Method for determining the fluid/pressure distribution of hydrocarbon reservoirs from 4D seismic data

A method comprising:

• defining a plurality of non-overlapping subsurface intervals in a hydrocarbon reservoir, each subsurface interval primarily comprising rock;
• separately analyzing 4D seismic data related to each of the subsurface intervals, the 4D seismic data including base seismic data and monitor seismic data;
• calculating seismic attributes for each of the subsurface intervals;
• applying rock physics relationships to the 4D seismic data related to each of the subsurface intervals based upon a permeability level of the respective subsurface interval;
• inferring a fluid saturation change of each of the subsurface intervals based on at least one of the rock physics relationships and the seismic attributes of said each of the subsurface intervals;
• verifying outputs of the hydrocarbon reservoir simulation model using the inferred fluid saturation change of each of the subsurface intervals;
• modifying the hydrocarbon reservoir simulation model according to the inferred fluid saturation change of each of the subsurface intervals;
• and
• outputting to a non-transient medium the verified hydrocarbon reservoir simulation model or the modified hydrocarbon reservoir simulation model;
• wherein the rock physics relationships include an equation to determine a bulk modulus of fluid in the interval using
• a harmonic average of bulk moduli of components in the fluid when the permeability level in said each of the subsurface intervals is less than a first predetermined amount, and
• an arithmetic average of bulk moduli of components of the fluid when the permeability level in said each of the subsurface intervals is greater than a second predetermined amount.

A method of extracting hydrocarbons from a subsurface reservoir, comprising:

• analyzing seismic data relating to a hydrocarbon reservoir comprising rock, wherein the seismic data includes a first set of seismic data relating to the hydrocarbon reservoir at a first time and a second set of seismic data relating to the hydrocarbon reservoir at a second time;
• defining an interval substantially comprising rock in the hydrocarbon reservoir, wherein the interval has a permeability level associated therewith;
• calculating 4D seismic attributes for the interval;
• applying a first set of rock physics relationships to seismic data related to the interval when the permeability associated therewith is in a first range;
• applying a second set of rock physics relationships to seismic data related to the interval when the permeability associated therewith is in a second range, the first and second ranges being non-overlapping;
• inferring one of a fluid saturation change and a pressure change of the interval based on outputs of one of the first and second sets of rock physics relationships and the calculated 4D seismic attributes for the interval;
• verifying an output of a reservoir simulation model using the one of the fluid saturation change and the pressure change of the interval;
• revising the reservoir simulation model so that a prediction from the simulation model is consistent with the fluid saturation change and the pressure change calculated from 4D seismic and selected rock physical relationships;
• outputting one of the corrected output of the reservoir simulation model and the verified output of the reservoir simulation model;
• and extracting hydrocarbons from the subsurface reservoir based on the outputted one of the corrected output of the reservoir simulation model and the verified output of the reservoir simulation model;
• wherein the first set of rock physics relationships includes an equation to determine a bulk modulus of fluid in the interval using a harmonic average of bulk moduli of components of the fluid, and the second set of rock physics relationships includes an equation to determine a bulk modulus of fluid in the interval using an arithmetic average of bulk moduli of components of the fluid.

A tangible computer readable medium having computer executable logic recorded thereon, comprising:

• code for defining a subsurface interval as primarily comprising rock;
• code for analyzing 4D seismic data related to the subsurface interval, the 4D seismic data including base seismic data and monitor seismic data;
• code for calculating seismic attributes for the subsurface interval;
• code for applying rock physics relationships to the 4D seismic data related to the subsurface interval based upon a permeability level of the subsurface interval;
• code for inferring a fluid saturation change of the subsurface interval based on at least one of the rock physics relationships and the seismic attributes of the subsurface interval;
• code for verifying an output of a hydrocarbon reservoir simulation model using the inferred fluid saturation change;
• code for correcting the hydrocarbon reservoir simulation model when the output is inconsistent with the inferred fluid saturation change;
• and
• code for outputting one of the verified output and the corrected output;
• wherein the rock physics relationships include an equation to determine a bulk modulus of fluid in the interval using
• a harmonic average of bulk moduli of components in the fluid when the permeability level in said each of the subsurface intervals is less than a first predetermined amount, and
• an arithmetic average of bulk moduli of components of the fluid when the permeability level in said each of the subsurface intervals is greater than a second predetermined amount.