Abstract:
The invention includes a method for determining a steam injection schedule for a set of subsurface formation subsurface regions of an oil field, the method including the steps of determining a thermal maturity for each subsurface region of the set; calculating a latent beat target for each subsurface region according to the determined thermal maturity therefore; calculating a steam injection target for each subsurface region according to the calculated latent heat target therefore; determining the availability of steam for injection to the subsurface regions; and calculating a steam injection schedule for each subsurface region according to the determined steam availability and calculated steam injection targets for all subsurface regions of the set.

Description:
COPYRIGHT NOTICE AND AUTHORIZATION 
       [0001]    This patent document contains material which is subject to copyright protection. 
         [0002]    (C) Copyright 2007. Chevron U.S.A. Inc. AH rights reserved. 
         [0003]    With respect to this material which is subject to copyright protection. The owner, Chevron U.S.A. Inc., has no objection to the facsimile reproduction by any one of the patent disclosure, as it appears in the Patent and Trademark Office patent files or records of any country, but otherwise reserves all rights whatsoever. 
       FIELD OF THE INVENTION 
       [0004]    The present invention relates to the use of steam for increasing oil recovery in fields characterized by a high viscosity crude oil. 
       BACKGROUND OF THE INVENTION 
       [0005]    Steam flooding is a method of increasing oil recovery from an oil field where the oil has a high viscosity. The high viscosity slows or prevents flow of oil thus inhibiting its recovery. Steam flooding greatly reduces the viscosity of the crude oil so that it can now flow from the reservoir into the production wells. 
         [0006]    Typically, in steam flood operations the steam generators are not completely automated. Additionally, there is no steam flood operation where the latent heat targets are used for the control of steam generation or steam distribution, and there is no place where steam generation and distribution controls are integrated, in summary, a need exists for complete integration and automation of the controls of steam generation and distribution driven by heat management design. Throughout the life of a steam flood project, steam generation and distribution need to be optimized to ensure that each injection well rate (and cyclic heat delivered to the reservoir to promote production) proceeds along the trajectory necessary to provide the appropriate latent heat to each part of the reservoir. Executing this reliably and efficiently, day in and day out, will increase the probability that a steam flood project achieves its planned operational efficiency and production. 
         [0007]    This invention overcomes the above-described shortcomings of known methods and systems. 
       SUMMARY OF THE INVENTION 
       [0008]    In one aspect, the present invention is a method for determining a steam injection schedule for a set of subsurface formation regions (or patterns) of an oil field, the method including the steps of: determining a thermal maturity for each subsurface region of the set; calculating a latent heat target for each subsurface region according to the determined thermal maturity therefore; calculating a steam injection target tor each subsurface region according to the calculated latent heat target therefore; determining the availability of steam for injection to the subsurface regions; and calculating a steam injection schedule for each subsurface region according to the determined steam availability and calculated steam injection targets for all subsurface regions of the set. 
         [0009]    Another aspect of the invention provides a system for determining a steam injection schedule for a set of subsurface formation regions of an oil field, the system including: a CPU; a memory operatively connected to the CPU, the memory containing a program adapted to be executed by the CPU; the program configured and adapted for: determining a thermal maturity for each subsurface region of the set; calculating a latent heat target for each subsurface region according to the determined thermal maturity therefore; calculating a steam injection target for each subsurface region according to the calculated latent heat target therefore; determining the availability of steam for injection to the subsurface regions; and calculating a steam injection schedule for each subsurface region according to the determined steam availability and calculated steam injection targets for all subsurface regions of the set. So that the above recited features and advantages of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof that are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0010]      FIG. 1  is a schematic context diagram showing the environment of the invention and its relationship to other systems. 
           [0011]      FIGS. 2-3  depict a schematic system level 0 data flow diagram of one embodiment of the invention and show the major process and logical data flow between the major processes. 
