(677d) Investigation of Scaling As a Means for Decreased Petroleum Production from the Utica/Point Pleasant Unconventional Play

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. Production wise unconventional plays see significantly larger production drops, about 75% [1], after one year compared to 5% in conventional [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 hydraulic fracturing materialize 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 precipitates. 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 lower production. Understanding, the mechanism of shale-fluid interactions will aid in identifying better hydraulic fracturing fluid chemistry to minimize or prevent formation of precipitates.

Ohio University (OHIO) is investigating scale formation as a means for the large decrease in production seen in unconventional wells, with a particular focus in the oil window of the Utica-Point Pleasant (UPP) Shale. In this work, shale-fluid interactions is investigated using experimental trials in a batch reactor at reservoir conditions. The effect of shale to fluid ratios to control reaction rates and scale inhibitors to prevent scale is also investigated. Pre- and post-trial analysis of the shale surfaces are performed using Scanning Electron Microscopy (SEM) paired with Energy-dispersive X-Ray spectroscopy (EDS) and Laser-Induced Breakdown Spectroscopy (LIBS), and fluids are analyzed using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) and Ion Chromatography (IC). Preliminary results in the absence of scale inhibitor indicate iron is a major concern for precipitation in the UPP oil window. These iron based scales are even formed at low pH values found in the hydraulic fracturing fluid chemistry. Additionally, Barium and strontium were found to be non-reactive. Furthermore, the effect of various commercially available scale inhibitors and different shale to fluid ratios will be presented. 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.