermal applications which took over disposal of these waters would actually save the f i e l d operator the expense of reinjection.
(Geothermal applications will, of course, themselves be subject t o the same waste disposal regulations as any other water use.) As w i t h the number of surface discharge points, the number of disposal wells reflects the degree of water concentration w i t h i n the field. (The number of wells and formation data of Table 1 on both waste and enhanced recovery injection come from the Wyoming O i l and Gas Conservation Comission (1980)) .
Of the three water disposition possibilities, waters used i n enhanced recovery injection operations would be the most logistically d i f f i c u l t t o u t i l i z e i n geothermal applications. Depending on how the field operators view the value of temperature t o the recovery processes, however, i t may be possible to extract significant heat i n "closed loop" processes which return the water f o r injection. While some portion of injected waters may cycle back through the system as produced water, this does not necessarily decrease their geothermal value. T h i s recyling of cooled waters is an accepted way t o usefully extract energy from very large subsurface heat sources.
Unlike the numbers of discharge permits or waste disposal wells, which represent the concentration of co-produced waters, the number of injection wells represents the dispersal of waters t o create the proper injection pattern. The maximum concentrations of thermal waters i n these fields will occur a t separation f a c i l i t i e s .