           [0012]      FIGS. 4-10  depict a schematic level 1 or 2 data flow diagram (a first or second decomposition of one process in the level 0 data flow diagram in  FIG. 2 , or others) and show the processes and logical data flow between the processes of the Determine Thermal Maturity process 1.0. 
           [0013]      FIG. 11  depicts a schematic level 1 data flow diagram of the processes and logical data flow between the processes of the Determine Latent Heat Target process 2.0. 
           [0014]      FIG. 12  depicts an exemplary constant steam Injection schedule. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0015]    Overview 
         [0016]    The major components (also interchangeably called aspects, subsystems, modules, functions, services) of the system and method of the invention, and examples of advantages they provide, are described below with reference to the figures. For figures including process/means blocks, each block, separately of in combination, is alternatively computer implemented, computer assisted, and/or human implemented. Computer implementation optionally includes one or more conventional general purpose computers having a processor, memory, storage, input devices, output devices and/or conventional networking devices, protocols, and/or conventional client-server hardware and software. Where any block or combination of blocks is computer implemented, it is done optionally by conventional means, whereby one skilled in the art of computer implementation could utilize conventional algorithms, components, and devices to implement the requirements and design of the invention provided herein. However, the invention also includes any new, unconventional implementation means. 
         [0017]    The System 
         [0018]      FIG. 1  is a schematic context diagram showing the environment of the invention and its relationship to other systems. Steam System Optimizer Process  100  interacts with several other systems or entities. Several processes/entities receive data from and send data to Steam System Optimizer Process  100 . Steaming schedule data passes from Steam System Optimizer Process  100  to Master Work Schedule Process  130  so that work tasks necessary to implement the steaming schedule can be scheduled. Steaming schedule data passes from Steam System Optimizer Process  100  to De-Watering Management Process  120  so that de-watering work tasks necessary to implement the steaming schedule can be scheduled, Steaming schedule data passes from Steam System Optimizer Process  100  to Surface Facility Development processes  160  so that surface facility work tasks necessary to implement the steaming schedule can be scheduled. These same external systems send results back to Steam System Optimizer Process  100  for calibration to keep it synchronized with actual field results. 
         [0019]    Several processes/entities provide data to Steam System Optimizer Process  100 . Subsurface region development data passes from Subsurface region Development (or Pattern Development) Management Process  150  to Steam System Optimizer Process  100  so that it can be taken into account in optimizing the steam system. Generator Management data passes from Generator Management Processes ( Steam Generators)  110  to Steam System Optimizer Process  100  so that it can be taken into account in optimizing the steam system. Generator management data passes from Well-Logging Processes  140  to Steam System Optimizer Process  100  so that it can be taken into account in optimizing the steam system. These same external systems will accept schedule information from Steam System Optimizer Process  100 . 
         [0020]      FIGS. 2-3  depict a schematic block system level 0 data, flow diagram of one embodiment of the invention and show the major process and logical data flow between the major processes. Determine Thermal Maturity process  205  passes output to Thermal Maturity File  240 . The output is an indication of thermally mature or not. 
         [0021]    Determine Latent Heat Target process  210  retrieves the Determine Thermal Maturity process  205  output as formatted data from Thermal Maturity File  240  and passes its own output to Latent Heat Target File  245 . The output from Determine Latent Heat Process  210  is a value having units of BTU′s, or other units measuring of heat, to be delivered to the subsurface region. Determine Steam. Injection Target process  220  retrieves Determine Latent Heat Target process  210  output as formatted data from Latent Heat Target File  245  and passes its own output to Steam Injection Target File  250 . The output is a target barrels of steam to be delivered to each subsurface region. 
