Method for determining porosity in an invaded gas reservoir
AssigneeSchlumberger Technology Corporation
InventorUrmi DasGupta
Life of this patent
Estimating the term…
Abstract
The formation porosity of a partially invaded gas reservoir in subsurface earth formation is determined from the sum of percentages of density and neutron tool porosities. During the method of this invention, density tool and neutron tool porosity measurements are taken of the formation. These porosity measurements are fitted to a predetermined porosity to determine the percentage of each porosity measurement that will be summed to estimate the formation porosity of the gas reservoir. The percentages of the density and neutron porosity measurements are dependent on a correction factor that is determined from the fitting process.
Claims23
A method of determining the porosity of a gas reservoir invaded by a fluid in an earth formation without knowledge of the formation lithology or the depth of invasion of the invading fluid comprising the steps of:
- (a) determining a porosity measurement of said formation from a density tool;
- (b) determining a porosity measurement of said formation from a neutron tool, said neutron tool porosity measurement being taken in a manner such that the depth of investigation of the neutron tool is similar to the depth of investigation of said density tool;
- (c) determining a correction factor from said porosity measurements;
- (d) incorporating said correction factor into the porosity measurements;
- and
- (e) determining true porosity of said gas reservoir from said density tool and neutron tool porosity measurements, said porosity being the sum of percentages of density tool and neutron tool porosities, said percentages being interdependent.
A method of determining the porosity of a gas reservoir invaded by a fluid in an earth formation, using density and neutron tool porosity measurements taken in a borehole traversing said earth formation, said method being insensitive to invasion depth of said fluid and comprising the steps of:
- (a) choosing a detector/source spacing of the neutron tool such that the depth of investigation of said tools is similar;
- (b) matching the depths of investigation of said density and neutron tools;
- (c) determining a porosity measurement of the earth formation from each of said density and neutron tools;
- (d) combining said porosity measurements from said density and neutron tools;
- and
- (e) generating a true reservoir porosity measurement, said porosity measurement being insensitive to the depth of invasion of fluids in said gas reservoir.
An apparatus for measuring the porosity of a gas reservoir invaded by a fluid in an earth formation without knowledge of the depth of invasion of the invading fluid or the formation lithology comprising:
- (a) a density tool capable of taking a porosity measurement;
- (b) a neutron tool adjacent said density tool, said neutron tool having a source and detector spaced apart at a distance such that the depth of investigation of said neutron tool is similar to the depth of investigation of said density tool;
- and
- (c) a means for combining density and neutron tool porosity measurements to get a true porosity measurement of said invaded gas reservoir.
Dependencies are inferred from the claim text.