Stratigraphic Geometries Research Articles

Abstract: Characterization of Miocene Temblor Formation, West Coalinga Field, San Joaquin Basin, California: Insights into the Stratigraphic Geometry of a Transgressive Reservoir

Abstract: Characterization of Miocene Temblor Formation, West Coalinga Field, San Joaquin Basin, California: Insights into the Stratigraphic Geometry of a Transgressive Reservoir

Carbonate production and offshore transport on a Late Jurassic carbonate ramp (Kimmeridgian, Iberian basin, NE Spain): evidence from outcrops and computer modelling

Abstract The complex interplay between shallow-water carbonate production, pelagic sedimentation, and sediment erosion and redeposition on a Kimmeridgian carbonate ramp is analysed from field data and computer modelling. Field data come from reconstructed cross-sections near Zaragoza and near Teruel, NE Spain. Inner ramp areas are dominated by coral patch reefs, ooid shoals and bioclastic packstones and grainstones, whereas middle ramp areas are typified by tempestites and pinnacle reefs. Outer ramp areas are dominated by carbonate muds and marls. The large-scale stratigraphic features of the ramp are simulated using the forward modelling computer program carbonate 6. A good match is found between real and simulated stratigraphic thicknesses along the two sections, large-scale internal stratigraphic geometries, amounts of aggradation and progradation, and the location of sequence boundaries, flooding surfaces and systems tracts in the two modelled cross-sections. To investigate the origin of the offshore carbonate mud, two synthetic stratigraphies, which both closely replicate the overall ramp geometries, were generated by computer simulation. These two simulations are based on two different hypotheses that had not been resolved from field investigation: (1) that most of the outer ramp mud was derived from erosion and redeposition from inshore areas; (2) that most of this mud originated from pelagic sedimentation. Detailed comparison between the simulated occurrence of sedimentary facies (characterized in the program by depth and process of deposition) and the real facies occurrence indicates that the closest match is given by hypothesis (1) where most of the offshore mud is produced by resedimentation from inshore areas. Offshore transport and resedimentation is thought to have been favoured by the windward orientation of the ramp, and offshore transport was highest during periods of sea-level highstands.

Sequence Stratigraphy and Stratigraphic Trap Potential of the Villeta Formation (Cretaceous), Putumayo Basin, Colombia: ABSTRACT

The Villeta Formation, which was deposited in -15 Ma (Cenomanian-Campanian), includes four 3rd-order sequences representing marine shelf, siliciclastic shoreface, and lower coastal-plain environments. Although these environments transgressed landward across the pre-Cretaceous basement during a 2nd-order base-level rise, several brief but important base-level falls and abrupt basinward and downward facies-shifts interrupted this trend. The 3rd-order base-level falls and subsequent transgressions led to the deposition of important hydrocarbon-bearing sandstones in the Villeta Formation. Sequence boundaries record abrupt downward facies shifts and separate black marine shales and deep-shelf limestones below from fluvial to tidally- and wave-influenced shoreface sandstones above. Each of these sands (Arenisca T, U inferior, U superior, and M2) laps out landward and passes upward into transgressive shales and thin highstand limestones. Base-level rise and retrogradation of the shoreline is indicated by upward thinning of transgressive sandstones and upward increase in marine shale. Sandstones thin or downlap basinward into shales. Transgressive deposits dominate the sequences. Highstand progradation of siliciclastic shorelines was minimal and limited by a relatively high accommodation/sediment-supply ratio. Base-level falls, however, allowed shorelines to advance basinward long distances. The stratigraphic geometries of the Villeta sandstones, as indicated by seismic data and well-log correlations, indicate that potentially large stratigraphic trapsmore » are present in the Putumayo Basin. Stratigraphic entrapment is indicated by landward onlap of the Villeta sandstones, the presence of shales and tight limestones overlying porous sandstones, and known hydrocarbon accumulations in the sandstones over structural highs.« less

Reservoir Description and Future Development Plans for the Unam/Mfem Fields OML 67, Nigeria: ABSTRACT

