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Shale-gas resource systems (view source)
Revision as of 15:38, 24 September 2015
, 15:38, 24 September 2015→Organic richness: total organic carbon assessment
Use of this nomograph is illustrated using data from the Barnett Shale ([[:File:M97FG6B.jpg|Figure 6B]]). Using a measured present-day TOC of 4.48%, with correction for bitumen and/or oil and kerogen in the rock and any increase in NGOC caused by hydrogen shortage, an original TOC of 6.27% is calculated. This means that the original generation potential (S2o) was 27.19 mg HC/g rock or, when converted to barrels of oil equivalent, 7.67 times 10minus2 m3/m3 (595 bbl/ac-ft). Data for this calculation are summarized in Table 2.
Use of this nomograph is illustrated using data from the Barnett Shale ([[:File:M97FG6B.jpg|Figure 6B]]). Using a measured present-day TOC of 4.48%, with correction for bitumen and/or oil and kerogen in the rock and any increase in NGOC caused by hydrogen shortage, an original TOC of 6.27% is calculated. This means that the original generation potential (S2o) was 27.19 mg HC/g rock or, when converted to barrels of oil equivalent, 7.67 times 10minus2 m3/m3 (595 bbl/ac-ft). Data for this calculation are summarized in Table 2.
{| class=wikitable
|+{{table number|2}}Computation of original TOC from measured TOC and Rock-Eval data.
|-
! Geochemical Description || Value || Derivation
|-
| HIo || 434 || Estimated from all data
|-
| HIpd || 28 || (S2pd/TOCpd x 100)
|-
| TR || 94% || (HIo - HIpd)/HIo
|-
| TOCpd (wt. %) || 4.48 || Measured
|-
| S1pd (mg HC/g rock) || 0.78 || Measured
|-
| S2pd (mg HC/g rock) || 1.27 || Measured
|-
| %OC in S1+S2 || 0.17 || (0.085 x [S1pd + S2pd])
|-
| TOCpdbkfree (wt. %) || 4.31 || (TOCpd - OC in S1 + S2)
|-
| NGOCcorrection (wt. %) || 0.35 || (HIo x 0.0008)
|-
| TOCpdNGOCadjusted (wt. %) || 3.96 || (TOCpd, bkfree-NGOC correction)
|-
| %GOC in TOCo || 37% || (HIo/1177)
|-
| TOCo (wt. %) || 6.27 || (TOCpd,adjusted/(1 - %GOC)
|-
| GOCo || 2.31 || wt. %
|-
| NGOCo || 3.96 || wt. %
|-
| S2o (mg HC/g rock) || 27.19 || (GOCo/0.085)
|-
| S2o (in boe/af) || 595 || boe/af (S2o 21.89)
|}
<sup>TOC = total organic carbon; HI = hydrogen index; subscript ‘‘o’’ = original value; subscript ‘‘pd’’ = present-day measured or computed value; TR = transformation ratio, the change in original HI, where TR = (HIoHIpd)/HIo; GOC = generative organic carbon (in weight percentage); NGOC = nongenerative organic carbon (in weight percentage); bkfree = bitumen- and kerogen-free TOC values; subscript ‘‘NGOCcorrection’’ = minor correction to TOCpd for added carbonaceous char from bitumen and/or oil cracking. S1 = Rock-Eval measured oil contents; S2 = Rock-Eval measured kerogen yields; boe/af = bbl of oil equivalent per acre-ft.</sup>
This nomograph provides a pragmatic method for estimating the elusive TOCo value and the original generation potential via determination of GOCo values when combined with either measured or estimated HIo data or using a sensitivity analysis via P10, P50, and P90 HIo values in the absence of other data. This is important because the total generation potential of the source rock can be estimated with these assumptions, and as such, the amount retained in the organic-rich shale can be estimated, that is, GIP, as well as the expelled amounts that may be recovered in a hybrid shale-gas resource system.
This nomograph provides a pragmatic method for estimating the elusive TOCo value and the original generation potential via determination of GOCo values when combined with either measured or estimated HIo data or using a sensitivity analysis via P10, P50, and P90 HIo values in the absence of other data. This is important because the total generation potential of the source rock can be estimated with these assumptions, and as such, the amount retained in the organic-rich shale can be estimated, that is, GIP, as well as the expelled amounts that may be recovered in a hybrid shale-gas resource system.