         [0022]    Determine Available Steam process  227  retrieves Determine Steam Injection Target process  220  output as formatted data from Steam Injection Target File  250  and passes its own output to Available Steam File  255 , The output is a table or other structured or unstructured data indicating steam availability over a time period of interest for each subsurface region of interest. Determine Steam Injection Schedule process  225  retrieves Determine Available Steam process  227  output as formatted data from Available Steam File  255  and passes its own output to Steam Injection Schedule File  260 . The output is a steam injection schedule. Given a latent heat target for one or more subsurface regions, available steam, along with other system constraints. Determine Steam Injection Schedule process  225  prepares a steaming schedule for a predetermined time period, e.g., number of days, weeks, or months. Various methods can be used to prepare a schedule based on pre-determined criteria, e.g., desired time to reach thermal maturity for each subsurface region. Methods of preparing a cyclic steaming schedule are described in U.S. Pat. No. 6,446,721, entitled System and method for scheduling cyclic steaming of wells, assigned to Chevron U.S.A. Inc., which is incorporated herein by reference in its entirety.: Methods of preparing a non-cyclic steaming schedule are described in U.S. Pat. No. 5,174,377, entitled Method for optimizing steam flood performance, assigned to Chevron Research and Technology Company, which is incorporated herein by reference In its entirety. 
         [0023]    Execute Steam Injection Schedule process  230  retrieves Determine Steam Injection Schedule process  223  output as formatted data from Steam Injection Schedule  260  and passes its own output to Steam Schedule Execution File  265 . The output is a list or schedule of tasks and operating procedures necessary to execute the steam schedule. Monitor Steam Injection process  235  retrieves Execute Steam Injection Schedule process  230  output as formatted data from Steam Schedule Execution Schedule  265  and passes its own output to Monitor Steam Injection File  270 . The output is a historical report of steam delivered to each subsurface region and each well within a subsurface region. Determine Steam Deficiency/Excess process  270  retrieves Monitor Steam Injection process  235  output as formatted data from Monitor Steam Injection File  270 . The output indicates any variances between the steam scheduled to be delivered and the steam actually delivered. 
         [0024]      FIGS. 4-10  depict a schematic level 1 data flow diagram (a first decomposition of one process in the level 0 data flow diagram in  FIG. 2 ) and show the processes and logical data flow between the processes of the Determine Thermal Maturity process  205 . 
         [0025]      FIG. 4   a  depicts a preferred embodiment of the overall Determine Thermal Maturity Process  205 . First (process  400 ) determine In steps  405  and  415  the reservoir type, i.e., if a single or multi-zone reservoir (step  405 ) and whether the reservoir is flat or dipping (step  415 ), This output will be used (step  417 ) in assigning weighting to thermal maturity indicators in step  460 . 
         [0026]    In  FIG. 4   b,  then (process  407 ) retrieve the latest neutron density (“ND”). Neutron density is dimensionless. If the ND is less than a predetermined threshold (step  430 ), then get temperature data (step  440 ). If the ND is not less, then the pre-determined threshold then this indicates more liquid is present and there is no steam chest, thus the subsurface region is not thermally mature (step  435 ). The pre-determined threshold temperature is determined, e.g., by identifying the saturation temperature of steam at the prevailing reservoir pressure. The temperature is retrieved via a query to a temperature survey database. 
         [0027]    After getting the temperature data from well logging data (step  440 ), determine if the temperature is above a pre-determined threshold (step  445 ). If not, then this indicates pores are filled with air and there is no steam chest, thus the subsurface region is not thermally mature (step  450 ), If the temperature is above a pre-determined threshold (step  445 ), then the subsurface region potentially thermally mature and the indicator status should be identified (step  455 ) and combined (step  460 ) by averaging them with appropriate weights. “Indicator status” refers to the indicator supporting the pattern being mature or immature. 
         [0028]    Then determine if the combined indicator value is at least at a pre-determined threshold (step  465 ). If not, men this indicates there is not enough evidence of a steam chest and the subsurface region is at most of mixed maturity (step  470 ). If yes, the there is sufficient evidence of thermal maturity (step  475 ). 
