Abstract:
Production based saturation models of subsurface reservoirs of interest are formed in a computer based on data from well logs, production data and core data. Data of these types obtained over a period of time are used to form 4-D actual or measured production based saturation models of a reservoir illustrative of fluid movement in the reservoir over time. Simulation models of fluid saturation of the reservoir are also formed for comparable times. Composite models of the production based saturation models and the simulation models are formed for analysts to evaluate accuracy of the simulation models of the reservoir taking into account production experience. The simulation models can then be adjusted for changes noted in the reservoir and based on how gas and water have actually moved within the reservoir over time.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority and is related to U.S. Provisional Patent Application No. 61/548,508 filed Oct. 18, 2011 titled, “Reservoir Modeling with 4D Saturation Models and Simulation Models” which is incorporated by reference in its entity. 
         [0002]    The present invention relates to fluid saturation modeling of subsurface reservoirs, as does commonly owned U.S. Non-Provisional patent application “4D SATURATION MODELING” (Attorney Docket No. 004159.007066) filed of even date herewith, of which applicant is investor. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to computerized modeling of subsurface reservoirs, and in particular to forming models of saturation based on measurements made in or about the reservoir during its production life. 
         [0005]    2. Description of the Related Art 
         [0006]    In the oil and gas industries, the development of underground hydrocarbon reservoirs typically includes development and analysis of computer models of the reservoir. These underground hydrocarbon reservoirs are typically complex rock formations which contain both a petroleum fluid mixture and water. The reservoir fluid content usually exists in two or more fluid phases. The petroleum mixture in reservoir fluids is produced by wells drilled into and completed in these rock formations. 
         [0007]    A geologically realistic model of the reservoir, and the presence of its fluids, helps in forecasting the optimal future oil and gas recovery from hydrocarbon reservoirs. Oil and gas companies have come to depend on geological models as an important tool to enhance the ability to exploit a petroleum reserve. Geological models of reservoirs and oil/gas fields have become increasingly large and complex, in such models, the reservoir is organized, into a number of individual cells. Seismic data with increasing accuracy has permitted the cells to be on the order of 25 meters areal (x and y axis) intervals. For what are known as giant reservoirs, the number of cells is the least hundreds of millions, and reservoirs of what is known as giga-cell size (a billion cells or more) are encountered. 
         [0008]    The presence and movement of fluids in the reservoir varies over the reservoir, and certain characteristics or measures as water or oil saturation and fluid, encroachment made during production from, existing wells in a reservoir, are valuable in the planning and development of the reservoir. 
         [0009]    When characterizing and developing a reservoir field, a model of the reservoir covering the entire reservoir has been required to be built to provide an accurate model for reservoir planning. Accurate indications of the presence and movement of reservoir are an essential input in fluids in reservoir evaluation and planning. 
         [0010]    Modeling of the presence and movement of reservoir fluids over a projected reservoir life has been based on reservoir simulation models. An example of such, a simulation model is that of U.S. Pat. No. 7,526,418, which is owned by the assignee of the present invention. However, calibration of the simulation model and confirmation that the simulation model continued to represent the reservoir presented a challenge. Additionally, additional reservoir Information, such as the presence of faults, was often gained, about the reservoir during production. So far as is known, it was problematic to accurately incorporate the additional information into simulation models. 
       SUMMARY OF THE INVENTION 
       [0011]    Briefly, the present invention provides a sew and improved computer implemented method of obtaining measures in a data processing system of fluid saturation of a subsurface reservoir from a simulation model and from a production based model from data measurements of wells in the reservoir during production. The computer implemented of the present invention processes initial data about formations in the reservoir received from wells in the reservoir to determine art initial measure of fluid saturation of formations in the reservoir at an initial time. The determined initial, measure of fluid saturation in formations of interest in the reservoir is transferred to a data memory of the data processing system. Production data during production subsequent to the initial time from wells in the reservoir is processed to determine production based measures of fluid saturation of formations during production. The determined production based measures of fluid saturation of formations in the reservoir are assembled in the data memory. A simulation model of fluid saturation of formations in the reservoir is also determined. A composite display of the simulation model of fluid saturation and the determined production based measures of fluid saturation in formations of interest in the reservoir is then formed for comparative analysis. 
