The Cerro Prieto geothermal field is located 30 km southeast of The border city of Mexicali, México. Surface exploration of this field was begun in 1959, and the first shallow drilling was made in 1961. In 1964, three exploration wells of greater depths were drilled, and later both exploration and production wells were constructed. To date, a total of 40 wells have been drilled (Fig. 1). In 1973, the two primary units (37.5 MW each) of the Cerro Prieto Plant I went into operation, generating 75,000 KW total. Since that time the two units have been in continuous operation except during preventive maintenance shutdowns or for some other contingency in the system. Each unit required maintenance once a year during the first few years, but more recently the maintenance schedule has been lenghthened to a year and a half. Consideration is now being given to extending this to two years. This has been possible because of improvements in the steam separation equipment as a result of condensate purge, as well as better overall operation of equipment in the plant. Occasionally there are unscheduled brief shutdowns due to problems in the auxiliary equipment or systems in contact with the geothermal fluid. In Cerro Prieto the geothermal fluid in contact with different equipment contains salts (e.g., sodium chloride, potassium chloride, silica, calcium and magnesium chlorides, fluorides, borates, sulfates, carbonates, etc.) and gases (e.g., hydrogen sulfide, carbon dioxide, methane, hydrogen, etc.). The majority of these components can be corrosive, depending on the surrounding conditions, especially if atmospheric oxygen is present.