         [0029]      FIG. 5  provides a preferred embodiment of a first deconstruction view determining the combined indicator value (step  455 )—showing specific indicators.  FIGS. 6-11  provide a preferred embodiment of a second deconstruction view of the individual indicators in  FIG. 5 . Five indicator categories are shown in  FIG. 5 . The first one listed is to determine if high temperature and low saturation or flat temperature for thick sands (step  515 ). If yes, this indicates thermal maturity  505 . IF not then determine if low temperature and high saturation or not flat temperature for thick sands (step  520 ). If yes, then this indicates a mixed maturity  510 . The determination of whether there is a high temperature and low saturation is by user specified thresholds. “High”temperature means higher than the user specified threshold, “Low” saturation means lower than the user specified threshold. 
         [0030]    The next listed indicator is to determine if the flow line or wellhead temperature is elevated (step  525 ). This is determined by measuring the temperature of flowing fluid at the wellhead. An “elevated” wellhead temperature in this context means higher than the user specified threshold. If yes, this indicates thermal maturity  505 . If not, this indicates mixed thermal maturity  510 . The next listed indicator is/to determine if production has peaked (step  530 ). If yes. this indicates thermal maturity  505 . If not, this Indicates mixed thermal maturity  510 , The next listed indicator is to determine if case vent rates are high (step  540 ). This is determined by user specified thresholds. “High” case vent rates in this context means higher than the user specified threshold. If yes, this Indicates thermal maturity  505 . If not, this indicates mixed thermal maturity  510 . The next listed indicator is to determine if a steam chest has developed (step  545 ). This is determined by an earth model. A “developed” steam chest means presence of steam at the top of the zone of consideration. If yes, this indicates thermal maturity  505 . If not, then check if there are pockets in the steam chest (step  550 ). If not, this indicates mixed thermal maturity  510 . 
         [0031]      FIG. 6  depicts in one embodiment a further decomposition  600  of the Determine if Flow line or Wellhead Temperature is Elevated indicator  525  ( FIG. 5 ). This is applicable in single-reservoir projects. First, for a given subsurface region retrieve the flow line temperature for associated wells and determine if it is high (step  605 ), This is determined by user specified thresholds, A “high” flow line temperature in this context means higher than specified threshold. If not, this indicates not thermal mature (step  610 ). If yes, validate whether the temperature can be used by determining If the well has not been recently steamed (step  615 ). If it has been recently steamed, then the temperature data cannot be used to indicate thermal maturity, so there is not a clear indicator of thermal maturity (step  620 ). If not recently steamed, determine if the flow rate is high (step  625 ), i.e., is it adequate when compared to the predicted production rate. If the flow rate is high (step  625 ), then this indicates thermal maturity (step  630 ). If not, there is no clear indicator of thermal maturity (step  625 ). As a follow-up it is recommended to look for FOP (fluid over pump) conditions. 
         [0032]      FIG. 7  depicts in one embodiment a further decomposition  700  of the Determine if Casing Vent Rates are High indicator  540  ( FIG. 5 ). This is applicable in single-reservoir projects. If the casing vent rate is not high when compared to the well baseline value (step  705 ), then there is no clear indicator of thermal maturity (step  710 ). If the easing vent rate is high, then this indicates thermal maturity (step  715 ). 
         [0033]      FIG. 8  depicts in one embodiment a further decomposition  800  of the Determine if the Production has Peaked indicator  530  ( FIG. 5 ). First, determine if the barrels of production per day per well is declining (step  805 ). This is determined by applying change point analysis to monthly production data. If no, then there is no clear indicator of thermal maturity (step  810 ), If it is declining (step  805 ), then determine if the recommended heat is being provided (step  815 ), i.e., enough heat to reach thermal maturity. “Recommended heat” in this context means the targeted pattern level injection rate. If no, then low heat may be the reason production is low and there is no clear indicator of thermal maturity (step  820 ). If the recommended heat is being provided (step  815 ), then validate the heat measurement to ensure the correct physical conditions are being met by determining if the injectors are in critical flow (step  825 ). If no, then there is not enough steam being injected and there is no clear indicator of thermal maturity (step  830 ). If the injectors are in critical flow (step  825 ), this indicates thermal maturity (step  835 ). This is determined by comparing the pressures upstream and downstream of the orifices. “Critical” flow in this context means fluid is flowing at sonic velocity. 
