Impact of Organics and Carbonates on the Oxidation and Precipitation of Iron during Hydraulic Fracturing of Shale

Abstract

Hydraulic fracturing of unconventional hydrocarbon reservoirs is critical to the United States energy portfolio; however, hydrocarbon production from newly fractured wells generally declines rapidly over the initial months of production. One possible reason for this decrease, especially over time scales of several months, is the mineralization and clogging of microfracture networks and pores proximal to propped fractures. One important but relatively unexplored class of reactions that could contribute to these problems is oxidation of Fe(II) derived from Fe(II)-bearing phases (primarily pyrite, siderite, and Fe(II) bound directly to organic matter) by the oxic fracture fluid and subsequent precipitation of Fe(III)-(oxy)hydroxides. The extent to which such reactions occur and their rates, mineral products, and physical locations within shale pore spaces are unknown. To develop a foundational understanding of potential impacts of shale iron chemistry on hydraulic stimulation, we reacted sand-sized (150-250 μm) and whole rock chips (cm-scale) of shales from four different formations

Effect of maturity and mineralogy on fluid-rock reactions in the Marcellus Shale

“…The low pH of NR-PF and HPT-PF is a common observation amongst HFF used in the Marcellus Shale region (Jew et al, 2017). HCl is a common additive used to prevent scaling of secondary minerals and was also used in creating the synthetic HFF used in this study.…”

“…In some cases, the shale acts as a buffering agent with increasing amounts of carbonate material and calcite dissolution. Previous fluid-rock reaction studies, conducted at ambient pressures, have shown that the dissolution or precipitation of iron bearing minerals is dependent upon dissolved organic compounds, carbonate content of the shale during (buffering capacity) and the overall pH of the system (Harrison et al, 2017, Jew et al, 2017.…”

Marcellus Shale Fracking and Susquehanna River Stakeholder Attitudes: A Five-Year Update

“…to [17]. In general, the average first year decline in natural gas production rates across Pennsylvania resemble a hockey stick ( Figure 5) with the drop off ranging from 60 to 80 percent.…”

“…The Susquehanna River Basin is in essence "the canary in the coal mine". If the rapid depletion of fracked well production after the first year and the predictions for growing demand to support natural gas pipeline shipments globally hold sway, the Basin is only in the early stages of development and thousands more wells will be drilled and fracked [17]. Conversely, if technological innovations lead to increased production from refracturing existing wells, then the industrialization of the Susquehanna River Basin could be reduced [18].…”

“…The Annual Energy Outlook 2017 projects the U.S. to be a net exporter of natural gas by 2018 [27], even though fracking production from a newly drilled well drops significantly within several months of initial production [17]. In general, the average first year decline in natural gas production rates across Pennsylvania resemble a hockey stick ( Figure 5) with the drop off ranging from 60 to 80 percent.…”