High-resolution Sequence Stratigraphic Framework Research Articles

葡西油田葡萄花油层高分辨率层序地层格架建立

随着勘探开发过程的不断深入，对沉积时间单元划分的精细程度也要求越来越高，长时间尺度的层序地层划分已经不足以满足油田的开发需求，而高分辨率层序地层格架的研究方法具有高度精细和准确的特征，是层序地层学的新发展方向。结合测井、岩心、地震和露头等资料，明确高分辨率层序地层格架的划分原则并且给出合理划分方案，建立封闭骨架剖面，由标准井出发，首先完成骨干剖面上井的层位对比，再把非骨干剖面井对比到与其相邻的骨干剖面井上，这样既保证了全区对比具有统一的标准，又确保了对比的精细程度。 As the exploration and development deepening, the requirement on the classificational accuracy of deposition time units becomes higher and higher, and the sequence stratigraphic division of long-time scales is not enough to meet the demand of development. But the research methods of high-resolution sequence stratigraphic framework have highly detailed and accurate characteristics, so it is a new developing direction of sequence stratigraphy. Combining logging, core, seismic and outcrop data, clearing the classification principles of high-resolution sequence stratigraphic framework and giving a reasonable plan, close skeleton section is established. From the standard well, firstly the strata contrast of the wells in backbone profile is accomplished, and then the wells out of backbone and the backbone of the adjacent sections are compared. This method not only ensures a unified standard of the contrast in the region, but also ensures the high resolution of the contrast.

The Research of High-Resolution Sequence Stratigraphy of Putaohua Reservoir in Daan Oilfield

By using geological and geophysical data and according to the basic characteristics of sequence boundary, Putaohua Reservoir in Daan Oilfield is divided into a rise hemicycle in long-term cycles, a full middle-term cycle, nine short-term cycles and a number of ultra-short-term cycles.The high-resolution sequence stratigraphic framework of Putaohua reservoir under monosandbody rank is established, and a set of techniques and methods to high-resolution sequence stratigraphy correlation in shallow delta is summed up.

High Resolution Sequence Stratigraphy of Silurian Strata in Tazhong Area

According to the fundamental principles of high resolution sequence stratigraphy, this paper focused on the application of high resolution sequence stratigraphy to Silurian strata in Tazhong area. Based on the comprehensive study of logging, drilling and seismic information, the high resolution sequence boundaries of Silurian strata and two scales of datum level cycles (long-term and intermediate-term) can be recognized in Tazhong area. Seven chronstratigraphic boundaries can be recognized in Silurian strata, including four sequence boundaries, which were the transformation from datum level falling to datum level rising, and three flooding surfaces, which the transformation from datum level rising to datum level falling. The Silurian strata in Tazhong area can be divided into three third-order sequences which correspond to three long-term datum level cycles, and 11 fourth-order sequences (parasequence sets) relating to 11 intermediate-term datum level cycles. The classification aforementioned can much better solved the corresponding problem between the six lithological sections of Silurian strata and sequence formations, finally establishes the high resolution sequence stratigraphic framework of Silurian strata in Tazhong area.

Sedimentary Microfacies Analysis of Xingbei 1-3 Zone in Daqing Oilfield

Putaohua reservoir is the principal producing formation in Daqing oilfield Xingbei block. The spatial distribution of single sand body is particularly important for the residual oil tapping in the middle-late stage of oilfield development. The paper studied sedimentary microfacies of Putaohua reservoirs in the zone, established high-resolution sequence stratigraphic framework of the area and a typical single sand body logging phase mode on the basis of logging features, finely portrayed single sand body type and spatial distribution on this basis to lay the solid geological foundation for oilfield subsequent residual oil tapping and provide a scientific geology guide.

Daqing Oilfield Sanan Putaohua Reservoir Sedimentary Microfacies Research

Putaohua reservoir is the principal producing formation in the Daqing oilfield sanan block. The spatial distribution of single sand body is particularly important for the residual oil tapping in the middle-late stage of oilfield development. The paper studied sedimentary microfacies of Putaohua reservoir in the area, established high-resolution sequence stratigraphic framework of the area and a typical single sand body logging phase mode on the basis of logging features, finely portrayed single sand body type and spatial distribution on this basis, laied the solid geological foundation for the oilfield subsequent residual oil tapping, provided a scientific geosteering.

Sedimentary Microfacies Analysis of S II Reservoir Group in the Block X of Daqing Oil Field

With the continuous and deepening development of oil field, reseach of sedimentary microfacies is more and more important on the basis of energy facies. The study area is the thin oil thermal recovery experimental zone of Daqing Oilfield. A variety of microfacies boundary has strong resistant and limiting effect for the filterring flow characteristics of underground fluid. This study is based on the fine contrast to reservoir, establish high resolution sequence stratigraphic framework, set up the logging facies mode of different levels of the energy levels on the basis, make the logging facies identification and combination of space for 17 sedimentary time units of SⅡ reservoir group by well to well and layer to layer, portray fine 17 sedimentary time units of the spatial distribution characteristics of sedimentary microfacies, and provid the scient geology-orientation for subsequent thermal recovery program and development effectiveness evaluation.

