Traditional water analyses can be used to assess the compatibility of formation brines with other fluids prior to injection into a production facility as well as to determine contamination of freshwater. These conventional analyses, though well established, still have drawbacks such as long turnaround times, high costs associated with high quality results, and difficulties identifying possible contamination or incompatibility problems. The objective of this work is to combine data from a conventional physiochemical water analysis and δ18O and δ2H water isotope ratios, which are essential to better prepare for potential spills, to assess environmental hazards, evaluate potential incompatibilities, and achieve better water management.

In this study, water fingerprinting refers to a geochemical technique used to differentiate sources of water/brine that make up the produced water stream. Fingerprinting of formation fluids is not a new concept, different approaches have been used for more than thirty years. The standard approach used in the industry is based on the use of plots, such as Stiff and Piper Diagrams, Catalog Values, etc., to establish a water chemical fingerprint. Those methods compare parameters in diagrams and use ratios to define differences between the analyzed waters. In this study water composition and isotope ratios were used.

Data quality is called into question when standard methods designed for low TDS waters are applied to higher TDS oilfield derived fluids. An improved workflow and analysis scheme that combines two natural tracer approaches using standard water properties and stable isotope analyses is presented. This methodology has been applied successfully to a water allocation study where the produced water stream comprised of waters from multiple reservoirs. It has also been used to identify what fluids were produced after the hydraulic fracturing process. Of particular importance is the assessment of whether there is new water migrating into the system so any environmental impact can be identified and mitigated during individual well or on a broader field development operations.

This proposed, improved water fingerprinting methodology can be used as an inexpensive analytical tool to assess different water sources and to understand how a commingled produced water stream may evolve with time. Based on this approach questions such as ‘Is there new water source coming into the system?’, ‘Are any incompatibility issues caused by chemicals that have been used?’ or ‘Are the fracturing operations having an effect on the shallower freshwater acquirer systems?’ can be answered.

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