Reservoir hydrocarbon calculations from surface hydrocarbon compositions

Abstract

An apparatus for performing reservoir hydrocarbon calculations from surface hydrocarbon compositions during a drilling operation in a reservoir using a drilling fluid is described herein. The apparatus comprises a processor and a memory device coupled to the processor. The memory device may contains a set of instructions that when executed by the processor cause the processor to determine a raw gas value for a gas species measured at a surface gas analyzer; determine a first set of constant values corresponding to the gas species and the reservoir; determine a fluid characteristic of the drilling fluid; and calculate a subsurface gas concentration for the gas species based, at least in part, on the raw gas value, the first set of constant values and the fluid characteristic.

What is claimed is: 
     
         1 . An apparatus for performing reservoir hydrocarbon calculations from surface hydrocarbon compositions during a drilling operation in a reservoir using a drilling fluid, comprising:
 a processor;   a memory device coupled to the processor, wherein the memory device contains a set of instructions that when executed by the processor cause the processor to:
 determine a raw gas value for a gas species measured at a surface gas analyzer; 
 determine a first set of constant values corresponding to the gas species and the reservoir; 
 determine a fluid characteristic of the drilling fluid; and 
 calculate a subsurface gas concentration for the gas species based, at least in part, on the raw gas value, the first set of constant values and the fluid characteristic. 
   
     
     
         2 . The apparatus of  claim 1 , wherein the set of instructions cause the processor to calculate the subsurface gas concentration using equation (1):
     X=A *[gas]* e   B(V)+C(W)    (1)
   
       where X corresponds to a calculated subsurface gas concentration value; A, B, and C comprise constant values from the first set of constant values; [gas] comprises the raw value for the gas species; V comprises a drilling fluid viscosity of the drilling fluid; and W comprises a drilling fluid density of the drilling fluid; and
 wherein the drilling fluid viscosity and the drilling fluid density comprise fluid characteristics of the drilling fluid. 
 
     
     
         3 . The apparatus of  claim 1 , wherein the set of instructions that cause the processor to determine the first set of constant values further cause the processor to calculate the first set of constant values based at least in part on a first reference data set. 
     
     
         4 . The apparatus of  claim 3 , wherein the first reference data set comprises at least one measured subsurface gas concentration and at least one reference raw gas value corresponding to the measured subsurface gas concentration; and
 the first set of constant values are generated using equation (1), the at leas one measured subsurface gas concentration, and the at least one reference raw gas value corresponding to the measured subsurface gas concentration.   
     
     
         5 . The apparatus of  claim 2 , wherein the set of instructions further cause the processor to
 determine a second set of constant values corresponding to the gas species and the reservoir;   determine a formation characteristic of the reservoir; and   calculate a headspace gas concentration for the gas species based, at least in part, on the raw gas value, the second set of constant values and the formation characteristic.   
     
     
         6 . The apparatus of  claim 5 , wherein the set of instructions cause the processor to calculate the headspace gas concentration using equation (2):
     Y=m *(resistivity÷gamma) n *[gas]+ b    (2)
   
       where Y corresponds to calculated headspace gas concentration value; m, n, and b comprise constant values from the second set of constant values; [gas] comprises the raw gas value for the gas species; resistivity comprises a formation resistivity value of the reservoir; and gamma comprises formation gamma value for the reservoir; and
 wherein the resistivity and gamma comprise formation characteristics of the reservoir. 
 
     
     
         7 . The apparatus of  claim 6 , wherein the set of instructions that cause the processor to determine the second set of constant values further cause the processor to calculate the second set of constant values based at least in part on a second reference data set. 
     
     
         8 . The apparatus of  claim 7 , wherein the second reference data set comprises at least one measured headspace gas concentration and at least one reference raw gas value corresponding to the measured headspace gas concentration; and
 the second set of constant values are generated using equation (2), the at leas one measured headspace gas concentration, and the at least one reference raw gas value corresponding to the measured headspace gas concentration.   
     
     
         9 . An method for performing reservoir hydrocarbon calculations from surface hydrocarbon compositions during a drilling operation in a reservoir using a drilling fluid, comprising:
 determining a raw gas value for a gas species measured at a surface gas analyzer;   determining a first set of constant values corresponding to the gas species and the reservoir;   determining a fluid characteristic of the drilling fluid; and   calculating a subsurface gas concentration for the gas species based, at least in part, on the raw gas value, the first set of constant values and the fluid characteristic.   
     