         [0012]    The present invention provides a new and improved data processing system for obtaining measures of fluid saturation of a subsurface reservoir from a simulation model and from a production based model from data measurements of wells in the reservoir during production. The data processing system includes a processor which processes initial data about formations in the reservoir received from wells in the reservoir to determine an initial measure of fluid saturation of formations in the reservoir at an initial time. The processor also transfers the determined initial measure of fluid saturation in formations of interest in the reservoir to a data memory of the data processing system. The processor also, based on production data during production subsequent to the initial time from wells in the reservoir, determines production based measures of fluid, saturation of formations during production. The determined production based measures of fluid saturation of formations in the reservoir are assembled in the memory. The processor also determines a simulation model of fluid saturation of formations in the reservoir. An output display of the data processing system forms a composite display of the simulation model of fluid saturation and the determined production based measures of fluid saturation in formations of interest in the reservoir for comparative analysis. 
         [0013]    The present invention also provides a new and improved data storage device having stored in a computer readable medium computer operable instructions for causing a data processing system to obtain measures of fluid saturation of a subsurface reservoir from, a simulation model and from a production based model from, data measurements of wells in the reservoir during production. The instructions stored, in the data storage device causing the data processing system to process initial data about formations in the reservoir received from wells in the reservoir to determine an initial measure of fluid saturation of formations in the reservoir at an initial time, and transfer the determined initial measure of fluid saturation in formations of interest in the reservoir to a data memory of the data processing system. The instructions also cause the data processing system to process production, data, during production subsequent to the initial time from wells in the reservoir to determine production based measures of fluid saturation of formations during production, and assemble in the memory the determined production based measures of fluid saturation of formations in the reservoir. The instructions stored in the data storage device also cause the processor to determine a simulation model of fluid saturation of formations in the reservoir and cause the data processing system to form a composite display of the simulation model of fluid saturation and the determined production based measures of fluid saturation in formations of interest in the reservoir for comparative analysis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a functional block diagram of a set of data processing steps performed in a data processing system for reservoir modeling with production based 4D saturation models and simulation models of fluid saturation of subsurface earth formations according to the present invention. 
           [0015]      FIG. 2  is a functional block diagram of an initial set of data processing steps of production based 4D saturation modeling of the diagram of  FIG. 1 . 
           [0016]      FIG. 3  is a functional block diagram of a subsequent set of data processing steps of production based 4D saturation, modeling of the diagram of  FIG. 1 . 
           [0017]      FIG. 4  is a schematic block diagram of a data processing system for reservoir modeling with production based 4D saturation models and simulation models of fluid saturation of subsurface earth formations according to the present invention. 
           [0018]      FIG. 5  is a display of a 4D production based saturation model according to the present invention for a region of interest in a subsurface reservoir at a particular time during it production life. 
           [0019]      FIG. 6  is a composite display according to the present invention of fluid saturation of a subsurface reservoir from a simulation model and from a production based model for a geological model at a depth of interest in a reservoir. 
           [0020]      FIGS. 7A ,  7 B,  7 C and  7 D are displays according to the present invention of differences between fluid saturation measures from a simulation model and from a production, based model at depths of interest in a reservoir. 
           [0021]      FIG. 7E  is an enlarged display of a color key used in conjunction with the displays of  FIGS. 7A through 7D . 
           [0022]      FIG. 8A  is a display according to the present invention of differences between fluid saturation measures from a simulation model and from a production based model at a depth, of interest in a reservoir. 
           [0023]      FIG. 8B  is a vertical cross-sectional of the saturation model according to the present invention, for a region of interest in the subsurface reservoir of  FIG. 8A  at a particular time in its production life. 
           [0024]      FIG. 8C  is an enlarged display of a color key used in conjunction with the displays of  FIGS. 5A and 5B . 
           [0025]      FIG. 9A  is a plot of comparative measures regarding of reservoir fluid parameters as functions of time, based on a saturation model according to the present invention for a region of interest in a subsurface reservoir. 
           [0026]      FIG. 9B  is a plot of measures regarding of reservoir fluid parameters as functions of depth based on a saturation model according to the present invention for a well of interest in a subsurface reservoir. 
