Legal aspects and technical alternatives for the treatment of reservoir brines at the Activo Luna Oilfield, Mexico

Deep formation water, extracted as an undesired byproduct from on-shore production wells at the Activo Luna oilfield and processed in adjacent oil fields, are highly enriched in salt minerals, especially in sodium chloride (NaCl) (262 000 mg/L), but also in metals and nonmetals, such as strontium (Sr) (2068 mg/L), bromine (Br) (2034 mg/L), boron (B) (396 mg/ Q, iodine (1) (43.4 mg/L), selenium (Se) (3.74 mg/L), and arsenic (As) (0.55 mg/L. Direct reinjection of the brine underground is not possible because of elevated pressure conditions within the petroleum reservoir. The disposal into near shore areas of the Gulf of Mexico without treatment must be rejected because of a) elevated concentrations of some toxic elements, such as B, silver (Ag), thallium (Tl), Se and cadmium (Cd), which exceed permissible limits of environmental legislation for surface discharge (Official Mexican norms NOM-001-ECOL-1998 and CE-CCA-001/89), and b) differences in density that could cause the descent of hypersaline fluid to the ocean floor, potentially affecting the diversity and survival of the benthic ecosystem. Conventional treatment techniques, such as microfiltration or reverse osmosis, are not suitable for the Activo Luna brines because of their extreme mineralization, which will cause pressure conditions exceeding 200 bars across the membrane. As an alternative process, the evaporation of the entire brine volume of approximately 200 m(3)/day by solar ponds or industrial crystallization plants is suggested. The residual precipitated residuals are composed mainly of chlorine (Cl) (9460 tons/year), sodium (Na) (4230 tons/ year), calcium (Ca) (1028 tons/year), potassium (K) (207 tons/year), and magnesium (Mg) (65.8 tons/year). As an alternative to its disposal on a dumpsite, some special minerals (especially NaCl, Mg, Sr, and Br) could be recovered for its economic value.