ABSTRACT The Cabo Frio High corresponds to a regional basement arch located on the continental platform between the Santos and Campos basins. The distal margin of the Cabo Frio Outer High is characterized by gravity and magnetic anomalies suggesting an association with magmatic centers that affected the salt basin. Volcanic rocks are observed both on the proximal margin, where the Cabo Frio Volcanic Complex is marked by several magmatic episodes, and on the distal margin, where the Cabo Frio Outer High is marked by intrusive and extrusive igneous features affecting the pre-salt and post-salt sedimentary successions. The most important magmatic events in the area are related to (a) the pre-rift phase, with massive lava flows both onshore and offshore of the incipient continental margin; (b) the synrift phase, as indicated by several wells that drilled subaerial basaltic lava flows intercalated with lacustrine sediments; (c) the sag basin and transitional evaporitic post-rift phase, as indicated by sills and laccoliths overlain by salt and also by discordant igneous structures intruded into salt layers; and (d) the post-breakup phase, with major magmatic activity registered in the Upper Cretaceous and in the Paleogene. Volcanic events in the Cabo Frio region are a major factor in basin development and greatly impact the petroleum resources assessment, particularly when igneous rocks intrude into pre-salt source rocks and reservoirs. The geochemical data from producing fields and exploratory wells in the Cabo Frio region indicate that the main source rock system for the known accumulations are the upper Barremian calcareous black shales, deposited in brackish-to-saline water lacustrine environments from the Coqueiros Formation. In the continental shelf, the oil fields are characterized by intense biodegradation, which has deteriorated the oil quality. Several factors are important elements that control the prospectivity of the Cabo Frio region, such as thermal maturity of the source rocks, reservoir depth, seal effectiveness, magmatic events, and mixing of oils generated from different maturity pulses.

Abstract Laggan, located in the west of Shetland, was discovered in 1986. There is now an improved understanding of Laggan, thanks to innovative and fully integrated geoscience studies and a successful appraisal campaign. Development studies are well advanced, with the discovery of Tormore in 2007 providing the potential for a combined development project. Laggan and Tormore are Paleocene gas condensate discoveries in approximately 600 m water depth. The traps are both mixed, stratigraphic with updip closure against bounding faults. The reservoir comprises sand-rich turbidite channelized lobes and lobes. Reservoir properties are good (permeability range 30–300 mD) due to the presence of chlorite and pre-sorting on the shelf. The geoscience evaluation of Laggan has matured over the last four years with the help of fully integrated studies using 3D seismic and well data. The depositional model has been defined on the basis of an evaluation of cores and seismic and supported by analogue studies. Seismic inversion studies have also helped constrain the reservoir architecture. Of particular value has been the application of AVO to quantify net gas sand, recognized as the principal static uncertainty. The main dynamic uncertainty is the risk of compartmentalization. This risk has been reduced through an improved definition of the fault configuration by re-processing the seismic and detailed seismic attribute analysis. The potential of Tormore was recognized by applying the geoscience understanding of Laggan to help de-risk the prospect. In particular, it was recognized that Laggan could be used as an analogue for the Tormore trapping configuration and reservoir potential and that AVO could be used to help define the Gas–Water Contact. The exploration well, drilled in 2007, was successful in finding a similar reservoir to that encountered in Laggan. The fluid encountered was a gas condensate, approximately three times richer than Laggan.

