Low-cost but accurate radioactive logging for determining gas saturation in a reservoir

Claim 1

A method of measuring the concentration of gas in an earth formation constituting a given depth interval of a region surrounding a well bore, comprising: a. running, over said given depth interval, separate first and second logs whose response to the carbon and oxygen contents of said region is substantially linear throughout the range of expectable carbon and oxygen contents, respectively, b. injecting into said region a solvent capable of replacing substantially all of the previous fluids in the part of said region to which said logs are responsive, c. running said logs a second time to obtain respective signals changed from those of the first running, the changes reflecting the effects of Step (b), d. injecting brine to replace substantially all of said solvent within the part of said region to which said logs are responsive, e. running said logs a third time to obtain signals changed from those of the second running, the changes reflecting the effects of Step (d), f. calculating gas saturation of said region from respective corresponding measured differences in the signals of said separate first and second logs of Steps (a), (c), and (e), respectively, in accordance with the Equation: ##EQU9## wherein C 1 , C 2 and C 3 and SO 1 , SO 2 and SO 3 refer to separate log responses recorded in Steps (a), (c) and (e) respectively; ρ d = density of liquid in the formation after Step (b); F o ,d = ratio of the mass of oxygen to the total mass of the above-specified liquid; F c ,d = ratio of the mass of carbon to the total mass of the above-specified liquid; ρ w = density of the formation brine; ρ o = density of the oil in the formation; F o ,w = ratio of the mass of oxygen to the over-all mass of the formation brine; F c ,w = ratio of the mass of carbon to the total mass of the oil; and Sg = fraction of the pore volume containing gas.

Claim 2

A method of measuring the concentration of gas in an earth formation constituting a given depth interval of a region surrounding a well bore, comprising: a. running, over said given depth interval, separate first and second logs whose response to the carbon and oxygen contents of said region is substantially linear throughout the range of expectable carbon and oxygen contents, respectively, b. injecting into said region a solvent capable of replacing substantially all of the previous fluids in the part of said region to which said logs are responsive, c. running said logs a second time to obtain respective signals changed from those of the first running, the changes reflecting the effects of Step (b), d. injecting brine to replace substantially all of said solvent within the part of said region to which said logs are responsive, e. running said logs a third time to obtain signals changed from those of the second running, the changes reflecting the effects of Step (d), f. calculating gas saturation of said region from respective corresponding measured differences in the signals of said separate first and second logs of Steps (a), (c), and (e), respectively, in accordance with the Equation: ##EQU9## wherein C 1 , C 2 and C 3 and SO 1 , SO 2 and SO 3 refer to separate log responses recorded in Steps (a), (c) and (e) respectively; ρ d = density of liquid in the formation after Step (b); F o ,d = ratio of the mass of oxygen to the total mass of the above-specified liquid; F c ,d = ratio of the mass of carbon to the total mass of the above-specified liquid; ρ w = density of the formation brine; ρ o = density of the oil in the formation; F o ,w = ratio of the mass of oxygen to the over-all mass of the formation brine; F c ,w = ratio of the mass of carbon to the total mass of the oil; and Sg = fraction of the pore volume containing gas.

Claim 3

A method of measuring the concentration of gas in an earth formation constituting a given depth interval of a region surrounding a well bore, comprising: a. running, over said given depth interval, separate first and second logs with respective responses to the carbon and oxygen content of said region and whose responses are substantially linear throughout the range of expectable carbon and oxygen contents, and running, over one or more other depth intervals known individually or in combination to contain substantially no water and no oil, the same said log, b. injecting into said region adjacent to said given depth interval a solvent capable of replacing substantially all of the previous liquids in the part of said adjacent region to which said log is responsive, c. running said log over said given depth interval a second time to obtain signals changed from those of the first running, the changes reflecting the effects of Step (b), d. calculating gas saturation from the measured difference in corresponding signals of said respective first and second logs of Steps (a) and (c), in accordance with the Equation: ##EQU10## where C 1 , C 2 and SO 1 and SO 2 refer to recorded responses of said first and second logs, respectively at said given depth interval in Steps (a) and (c); C 3 and SO 2 refer to the recorded log response at said one or more other depth intervals known to contain substantially no oil and no water, respectively; ρ d = density of liquid in the formation after Step (b); F o ,d = ratio of the mass of oxygen to the total mass of the above-specified liquid; F c ,d = ratio of the mass of carbon to the total mass of the above-specified liquid; ρ w = density of the formation brine; ρ o = the density of oil in the formation; F o ,w = ratio of the mass of oxygen to the over-all mass of the formation; F c ,w = ratio of the mass of carbon to the formation total mass brine of the oil; and Sg = fraction of the pore volume containing gas.

