Method for determining properties of fractured rock formations using computer tomograpic images thereof

1. A method for estimating a petrophysical parameter of a porous material from a sample thereof, comprising:

making a three dimensional tomographic image of the sample of the material;

segmenting the image into pixels each representing pore space or rock grain;

determining porosity of the sample from the segmented image;

introducing an image of at least one fracture into the segmented image to generate a fractured image;

determining porosity of the fractured image;

determining at least one petrophysical parameter comprising permeability, electrical resistivity formation factor, elastic modulus, bulk modulus or shear modulus; and

at least one of storing and displaying the at least one petrophysical parameter.

2. The method of claim 1 wherein the tomographic image comprises a value of gray scale allocated to each of a plurality of pixels in the image.

3. The method of claim 2 wherein the segmenting comprises:

(a) determining an initial gray scale threshold for each of pore space and rock grain;

(b) allocating each pixel in the image to pore space or rock grain for each pixel meeting threshold criteria for each of the pore space and rock grain thresholds, respectively;

(c) interrogating pixels adjacent to each seed;

(d) allocating the interrogated adjacent pixels previously not allocated to a seed to the pore space seed or the rock grain seed based on threshold criteria; and

(e) repeating (c) and (d) until substantially all pixels in the image are allocated to the rock grain or the pore space.

4. The method of claim 3 wherein the determining initial gray scale thresholds comprises histogram analysis of the tomographic image.

5. The method of claim 3 wherein the allocating interrogated adjacent pixels comprises determining a difference between a gray scale value and a gray scale value of the adjacent pixel in the seed, and allocating the interrogated pixel to the seed if the difference falls below a selected threshold.

6. The method of claim 5 further comprising:

determining whether unallocated pixels exist in the image;

increasing the selected difference threshold; and

repeating the interrogating adjacent and allocating the interrogate pixels having gray scale values wherein the difference is below the increased difference threshold.

7. The method of claim 1 wherein the material comprises a rock formation.

8. The method of claim 7 wherein the at least one petrophysical parameter comprises permeability.

9. The method of claim 8 wherein permeability is estimated using the Lattice-Boltzmann approximation.

10. The method of claim 7 wherein the at least one petrophysical parameter comprises electrical resistivity formation factor.

11. The method of claim 7 wherein the at least one petrophysical parameter comprises at least one of elastic modulus, bulk modulus and shear modulus.

12. The method of claim 1 wherein the introducing at least one fracture includes defining a plane at a selected orientation with respect to the segmented image, and changing pixels allocated to rock grain into pixels allocated to pore space at a selected distance normal to the defined plane.