(681e) Incorporation of Sustainability and Economic Considerations in Process Control of Hydraulic Fracturing in Unconventional Reservoirs

Typically, the term shale oil refers to natural oil trapped in rock of low porosity and ultra-low permeability. What has made the recovery of shale oil and gas economically viable is the extensive use of hydraulic fracturing. Research on the relationship between the distribution of propping agent, called proppant, and well performance indicates that uniformity of proppant bank height and suspended proppant concentration across the fracture at the end of pumping determines the productivity of produced wells. Therefore, in our previous work [2], we calculated the optimal flow rate of fracturing fluids, the optimal number of horizontal wells and fractures per well, the length of the fracture, and the drainage area aspect ratio that maximize the overall productivity of the well-fracture system. It is important to note that the obtained pumping schedule did not consider the environmental and economic impacts of the post-fracking process such as treatment and reuse of flowback and produced water from fractured wells; therefore, from the sustainability point of view, utilizing energy and water resources just enough to stimulate the formation was not of our interest.

Motivated by this consideration, in this work, we propose a new control framework that has integrated sustainability considerations into the post-fracturing process. In this regard, a dynamic model is developed to describe the flow rate and the concentration of total dissolved solids (TDS) in flowback water from fractured wells, provided that the amount of water injected into the fracture well is known. Then, a thermal membrane distillation (TMD) unit is considered for the removal of TDS. A multiobjective optimization problem is formulated to determine the amount of water to be injected by considering the entire superstructure that consists of hydraulic fracturing, storage, transportation, and water treatment, maximizing annualized profit from recovered water per period while minimizing the water footprint of the process through Pareto optimal solution. The obtained water amount will be included in a model-based pumping schedule design technique to compute the optimal pumping schedule during a hydraulic fracturing process that will regulate the distribution of proppant bank height and suspended proppant concentration [2]; this flow may not be sufficient to achieve the desired fracture length, which will lower the productivity of the produced well, however, it will maximize the annualized profit of the entire superstructure as well as reduce environmental impact.

References:

[1] Siddhamshetty, P., Kwon, J.S., Liu, S., Valkó, P. (2017), Feedback control of proppant bank heights during hydraulic fracturing for enhanced productivity in shale formations. AIChE J., 64, 138-147.

[2]Elsayed, N. A., Barrufet, M. A., Eljack, F. T., El-Halwagi, M. M. (2015). Optimal design of thermal membrane distillation systems for the treatment of shale gas flowback water. Int. J. Membr. Sci. Technol., 2, 1-9.