ABSTRACT In this paper, we analyze source, seal, trap, reservoir, timing, and migration to explain petroleum occurrence and exploration prospectiveness in the southernmost San Joaquin basin. The factors that control oil occurrence and field size vary greatly among the three productive geologic domains in the area. We term these three domains the Foothills, the Basin, and the Upturn. The Upturn lies in between the structurally high Foothills and the structurally low Basin, and is a near-vertical panel of highly faulted strata with 5,000’-15,000’ of structural relief. Monterey Formation source rock in the southernmost San Joaquin basin has reached oil maturity mainly within the Basin. Oil generation there began about 4 Ma and continues today. However, the onset of anticlinal growth in the Basin at about 1 Ma dramatically changed oil migration pathways and delivery destinations. Prior to 1 Ma, oil migrating out of the Basin was delivered broadly across the entire east-west extent of the Upturn and Foothills. After 1 Ma, migration pathways became more complex and more east to west, resulting in very large oil pools in the southwestern San Joaquin basin. In the Basin, abundant oil has been generated, seal is ubiquitous, and early-formed traps are present. However, reservoir presence, reservoir quality, and the availability of migration pathways limit the amount of commercial production. Commercial oil is found mainly within gently dipping upper Miocene Reef Ridge and Stevens submarine-fan sand stratigraphic traps. The upper Miocene is sand poor, so sand mapping is critical. Fortunately, modern 3-D seismic combined with well data allow reliable mapping of sand fairways and fan facies. Little oil production exists above the upper Miocene because the high-angle faults that facilitate migration from the lower Monterey hydrocarbon kitchen do not penetrate high enough to allow charging of shallower strata. Little commercial production exists below the upper Miocene because depths are too great for sands to retain reservoir quality. The Upturn is well charged with oil, has abundant migration pathways, and contains numerous fault traps, many of which formed before oil migration began. However, it is sparsely drilled and difficult to image seismically, so exploration for the fault-footwall traps that are the typical targets is risky. Perhaps surprisingly given the active dense faulting, the presence of several oil fields in the Upturn indicates that seals can be effective. As in the Basin, sand is generally sparse, so sand presence is an important play control. The eastern Upturn toward the Tejon embayment is sandy, but the western and central parts generally are not. Where sand is present, reservoir quality is adequate even in lower Monterey and older strata that are tight in the Basin because burial of these strata was never deep. Most Foothills fields are located in Quaternary surface anticlines. However, central and eastern Foothills anticlines are undercharged because their present-day fetch areas are small and their trap timing is late: most of the anticlines are extremely young, so were not available to capture early-generated oil migrating from the Basin. To date more oil has been produced in the eastern than in the western Foothills, partly because sand content increases eastward.

ABSTRACT Study of Aqueduct field has revealed insights about the seismic signature, reservoir distribution, and possibly oil charging of Stevens fans. These relationships are especially well revealed at Aqueduct because of the field’s structural simplicity and the availability of a diverse data set including high-quality 3-D seismic. Aqueduct field is a stratigraphic trap formed by pinchout of the upper Monterey Stevens submarine-fan reservoir sand combined with a gentle structural bowing. The sand is time equivalent to updip interfan pelagic siliceous shale that provides the seal. Aqueduct field lies within the Aqueduct fan system, one of several southernmost San Joaquin basin upper Stevens fan systems deposited within the Monterey. The fan system is expressed on seismic profiles, cross sections, and interval isopach maps as a thick, which is typical for Stevens fans. The distal part of the system is fan shaped, but the proximal part is narrow and linear. Aqueduct field lies in the proximal part of the fan, where the lateral pinchouts of sand from the fan axis to flanking shale are abrupt. In spite of the linear proximal fan shape, we interpret that erosion at the base of the fan was minor. In the distal fan, sand passes gradationally from the fan axis to siliceous shale in the interfan area. Seismic, geochemical, and oil-water contact data suggest that Aqueduct field probably is compartmentalized into at least three separate oil pools. Sands at Aqueduct field may have been deposited as a series of prograding shingled fan lobes. If so, we interpret that the shales between these shingled lobes isolated the pools from one another. Aqueduct field has smaller reserves than nearby fields that are otherwise similar and is remarkably unfaulted. The small size may be due to charge limitation. At Aqueduct field, the absence of faults to facilitate vertical oil migration from the lower Monterey hydrocarbon kitchen upward into the reservoir may limit field size.

