Thermo-Poro-Elasticity

Water injection is a long-term, low viscosity operation. There can be significant changes in the total stresses due to reservoir cooling (seawater), reservoir heating (possibly produced water) and pore pressure changes with the substantial injection volumes. Perkins and Gonzalez, 1984, 1985, provided a view of stress alteration due to cold water injection. "During ordinary hydraulic fracturing operations - leakoff is controlled so that injected fluid volumes will be minimized. As a result, pressure and temperature changes in the rock surrounding the fracture do not ordinarily have a very significant effect on the fracturing operation. Therefore, the primary concern has been the effect that temperature has on fracturing fluid rheology and leakoff behavior."

"... in some cases injection of cold fluid can significantly reduce tangential earth stresses around an injection well. It follows that vertical hydraulic fractures can be initiated and propagated at lower pressures than would be expected for hydraulic fracturing of a nearby producing well. The injection well fracture, however, would tend to be confined to the low stress region that lies within the flooded zone surrounding the injection well. If the injection rate is sufficiently high, or if injected solids plug the face of the fracture, then the pressure within the fracture could rise, thus permitting the fracture to extend beyond the confines of the cooled region. After breakout, the fracture extension pressure should approach (and probably exceed because of the increased pressure field surrounding an injection well) the fracture extension pressure of nearby producing wells. The thermoelastic effect could have significant impact on fracture confinement at bounding zones. For injection wells, impermeable layers could confine fractures in vertical extent partly because the impermeable layers have not been cooled as much as the pay zone."

Similar considerations apply to competing poroelastic effects. Detailed considerations of poroelastic calculations are available in the literature (for example, Detournay et al., 1989 ). Their real significance may be in produced water reinjection. Stevens et al., 2000, gave examples specifically relevant to produced water reinjection. "Cooling is principally due to convection, and since the rock heat capacity per unit reservoir volume is approximately twice that of the water, the thermal front advances at about one-third the rate of the water saturation front." These are two competing phenomena. Thermal changes in viscosity are also a factor.

<Fluids Fluids   Stimulation fracturing fluids are usually viscofied, in order to carry proppant. The characteristic elements of produced water are micron-sized solids, bacteria and carried-over oil.
Differences From Stimulation Models

An Introduction to PWRI Models

PWRI Models
  Plugging> Plugging   Plugging due to solids in produced water is represented with varying degrees of sophistication in PWRI fracturing models. What are the basic considerations?
 
Differences From Stimulation Models

Types of PWRI Models

Audit of PWRI Models

PWRI Fluids Top Previous Main Documents