           [0027]      FIG. 10A  is a vertical cross-sectional composite display of a fluid saturation according to the present invention for a region of interest in a subsurface reservoir at a particular time in its production life. 
           [0028]      FIG. 10B  is a display according to the present invention of differences between fluid saturation measures from a simulation model and from a production based model at a depth of Interest in the same reservoir as  FIG. 10A . 
           [0029]      FIG. 10C  is a display in an Isometric view according to the present invention of differences between fluid saturation measures from a simulation model and from a production based model at a depth of interest in the same reservoir as  FIG. 10A . 
           [0030]      FIG. 11A  is a plot of comparative measures regarding of reservoir fluid parameters as functions of time based on a saturation model according to the present invention for a region of interest in a subsurface reservoir. 
           [0031]      FIG. 11B  is a plot of measures regarding of reservoir fluid parameters as functions of depth based on a saturation model according to the present invention for a well of interest in a subsurface reservoir. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    In the drawings, a flowchart F shown in  FIG. 1  illustrates the basic computer processing sequence of the present invention for reservoir modeling with production based 4D saturation models and simulation models of fluid saturation of subsurface earth formations according to the present invention. The steps Illustrated in  FIG. 1  each represent formation of a 4D model. During step  12 , a static reservoir saturation model over time is formed, while step  10  represents formation of a history matched simulation model. Step  14  represents from composite display from both, models formed during steps  10  and  12  to compare the calculated saturation (from the simulation model) with the actual saturation from the static model. The location and the time can be changed as desired. The processing of data according to  FIG. 1  of a subsurface reservoir modeling is performed in a data processing system D ( FIG. 4 ) as will be described. 
         [0033]    As shown in  FIG. 1 , processing in data processing system D begins during step  10  ( FIG. 1 ) to form, production based measures of 4D reservoir fluid saturation based on measurements made in or about the reservoir during its production life according to the present invention. The computer implemented determination of production based reservoir fluid saturation measures during step  10  is set forth in more detail in a flow chart I ( FIG. 2 ) and a flow chart M ( FIG. 3 ), as will be set forth below. 
         [0034]    During a step  12  of the flowchart F ( FIG. 1 ), a simulation model of fluid saturation of the subsurface is also formed. An example of such a simulation model and its formation is, for example, that of U.S. Pat. No. 7,526,418, which is owned by the assignee of the present invention. The disclosure of such U.S. patent is incorporated herein by reference. It should also be understood that techniques of forming simulation models can also be used, if desired. 
         [0035]    The production based fluid saturation measures of the reservoir determined during step  10  and the simulation model of the reservoir during step  12  are formed for various corresponding times during the production life of die reservoir, and are then stored in data memory of the data processing system D. As indicated at step  14  ( FIG. 1 ) composite displays of measures of fluid saturation of a subsurface reservoir from the simulation model determined during step  12  and from the production based model determined during step  10  based on data measurements of wells in the reservoir during production, are formed for comparative analysis. 
         [0036]      FIGS. 2 and 3  indicate the basic computer processing sequence of step  10  according to the present invention for forming production based 4D saturation models based on measurements made in or about the reservoir during its production life according to the present invention. The processing sequence of step  10  includes the flow chart I ( FIG. 2 ) illustrating the processing sequence of the present invention relating to formation, of a database and initial, reservoir saturation model based on data obtained from wells in the reservoir and other data sources. The processing sequence of step  10  also includes the flow chart M ( FIG. 3 ) illustrating the sequence for processing data resulting from the procedure&#39;s of the flow chart I and data obtained during production from the reservoir for purposes of fluid encroachment modeling, as will, be described in detail below. 
         [0037]    Turning to  FIG. 2 , processing in data, processing system D includes a screening of the available data being conducted aid an inventory of the information being reported. Based on that, missing and wrong format information are identified and corrected and consequently incorporated into the project data base. A petrophysical modeling project is created and the data previously screened is populated at this phase. Geological model, OH logs, PNL logs, production, completion, etc. are populated, and quality control performed. Initial project workflow is revised and modified accordingly. Extensive petrophysics review for entire field is conducted and initial contact is defined. Processing begins during step  20  ( FIG. 2 ) by auditing or collection, collation or arrangement and quality control of input parameters or data for processing according to the present invention. The input parameters or data include the following: an initial set of 3D geological model data for the reservoir of interest; Individual cell dimensions and locations in the x, y and z directions for the reservoir; existing well locations and directions through the reservoir; petrophysical measurements and known values of attributes from core sample data; and data, available from well, logs where log data have been obtained. During step  20 , the input parameters and data are thus evaluated and formatted for processing during subsequent steps. If errors or irregularities are detected in certain data during quality control in processing during step  20 , such data may be omitted from processing or may be subject to analysis for corrective action to be taken. 
