Unconventional play produced water: a geochemical journey across Texas

Water produced from conventional oil and gas has historically been reinjected either as pressure support / water flood or disposed into permeable close-by formations. However, unconventional play produced water can only rely on the latter option, which has locally created issues of their own such as overcapacity and seismic activity and brought this usually minor operational aspect to the fore. Potential remedies include reuse of the produced water for stimulating additional wells, treatment of the water for different purposes such as irrigation, and extraction of valuable dissolved mineral resources. In the context of understanding the geochemistry of produced water of active unconventional plays in Texas, ~500 samples were taken and analyzed for major, minor and trace elements as well as for water isotopes and occasionally strontium and other isotopes. Making use of total dissolved solids (TDS), water isotopes, and stimulation and production history, unconventional produced water is assessed whether it is representative of formation water. Formation water TDS range from <20,000ppm to >300,000ppm with variable ionic make-up but always dominated by Na-Cl. In addition to promoting the practical operational objectives mentioned above, sampling of low-permeability formation waters, seldom undertaken in the past, adds to the general geochemical knowledge of the subsurface and informs regional-scale fluid flow within several basins.