Uncertainty analysis on environmental impacts of hydraulic fracturing

Abstract

Uncertainty is an undeniable aspect of underground operations, such as wellbore stimulation treatments, where combined rock and fluid interaction add a layer of complexity to the uncertainty. There are social and environmental concerns about the probable outcome of operations like hydraulic fracturing. Hydraulic fracturing treatments may affect the integrity of sub-surface geological strata or might initiate unexpected potential risks to the environment when the created fracture extends beyond its engineered design. Therefore, it is necessary to investigate a range of possible scenarios by which the fracture may experience a deviation from its planned behaviour. In this study, we model the uncertainty associated with hydraulic fracturing using fracture growth simulation. The uncertainty of a range of treatment parameters, such as pumping flow rate, injection duration and mechanical properties of the underground geological layer, is investigated. Monte Carlo simulation is used to examine different probable fracturing scenarios and numerous fracturing simulations with numerical and analytical models. The probability analysis is performed in a case study to identify the cumulative distribution functions (CDFs) of fracture growth. The emerging least, median and most likely situations of fracture growth are analysed to evaluate the fracturing uncertainty. Our results indicate that the numerical modelling approach may predict a more extensive fracture growth in the vertical plane. The numerical model may suggest a more conservative way to address environmental concerns. The resulting cumulative distribution of probabilities suggests the CDFs of the analytical model as the lower band for fracture length, whereas the numerical CDFs presents the upper band.