Methods of Quantifying Gas Content of a Gas-Sorbed Formation Solid

Abstract

The evaluation and assessment of geologic formations comprising undersaturated methane reservoirs. In some embodiments, the present invention provides for inductively quantifying critical desorption pressure of the solid in an undersaturated methane reservoir from an unrelated substance, the formation water. By using these techniques, the characterization of undersaturated methane reservoirs may be more quickly and economically made based upon a methane content characteristic such as critical desorption pressure, gas content, and in some embodiments gas content as calculated from isotherm evaluation, estimates of dewatering for production, and ratios of critical desorption pressure to initial reservoir pressure, among other possible characteristics. The features of the invention may further have applicability in combination with conventional reservoir analysis, such as coring, logging, reservoir isotherm evaluation, or other techniques.

1 . A method of calculating a production characteristic for an undersaturated methane reservoir comprising the steps of: 
 a. accessing a well admitted to an undersaturated methane reservoir;    b. sampling formation water from said undersaturated methane reservoir;    c. conducting a test based on said formation water sample;    d. inductively quantifying a methane content value of sorbed methane that is sorbed in a solid formation substance from said water sample;    e. calculating an economic production characteristic for said methane reservoir; and    f. applying said economic production characteristic to calculate and report a practical production quantity for said methane reservoir.    
   
   
       2 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 1  wherein said step of sampling formation water from said undersaturated methane reservoir comprises the step of capturing substantially pure formation fluid.  
   
   
       3 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 1  wherein said step of sampling formation water from said undersaturated methane reservoir comprises the step of assuring that said formation water sample is representative of fluid from said undersaturated methane reservoir.  
   
   
       4 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 3  wherein said step of assuring that said formation water sample is representative of fluid from said undersaturated methane reservoir comprises the step of producing at least a well pathway volume of fluid.  
   
   
       5 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 3  wherein said step of assuring that said formation water sample is representative of fluid from said undersaturated methane reservoir comprises the step of producing at least a well tubing volume of fluid.  
   
   
       6 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 3  wherein said well has a well bottom and wherein said step of assuring that said formation water sample is representative of fluid from said undersaturated methane reservoir comprises the steps of: 
 a. ceasing production on said well for a period of time; and    b. allowing equilibrium methane conditions to be established at said well bottom.    
   
   
       7 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 3  wherein said well has a well bottom, wherein said methane reservoir has a natural reservoir pressure at said well bottom location, and a well bottom pressure and wherein step of assuring that said formation water sample is representative of fluid from said undersaturated methane reservoir comprises the step of permitting said well bottom pressure to substantially equal said natural reservoir pressure.  
   
   
       8 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 1  and further comprising the step of having a constant fluid production from said well at the time of said sampling.  
   
   
       9 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 1  wherein said well has a well bottom and wherein said step of sampling formation water from said undersaturated methane reservoir comprises the step of collecting a single phase fluid from about said well bottom.  
   
   
       10 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 1  wherein said step of sampling formation water from said undersaturated methane reservoir comprises the step of effecting only a small drawdown.  
   
   
       11 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 10  wherein said step of effecting only a small drawdown comprises the step of effecting only a small drawdown for a long period of time.  
   
   
       12 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 11  wherein said step of effecting only a small drawdown for a long period of time comprises the step of effecting only a small drawdown for a period of time selected from a group consisting of about one week, several days, about one day, longer than a traditional formation water sampling time.  
   
   
       13 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 10  wherein said step of sampling formation water from said undersaturated methane reservoir comprises the step of sampling formation water after a period of nonproduction from said well.  
   
   
       14 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 1  wherein said step of sampling formation water from said undersaturated methane reservoir comprises the step of sampling formation water until a gas-water ratio of said water is constant.  
   
   
       15 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 1  wherein said step of sampling formation water from said undersaturated methane reservoir comprises the step of contained sampling said formation water.  
   
   
       16 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 15  wherein said step of contained sampling said formation water comprises the step of uncased drill stem sampling.  
   
   
       17 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 15  wherein said step of contained sampling said formation water comprises the steps of: 
 a. lowering a tool in said well;    b. isolating a sampling area by packing; and    c. transporting a sample to a surface in a drill pipe.    
   
   
       18 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 1  and further comprising the steps of: 
 a. permitting a pressure in said undersaturated methane reservoir to go below a critical desorption pressure of said undersaturated methane reservoir; and    b. affirmatively allowing pressure to in said undersaturated methane reservoir to naturally rebuild to a pressure above said critical desorption pressure of said undersaturated methane reservoir prior to accomplishing said step of sampling formation water from said undersaturated methane reservoir.    
   
   
       19 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 15  wherein said step of accessing a well admitted to an undersaturated methane reservoir comprises the step of pumping a fluid from said well.  
   
   
       20 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 19  wherein said step of contained sampling said formation water comprises the step of isolating said formation water both before and after it is subjected to said step of pumping a fluid from said well.  
   
   
       21 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 19  wherein said step of pumping a fluid from said well comprises the step of pumping adjacent said undersaturated methane reservoir.  
   
   
       22 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 19  wherein said step of pumping a fluid from said well comprises the steps of: 
 a. pumping at a location remote from said undersaturated methane reservoir; and    b. avoiding a phase separation prior to accomplishing said step of pumping a fluid from said well.    
   
   
       23 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 19  wherein said step of sampling formation water from said undersaturated methane reservoir comprises the step of avoiding a pressure drop below a bubble point of said formation water prior to accomplishing said step of pumping a fluid from said well.  
   
   
       24 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 19  wherein said well has a well bottom and wherein said step of sampling formation water from said undersaturated methane reservoir comprises the step of maintaining said well bottom at least a bubble point of said formation water.  
   
   
       25 . A method of calculating a production characteristic for an undersaturated methane reservoir as described in  claim 15  wherein said step of contained sampling said formation water comprises the step of contained sampling both formation water and gas from said well at a surface.  
   
   
       26 - 145 . (canceled)  
   
   
       146 . A method of calculating a production characteristic for an undersaturated methane reservoir comprising the steps of: 
 a. accessing an existing well admitted to a methane reservoir;    b. sampling formation water from said methane reservoir;    c. conducting a test based on said formation water sample;    d. estimating an economic factor for commercial production from said well based upon said step of conducting a test based on said formation water sample; and    e. applying said economic factor to calculate and report a practical production quantity for said methane reservoir.    
   
   
       147 - 153 . (canceled)  
   
   
       154 . A dynamic method of surface sampling subsurface formation water comprising the steps of: 
 a. accessing a well admitted to an undersaturated methane reservoir;    b. assuring that a formation water sample is representative of fluid from said undersaturated methane reservoir;    c. initially sampling formation water from said undersaturated methane reservoir;    d. conducting an initial test based on said initial formation water sample;    e. additionally sampling formation water from said undersaturated methane reservoir;    f. conducting a similar test based on said additional formation water sample;    g. comparing results of said initial sampling and said additional sampling; and    h. achieving a constancy in said comparing the results through alteration of actions affecting said step of sampling formation water from said undersaturated methane reservoir;    wherein said step of achieving a constancy in said comparing the results of said multiple similar tests through alteration of actions affecting said step of sampling formation water from said undersaturated methane reservoir comprises the step of achieving a substantially constant critical desorption pressure result.    
   
   
       155 - 336 . (canceled)