ABSTRACT Miocene Monterey Formation reservoirs of California contain unique reservoir rocks and additional complexity from fractures. The rocks contain a high proportion of biogenic silica derived from diatoms. Porcelanite, chert, and siliceous shale, along with dolomite, are the primary reservoir rocks of these fine-grained siliceous reservoirs. Strata are typically thinly-bedded and heterogeneous, and are difficult to adequately describe using standard reservoir characterization techniques. Our approach focuses on opal CT and quartz-phase rocks, and relies on an integration of tools to characterize both the matrix and the fractures. We attempt to quantify rock and reservoir properties, and examine the controls these factors exert on reservoir performance with field examples from Hondo (offshore), offshore Santa Maria, Elk Hills, and North Shafter. Matrix properties are affected by two primary factors, the ratio of silica to fine-grained detritus (mostly clay), and the silica phase of the rocks. The best matrix properties are found in quartz-phase porcelanite with low clay content. Rocks with higher clay volumes, or those with a high proportion of opal CT silica, have smaller pore throats, lower oil saturation, and lower permeability. In most cases, well-log techniques relying on porosity logs and spectral gamma ray logs successfully predict the clay volume and silica phase of rocks in the subsurface. Fractures are common in nearly all Monterey Formation reservoirs. Fracture distribution is controlled by mechanical stratigraphy and structural position. Cores and outcrops have traditionally supplied data and analogs for fracture characterization. This data set has been vastly expanded by the use of borehole image logs, particularly from horizontal wells. Organizing fracture data using a fracture network model enhances our predictive capability for fracture distribution and the ability to visualize likely flow paths in the reservoir. Fluid properties are also an important factor influencing Monterey reservoir behavior. Low-gravity, high-viscosity oils are generated by high-sulfur Monterey source facies, and are difficult to produce economically even from some reservoirs with excellent matrix and fracture properties. Knowledge of source facies distribution, burial history, and generation kinetics is needed to predict the hydrocarbon properties of Monterey reservoirs.

The Oneonta Formation (Catskill Magnafacies) in south-central New York is composed of two lithofacies associations: (1) Medium- to very fine-grained, cross- and planar-stratified sandstone bodies, with bedsets (lithofacies) arranged into one or (usually) more erosively based storeys. Individual storeys generally have upward-fining lithofacies, also lateral-accretion bedding and channel fills: (2) Interbedded mudstones and erosively based sandstones with a diversity of primary sedimentary structures, calcareous concretions, plant remains and trace fossils. Upward-fining bedsets (lithofacies) are sheet-like or channel-filling, and are arranged in meter-scale lithofacies sequences. The sandstone bodies are interpreted as deposits of laterally migrating and aggrading single-channel (perennial) rivers. Vegetated point-bar tops were subjected to both sheet floods and chute-channel formation. Minor low-flow deposition occurred on bar surfaces. Quantitative reconstruction of bankfull channel geometry and hydraulics gives channel widths, mean depths and slopes of approximately 60 m., 2.5 m., and 10 −4 respectively: low reconstructed bend sinuosities (1.1 to 1.2) are supported by paleocurrent data, and help to explain the dominantly coarse-grained channel fills associated with chute cut-off. Sinuosity changes during lateral migration are documented quantitatively. The sandstone-mudstone lithofacies association is interpreted as overbank flood deposits, on levees, crevasse channels and splays, and flood basins. Plant and faunal activity, and soil-forming processes, were abundant. Periodic channel-belt diversions (avulsions) caused the meter-scale lithofacies sequences in this association, also the cyclicity of the two lithofacies associations. If avulsion frequency averaged about once per 10 3 years, floodplain deposition rates are estimated at about 2 × 10 −3 m/year.

Abstract The Jurassic Period was a time of only moderate latitudinal variation in temperature. On land, vegetation and animal life were broadly similar over great distances, but in the sea invertebrate life showed evidence of provincialism from the very beginning. This provincialism intensified as the period progressed. The provincialism is considered to result primarily from the influence of latitudinal temperature gradients. These temperature gradients declined away from the tropical Tethyan zone more sharply in the northern hemisphere than in the southern hemisphere. The changing configuration of land and sea under the effects of continental drift seems to be the cause of gradually strengthening climatic differentiation as the Arctic Ocean became more and more enclosed by land, and so became a semi-isolated reservoir of cool water. Marine currents were a significant influence on the distribution of the life of the time. The principal center of evolution and dispersal in Jurassic seas was the Tethys.