         [0038]    During step  22  of processing in the data processing system D, the stored initial 3D geological model data is migrated from database memory for processing by petrophysical modeling. In one embodiment of the present invention, such petrophysical modeling may be performed for Instance by a processing system known as PETREL available from Schlumberger Corporation. It should also be understood that the petrophysical modeling may, if desired, be performed according to other available techniques such as those available as: GOCAD from OoCAD Consortium; Vulcan from Vulcan Software; DataMine from Datamine Ltd; FracSys from Colder Associates, Inc.; GeoBioek from Source Forge; or deepExploration from Right Hemisphere, Inc.; or other suitable source. 
         [0039]    During step  24 , input saturation data obtained from processing data from well logs including open hole (OH) logs from the wells in the reservoir before production, as well as data eased hole (CH) logs such as pulsed neutron (PNL) or production logging tool (PLT) logs after casing has been installed in wells are populated or made available to be located into the geological model being processed. In addition during step  24 , data regarding well production, completion, well markers, well head data, well directional survey are populated or made available to be located into the geological model being processed. 
         [0040]    During step  26 , a quality control analysis or correlation is made between the geological model data migrated for processing during step  22  and the open hole log data from step  24 . If errors or irregularities are detected between geological model data, and open hole log data during quality control in processing during step  26 , such data may be omitted from processing or may be subject, to analysis for corrective action to be taken. Also during step  26 , a quality control, analysis or correlation is made between the fluid saturation measures available form production log data, open hole log data and also the initial saturation model. 
         [0041]    During step  28 , initial fluid contacts (for both Free Water Level and Gas-Oil) are determined for each of the various regions, platforms, domes and fields of interest in the reservoir. The processing during step  28  is done by a petrophysical model system of the type described above in connection with step  22 . As a result of step  28 , a fluid encroachment database and an initial fluid encroachment for the reservoir is formed and available in the data, processing system D for further fluid encroachment modeling according to the step  30  in the flow chart, as will be described. 
         [0042]    Fluid encroachment modeling and reservoir analysis ( FIG. 3 ) involves the contacts (GOC, lowest gas, OCW, shale water contact, etc) for entire field being re-evaluated and picked direct in the petrophysical model, creating a data base of contacts for the entire history. The geological model is revised in detail as well the field production and by this, a model is ready. The present invention begins with step  30 . During step  30  oil-water contact (OWC) well tops, or the depth of the geological layer wherein such contact occurs, are determined from either or both of PML logs and OH logs. Further, any OWC information reported on well events in the input data is taken into account in the input data. Also, during step  30 , indications of oil-water contact (OWC) are generated for each year during previous and projected production life of the reservoir for the well tops in the geological model so that all locations of such contact in the reservoir model are identified. During step  30 , OWC in the years where OWC from, logs is hot available are determined by interpolation using measures of production of the well or platform in question, for those years. 
         [0043]    Next, during step  32  a measure of the location of OWC surface for each year or time steps over the time of interest for the reservoir is established. During step  32 , quality control of OWC surfaces previously generated is performed: Synthetic OWC logs×Water Production. 
         [0044]    During step  34  gas-oil contact (GOC) well tops, or the depth of the geological layer wherein such contact occurs, are determined from either or both of PNL logs and OH logs. Further, any GOC information reported on well events in the input data is taken into account in the input data. 
         [0045]    During step  36 , indications of gas-oil contact (GOC) are generated for each year during previous and projected production life of the reservoir for the well tops in the geological model so that all locations of such contact in the reservoir model are identified. During step  36 , GOC in the years where GOC from logs is not available are also determined by interpolation using measures of production of the well or platform in question for those years. 
