Boletín de la Sociedad Geológica Mexicana
Volumen 67, núm. 3, 2015, p. 517-531
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
Luis E. González-Ruiz1,2,*, Eduardo González-Partida3, Luis Martínez4, Jacques Pironon1, Antoni Camprubí5, Marina Vega-González3
1 Université de Lorraine, CNRS, CREGU, GeoRessources lab, F-54506, Vandoeuvre-lès-Nancy, Francia.
2 Centro Nacional de Investigación Avanzada en Petrofísica y GEOMINCO S.A. de C.V., 076100, Santiago de Querétaro, Qro., México.
3 Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, 07600, Santiago de Querétaro, Qro., México.
4 École et Observatoire des Sciences de la Terre, UMR CNRS/UdS 7516, Université de Strasbourg. 1 rue Blessig, 67084 Strasbourg Cedex, Francia.
5 Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán, D.F., 04510, México.
The petroleum systems of the Southeast basin (Tabasco, Mexico) are characterized by having source rocks mainly from the Upper Jurassic, Cretaceous storage rocks, and Upper Cretaceous to Cenozoic seal rocks. In general, most of these reservoirs reflect a complex diagenetic history that depends on the prevailing porosity and permeability. A new approach using tools such as scanning electron microscopy (SEM) and X-ray 3D microtomography contribute to the understanding of how hydrocarbons accumulate and flow even at low permeabilities.
The rock specimens observed by means of SEM are strongly altered by diagenetic processes of corrosion-dissolution-precipitation, which generated fractures, dissolution, stylolites, vug lining, decarbonatization, and dedolomitization. The paragenetic succession of such diagenetic processes can be schematized thus: dolomite1 → calcite1 → quartz1 → pyrite → dolomite2 → calcite2 → quartz2 → calcite3 → quartz3 → chlorite → zeolites → clay minerals → celestine → calcite4 with hydrocarbons. It is worth noting the widespread presence of quartz and the partial replacement of some fossils by framboidal pyrite. The latter, along with clays and zeolites usually occupy spaces left after the corrosion of dolomite crystals, and also occur within vugs and fractures, as an intermediate to late stage in the paragenetic sequence. The latter is characterized by the following stages:
(1) cementation of carbonates,
(2) thermobaric alteration, associated with the incursion of fluids that were characterized by means of microthermometry of fluid inclusions:
a. in dolomite, with salinities that range between 12 and 19 wt. % NaCl equiv., and temperatures of homogenization (Th) between 99 and 141 °C,
b. in diagenetic quartz in vugs and fractures, with salinities that range between 12 and 15 wt. % NaCl equiv., and Th between 112 and 131 °C, c. in the earliest calcite, with salinities that range between 12 and 14 wt. % NaCl equiv., and Th between 110 and 149 °C,
(3) a late stage of corrosion.
New information obtained by means of X-ray microtomography reveals that most of the vugs are not interconnected, and that the samples have abundant fossils randomly distributed in the micritic matrix and oriented according to the stratification. Microfracturesand nano-pores in the matrix are partially responsible for the development of the vugs where cavities are formed after corrosive solutions that initially generated micro-breccias, followed by a partial lining by quartz and calcite.
Keywords: diagenesis, dolomitization, corrosion, dissolution, precipitation, microtomography.