Water as proppant

Abstract

The horizontal well with multiple transverse fractures, has proven to be a successful approach for production of gas from shale. As many as 80 fractures and nearly 10 million gallons of fracture fluid have been employed in a single well. However, unlike for conventional hydraulic fractures, in shale gas wells most of the treatment water never flows back. In this paper we postulate that the water has actually stayed in the created fractures and/or in enhanced natural fractures. The reason why fractures exhibit high conductivity flow behavior even with very little proppant is because the water injected in the fractures cannot leak off into the shale matrix, and relative permeability in the fracture impairs the water from flowing back. Water remaining in the fractures actually prevents them from closing. Gas bubbles or channels to the horizontal borehole through water in the fractures. In shale gas formations some diagnostic fluid injection tests appear to never exhibit closure or close with indicated fluid efficiency of 90% or more. In the period during execution and before flow back, water is too viscous for the large fluid volumes injected to flow into the extremely low permeability shale matrix. If treatment water could leak off, unpropped fractures in shale would likely close. Because the gas is water-saturated as it enters the water filled fracture, there is little tendency to vaporize the water. Therefore, water as proppant resolves both the question why so much treatment water never flows back and why fracture complexity can remain open indefinitely without proppant slurry. Copyright 2011, Society of Petroleum Engineers.