         [0046]    During step  38 , indications of secondary GOC are identified and the 3D fluid contact properties determined during step  34  are updated with identified secondary GOC 3D fluid contact for the platforms, regions and domes of interest in the reservoir. Adjustments are also made during step  38  for changes in GOC levels in wells affected by gas conning and the 3D fluid contact model updated accordingly. 
         [0047]    During step  40 , a 3D fluid contact property is generated for each year or time step over the time of interest for the reservoir. Daring step  40 , a quality control analysis or correlation is made between the 3D fluid contact properties for the various time steps generated based on the data from the various logs available from wells in the reservoir: production/completion, OH and PNL. If errors or irregularities are detected in the 3D fluid contact properties, such data may be subject to analysis for corrective action to be taken. 
         [0048]    During step  42 , a measure of 3D saturation properties is determined for the various time steps of interest, and thus a 4D saturation property for the reservoir of interest is obtained. The 4D saturation property obtained is obtained from actual data measurements obtained for wells in the reservoir before and during production and is thus not based on simulation. Reservoir saturation over the production life is thus determined from production data. Actual fluid movement over time is determined and observed. 
         [0049]    From the 4D simulation property obtained during step  42 , a 3D measure of remaining oil in place (REMOIP) properties per time step (and thus a 4D REMOIP property) is formed during step  44 . Also during step  44 , maps of remaining oil in place or REMOIP may be formed for layer or zones of interest in the reservoir being modelled according to the present invention data. 
         [0050]    During step  46 , the reservoir fluid encroachment measures resulting from saturation modelling according to the present invention are evaluated for accuracy and acceptability. During step  48 , if the results of step  46  indicate acceptable results, the results are updated in memory of the data processing system D. The updated results can then be displayed or otherwise made available during step  48  as deliverable output data. If further processing is indicated necessary during step  46 , processing returns to steps  30  and  34 , as indicated in  FIG. 2 . 
         [0051]    As illustrated in  FIG. 4 , a data processing system D according to the present invention, includes a computer C having a processor  50  and memory  52  coupled to processor  50  to store operating instructions, control information and database records therein. The computer C may, if desired, be a portable digital processor, such as a personal computer in the form of a laptop computer, notebook computer or other suitable programmed or programmable digital data processing apparatus, such as a desktop computer. It should also be understood that the computer C may be a multicore processor with nodes such as those from Intel Corporation or Advanced Micro Devices (AMD), an HPC Linux cluster computer or a mainframe computer of any conventional type of suitable processing capacity such as those available from International Business Machines (IBM) of Armonk, N.Y. or other source. 
         [0052]    The computer C has a user interface  56  and an output data display  58  for displaying output data, or records of lithological facies and reservoir attributes according to the present invention. The output display  58  includes components such as a printer and an output display screen capable of providing printed output information or visible displays in the form of graphs, data sheets, graphical images, data plots and the like as output records or images. 
         [0053]    The user interface  56  of computer G also includes a suitable user input device or input/output control unit  60  to provide a user access to control or access information and database records and operate the computer C. Data processing system. D further includes a database  62  stored in computer memory, which may be internal memory  52 , of an external, networked, or non-networked memory as indicated at  66  in an associated database server  68 . 
         [0054]    The data processing system D includes program code  70  stored in memory  52  of the computer C. The program code  70 , according to the present invention is in the form of computer operable instructions causing the data processor  50  to perform the computer implemented method of the present invention in the manner described above and illustrated in  FIGS. 1 through 3 . 
         [0055]    It should be noted that program code  70  may be in the form of microcode, programs, routines, or symbolic computer operable languages that provide a specific set of ordered operations that control the functioning of the data processing system D and direct its operation. The instructions of program code  70  may be may be stored. In memory  52  of the computer C, or on computer diskette, magnetic tape, conventional hard disk drive, electronic read-only memory, optical storage device, or other appropriate data storage device having a non-volatile computer usable medium stored thereon. Program code  70  may also be contained on a data storage device such as server  58  as a computer readable medium, as shown. 
         [0056]    The method of the present invention performed in the computer C can be implemented utilizing the computer program steps of  FIGS. 1 ,  2  and  3  stored in memory  52  and executable by system processor  50  of computer C. The input data to processing system D are the well log data and other data regarding the reservoir described above. 
