Geochemical Sourcing of Produced Waters From Soil Dumps and Spills: A Case Study From the Permian Basin
In some cases produced waters associated with oil and gas development are released into the environment, often directly onto the surface, which subsequently contaminates soils or nearby water bodies. The U.S. Geological Survey and Bureau of Land Management collected 51 soil samples (23 control and 28 spill, primarily from 0-5 cm depth) from 7 sites in the Permian Basin affected by produced water dumping to determine the source reservoir (conventional oil, tight oil, or conventional gas) of the residual produced water. Soils from spill sites are enriched 3 to 5.5 times (averages) in water extractable Sr, Mg, K, Ca, SO4, Na, and Cl, all found in local produced water, relative to control sites. These sites are also depleted in water extractable Fe, Al, and Si relative to control sites, suggesting that produced water dumping may have transported colloidal materials away from the soil surface. Relationships between control site-corrected water extractable Br, Cl, and Na concentration data indicate that the dumped produced water is paleoseawater. Paleoseawater sourced brines are typically found in deeper petroleum reservoirs in the Permian Basin, rather than meteoric water in shallower, conventional oil reservoirs. Initial model results from positive matrix factorization account for 95% of the variance in the total water soluble mass from 3 sources: 1) fracturing fluid or early flowback (large contributions to Si, B, and K); 2) formation water (large contributions to Ba and Sr); and 3) native salts (very low contributions to Si, Li, and Ba). For many of the spill site soil samples, Raman spectroscopy identified aromatic hydrocarbons and in one sample, sorbed sulfate from oil and produced waters, respectively. Leachable isotope ratios of δ¹¹B and ⁸⁷Sr/⁸⁶Sr and whole sample 228Ra/226Ra ratios from the soils will be compared against values from produced waters for potential end-member waters collected within 5 km of the spill sites. These results will be followed by a complementary study examining the environmental effects from produced water dumps on local flora and fauna.
AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019