Method for determining porosity, clay content and mode of distribution in gas and oil bearing shaly sand reservoirs

Claim 1

A method for determining formation porosity and volume of clay content in fluid bearing shaly sand reservoirs, regardless of whether the density of the fluid is known, comprising: (a) determining which one of the following conditions obtain and proceeding to the method step indicated therewith: (i) density of hydrocarbons is known and there is no invasion of mud filtrate: step (b), (ii) density of hydrocarbons is known and there is invasion of mud filtrate: step (e), (iii) density of hydrocarbons is unknown and may vary, and clays which are present are dispersed clays only: step (c), (iv) density of hydrocarbons is unknown and may vary, and both dispersed and laminated clays are probably present: step (t), (b) determining the hydrogen index and electron density of the hydrocarbons, (c) selecting an arbitrary value for water saturation, (d) proceeding to step (g), (e) determining the depth of invasion, (f) determining a staring value for water saturation, (g) determining water saturation in the density and neutron zones of investigation; (h) determining the hydrogen index and electron density of the reservoir fluid using the water saturation values, (i) determining the volume of clay using the hydrogen index and electron density determined in the preceding step, (j) determining effective porosity using the clay volume determined in the preceding step, (k) computing water saturation using the porosity determined in the preceding step, the value which is computed becoming the latest computed water saturation value, (l) comparing the latest computed water saturation value with the later of the starting and previously computed values, and, until the latest computed value substantially agress with the value with which it is compared, returning to step (g) and using the latest computed water saturation value therein, (m) then utilizing the last values determined in steps (h) and (i) as the values for the volume of clay and the effective porosity, and (n) proceeding to step (z), (o) determining the apparent fluid density, (p) determining the apparent porosity using the apparent fluid density determined in the preceding step, (q) calculating the dispersed clay content using the apparent porosity determined in the preceding step, (r) determining the effective porosity using the dispersed clay content calculated in the preceding step, and (s) proceeding to step (z), (t) determining the laminated and dispersed clay volumes, (u) correcting the determined dispersed clay volume to compensate, where appropriate, for the presence of invasion, laminated clay, high water saturation, and very low and very high hydrocarbon density, (v) as a function of the laminated and dispersed clay volumes, selecting an initial value of effective porosity, (w) determining the hydrogen index and electron density of the reservoir fluid using the effective porosity value determined in the preceding step, (x) when the difference between the hydrogen index and the electron density determined in the preceding step is greater than a predetermined amount, reducing the value for the laminated clay volume and returning to step (u) until this condition is satisfied, (y) computing the effective porosity using at least one of the values determined in step (w), and (z) outputting the porosity and clay content values.

Claim 2

A method for determining formation porosity and volume of clay content in fluid bearing shaly sand reservoirs, regardless of whether the density of the fluid is known, comprising: (a) determining which one of the following conditions obtain and proceeding to the method step indicated therewith: (i) density of hydrocarbons is known and there is no invasion of mud filtrate: step (b), (ii) density of hydrocarbons is known and there is invasion of mud filtrate: step (e), (iii) density of hydrocarbons is unknown and may vary, and clays which are present are dispersed clays only: step (c), (iv) density of hydrocarbons is unknown and may vary, and both dispersed and laminated clays are probably present: step (t), (b) determining the hydrogen index and electron density of the hydrocarbons, (c) selecting an arbitrary value for water saturation, (d) proceeding to step (g), (e) determining the depth of invasion, (f) determining a staring value for water saturation, (g) determining water saturation in the density and neutron zones of investigation; (h) determining the hydrogen index and electron density of the reservoir fluid using the water saturation values, (i) determining the volume of clay using the hydrogen index and electron density determined in the preceding step, (j) determining effective porosity using the clay volume determined in the preceding step, (k) computing water saturation using the porosity determined in the preceding step, the value which is computed becoming the latest computed water saturation value, (l) comparing the latest computed water saturation value with the later of the starting and previously computed values, and, until the latest computed value substantially agress with the value with which it is compared, returning to step (g) and using the latest computed water saturation value therein, (m) then utilizing the last values determined in steps (h) and (i) as the values for the volume of clay and the effective porosity, and (n) proceeding to step (z), (o) determining the apparent fluid density, (p) determining the apparent porosity using the apparent fluid density determined in the preceding step, (q) calculating the dispersed clay content using the apparent porosity determined in the preceding step, (r) determining the effective porosity using the dispersed clay content calculated in the preceding step, and (s) proceeding to step (z), (t) determining the laminated and dispersed clay volumes, (u) correcting the determined dispersed clay volume to compensate, where appropriate, for the presence of invasion, laminated clay, high water saturation, and very low and very high hydrocarbon density, (v) as a function of the laminated and dispersed clay volumes, selecting an initial value of effective porosity, (w) determining the hydrogen index and electron density of the reservoir fluid using the effective porosity value determined in the preceding step, (x) when the difference between the hydrogen index and the electron density determined in the preceding step is greater than a predetermined amount, reducing the value for the laminated clay volume and returning to step (u) until this condition is satisfied, (y) computing the effective porosity using at least one of the values determined in step (w), and (z) outputting the porosity and clay content values.

Claim 8

A method for determining formation porosity and volume of clay content in fluid bearing shaly sand reservoirs wherein the clay may be dispersed or laminated or both forms of clay where the density of the hydrocarbons is unknown and may vary comprising the steps of: (t) determining first values for the laminated and dispersed clay volumes, (u) correcting the determined dispersed clay volume to compensate, where appropriate, for the presence of invasion, laminated clay, high water saturation, and very low and very high hydrocarbon density, (v) as a function of the laminated and dispersed clay volumes, selecting an initial value of effective porosity, (w) determining the hydrogen index and electron density of the reservoir fluid using the effective porosity value determined in the preceding step, (x) when the difference between the hydrogen index and the electron density determined in the preceding step is greater than a predetermined amount, reducing the value for the laminated clay volume and returning to step (u) until this condition is satisfied, (Y) computing the effective porosity using at least one of the values determined in step (w), and (z) outputting the porosity and clay content values.

Claim 9

A method for determining formation porosity and volume of clay content in fluid bearing shaly sand reservoirs wherein the clay may be dispersed or laminated or both forms of clay where the density of the hydrocarbons is unknown and may vary comprising the steps of: (t) determining first values for the laminated and dispersed clay volumes, (u) correcting the determined dispersed clay volume to compensate, where appropriate, for the presence of invasion, laminated clay, high water saturation, and very low and very high hydrocarbon density, (v) as a function of the laminated and dispersed clay volumes, selecting an initial value of effective porosity, (w) determining the hydrogen index and electron density of the reservoir fluid using the effective porosity value determined in the preceding step, (x) when the difference between the hydrogen index and the electron density determined in the preceding step is greater than a predetermined amount, reducing the value for the laminated clay volume and returning to step (u) until this condition is satisfied, (Y) computing the effective porosity using at least one of the values determined in step (w), and (z) outputting the porosity and clay content values.