         [0057]      FIG. 5  is a view looking downwardly on an example formation of interest in a 4D saturation model formed of a subsurface reservoir at a particular time during it production life according to the present invention. In  FIG. 5 , those portions  84  of the formation in red are indicative of saturation values based on processing results where gas is present in the formation, those portions  86  in green are indicative of saturation values where oil is present, and those areas  88  in blue indicate saturation values where water is present. A higher resolution areal sweep can be visualised in different parts of the reservoir to indicate gas oil and water movement. These impressive fluid saturation results were obtained from all historic logging information that can be matched with, dynamic simulation results. 
         [0058]      FIG. 6  is a composite display  90  according to the present invention, of fluid saturation of a subsurface reservoir from a simulation model  92  and from a production based model  94  for a geological model  96  at a depth of interest in a reservoir. A simulation model  92  of fluid saturation at the depth of interest is shown a production based or 4D fluid saturation model  94  for a common time of interest.  FIG. 6  shows the saturation display from the simulation model  92  at the top and the static model  96  at the bottom while the display  94  in the middle shows the difference between the static model  96  saturations and the saturation from the simulation model  92 . Existing wells in the reservoir are indicated at  98  in the composite display  90 . Thus, the present invention provides composite model including a production based model  94  from actual reservoir production data at a known time. The saturation model  94  of the present invention based on actual data then can serve as a reference for verifying the simulation model  92  for that known time, and thus serves as an independent check of the simulation model  92 . 
         [0059]      FIGS. 7A ,  7 B,  7 C and  7 D are displays  100 ,  102 ,  104 , and  106 , respectively, according to the present invention of differences between fluid saturation changes from a simulation model determined during step  20  and from a production based model determined during step  10  at depths of interest in a reservoir. The differences are arithmetical measures of the two saturation measures, on a cell by cell basis at the region or depth of interest which may be determined during step  14  or as an intermediate step before step  14 . The fluid saturation difference measures shown in  FIGS. 7A through 7D  are differences in water saturation or S w  measures at different layers or depths in the model. 
         [0060]    A color key or scale  108  ( FIG. 1E ) indicates by differences in color and intensity the magnitude and nature of the differences between water saturation measures from, a simulation model, and from a production based model in displays such as those  FIGS. 7A through 7D . The color blue in these displays indicates that the simulation measures of water saturation are greater in magnitude than the 4D or production based measures. The higher intensity or hue of the color blue indicates a greater difference in the simulation wafer saturation measures, while a lighter blue indicates a lesser difference between the simulation measure and the production based measure. Correspondingly, the color red in the displays indicates that the 4D or production based measures of water saturation are greater in magnitude than the simulation measures. The higher intensity or hue of the color red indicates a greater difference in the production based water saturation measures, while a lighter red indicates a lesser difference between the production based measure and the simulation measure. 
         [0061]      FIG. 8A  is a display  112  like those of  FIGS. 7A through 7D  according to the present invention of differences between water saturation measures from a simulation model and from a production based model at a depth of interest in a reservoir.  FIG. 5B  is a vertical cross-sectional display  114  of the same subsurface reservoir as the display of  FIG. 8A , indicating differences between fluid saturation measures from a simulation model and from a production based model laterally across reservoir as functions of depth at a particular time in its production life. Again, the displays indicate by color and intensity variations in red and blue the difference between production based measures and simulation measures of S w  in the manner described above. A color scale or key  116  defines the magnitude of the differences displayed. A region  118  is to be noted in the display  114  of  FIG. 8B  where the simulation measure shows a markedly lower S w  than the production based model. 
         [0062]      FIG. 9A  is a display or plot  120  of comparative measures of reservoir fluid parameters (oil production rate, water cut and gas-oil ratio (GOR)) as functions of time based on simulation models according to the present invention and the actual Held data for a region of interest in a subsurface reservoir. The simulation model measures are plotted as red in plots for each of oil production rate  122 , water cut  124  and gas-oil ratio (GOR)  126  for the region of interest. Production data based measures are plotted in black for each of oil production rate  122 , water cut  124  and gas-oil ratio (GOR)  126  for the same region of interest over corresponding times. As indicated at  128  in the water cut plot  124 , the production based data indicates an increasing water cut from the region of interest over time, while the simulation data indicates little or no change. The saturation modeling techniques according to the present invention as illustrated in  FIG. 9A  provide an excellent mechanism for detecting or flagging discrepancies between the saturation models and providing quality control, of simulation models. 