     
         10 . The method of  claim 9 , wherein calculating the subsurface gas concentration comprises using equation (1):
     X=A *[gas]*e B(V)+C(W)    (1)
   
       where X corresponds to a calculated subsurface gas concentration value; A, B, and C comprise constant values from the first set of constant values; [gas] comprises the raw value for the gas species; V comprises a drilling fluid viscosity of the drilling fluid; and W comprises a drilling fluid density of the drilling fluid; and
 wherein the drilling fluid viscosity and the drilling fluid density comprise fluid characteristics of the drilling fluid. 
 
     
     
         11 . The method of  claim 9 , wherein determining the first set of constant values comprises calculating the first set of constant values based at least in part on a first reference data set. 
     
     
         12 . The method of  claim 11 , wherein
 the first reference data set comprises at least one measured subsurface gas concentration and at least one reference raw gas value corresponding to the measured subsurface gas concentration; and   the first set of constant values are generated using equation (1), the at leas one measured subsurface gas concentration, and the at least one reference raw gas value corresponding to the measured subsurface gas concentration.   
     
     
         13 . The method of  claim 10 , further comprising
 determining a second set of constant values corresponding to the gas species and the reservoir;   determining a formation characteristic of the reservoir; and   calculating a headspace gas concentration for the gas species based, at least in part, on the raw gas value, the second set of constant values and the formation characteristic.   
     
     
         14 . The method of  claim 13 , wherein calculating the headspace gas concentration comprises using equation (2):
     Y=m* (resistivity÷gamma)*[gas]+ b    (2)
   
       where Y corresponds to calculated headspace gas concentration value; m, n, and b comprise constant values from the second set of constant values; [gas] comprises the raw gas value for the gas species; resistivity comprises a formation resistivity value of the reservoir; and gamma comprises formation gamma value for the reservoir; and
 wherein the resistivity and gamma comprise formation characteristics of the reservoir. 
 
     
     
         15 . The method of  claim 14 , wherein determining the second set of constant values comprises calculating the second set of constant values based at least in part on a second reference data set. 
     
     
         16 . The method of  claim 15 , wherein
 the second reference data set comprises at least one measured headspace gas concentration and at least one reference raw gas value corresponding to the measured headspace gas concentration; and   the second set of constant values are generated using equation (2), the at leas one measured headspace gas concentration, and the at least one reference raw gas value corresponding to the measured headspace gas concentration.   
     
     
         17 . A system for performing reservoir hydrocarbon calculations from surface hydrocarbon compositions while drilling a borehole in a reservoir using a drilling fluid, comprising:
 a gas analyzer positioned at a surface above a reservoir, wherein the gas analyzer is in fluid communication with the borehole;   an information handling system communicably coupled to the gas analyzer, wherein the information handling system comprises a processor and a memory device coupled to the processor containing a set of instructions that when executed by the processor cause the processor to:
 receive a raw gas value for a gas species from the gas analyzer; 
 determine a first set of constant values corresponding to the gas species and the reservoir; 
 determine a fluid characteristic of the drilling fluid; and 
 calculate a subsurface gas concentration for the gas species based, at least in part, on the raw gas value, the first set of constant values and the fluid characteristic. 
   
     
     
         18 . The system of  claim 17 , wherein the set of instructions cause the processor to calculate the subsurface gas concentration using equation (1):
     X=A *[gas]* e   B(V)+C(W)    (1)
   
       where X corresponds to a calculated subsurface gas concentration value; A, B, and C comprise constant values from the first set of constant values; [gas] comprises the raw value for the gas species; V comprises a drilling fluid viscosity of the drilling fluid; and W comprises a drilling fluid density of the drilling fluid; and
 wherein the drilling fluid viscosity and the drilling fluid density comprise fluid characteristics of the drilling fluid. 
 
     
     
         19 . The system of  claim 18  wherein the set of instructions further cause the processor to
 determine a second set of constant values corresponding to the gas species and the reservoir; 
 determine a formation characteristic of the reservoir; and 
 calculate a headspace gas concentration for the gas species based, at least in part, on the raw gas value, the second set of constant values and the formation characteristic. 
 
     
     
         20 . The system of  claim 19 , wherein the set of instructions cause the processor to calculate the headspace gas concentration using equation (2):
     Y=m *(resistivity÷gamma) n *[gas]+ b    (2)
   
       where Y corresponds to calculated headspace gas concentration value; m, n, and b comprise constant values from the second set of constant values; [gas] comprises the raw gas value for the gas species; resistivity comprises a formation resistivity value of the reservoir; and gamma comprises formation gamma value for the reservoir; and
 wherein the resistivity and gamma comprise formation characteristics of the reservoir.