The Unam/Mfem fields, which are currently produced from three platforms, are, located 25 km offshore (southeastern Nigeria) in water depths of 60 feet to 100 feet. Over 100 MMBO have been produced to date from both unconformity bounded and fault trap reservoirs in the Upper and Middle Biafra Sands. These structural and stratigraphic geometries define at least eleven different reservoirs that are not interconnected. STOIIP for all eleven reservoirs is estimated to exceed 900 MMBO based on a recently completed reservoir characterization study. A two year reservoir description study followed the acquisition of a 1991 3-D seismic survey and resulted in the drilling of six successful wells and two sidetracks. A 3-D model of reservoir geometries and fluid flow properties was generated by integrating geologic, geophysical, and reservoir engineering data. These diverse data sets were interpreted using a combination of workstations, software packages, and displays that included Landmark, IREX, wireline log and seismic correlation charts. A detailed stratigraphic zonation scheme with 28 zones was defined and correlated field wide and subregionally to build the reservoir framework. Twenty seismic horizons were created. More than 300 critical compute, generated grids were then used to calculate STOIIP volumes. This study led to themore » identification of new pay zones along with a much better understanding of the spatial distribution of all pays within the fields. A revised exploitation strategy has subsequently been proposed which calls for 5 new platforms and the drilling of 21 additional wells over the next few years.« less

Stratigraphic Geometry of Cavern Collapse and Seismic Modeling - A Predictive Tool for Exploration: ABSTRACT

Stratigraphic Geometry of Cavern Collapse and Seismic Modeling - A Predictive Tool for Exploration: ABSTRACT

Stratigraphic architecture of extensional basins: Insights from a numerical model of sedimentation in evolving half grabens

We present a numerical model for the tectonostratigraphic evolution of half grabens which duplicates many of the stratigraphic relationships observed in extensional terranes of the southwestern United States and elsewhere. The model also generates insights and predictions on the impact of fault geometry, rates of faulting, and rates of erosion and sediment transport on landscape evolution, stratal geometry, and facies distributions. Three processes control basin development in the model: faulting, erosion/deposition, and isostasy. Assumptions are thin plate flexure, normal fault hanging wall deformation by vertical simple shear, linear dependence of sediment flux on slope, and perfect sorting of sediment during deposition. Model limitations reflect oversimplification of the dynamics of sediment erosion and redistribution. During periods of fault motion, half grabens bounded by listric faults accumulate strongly asymmetric sedimentary units. The degree of under‐ or overfilling of the basin is controlled in the short term by basin geometry (fault dip) and in the longer term by extension rates, sediment supply, and out‐of‐plane sediment transport. After fault motion ceases, erosion and sedimentation redistribute the loads on the lithosphere, resulting in progressively more symmetric sedimentary units which overlap the original basin boundaries. Model facies architecture is affected by changing subsidence patterns, stratigraphic geometries, and sediment flux. Under most conditions, syntectonic gravels are trapped near the basin edge on the fault‐bounded side but prograde far out into the basin on the hinge (opposite the fault) side. When fault movement ceases, coarse‐grained sediment from the fault‐bounded side may initially be able to reach farther out into the basin, but overall retrogression is observed on both sides of the basin as topography is eroded and as posttectonic sedimentation buries former sediment sources. Changing fault dips and lithospheric rigidity affect facies patterns, whereas altering the ratio between rates of erosion and sediment transport affects landform development and depositional geometries.

Sedimentation Response to Earthquake-Related Events, Middle Eocene Ventura Basin, California: ABSTRACT

Middle Eocene strata in the Topatopa Mountains, northeastern Ventura Basin, California, were deposited as five unconformity-bounded depositional sequences in a seismically-active basin characterized by rapid, episodic subsidence. Analysis of stratigraphic geometries, detailed facies analysis, and backstripping-derived subsidence rates indicate that tectonically-induced differential subsidence caused basin-wide migrations of the Topatopa depocenter at least every 2 m.y. Unusually abundant convolute laminations and a slumped interval may record the influence of earthquakes. The convulate laminations do not grade downward into ripple laminations and are not associated with dewatering dikes and pipes as would be expected if the laminations were formed by shear from an overlying current or by dewatering during rapid burial. Thus, formation during shock-induced liquefaction is more likely. Also a 20-m thick slumped interval in the uppermost Cozy Dell Formation underlies a sequence boundary interpreted as a surface across which depocenter migration took place. Association of this slumped interval with a tectonically-formed surface is consistent with deposition in a seismically-active environment. Rapid, differential subsidence in the Topatopa depocenter was probably episodic and associated with seismic events. Rapid, episodic subsidence with attending earthquakes is recorded in Holocene strata of the Humboldt basin, an analog to the Topatopa depocenter. Also, A Middle Tertiarymore » slumped interval in the southernmost San Joaquin basin is attributed to a seismic event. Similar earthquake-related events are recorded by sedimentation patterns in the Middle Eocene Ventura Basin and may be evident in the strata of other active-margin basins as well.« less

