A successful qualitative and quantitative integrated interpretation of Lower Miocene wells and seismic data in Salina del Istmo Basin, Mexico

The study area is located in middepth to deep waters of the Salina del Istmo Basin where Repsol operates Block 29. The objective of this work is to integrate qualitative and quantitative interpretations of rock and seismic data to predict lithology and fluid of the Early Miocene prospects. The seismic expression of those prospects differs from age-equivalent well-studied analog fields in the U.S. Gulf of Mexico Basin due to the mineralogically complex composition of abundant extrusive volcanic material. Offset well data (i.e., core, logs, and cuttings) were used to discriminate lithology types and to quantify mineralogy. This analysis served as input for developing a new rock-physics framework and performing amplitude variation with offset (AVO) modeling. The results indicate that the combination of intercept and gradient makes it possible to discriminate hydrocarbon-filled (AVO class II and III) versus nonhydrocarbon-filled rocks (AVO class 0 and IV). Different lithologies within hydrocarbon-bearing reservoirs cannot be discriminated as the gradient remains negative for all rock types. However, AVO analysis allows discrimination of three different reservoir rock types in water-bearing cases (AVO class 0, I, and IV). These conclusions were obtained during studies conducted in 2018–2019 and were used in prospect evaluation to select drilling locations leading to two wildcat discoveries, the Polok and Chinwol prospects, drilled in Block 29 in 2020.

Development of Detachment Folds in the Mexican Ridges Foldbelt, Western Gulf of Mexico Basin

<p>Examples of natural folds growing in a homogenous mechanical stratigraphy of alternating competent and incompetent thin layers of fine- and coarse-grained sediments are examined, and the fold growth process is quantified. Our analysis reveals that the overall response to loading of siliciclastic sequences corresponds to that of flexural flow and parallel-to-bedding heterogeneous pure shear. Folds start out as low-amplitude sinusoidal disturbances that rapidly become finite-amplitude folds of heterogeneous strain. We also derive the following scaling relations: (i) degree of amplification scales with both the height above the detachment and strain, (ii) wavelength selectivity broadens with increasing strain, and (iii) deposition of syn-sedimentary geometries is function of strain. These relations are a natural consequence of idealized area-preserving laws of fold growth. From these results we devise a method to estimate fold strain by means of an amplitude versus depth diagram. We are also able to define a progression of fold shape change as a function of the fundamental parameter strain. Initially, structures grow by limb rotation and the selective amplification of a single dominant wavelength giving rise to sinusoidal folds. When strain reaches ~8%, softening/plastic yielding around hinges results in the development of sharp fold profiles. Limbs lock their dips at 35°–45°, suggesting that growth in this stage is permitted by hinge mobility along ramps and blind faults. Moreover, hinge migration causes fold development to accelerate spontaneously. These findings suggest that conclusions relating periods of accelerated erosion/uplift in contractional structures to tectonic processes should be treated with caution.</p>

Deep-water sedimentary bedforms in a mobile substrate terrain: examples from the central Gulf of Mexico basin

We have used high-resolution geophysical data to investigate depositional and erosional bedforms in two geomorphologic provinces of the deepwater central Gulf of Mexico Basin: (1) the Mad Dog and Atlantis areas in the Sigsbee Escarpment region and (2) the Holstein minibasin within the salt canopy in the slope. Multibeam bathymetry indicates that the seafloor relief in the study areas is highly irregular because it is influenced by the dynamic behavior of underlying salt bodies resulting in the development of diverse bathymetric features. Side-scan images reveal erosional furrows of different morphologies at the base of the Sigsbee Escarpment that are oriented subparallel to the escarpment. Wide and sinuous furrows overlie mass transport deposits (MTDs), whereas, in other areas along strike, narrow rectilinear furrows are found beneath MTDs. The furrow fields in the Sigsbee Escarpment are located within a large series of erosional features that are linked to the action of westward flowing bottom currents associated with topographic Rossby waves that manage to rework sediments at water depths up to 2000 m. The interaction between the bottom current flow and the seafloor is likely influenced by the MTD’s irregular top surface relief and lateral changes in the escarpment’s morphology resulting in the development of complex sinuous furrow morphologies. North of the escarpment, subbottom profiles indicate a series of buried sediment waves found in the southern rim of the Holstein minibasin. Sediment wave morphometry indicates wavelengths ranging from 116 to 339 m and wave heights between approximately 0.8 and 2.4 m. Sediment waves were likely formed by turbidity currents as they exited the minibasin. The vertical change in topographic relief from the minibasin to the salt high led to variations in flow thickness and flow velocity of turbidity currents passing over the minibasin’s open rim. Consequently, these changes in flow regime led to the formation of sediment waves.

Late Cretaceous–Paleocene transition from calcareous platform to basinal deposition in western Chiapas, Mexico: Opening of the Chiapanecan embayment

ABSTRACT Tracing the evolution of the Cretaceous shelf margin of the southwestern Gulf of Mexico reveals a relatively stable area in northeastern Chiapas, Mexico, northern Guatemala and Belize, and the Yucatán Peninsula, where carbonate and evaporite platform conditions prevailed from the Aptian until at least the Paleocene. The area was flanked by zones of greater subsidence, where platform thickness reached several thousand meters and where foredeep depocenters were established due to collision of the Great Antilles arc with the passive margin of North America. Foredeep deposition initiated as early as the Maastrichtian in central Guatemala and in the Paleocene in Chiapas and south Petén, Guatemala. Northwestern Chiapas was characterized by a relatively deep basin and by southward retreat of the shelf break from the Albian to Maastrichtian. The retreat can be traced by the occurrence of periplatform slope facies. During the Santonian–early Campanian lowstand, the periplatform slope is thought to have become a bay, herein called the Chiapanecan embayment. Slope conditions reached the Tuxtla area (western Chiapas) in the Campanian, ultimately connecting Paleocene foreland basins with the Gulf of Mexico basin. Whereas the foredeep in Guatemala and Belize (Sepur and Toledo formations) was constrained by a backstop produced by the southernmost stable Yucatán platform (Lacandón Formation), the Tuxtla basin (Soyaló and Nanchital formations) was connected to the Gulf of Mexico, potentially allowing Paleocene bypass of sediment sourced in the colliding Great Antilles arc.