Water Softening of High TDS Produced Water

Generating steam with an oil field water containing high concentration of total dissolved solids (TDS as sum of total ions) and high silica was tested at 1200 psi in the Wilmington Field in Wilmington, California. This work was during 1990 and 1991. Waters with total hardness of 1000-2500 ppm as CaCO 3 with 200-300 ppm silica and TDS of 10,000 and 28,000 were treated with conventional strong acid and weak acid softeners. The steam was generated in a small 1 MM Btu/hr steam generator at 75% and 70% steam quality respectively. Besides obtaining operating costs to compare with previous laboratory and field data, this pilot was to confirm on a larger scale, laboratory data that high TDS, high silica waters could be used in steam generation without silicate problems if the hardness and the iron level were controlled to low levels. Our previous experience had indicated that a low iron level was not controlled in most steam generation using recycle produced waters which resulted in silicate problems, sodium iron silicate or acmite. Other softener pretreat systems such as hot lime, caustic, and steam stripping were considered or tested and would need to be considered for a large installation with water of this high hardness. A patent on using steam stripping as a pretreatment has just been issued as the result of associated pilot testing. In water softening,TDS is usually the sum of the cations or anions as CaCO 3 but in this paper TDS is the sum of all the ions except sulfides unless otherwise noted.