(GP/GT) for Additional Water Supply in the Lower Rio Grande

Ill-I 7
ill. ALTERNATIVE-DESIGN SYSTEMS EVALUATION
B. BRINE DISPOSAL METHODS
GENERAL
Two issues pervade all of geothermal fluids utilization-the resource and the economics of producing and
utilizing it and the effluent and th~ economics of disposing of it in an environmentally acceptable manner.
Clearl y, the resource must be available; its availability, however, will not be attractive unless the effluents
can be disposed of economically. The purpose of this chapter is to discuss the accumulated evidence
concerning brine disposal alternatives (whether GP/GT derived or from desalination waste streams) from
the standpoint of technology, economics, and the environment. It is an interesting commentary on our
technical and philosophical outlook that brine disposal has heretofore received dramatically less attention
from the geothermal industry than has resource assessment and production.
EVIDENCE OF LARGE SCALE BRINE DISPOSAL
Large quantities of brine effluent produced by the Frasch sulfur industry and the oil and gas industry are
disposed of annually along the Gulf Coast Plain. The Frasch sulfur industry currently disposes of its high
salinity mine "bleed" fluids by draining them into bodies of saline water or by holding them in large
ponds preparatory to discharge into fresh water streams at flood stage. Although new disposal projects
of this type are possible, the probability of such a project being permitted is low. For some years the
oil and gas industry used brine pits for oil field brine disposal; that practice led to saline creeks, salination
of potable ground water, and a change to deep, protected subsurface disposal.
Many producing oil and gas fields produce large quantities of brine along with petroleum products; a
good example is the East Texas field. There the problem was so important that a special company-the
East Texas Salt Water Disposal Company-was established to collect and dispose of the brines produced
by member operators. The quantities of brine injected daily are large, but it is important to note that the
brines are injected over a very large area. Considerable quantities of saline water (> 3,000 ppm
dissolved solids) are injected into oil and gas fields for secondary recovery and pressure maintenance
purposes. The Texas Railroad Commission (1972) reported that secondary recovery saline water injection
in all Texas districts during 1971 amounted to 1.31 x 1(1' BBL. Districts 2, 3, and 4, which include the
Texas Gulf Coast Plain, had secondary recovery saline water injection of 218 x 1(f BBLs in 1971 (or
about 600,000 BBL/Day) in an area of about 50,000 square miles.
It is true that not all oil and gas field brines are injected into producing reservoirs for secondary recovery
or pressure maintenance. The volume of fluids not injected for secondary recovery or pressure
maintenance is probably much larger than that used for recovery and maintenance.
Saline water injection strictly for disposal is performed under approximately 190 separate permits in
Nueces County and 150 in San Patricio County (Railroad Commission, 1975), as an example. Many of
these operations are located within the Corpus Christi fairway. The injection zone depths are from 1,000
to 7,000 feet below sea level. The production zones from which the fluids originate are located from
1,000 to 7,000 feet below sea level. Injection we1\head pressures range from 50 to 1,000 psia.