NEW GEOCHEMICAL EVIDENCE OF HYDROCARBONS ALONG THE LA POPA SALT WELD, LA POPA BASIN, NORTHEASTERN MEXICO

New studies show evidence of hydrocarbons along the La Popa salt weld in northeastern Mexico, reinforcing the idea that salt diapirs/welds significantly affect the migration pathways of hydrocarbons. Geochemical testing (i.e. TOC, Rock-Eval, and molecular organic geochemistry) of samples taken along the length of the weld indicate that at least some of this material is not in situ, but has migrated along the weld. TOC values between 0.5 and 1.0 weight percent, while not high from a production standpoint, do indicate that organic carbon is present along the weld. Rock-Eval results from the majority of these samples show S1 peaks that are greater than the corresponding S2 peaks, indicating that the organic matter has migrated to its current position along the weld. Molecular organic geochemistry (biomarker analyses) revealed hydrocarbon compounds that show mature signatures for these samples. Many of the samples also show significant biodegradation, probably as a result of near-surface exposure along the weld.

Of the lithologies above the basement, those that are considered the best possible source rocks after sampling and geochemical testing are the Upper Mudstone Member of the Porterillos Formation, the Parras Formation, and a sample collected along the weld which is thought to have been rafted up within the weld-forming salt from a lower stratigraphic level. Vitrinite reflectance testing shows a range of 0.76 to 1.47 from the basal Minas Viejas Formation to the Eocene Carroza Formation (the youngest formation in the basin), which puts these samples in the peak to late oil generation window, and into the condensate/wet gas stages of maturity. Similar to the migrated samples collected along the weld, these lithologies have TOC values of 0.5 to 1.0 weight percent, indicating that they are fair source rock candidates. Rock-Eval shows S2 peaks that are higher than the corresponding S1 peaks, which is consistent with in situ organic material. Using results from gas chromatography, GC-MS, and GC-MS-MS geochemical analyses, the correlation of a source to the migrated material along the weld will be attempted. Once a source rock-migration pathway correlation has been established, the effects of the La Popa salt weld on maturation and migration of hydrocarbons within the basin will be better understood.