(270c) Evaluation of Iron Precipitation in the Utica/Point Pleasant Unconventional Play Using Laser Induced Breakdown Spectroscopy (LIBS)

The development of U.S. unconventional resources has had a dramatic impact on global energy supply, with the U.S. becoming the world’s leading producer of petroleum and natural gas. This change has been beneficial to the public lowering energy prices, while increasing energy security. Unconventional (or shale) resources differ from conventional reservoirs in a multitude of ways. Unconventional plays undergo significant production drops up to 75% [1] after one year, compared to 5% in conventional wells [2]. Unconventional wells also differ structurally and geologically as they consist of micro-pore and mainly nano-pore structures of interbedded carbonate and hydrocarbon containing shale layers which serve as the source for reactions with fracturing fluid. A majority of the reactions that occur during fracture process happen in the early stages, as the fracturing fluid has yet to come to equilibrium with the reservoir. While some reactions will create the pathways for hydrocarbons to flow through the well; others may cause the shale surface to be coated with insoluble barium, calcium, strontium or iron based solids/precipitate. These insoluble solids tend to clog the fracture and pore networks creating large decreases in production. Prevention of scaling is vital for maintaining well integrity, which is usually achieved by adding scale inhibitors to the fracturing fluid. However in some wells, a scale inhibitor may be incompatible with well geology or ineffective once equilibrium has been reached resulting in scaling and decrease production. Understanding shale-fluid chemistry aids identification of effective scale inhibitor(s) or fracturing fluid formulation modification to improve well performance.

Ohio University (OHIO) is investigating scale formation as significant contributor to unconventional well performance loss, with a particular focus on the Utica/Point Pleasant (UPP) shale play. Shale-fluid interactions are being investigated in bench-scale equipment at reservoir conditions. Previously, it was found iron-based precipitates are forming in UPP wells under experimental trials and iron control additives are effective in maintaining iron in the aqueous phase. This study will evaluate modifications to hydraulic fracturing formula chemistry in order to evaluate the effect on iron precipitation. Pre- and post-trial analysis of the shale surfaces will be performed using Laser-Induced Breakdown Spectroscopy (LIBS), and fluids will be analyzed using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) and Ultra-Violet Visible spectroscopy (UV-Vis). The effect of various commercially available inhibitors and their concentrations will be evaluated. In addition, modeling of the shale-fluid interactions using Geochemist Workbench will be performed and presented.

[1] H. Wachtmeister, L. Lund, K. Aleklett, and M. Höök, “Production Decline Curves of Tight Oil Wells in Eagle Ford Shale,” Nat. Resour. Res., vol. 26, no. 3, pp. 365–377, Jul. 2017.

[2] M. Höök, R. Hirsch, and K. Aleklett, “Giant oil field decline rates and their influence on world oil production,” China Energy Effic., vol. 37, no. 6, pp. 2262–2272, Jun. 2009.