Fenómenos diagenéticos en calizas del Jurásico-Cretácico de un sector de las cuencas de Huimanguillo-Comalcalco-Alto de Jalpan y primeras observaciones mediante microscopio electrónico de barrido y microtomografía 3D

Abstract

The petroleum systems of the Southeast basin (Tabasco, Mexico) are characterized by having source rocks mainly from the Upper\rJurassic, Cretaceous storage rocks, and Upper Cretaceous to Cenozoic seal rocks. In general, most of these reservoirs reflect a complex\rdiagenetic history that depends on the prevailing porosity and permeability. A new approach using tools such as scanning electron\rmicroscopy (SEM) and X-ray 3D microtomography contribute to the understanding of how hydrocarbons accumulate and flow even\rat low permeabilities.\rThe rock specimens observed by means of SEM are strongly altered by diagenetic processes of corrosion-dissolution-precipitation,\rwhich generated fractures, dissolution, stylolites, vug lining, decarbonatization, and dedolomitization. The paragenetic succession of\rsuch diagenetic processes can be schematized thus: dolomite1 → calcite1 → quartz1 → pyrite → dolomite2 → calcite2 → quartz2 →\rcalcite3 → quartz3 → chlorite → zeolites → clay minerals → celestine → calcite4\r with hydrocarbons. It is worth noting the widespread\rpresence of quartz and the partial replacement of some fossils by framboidal pyrite. The latter, along with clays and zeolites usually\roccupy spaces left after the corrosion of dolomite crystals, and also occur within vugs and fractures, as an intermediate to late stage\rin the paragenetic sequence. The latter is characterized by the following stages:\r(1) cementation of carbonates,\r(2) thermobaric alteration, associated with the incursion of fluids that were characterized by means of microthermometry of fluid\rinclusions:\ra. in dolomite, with salinities that range between 12 and 19 wt. % NaCl equiv., and temperatures of homogenization (Th)\rbetween 99 and 141 °C,\rb. in diagenetic quartz in vugs and fractures, with salinities that range between 12 and 15 wt. % NaCl equiv., and Th between\r112 and 131 °C,\rc. in the earliest calcite, with salinities that range between 12 and 14 wt. % NaCl equiv., and Th between 110 and 149 °C,\r(3) a late stage of corrosion.\rNew information obtained by means of X-ray microtomography reveals that most of the vugs are not interconnected, and that the\rsamples have abundant fossils randomly distributed in the micritic matrix and oriented according to the stratification. Microfractures\rand nano-pores in the matrix are partially responsible for the development of the vugs where cavities are formed after corrosive solutions\rthat initially generated micro-breccias, followed by a partial lining by quartz and calcite.