Dilatant Technology

There is more than one definition of Dilatancy:

1.   Dilatancy is a permanent deformation registered in rocks that are subjected to non-uniform dynamic stress. It can be best explained as volume changes, porosity increases of up to 60% and permeability increases 200% or more, due to micro-fracturing or cracking that have been measured in laboratory experiments using core samples and in the field tests by implementing SWTorpedo well stimulation services.

Dilatancy

2.   Dilatancy is the increase in volume of a granular substance when its shape is changed, because of greater distance between its component particles.

3.   Dilatancy is the deformation by expansion or volumetric change of the rock properties.

Dilatant Technology is used for Well Stimulation. Its goal is to increase production of oil and gas cost-effectively by increasing permeability of the producing interval. Based on the information provided by the client Sigor Corporation's employees design SWTorpedo Tool

A

B

C

D

Figure 1. 
A - Schematic view of internal design; B - Top view with Tool Head attached; C - Bottom view; D - Tool Head.

SWTorpedo internal designs are individual for each well and No mass production is possible. High explosives such as TNT, HMX or RDX are strategically placed in the Tool and detonated in rapid succession to generate multiple shock waves that in return creates changing in time stress state which approaching uniaxial compression and perfect shift. At this point fast growing increase in volume of rock can be observed, even though active forces are still working in compressive regime.

Explosive forces create pressure of 10⁸...10⁹ MPa per second. In such environment areas of initiated fractures and rock crushing are multiple. The area of Dilatancy or micro-fractures is on average 6 times larger than an area of radial fractures.

Shear strength of rock's sediment depend on:

1.   Normal stresses

2.   Cohesion

·       Electrostatic forces important for particles < 1 micron

·       Not important are the chemical bonds

3.   Internal friction

·       Resistance of particles

·       Angle of internal friction depend on:

-      Grain arrangement

-      Size

-      Shape

-      Resistance to crushing

Factors that affect deformation are:

1.   Dilatancy

2.   Grain crushing

3.   Size of the grain

4.   Thermal characteristics

5.   Spatial variations in bed strength

6.   Decoupling

Figure 2.  Volumetric deconsolidation of sandstone:
    Line 1 (dash) depict static loads as a precondition,
    Line 2, 3 and 4 depict dynamic stress generate by multiple shock waves.
    Where:

q                      Volumetric deformation by expansion or Dilatancy
σ₃/σ₁=0            depict by Line 1 and 2
σ₃/σ₁=0.132     depict by Line 3
σ₃/σ₁=0.144     depict by Line 4
σ₃/σ₁=1            depict by Line 5

Click on the following link to check references: Development of microcracks Slide#45