Final answer:
Tortuosity in the frac proppant pack relates to the complexity of fluid pathways and impacts the flowback to the wellbore, affecting the rate at which fracturing fluid, containing various contaminants, is removed from fracture networks in the rock.
Step-by-step explanation:
Tortuosity in a frac proppant pack plays a significant role in hydraulic fracturing, particularly concerning flowback to the wellbore. In the context of hydraulic fracturing, or 'fracing,' a mixture of water, sand, and chemicals is injected at high pressure into horizontally drilled wells. This process creates fractures in the rock layer (such as the Marcellus Shale), and these fissures are held open by sand particles, known as proppant, allowing natural gas or oil to flow to the wellbore.
The tortuosity refers to the complexity or twistiness of the pathways through which the fluids must travel within the proppant pack. High tortuosity means that the pathways for the fluids, including the fracking fluid flowback, are more complex and convoluted. This can inhibit the flowback rate, potentially trapping more chemicals and contaminants within the proppant pack, which may increase concerns over groundwater contamination if not managed properly.
Therefore, understanding and managing tortuosity is crucial in ensuring effective flowback and minimizing the potential environmental impacts associated with the release of harmful substances, such as heavy metals, VOCs, and other hazardous air pollutants contained within the flowback fluid.