         [0034]      FIG. 9  depicts in one embodiment a further decomposition  900  of the step of determining if high temperature and low saturation or flat temperature for thick sands (step  515 ), First, determine if the target sands are thick (step  905 ). This is determined by interpretation of geologic parameters. “Thick” target sands In this context means thicker than a user specified threshold. If yes, then determine if the temperature is greater than a pre-determined threshold temperature (step  910 ), typically measured in an observation well. This is determined by see above. The predetermined threshold temperature is determined by user specified parameters. If not, then this measurement is not valid and there is no clear indicator of a steam chest and thermal maturity (step  915 ). If yes, then this indicates thermal maturity (step  920 ). The predetermined threshold temperature is derived from the known reservoir pressure at the observation well. 
         [0035]      FIG. 10  depicts in one embodiment a further decomposition  1000  of the Determine if a Steam Chest has Developed indicator  545  ( FIG. 5 ). Firsts determine if an Earth Model, e.g., GOCAD™ brand Earth Model is available (step  1010 ), i.e., whether an earth model is available that can accept the thermal data. If yes, then read the Earth Model output and determine if visualizations provide evidence of a steam chest (step  1020 ). This is determined, e.g., by model observation. If not, there is no clear indicator of a steam chest and thermal maturity (step  1030 ). If yes, then this indicates thermal maturity (step  1040 ). 
         [0036]      FIG. 11  depicts a schematic level 1 data flow diagram of the processes and logical dataflow between the processes of the Determine Latent Heat Target process  210 . The status of either thermally mature on not thermally mature is retrieved by Determine Latent Heat Target process  210 . This can be Implemented via a thermally mature variable for each subsurface region which is either set or not set, i.e., set being a value of 1 and indicating thermal maturity, and not set being a value of 0 indicating not thermally mature. If the thermally mature variable is set, control is passed to Heat Maintenance Rate Calculator process  1120 . Otherwise, control is passed to Neumann Rate Calculator process  1110 . The output from Determine Latent Heat Process  210  is a value having units of BTU&#39;s, or other units measuring of heat, to be delivered to the subsurface region. 
         [0037]    Determine Steam Injection Target process  220  ( FIG. 2 .) is a calculation. The heat in BTU&#39;s from Determine Latent Heat Process  210  is divided by the amount of heat per barrel of steam to determine the needed barrels of steam. Steam quality will vary so this calculation must be updated periodically. 
         [0038]    Constraints used in determining Steam Injection Schedule  225  (  FIG. 3 ) include fresh water availability, distribution system limits, well injection limits, steam generator capacity and maintenance schedules, cyclic steam rig availability and well availability for cyclic steaming. Distribution system limits include steam delivery limits of the distribution system header, well choke size or control valve setting, and pipe sizes. 
         [0039]      FIG. 12  depicts an exemplary constant steam schedule  1200 . Each well is identified in No. column  1210  arid name column  1215 . The steam rate column  1220  gives steam rates, e.g., barrels per day or other suitable expression of unit volume per unit time. Steam quality column  1225  gives the steam quality in, e.g., percent vapor. Valve/Choke settings  1230  indicates the size, e.g., diameter, of a variable opening at the well head. This setting must typically be changed manually if a change is desired. The date  1235  the new steaming schedule  1200  is to take effect is given, or alternatively, each well may have a separate date field. 
         [0040]    Other Implementations 
         [0041]    Other embodiments of the present invention and its Individual components will become readily apparent to those skilled in the art from the foregoing detailed description. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the spirit and the scope of the present invention. Accordingly, the drawings and detailed description are to he regarded as illustrative in nature and not as restrictive. It is therefore not intended that the invention be limited except as indicated by the appended claims.