Characterizing and modeling natural fracture networks in a tight carbonate reservoir in the Middle East: A methodology

Fractured reservoirs are challenging to handle because of their high level of heterogeneity. In particular, natural fractures have a significant impact on well performance and water production. Therefore, understanding their significance through fracture characterization is helpful in well placement and field development. This paper presents a best practice methodology for building a 3D stochastic fracture model using a Middle Eastern tight carbonate field example. This model is generated through the analysis and integration of data including cores, borehole images (BHI), logs, mud losses, production logs, well test data and 3D seismic data. The impact of lithology on fracture occurrence was quantified based on rock-typing. Rock-types are distributed in a 3D geological model using a high resolution sequence stratigraphic framework. The length, dip angle and orientation of fractures, together with the shale content of the facies where they occur, were defined to sort the tectonic fractures from the non-tectonic (diagenetic) ones. It was found that multiple sets of tectonic diffuse fractures are generally associated with cleaner limestone units. Altogether, three sets of diffuse fractures were identified from BHI data: NE-SW, EW and NW-SE. In addition, large-scale fracture corridors, including sub-seismic faults identified from seismic analysis, were detected and calibrated with cores and BHI. The final model incorporates two scales of tectonic fractures with a direct bearing on field production behavior: diffuse fractures and large fracture corridors. Fracture calibration was performed using production logs and well production data. Permeability at wells was computed in the 3D fracture model and matched with real build-up data. These data were then used to propagate 3D fracture properties (fracture porosity, fracture permeability and equivalent block size) in the upscaled geological model, for constructing a full-field reservoir simulation model. Few changes of the fracture properties were needed to obtain a good history match, indicating that the fracture model produced is robust.

Sedimentology and sequence stratigraphy of the Lopingian (Late Permian) coal measures in southwestern China

The Lopingian coal measures of southwestern China were deposited within a range of facies associations spanning a spectrum of settings from fluvial to marine carbonate platform. The transitional to terrestrial coal measures are dominated by siliciclastics, but they also contain fifteen laterally extensive marine bands (limestone beds and mudstone). These bands act as marker horizons that enable correlation between fully marine and terrestrial facies. Examination of this range of facies and their sedimentology has enabled the development of a high-resolution sequence stratigraphic framework. Set against the established backdrop of second-order Lopingian transgression, sixteen fourth-order sequences and three composite sequences (third-order) are recognized. Results show that, in the composite sequences, peat accumulation in the seaward parts of the study area predominantly correlates with early transgressive sequence sets (TSS), while in more landward areas it correlates with the middle TSS to late highstand sequence sets (HSS). Differences in peat-accumulation regimes within the sequence stratigraphic framework are attributed to variations in subsidence and background siliciclastic input rates in different depositional settings, with these combining to produce differences in the rate of accommodation change. The preservation of coal resources in the middle to late HSS in this area was most likely related to the rise of the regional base level throughout the Lopingian.

High-resolution transgressive-regressive sequence stratigraphy of Chang 8 Member of Yanchang Formation in southwestern Ordos basin, northern China

The reservoirs within the Chang 8 Member of Yanchang (延长) Formation in the southwestern Ordos basin are characterized by low permeability. It is significant to build a high-resolution sequence stratigraphic framework for the exploration and development of these reservoirs. Based on an integrated investigation of well logs, seismic data, cores and outcrops, the Chang 8 Member is interpreted as a 3rd-order transgressive-regressive (T-R) sequence, which consists of six 4th-order T-R sequences, namely, K1, K2, K3, K4, K5 and K6, respectively, from base to top. Each 4th-order sequence comprises a transgressive systems tract overlain by a regressive systems tract. From K1 to transgressive systems tract of K4, it is characterized by the landward shifts of facies and overall retrogradational sequence stacking pattern due to accommodation increase more than sediment supply during the 3rd-order base-level rise. The distributary channels are mainly deposited in the transgressive systems tracts, and the interdistributary bays, sheet sands, and small-scale mouth bars are primarily developed in the regressive systems tracts in response to the 4th-order base-level fluctuations. From the regressive systems tracts of K4 to K6, it is characterized by the basinward shifts of facies and overall progradational sequence stacking pattern because of accommodation increase less than sediment supply during a fall in 3rd-order base level. The distributary channels are mainly accumulated in the transgressive systems tracts, and distributary channels and mouth bars are deposited in the regressive systems tracts as a result of the 4th-order base-level changes. Detailed stratigraphic and sedimentological analyses indicate that sequences K1, K2, K5 and K6, as well as the basin edge of K3 and K4, remain potential for exploration and development due to their high reservoir quality in response to the low accommodation and more sediment supply.