         [0063]      FIG. 9B  is a display or plot  130  of well log measures regarding reservoir water saturation as functions of depth based on the actual field measurements and the simulation model data for a well of interest in the reservoir. A plot  132  represents S w  as a function of depth, based on simulation measures, while a plot  134  represents S w  as a function, of depth obtained from, production based or 4D measures. It is to be noted that the plot  132  indicates again little or no water cut, while the production based data indicates a water cut of 40% at the same depths. Also the 4D model data indicates at  136  for bottom perforations in the well a value of 100% for residual oil saturation (S or ). 
         [0064]      FIG. 10A  is a display  140  like that of  FIG. 8A  according to the present invention of differences between water saturation measures from a simulation model and from a production based model at a depth of interest in a reservoir.  FIG. 10B  is a vertical cross-sectional display  142  of the same subsurface reservoir as the display of  FIG. 10A , while  FIG. 10C  is an isometric view or display  144  of the same subsurface reservoir. Again, the displays  140 ,  142  and  144  indicate differences between fluid saturation measures from a simulation model and from a production based model for the reservoir at a particular time in its production life. Again, the displays indicate by color and intensity variations in red and blue the difference between production based measures and simulation measures of Sw in the manner described above. A region  146  is to be noted in each of the displays of  FIGS. 10A ,  10 B and  10 C where the simulation measure shows a markedly higher Sw than the production based, model.  FIGS. 10A ,  10 B and  10 C are displays to demonstrate the capability of the present invention to highlight areas that need more work in the simulation model. 
         [0065]      FIGS. 11A and 11B  show different individual well performance and log plots that compare actual data with the simulation results.  FIG. 11A  is a display or plot  150  of comparative measures of reservoir fluid parameters as functions of time based on saturation models according to the present invention for a region of interest in a subsurface reservoir. The simulation model measures are plotted as blue in plots for each of oil production rate  152 , water cut  154  and gas-oil ratio (GOR)  156  for the region of interest. Production data based measures are plotted in red for each of oil production rate  152 , water cut  154  and gas-oil ratio (GOR)  156  for the same region of interest over corresponding times. As indicated at  158  in the water cut plot  154 , the simulation based data indicates a water cut of about 6% from the region of interest over time, while the simulation data indicates a lower value. 
         [0066]      FIG. 11B  is a display or plot  160  of well log measures regarding reservoir fluid parameters as functions of depth based on the saturation model data from which the data plots of  FIG. 11A  are based, and for a well of interest in the reservoir. A plot  162  represents S w  as a function of depth based on simulation measures, while a plot  164  represents S w  as a function of depth obtained from production based or 4D measures. It is to be noted as indicated at  162  that the plot  164  indicates again the same higher water cut shown in  FIG. 11A , while the production based data plot  166  indicates a lower water cut at the same depths. 
         [0067]    From the foregoing. It can be seen that the present invention, provides saturation models based on actual reservoir data, such as production data and well logs over time during production from the reservoir. Thus, evaluation of fluid presence and movement over time hi the reservoir is available based on actual measured data. 
         [0068]    One of the difficult tasks in reservoir engineering is to obtain a perfect match for reservoir simulation models at different time during simulation of reservoir production. However, the present invention provides a reservoir saturation model based on actual data at a known time. The saturation model of the present invention based, on actual data then can serve as a reference for verifying a simulation model for that known time, and thus serves as an independent check of the simulation model. 
         [0069]    The invention has been sufficiently described so that a person with average knowledge in the matter may reproduce and obtain the results mentioned in the invention herein Nonetheless, any skilled person in the field of technique, subject of the invention herein, may carry out modifications not described in the request herein, to apply these modifications to a determined structure, or in the manufacturing process of the same, requires the claimed matter in the following claims; such structures shall be covered within the scope of the invention. 
         [0070]    It should be noted and understood that there can be improvements and modifications made of the present invention described in detail above without departing from the spirit or scope of the invention as set forth in the accompanying claims.