A New Hydraulic Fracturing Process
Authors: Kiel Othar M. 
Published: December 2007

In this new fracturing method, high-viscosity fracturing fluids are used to obtain greater fracture length and width. The technique is characterized by higher propagation pressures and lower fluid loss at the fracture face. A film of water surrounding the fracturing fluid reduces friction losses in the tubing, and this lowers surface treatment pressures and pumping power requirements.

Introduction

A new method has been developed in which high-viscosity fracturing fluids are used for stimulating production from formations having a wide range of production from formations having a wide range of permeabilities. The fluids that have been used to date permeabilities. The fluids that have been used to date have ranged generally from about 500 cp to about 100,000 cp at ambient temperatures. The new method is used commercially under the names "Superfrac", "Super Frac", and "Super Sand Frac". The preferred fluids for use in the new method are loose water-in-oil dispersions or emulsions prepared by blending brine and a surface-active agent into a crude oil or petroleum fraction that has these high viscosities. When properly prepared, these emulsions will not readily change composition in the presence of free water. The emulsions are isolated from the inner wall of the tubing string or casing by a film of free water during injection and are generally pumped with about the same pressure drop as 1-cp oil or water. Studies indicate that the free water is lost to the formation after the fluids enter the fracture and that the high viscosity fracturing fluid remains behind for propagation of the fracture and placement of the propping agent. propping agent. This technique can be used to fracture any formation, but it has particular advantages

when a large fracture conductivity ratio cannot be realized with small proppants, when thick or high-permeability formations are to be fractured, when a well must be fractured through small-diameter tubing or casing, and when proppant must be carried great distances from the wellbore.

This paper gives the relationships of fluid viscosity to fracture geometry and proppant placement, establishes the advantages of using high-viscosity fluids for stimulating high- and low-permeability formations, and tells how the high-viscosity fluid system is maintained and pumps and Field tests have shown that excellent, sustained productivity increases have been obtained with this new hydraulic fracturing process.

Fracture Geometry

The use of very viscous oils as fracturing fluids has several benefits, including good fluid-loss control, increased fracture width, and improved sand transport.

Fluid Loss Control

Since Howard and Fast showed that the rate of fluid leakoff from a fracture depends upon the resistance of the invaded zone, the resistance of the filter cake, and the resistance of the compressible formation fluids, much of the work on fracturing has been directed toward the use of water-based fluids that can be injected at high rates and toward the development of better fluid loss control additives. Results to date indicate that gelled fluids and other water-based systems generally have low viscosities under the temperature and shear conditions existing in most fractures, and also that fluid loss control additives are normally much less effective under dynamic filtration conditions than they were once thought to be. Increased fluid loss can explain many of the difficulties encountered in conventional fracturing operations.

JPT

P. 89