US 12,443,775 B2
Determining maturity of paleozoic unconventional shale gas
Feng Hu Lu, Dhahran (SA)
Assigned to SAUDI ARABIAN OIL COMPANY, Dhahran (SA)
Filed by SAUDI ARABIAN OIL COMPANY, Dhahran (SA)
Filed on Nov. 2, 2021, as Appl. No. 17/453,204.
Prior Publication US 2023/0138017 A1, May 4, 2023
Int. Cl. G06F 30/20 (2020.01); E21B 49/08 (2006.01)
CPC G06F 30/20 (2020.01) [E21B 49/08 (2013.01); E21B 2200/20 (2020.05)] 13 Claims
OG exemplary drawing
 
1. A method for determining a maturity level of a hydrocarbon gas of an unconventional reservoir, the method comprising:
analyzing a plurality of samples from at least one Paleozoic or pre-Paleozoic shale or sandstone reservoir to obtain a historical dataset comprising historical data points,
where the historical dataset provides carbon isotopic ratio values δ13C1 and δ13C2 and vitrinite reflectance equivalents (VRE) value of the analysed plurality of samples, and
wherein the plurality of samples comprise hydrocarbon gas samples, formation samples, or combinations thereof;
fabricating an unconventional reservoir maturity chart by:
plotting the δ13C1 versus δ13C2 included the historical dataset to obtain a δ13C1 versus δ13C2 plot, δ13C1 and δ13C2 are in units of parts per thousand (%) Vienna Pee Dee Belemnite (VPDB);
plotting a first maturity shape having an enclosed first boundary on the δ13C1 versus δ13C2 plot such that a substantial number of the historical data points having a VRE value in a range of from about 0.5% to 1.5% reflectance equivalents are located within a first maturity area, where the first maturity area is defined by the first boundary of the first maturity shape;
plotting a second maturity shape having an enclosed second boundary on the δ13C1 versus δ13C2 plot such that a substantial number of the historical data points having a VRE value in a range of from about 1.5% to 2.0% reflectance equivalents are located within a second maturity area, where the second maturity area is defined by the second boundary of the second maturity shape and where a lower portion of the second boundary is defined by the relationship δ13C1=δ13C2;
plotting a third maturity shape having an enclosed third boundary on the δ13C1 versus δ13C2 plot such that a substantial number of the historical data points having a VRE value in a range of from about 2.0% to about 3.5% reflectance equivalents are located within a third maturity area, where the third maturity area is defined by the third boundary of the third maturity shape and where an upper portion of the third boundary is defined by the relationship δ13C1=δ13C2; and
plotting a fourth maturity shape having an enclosed fourth boundary on the δ13C1 versus δ13C2 plot such that a substantial number of the historical data points having a VRE value in a range of from about 3.5% to 5.0% reflectance equivalents are located within a fourth maturity area, where the fourth maturity area is defined by the fourth boundary of the fourth maturity shape and where an upper portion of the fourth boundary is defined by the relationship δ13C1=δ13 C2;
performing compositional and isotropic analyses on the hydrocarbon gas of the unconventional reservoir which the maturity level is to be determined to obtain carbon isotopic ratio values δ13C1 and δ13C2 of the hydrocarbon gas;
plotting a data point on the unconventional reservoir maturity chart from the δ13C1 and the δ13C2 of the hydrocarbon gas; and
determining the maturity level of the hydrocarbon gas of the unconventional reservoir by determining a position of the data point relative to positions of the first maturity shape, the second maturity shape, the third maturity shape and the fourth maturity shape.