Alternative Sea Level Curves and Resultant Stratigraphic Geometries: High Resolution Computer Simulations Applied to the Middle Pennsylvanian (Desmoinesian), SE Utah

Alternative Sea Level Curves and Resultant Stratigraphic Geometries: High Resolution Computer Simulations Applied to the Middle Pennsylvanian (Desmoinesian), SE Utah

Neotectonics and Taphonomy: Pleistocene Molluscan Shell Accumulations in the Northern Gulf of California

Late Middle to early Late Pleistocene shallow marine deposits west of Bahia Adair, to the northern Gulf od California, have been exposed by tectonic uplift along the coast. Represented sedimentary environments include shallow subtital, tidal falt, tidal estuary, tidal channel and shoreface. The deposits contain a diverse molluscan fauna, often concentrated in shell beds. Based on taphonomic data, stratigraphic geometry and faunal composition, the shell beds are identified as beach berm accumualtions, tidal channel lags, subtidal community beds, or unconformity beds. While the first three types of shell beds form on many continental margins, the unconformity beds reflect the active tectonic setting of the northern Gulf of California

Stratigraphic Geometries of Miocene Reservoir Units in the Southern San Joaquin Basin, California: Implications for Sequence Analysis along Active Margins

Stratigraphic Geometries of Miocene Reservoir Units in the Southern San Joaquin Basin, California: Implications for Sequence Analysis along Active Margins

Three-Dimensional Foreland Basin Stratigraphic Geometry and Subsidence History: Colville Trough, Alaska

Three-Dimensional Foreland Basin Stratigraphic Geometry and Subsidence History: Colville Trough, Alaska

Linked fault families in basin formation

Recent models of faulting tectonics in basins and passive margins have emphasized the linked nature of faults in a way that is analogous to that developed for thrust regimes. A linked fault system requires three components; ramps, flats and sidewalls or transfers. Basins that are the result of other processes are not considered in this contribution, and the examples used are drawn from the Midland Valley and Northumberland basins of the U.K. where existing mapping by the British Geological Survey as well as field work undertaken by the author indicate that such models are appropriate. This paper summarizes the geometric features and constraints of such models and emphasizes the role of each of the three critical components of a linked system. For large deformations that result in the formation of major extensional and strike-slip basins, the principal geometries can be understood by reference to regionally and locally balanced fault models that involve detachment, ramp and sidewall or transfer elements. Tip strains, and both lateral and vertical accommodation zones are included in the general model but these probably account for less than 10% of the total upper crustal strain. The basic analysis of a linked basin system requires the transfer of displacement on and between the fault and shear zone components. The geometry of the stratigraphic units is used to deduce the active linkage on the fault system. In oblique-slip systems and where the dominant extensional ramp is connected to oblique transfer and detachment systems, lateral and sidewall sub-basins and intra-basin uplifts occur as part of continuing slip on the fault system. These control facies distribution and depocentre evolution. The existence of a basin-forming linked system frequently controls later deformation of basins and margins, and an appreciation of basin growth faults and stratigraphic geometry is essential in the interpretation of inverted basins and orogenic belts involving supracrustal formations.

Stratigraphic Simulation of Sedimentary Basins: Concepts and Calibration (1)

