Filtercake forming mechanisms at fracture and cavity openings

Abstract

Oil wells can be stimulated to increase productivity by creating fractures and cavities in the sides of the bore hole which extend into the surrounding rock. These high-permeability channels are created by pumping into the bore hole at high pressure, which can crack the rock.
Once established most of the subsequent fluid flows out of the fractures as a result of their high permeability, thus inhibiting further cracking. This problem is resolved by injecting a containing particles and fibres, to plug the fractures temporarily and allow another cycle of fracturing fluid to stimulate a different region of the oil well. Finally the plugs, termed are removed and oil production in the well commences.

In this report we investigate how the size and shape distributions, concentration, and material properties of particles and fibres in the diverter fluid affect the formation of the filtercakes. We consider how these properties may be engineered to maximize clogging in fractures and cavities, as near to the bore hole as possible, whilst minimizing the amount of material wasted.

The problem is approached by considering the two distinct aspects of the behaviour, namely the flow of particulates from the bore into the fracture, and the fracture clogging. A series of mathematical models are employed that elucidate the system behaviour, allowing us to offer guidance on the appropriate choice for the design parameters to optimize clogging.