Controlled permeability enhancement in the near well field using “smart” cyclical pulses

Abstract

Key to most geothermal applications is ensuring that there is high enough subsurface permeability within the reservoir for the overall operation to circulate fluid without excessive pressure gradients or parasitic energy costs whilst maintaining a workable temperature. The permeability of the near well field is particularly dominant in both dictating the fluid connection to the far field reservoir, and the connection to natural preferential flow features, such as fractures as part of a fracture and discontinuity network. Being able to enhance the near well field permeability is therefore extremely valuable, reducing the costs of the fluid circulation operation and potentially accessing larger areas of the reservoir pore space. Soft cyclical stimulation techniques present an opportunity of being able to enhance near well field permeability without causing significant microseismic hazard. By managing pulse stimulation frequencies using smart feedback, we demonstrate, through both experimental work and modelling, how it is possible to control the superposition of pulses within the borehole. By using the physical phenomena of pulse superposition to create enhanced pulses, the surface working pulse pressure remains well below the fracture pressure of the rock, and thereby increases the borehole life as well as reducing the overall risk of unexpected microseismic events through pressure spikes. The repeated application of these enhanced pulses can lead to the growth and development of new fractures, and the increase in shear movement thereby mismatch along existing fractures. The combined effect of these processes should lead to a significant enhancement of the near well permeability and an enhancement in the productivity of wells.