Claim 4

A method of measuring the concentration of gas in an earth formation constituting a given depth interval of a region surrounding a well bore, comprising: a. running, over said given depth interval, separate first and second logs with respective responses to the carbon and oxygen content of said region and whose responses are substantially linear throughout the range of expectable carbon and oxygen contents, and running, over one or more other depth intervals known individually or in combination to contain substantially no water and no oil, the same said log, b. injecting into said region adjacent to said given depth interval a solvent capable of replacing substantially all of the previous liquids in the part of said adjacent region to which said log is responsive, c. running said log over said given depth interval a second time to obtain signals changed from those of the first running, the changes reflecting the effects of Step (b), d. calculating gas saturation from the measured difference in corresponding signals of said respective first and second logs of Steps (a) and (c), in accordance with the Equation: ##EQU10## where C 1 , C 2 and SO 1 and SO 2 refer to recorded responses of said first and second logs, respectively at said given depth interval in Steps (a) and (c); C 3 and SO 2 refer to the recorded log response at said one or more other depth intervals known to contain substantially no oil and no water, respectively; ρ d = density of liquid in the formation after Step (b); F o ,d = ratio of the mass of oxygen to the total mass of the above-specified liquid; F c ,d = ratio of the mass of carbon to the total mass of the above-specified liquid; ρ w = density of the formation brine; ρ o = the density of oil in the formation; F o ,w = ratio of the mass of oxygen to the over-all mass of the formation; F c ,w = ratio of the mass of carbon to the formation total mass brine of the oil; and Sg = fraction of the pore volume containing gas.

Claim 5

A method of measuring the concentratioan of gas in an earth formation constituting a given depth interval of a region surrounding a well bore, comprising: a. running, over said given depth interval, separate first and second logs whose response to the carbon and oxygen contents of said region is substantially linear throughout the range of expectable carbon and oxygen contents, respectively, b. injecting into said region a solvent capable of replacing substantially all of the previous fluids in the part of said region to which said logs are responsive, c. running said logs a second time to obtain respective signals changed from those of the first running, the changes reflecting the effects of Step (b), d. injecting brine to replace substantially all of said solvent within the part of said region to which said logs are responsive, e. running said logs a third time to obtain signals changed from those of the second running, the changes reflecting the effects of Step (d), f. calculating gas saturation of said region from respective corresponding measured differences in the signals of said separate first and second logs of Steps (a), (c), and (e), respectively.

Claim 6

A method of measuring the concentratioan of gas in an earth formation constituting a given depth interval of a region surrounding a well bore, comprising: a. running, over said given depth interval, separate first and second logs whose response to the carbon and oxygen contents of said region is substantially linear throughout the range of expectable carbon and oxygen contents, respectively, b. injecting into said region a solvent capable of replacing substantially all of the previous fluids in the part of said region to which said logs are responsive, c. running said logs a second time to obtain respective signals changed from those of the first running, the changes reflecting the effects of Step (b), d. injecting brine to replace substantially all of said solvent within the part of said region to which said logs are responsive, e. running said logs a third time to obtain signals changed from those of the second running, the changes reflecting the effects of Step (d), f. calculating gas saturation of said region from respective corresponding measured differences in the signals of said separate first and second logs of Steps (a), (c), and (e), respectively.

Claim 10

A method of measuring the concentration of gas in an earth formation constituting a given depth interval of a region surrounding a well bore, comprising: a. running, over said given depth interval, separate first and second logs with respective responses to the carbon and oxygen content of said region and whose responses are substantially linear throughout the range of expectable carbon and oxygen contents, and running, over one or more other depth intervals known individually or in combination to contain substantially no water and no oil, the same said log, b. injecting into said region adjacent to said given depth interval a solvent capable of replacing substantially all of the previous liquids in the part of said adjacent region to which said log is responsive, c. running said log over said given depth interval a second time to obtain signals changed from those of the first running, the changes reflecting the effects of Step (b), d. calculating gas saturation from the measured difference in corresponding signals of said respective first and second logs of Steps (a) and (c).

Claim 11

A method of measuring the concentration of gas in an earth formation constituting a given depth interval of a region surrounding a well bore, comprising: a. running, over said given depth interval, separate first and second logs with respective responses to the carbon and oxygen content of said region and whose responses are substantially linear throughout the range of expectable carbon and oxygen contents, and running, over one or more other depth intervals known individually or in combination to contain substantially no water and no oil, the same said log, b. injecting into said region adjacent to said given depth interval a solvent capable of replacing substantially all of the previous liquids in the part of said adjacent region to which said log is responsive, c. running said log over said given depth interval a second time to obtain signals changed from those of the first running, the changes reflecting the effects of Step (b), d. calculating gas saturation from the measured difference in corresponding signals of said respective first and second logs of Steps (a) and (c).