A two-dimensional stratigraphic simulation program based on semiempirical algorithms has been successfully applied to clastic, carbonate, and mixed clastic/carbonate depositional regimes. The program may be used to predict reservoir distribution, to constrain interpretations of well and seismic data, to test exploration scenarios in frontier basins, and to evaluate the fundamental controls on basin stratigraphy. Applications to seismic and well-log data sets from Main Pass (U.S. Gulf Coast), offshore Sarawak (Malaysia), and the Baltimore Canyon (U.S. East Coast) demonstrate that the program simulates stratigraphy on a basin-wide scale as well as on the scale of individual prospects. The Main Pass section is an offlapping sequence of Neogene clastics. The model simulates 17 m.y. of geologic history at a 200,000-yr resolution and reproduces gross basin geometry, major sequence boundaries, depth and location of nearshore marine sands, intervals of sediment bypass into deep water, shelf margin positions, and paleobathymetry. Three Neogene carbonate buildups of central Luconia, offshore Sarawak (Malaysia), were simulated using a sea level history optimized to reproduce the carbonate growth anatomy. The model reproduced observed seismic reflection geometries and transgressive, aggradational, progradational, retrogradational, and subaerial exposure phases. The program has also simulated Jurassic-Pleistocene basin and stratigraphic sequence geometries and mixed clastic/carbonate facies distribution along a 300-km regional dip line of the Baltimore Canyon Trough. Modeled features of interest include a progradational Middle Jurassic carbonate margin punctuated by clastic deposition during sea level lowstands and a Late Jurassic-Early Cretaceous aggradational carbonate margin culminating in the development and subsequent drowning of isolated carbonate buildups. Simulated bathymetries, facies relations, and subaerial exposure surfaces for the Early Cretaceous aggradation margin are consistent with detailed petrographic, paleontologic, and seismic stratigraphic interpretations.

Model for Hydrocarbon Migration and Entrapment Within Faulted Structures

A model is presented that relates faults to migration and entrapment. The basic assumption of the model is that a fault is neither a seal nor a conduit. Therefore, the effect of faulting on both migration and entrapment depends on the rock properties of strata juxtaposed by the fault and on the structural attitude of the juxtaposed fault blocks. Fault-plane sections used with structure maps give a three-dimensional view of migration and trapping, and they illustrate the interplay of three critical parameters: (1) closure style, i.e., unfaulted anticline, faulted anticline, or nose, (2) cross-fault geometry, i.e., the throw and change of throw along a fault, and (3) stratigraphic geometry, i.e., the thickness and spacing of permeable and impermeable units. Cross-fault spil points define limits of trapping potential and paths for vertical migration. Synclinal spillpoints define stratigraphic tops of vertical migration paths and egress points for lateral migration. The validity and importance of the basic assumptions of the model can be evaluated by comparison with oil field characteristics in specific provinces.

Stratigraphic Sequences, Geometry, and Tectonic History of Mid-Continent Rift System: Alternate Hypotheses: ABSTRACT

Prior to late 1981, geologic models for the Mid-Continent rift system (MRS) were based almost entirely on potential-field geophysical data and studies of outcrops along the periphery of only one segment of the structural trend. Since that time, several thousand miles of reflection seismic data and two deep borehole penetrations have provided significant (although largely proprietary) data to expand their understanding of the MRS. Seismic-defined geometry confirms that sources of the large-scale gravity anomalies which characterize the MRS are not entirely, if even mostly, within the rift-fill sequences. In addition to layered basic volcanics, sedimentary rocks must comprise a significant part of the fill. Magnetic signatures distinguish between volcanic and sedimentary lithic packages near the Proterozoic surface, thereby allowing better delineation of seismic stratigraphic sequences. A review of known rock properties from outcrops and boreholes, in conjunction with seismic and potential-field data, provides alternatives for reconstructing stratigraphic sequences in the fill. This approach gives better insight into the tectonic history of the MRS. The presence of large volumes of sedimentary fill and the probability that such sedimentary fill developed at different times and places during rift history allow a variety of models for hydrocarbon entrapment to be constructed. The factmore » that over the entire extent of the MRS only two deep tests have resulted from an intense exploration effort spanning more than five years indicates that very few hydrocarbon models have actually been tested.« less

Complex Oolite Reservoirs in Ste. Genevieve Limestone (Mississippian) at Folsombille Field, Warrick County, Indiana: ABSTRACT

Correlation of productive zones at the Folsomville field is difficult because lithology in the upper part of the Ste. Genevieve Limestone, which contains oolite bodies, is both laterally and vertically variable. The problem is further complicated by significant thickness variations of this interval that result in juxtaposed positions of porosity zones when geophysical logs are correlated side by side. Subsurface slice mapping, now an infrequently used method of subsurface analysis, can resolve complex geometries of oolite bodies and account for seemingly incongruous patterns of hydrocarbon production. Any mappable parameter can be envisioned in three dimensions by using the slice-map method. Net porosity and lithofacies slice maps, constructed at 2-ft intervals beneath a persistent stratigraphic marker near the top of the Ste. Genevieve Limestone, describe the stratigraphic geometries of oolite reservoirs at the Folsomville field. Integrating fluid content and well-production histories with the slice maps allows patterns of hydrocarbon production to be deciphered, a procedure that should provide a valuable guide in designing the most effect enhanced recovery program for the field.

