Method for constructing 3-D geologic models by combining multiple frequency passbands

Abstract

A process for constructing a three-dimensional geologic model of a subsurface earth volume wherein resolution scales of multiple diverse data types, including seismic data, are accounted for by generating multiple frequency passband models and combining them together to form the complete geologic model. Preferably, a model is generated for each of a low-frequency passband, a mid-frequency passband, and a high-frequency passband. When integrating seismic data into the modeling process, the seismic-frequency passband constitutes the mid-frequency passband model. The process further contemplates updating tentative frequency-passband models through optimization of assigned rock property values in each tentative model according to specified geological criteria. Such optimization is carried out by perturbation of the rock property values in a manner wherein the frequency content of each model is maintained.

1 . A method for constructing a three-dimensional geologic model of a subsurface earth volume according to specific geological criteria comprising: 
 generating a plurality of frequency-passband models of the subsurface earth volume, wherein each of the plurality of frequency-passband models are associated with at least one frequency passband;    assigning at least one rock property value associated with at least one rock property to different portions of each plurality of frequency-passband models;    combining the plurality of frequency-passband models to form an initial complete three-dimensional geologic model of the subsurface earth volume; and    optimizing the initial complete three-dimensional geologic model by perturbing the rock property values in at least one of the plurality of frequency-passband models according to specified geological criteria.    
   
   
       2 . The method of  claim 1 , wherein the plurality of frequency-passband models comprise a low-frequency passband model associated with frequencies in a range of about 0 Hz to about 20 Hz, a mid-frequency passband model associated with frequencies in a range of about 20 Hz to about 56 Hz, and a high-frequency passband model associated with frequencies greater than 56 Hz.  
   
   
       3 . The method of  claim 1 , wherein each of the plurality of frequency-passband models are built in seismic time or depth.  
   
   
       4 . The method of  claim 1 , wherein the generating the plurality of frequency-passband models comprises: 
 specifying an initial geologic architecture to define the limits of the each of the plurality of frequency-passband models; and    creating a three-dimensional array of contiguous model blocks to represent the subsurface earth volume within each of the plurality of frequency-passband models, wherein the model blocks are the different portions of each plurality of frequency-passband models.    
   
   
       5 . The method of  claim 1 , wherein the generating the plurality of frequency-passband models comprises: 
 specifying an initial geologic architecture to define stratigraphic correlations within each of the plurality of frequency-passband models; and    creating a three-dimensional array of contiguous model blocks to represent the subsurface earth volume within each of the plurality of frequency-passband models, wherein the model blocks are the different portions of each plurality of frequency-passband models.    
   
   
       6 . The method of  claim 1 , wherein generating the plurality of frequency-passband models comprises: 
 specifying an initial geologic architecture to define the limits of each of the plurality of frequency-passband model; and    creating a three-dimensional array of discrete model points to represent all portions of the subsurface earth volume to be included within the model, wherein the discrete model points are the different portions of each plurality of frequency-passband models.    
   
   
       7 . The method of  claim 1 , wherein generating the plurality of frequency-passband models comprises: 
 specifying an initial geologic architecture to define stratigraphic correlations within each of the plurality of frequency-passband models; and    creating a three-dimensional array of discrete model points to represent the subsurface earth volume to be included within the model, wherein the discrete model points are the different portions of each plurality of frequency-passband models.    
   
   
       8 . The method of  claim 1  wherein each rock property value is a measurable property of the subsurface volume, and the rock property is one of porosity, shale volume, net sand percent, net pore volume, hydrocarbon saturation, hydrocarbon pore volume, impedance, and permeability.  
   
   
       9 . The method of  claim 1 , wherein each rock-property value is consistent with the frequency band of the respective frequency-passband models.  
   
   
       10 . The method of  claim 1 , wherein the initial complete geologic model is formed by weighted summation of each of the plurality of frequency-passband models.  
   
