Major reserves of oil exist in the Reforma area of Tabasco and Chiapas states and the Campeche Shelf of SE Mexico in high‐energy, bank‐edge, reef‐derived or reef‐associated carbonate rocks, ranging in age from Late Jurassic to earliest Late Cretaceous. It is the conclusion of this study that the Reforma reservoir facies does not extend into W Guatemala. However, there the potential for major reserves in bank and lagoonal carbonates of similar age is considered excellent. A variety of structures, mostly resulting from salt tectonics, is present. Known reservoir rocks include fractured carbonates with secondary porosity resulting from solution and dolomitization, and limestones with primary intergranular porosity. An indigenous source is likely for the large quantitis of oil which have been tested at Rubelsanto. Seals, in the form of thick intervals of Cretaceous anhydrite and, in places, of Tertiary fine‐grained clastics, are abundant.
The area E of Rubelsanto may have considerable merit, particularly if detailed structural analysis indicates that similar salt‐tectonic features are present. The less deeply buried areas of Cretaceous carbonates are not highly regarded because: (1) salt is absent: (2) temperatures sufficient for maturation of hydrocarbons may be lacking: and (3) a considerable number of dry holes with no significant shows has been drilled. N Guatemala is somewhat attractive, because the proper combination of unmetamorphosed Paleozoic organic shale on basement highs, well‐developed Todos Santos sandstone reservoirs, and the overlying thick evaporite seal could trap sizable hydrocarbon accumulations. However, as degree of metamorphism decreases, presumably basinward, distance from source terrain for detritus increases and reservoirs may be inadequate.
Studies of more than 10,000 km of geophysical data from an area situated 45 km south of Malta, supported by stratigraphic projections from wells in offshore Sicily, Tunisia and Libya, indicate facies different from the continuous carbonate sequence encountered in wells on the Malta Platform. Geologic structures in the study area range from a broad anticlinal high to complex horst‐and‐graben systems that are mostly of post‐Miocene age. One graben is believed to be an Early Mesozoic rift associated with break‐up of Gondwana, and may contain deep‐water Triassic‐Jurassic strata similar to those of the Ragusa Basin in SE Sicily.
Triassic and Jurassic shallow‐water carbonates were penetrated in wells to the north of the study area. These wells also encountered Upper Jurassic — Cretaceous carbonates, which consist mostly of restricted‐shelf dolomites; pelagic limestones are present at one well located in a re‐entrant of the Malta Platform.
During Cretaceous time, part of the study area was transitional between platform and basin settings, and the presence of deeper‐water strata, similar to those which provide proved or potential source rocks and seals in Tunisia, is predicted. Shelf‐edge carbonates can provide good reservoirs; rudistid reefs probably developed on bathymetric highs.
Based on the temperature gradient in a well near the study area, most of the Cretaceous section, at least in the Mesozoic graben, is capable of peak oil generation. Cretaceous source rocks reached maturity in the SE part of the study area during Miocene times, and elsewhere between the Pliocene and the present day. Restored seismic sections indicate that faults were active and structures developed by the beginning of Tertiary time. Several trap types are present, and the area has the potential to contain major hydrocarbon reserves.
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