Internal Geometry, Seismic Facies, and Petroleum Potential of Canyons and Inner Fan Channels of the Indus Submarine Fan

The Indus Fan, the second largest submarine fan in the world, covers 1,250,000 km2 (500,000 mi2) and contains sediment more than 7 km (23,000 ft) thick. Multichannel (24-fold) CDP seismic data provide the bases for evaluating the Indus Fan and consist of four seismic facies. Of these, only the high-amplitude, discontinuous (H-D) facies is thought to contain reservoir-quality sandstones. The H-D facies is confined to the axes of leveed channels. Canyon-channel systems that fed the fan in the past can be divided into three zones. The degradational zone is composed of an erosional canyon complex filled by prodelta mud. The transitional zone, located near the canyon mouth, consists of superimposed channels that initially were erosional but eventually aggraded and developed levees. The headward termination of the H-D facies occurs in this zone. The aggradational zone consists of superimposed leveed channels confined solely by their own levees. The H-D facies forms extensive interconnected bodies several kilometers (about 2 mi) wide and 100 m (330 ft) thick in aggradational channels. The proximal termination of the H-D facies near canyon mouths implies the presence of reservoir-quality sandstone surrounded by source/seal mudstone in the transitional zone. This stratigraphic trapping geometry and structural leads may represent a vast, untapped petroleum province.

Depositional Model for Submarine Fan Deposits of Vedder Sandstone, Eastern San Joaquin Basin: ABSTRACT

The Vedder sandstone is an informal subsurface term applied collectively to a series of offlapping clastic wedges of late Oligocene through early Miocene age that subcrop beneath the basal Saucesian unconformity along the southeastern flank of the San Joaquin basin. Although the Vedder has generally been accepted as a shoreface to shallow-water shelf deposit, such an interpretation is inconsistent with the sandstone body geometry, vertical and lateral sequence architecture, and inferred paleobathymetry of foraminiferal assemblages for the interval over the greater part of the northwestern subcrop trend. The Vedder sandstone in that region represents deposition in a series of small submarine fans that coalesced at the base of a fault-controlled slope along the eastern margin of the Zemorrian San Joaquin basin. The Vedder fans exhibit a relatively broad inner fan apron composed of amalgamated, channel-fill deposits that pass quickly downdip into a highly variable midfan belt of channel-levee complexes. The outer fan is characterized by thick, sand-rich depositional lobes with a narrow outer fan fringe. Three periods of fan progradation are recognized in the Vedder interval, each corresponding to a relative sea level drop related to local tectonic pulses in the active forearc setting. A subsequent lowstand coincident with majormore » uplift along the basin margin resulted in a regional unconformity that beheaded the Vedder fans and stripped off much of the equivalent slope and shelf facies. This unconformity juxtaposed the updip Vedder sandstones against an overlying transgressive sandstone, thus reducing the otherwise excellent stratigraphic trap geometries of the Vedder interval.« less

Deltaic Cherokee Sandstones of Central Oklahoma: ABSTRACT

Exploration for delta reservoir sandstones on the Mid-Continent craton can be enhanced by a better understanding of facies character, depositional environments/processes, and factors that controlled their distribution. Appreciation of the dynamic nature of deltaic sedimentation permits the geologist to predict more precisely the stratigraphic relations and sandstone geometry. It also enables the explorationist to predict areas or trends that may previously have been overlooked. A detailed, subsurface stratigraphic study of the Cherokee sandstones (early Desmoinesian) in central Oklahoma (including parts of Lincoln, Logan, Oklahoma, Cleveland, and Pottawatomie Counties) gives insight into the processes of deltaic sedimentation which should provide help in local exploration and development operations, and in regional exploration in similar rocks encountered throughout the world. Interpretations will be based on core analyses, examination of well cuttings, study of regional and detailed stratigraphic cross sections, and analysis of structure, paleotopographic/paleodrainage, paleogeologic (subcrop), and isolith maps of several key horizons. End_of_Article - Last_Page 1016------------

Precambrian Iron-Formations of Australia

Distribution, age, lithologic type, stratigraphic geometry, Western Australia, South Australia, Northern Territory, Queensland