   
       11 . The method of  claim 1 , wherein optimizing the initial complete three-dimensional geologic model by perturbing the rock-property values comprises: 
 (a) specifying training criteria for the initial complete three-dimensional geologic model, said training criteria being consistent with the frequency content of the corresponding model;    (b) calculating statistics that describe the characteristics of the assigned rock-property values in the initial complete three-dimensional geologic model;    (c) calculating the initial objective function;    (d) perturbing the rock-property values in the initial complete three-dimensional geologic model so that the rock-property values more closely correspond to the training criteria;    (e) calculating the objective function for an updated complete three-dimensional geologic model;    (f) retaining the perturbed rock-property values and the new tentative objective function if the objective function is reduced;    (g) repeating steps (d) through (f) until the objective function is reduced to a specified limit; and    (h) outputting the updated complete three-dimensional geologic model to file.    
   
   
       12 . The method of  claim 11 , wherein the subsurface earth volume includes more than one region and specified training criteria are unique for each region.  
   
   
       13 . The method of  claim 11 , wherein the rock-property values in the initial complete three-dimensional geologic model are perturbed by simultaneously optimizing more than one initial model.  
   
   
       14 . The method of  claim 11 , wherein the frequency content of each updated complete three-dimensional geologic model is maintained during perturbation of the rock-property values.  
   
   
       15 . A method for constructing a three-dimensional geologic model of a subsurface earth volume according to specific geological criteria comprising: 
 generating a model having a plurality of blocks to represent a subsurface earth volume;    assigning at least one rock property value associated with at least one rock property to each of the model blocks to create a plurality of frequency-passband models that are each associated with at least one frequency passband;    combining the plurality of frequency-passband models to form an initial complete three-dimensional geologic model of the subsurface earth volume; and    optimizing the initial complete three-dimensional geologic model by perturbing the rock property values in at least one of the plurality of frequency-passband models according to specified geological criteria.    
   
   
       16 . The method of  claim 15 , wherein the plurality of frequency-passband models comprise a low-frequency passband model associated with frequencies in a range of about 0 Hz to about 20 Hz, a mid-frequency passband model associated with frequencies in a range of about 20 Hz to about 56 Hz, and a high-frequency passband model associated with frequencies greater than 56 Hz.  
   
   
       17 . The method of  claim 15 , wherein the generating the model having the plurality of blocks to represent the subsurface earth volume comprises specifying an initial geologic architecture to define the limits of the each of the plurality of frequency-passband models.  
   
   
       18 . The method of  claim 15  wherein each rock property value is a measurable property of the subsurface volume, and the rock property is one of porosity, shale volume, net sand percent, net pore volume, hydrocarbon saturation, hydrocarbon pore volume, impedance, and permeability.  
   
   
       19 . The method of  claim 15 , wherein each rock-property value is consistent with the frequency band of the respective frequency-passband models.  
   
   
       20 . The method of  claim 15 , wherein the initial complete geologic model is formed by weighted summation of each of the plurality of frequency-passband models.  
   
   
       21 . The method of  claim 15 , wherein optimizing the initial complete three-dimensional geologic model by perturbing the rock-property values comprises: 
 (i) specifying training criteria for the initial complete three-dimensional geologic model, said training criteria being consistent with the frequency content of the corresponding model;    (j) calculating statistics that describe the characteristics of the assigned rock-property values in the initial complete three-dimensional geologic model;    (k) calculating the initial objective function;    (l) perturbing the rock-property values in the initial complete three-dimensional geologic model so that the rock-property values more closely correspond to the training criteria;    (m) calculating the objective function for an updated complete three-dimensional geologic model;    (n) retaining the perturbed rock-property values and the new tentative objective function if the objective function is reduced;    (o) repeating steps (d) through (f) until the objective function is reduced to a specified limit; and    (p) outputting the updated complete three-dimensional geologic model to file.    
   
   
       22 . The method of  claim 21 , wherein the subsurface earth volume includes more than one region and specified training criteria are unique for each region.  
   
   
       23 . The method of  claim 21 , wherein the rock-property values in the initial complete three-dimensional geologic model are perturbed by simultaneously optimizing more than one initial model.  
   
   
       24 . The method of  claim 21 , wherein the frequency content of each updated complete three-dimensional geologic model is maintained during perturbation of the rock-property values.