US 4,540,882 A · Method of determining drilling fluid invasion

Abstract

A method of determining the invasion of drilling fluid into a core sample taken from a borehole. A first material is added to the drilling fluid to obtain a first fluid that has an effective atomic number that is different than the effective atomic number of the connate fluids in the rock formation surrounding the borehole. A preserved core sample is collected from the borehole for scanning by a computerized axial tomographic scanner (CAT) to determine the attenuation coefficients at a plurality of points in a cross section of the core sample. The preserved core sample is scanned with a CAT at first and second energies, and the determined attenuation coefficients for the plurality of points in the cross section at each energy are used to determine an atomic number image for the cross section of the core sample. The depth of invasion of the first fluid is then determined from the atomic number image, as an indication of the depth of invasion of the drilling fluid into the core sample.

Claims25

Dependent claims

A method of determining the invasion of drilling fluid into a core sample from a borehole, said method comprising the steps of:

adding a first material to the drilling fluid to obtain a first fluid that has an effective atomic number that is different than the effective atomic number of the connate fluids in the rock formation surrounding said borehole;
collecting a preserved core sample from said borehole;
scanning said core sample with a computerized axial tomographic scanner (CAT) at a first energy to determine the attenuation coefficient at a plurality of points in a cross section of said core sample at said first energy;
scanning said core sample with a CAT at a second energy to determine the attenuation coefficient at said plurality of points in said cross section of said core sample at said second energy;
using the attenuation coefficients determined for said core sample at said first and second energies to determine an atomic number image for said cross section of said core sample;
determining from said atomic number image the depth of invasion of said first fluid into said core sample as an indication of the depth of invasion of said drilling fluid.

3 more elements

A method of determining the invasion of drilling fluid into a core sample from a borehole, said method comprising the steps of:

adding a first material havng a K-edge at a first energy to the drilling fluid;
collecting a preserved sample from said borehole;
scanning said core sample with a computerized axial tomographic scanner (CAT) at a second mean energy that is less than said first energy to determine the attenuation coefficients at a plurality of points in a cross section of said core sample at said second energy;
scanning said core sample with a CAT at a third mean energy that is greater than said first energy to determine the attenuation coefficients at said plurality of points in said cross section at said third energy;
using the attenuation coefficients determined for said core sample at said second and third energies to determine a concentration map of said first material in said cross section;
determining from said concentration map the depth of invasion into said core sample of said first material as an indication of the depth of invasion of said drilling fluid.

3 more elements

A method of determining the invasion of drilling fluid into a core sample from a borehole, said method comprising the steps of:

adding a first material to the drilling fluid to obtain a first fluid that has either an effective atomic number that is different than the effective atomic number of the connate fluids in the rock formation surrounding said borehole or a density that is different than the density of the connate fluids in the rock formation surrounding said borehole or both;
collecting a preserved core sample from said borehole;
scanning said core sample with a computerized axial tomographic scanner (CAT) at a first energy to determine the attenuation coefficient at a plurality of points in a cross section of said core sample at said first energy;
determining from said attenuation coefficients for said plurality of points the depth of invasion of said first fluid into said core sample as an indication of the depth of invasion of said drilling fluid.

1 more element

Dependencies are inferred from the claim text.

Method of determining drilling fluid invasion

Life of this patent

Method of determining drilling fluid invasion

Life of this patent

Abstract

Claims25