Use of spectral gamma-ray data to refine subsurface fluvial stratigraphy: late Cretaceous strata in the Book Cliffs, Utah, USA

High-resolution (sub-seismic) stratigraphic correlation in fluvial strata is extremely difficult using conventional subsurface core and wireline-log data (e.g. gamma-ray, neutron, density, sonic logs). Spectral gamma-ray logs provide additional data on lithological composition that can aid identification of chronostratigraphic surfaces in a high-resolution sequence stratigraphic correlation framework. The application of spectral gamma-ray data in constructing such a framework is demonstrated using data from exposures and the subsurface from the Cretaceous non-marine Blackhawk Formation and Castlegate Sandstone of the Book Cliffs area, Utah, USA. These strata provide an ideal test case for the use of spectral gamma-ray data in fluvial stratigraphy, because interpretations can be compared directly with a high-resolution sequence stratigraphic framework from coeval shallow-marine strata exposed nearby. The stratigraphic abundance of coals and relatively uniform Th/K ratio, which indicates uniform clay mineralogy, in mudstone sections of the non-marine Blackhawk Formation implies a humid, subtropical climate throughout its deposition. Variations in facies architecture and stratigraphy are therefore interpreted to have been driven principally by fluctuations in relative sea level and hinterland tectonics. Fluvial and fluvio-tidal sandstones within incised valleys, which lie above erosional sequence boundaries, have a highly variable spectral gamma-ray character, but locally are marked by distinctive heavy mineral lags and concentrations (Th consistently >3 ppm). On the interfluves of incised valleys, sequence boundaries are marked by palaeosols that locally have a distinctive leached, potassium-depleted character (Th/K ratio >17). Lateral variability in spectral gamma-ray character of sequence boundaries is consistent with facies and sequence stratigraphic models of the non-marine Blackhawk Formation and Castlegate Sandstone, but sequence boundaries do not exhibit a clear, diagnostic character in every location. In addition, high Th/K ratios of the type noted at interfluve palaeosols may be produced by potassium depletion beneath coal seams as a result of acid groundwater percolation during early diagenesis, and by thorium enrichment in heavy mineral lags within foreshore sandstones. These alternative interpretations can be eliminated if high Th/K ratios occur in intervals lacking coal seams and shallow-marine sandstones, respectively. Thus, within the context of a sound understanding of detrital mineralogy, diagenetic history, facies and appropriate sequence stratigraphic models, spectral gamma-ray data allow sequence boundaries to be identified and correlated in non-marine fluvial strata at least 80 km from the interpreted coeval shoreline.

Ichnofabric analysis of the shallow marine Nukhul Formation (Miocene), Suez Rift, Egypt: implications for depositional processes and sequence stratigraphic evolution

The shallow marine, early, syn-rift, Miocene, Nukhul Formation, Suez Rift, Egypt, is highly bioturbated and allows relationships between changes in trace fossils and ichnofabrics within a shallow marine depositional system to be documented and placed in a high resolution sequence stratigraphic framework. Seven ichnofabrics are present in a succession of interfingering, calcareous mudstones and calcarenites forming coarsening-up units of up to 30 m thick, bounded by marine flooding surfaces. The units grade upwards from a basal mudstone package with bed parallel concretions and a Planolites–Chondrites ichnofabric (offshore), through a coarsening-up succession of alternating calcarenites and mudstones with Thalassinoides–mottled sediment (offshore transition), Ophiomorpha irregulaire (lower shoreface), Ophiomorpha nodosa–Thalassinoides (lower middle shoreface), Thalassinoides–Taenidium (middle shoreface) and O. nodosa (upper shoreface) ichnofabrics. Gastrochaenolites (hardground) ichnofabric is separate, as it is not genetically related to the other ichnofabrics. Ichnofabric development is primarily controlled by depositional environment, e.g. bottom water oxygenation, sediment type, food abundance and energy level, which control substrate colonisation, sedimentation rate. Marine flooding surfaces are generally well-cemented and marked by distinctive epifaunal and infaunal colonisation and can be traced out from proximal to distal settings over distances of >5 km. The epifaunal colonisation in proximal settings consists of abundant oysters and corals with the substrate below marine flooding surfaces containing abundant Thalassinoides and Ophiomorpha isp. Abundance and diversity of epifauna and trace fossils and burrow size decreases distally into the basin. In the most distal settings, epifaunal colonisation is absent and only Planolites and Chondrites colonise the basinal mudstone. Marine flooding surfaces in the most distal settings are poorly cemented, but are marked by carbonate concretions 10–15 cm below the surface.

The stratigraphic architecture and evolution of the Burdigalian carbonate—siliciclastic sedimentary systems of the Mut Basin, Turkey

This study describes the coeval development of the depositional environments in three areas across the Mut Basin (Southern Turkey) throughout the Late Burdigalian (early Miocene). Antecedent topography and rapid high-amplitude sea-level change are the main controlling factors on stratigraphic architecture and sediment type. Stratigraphic evidence is observed for two high-amplitude (100–150 m) sea-level cycles in the Late Burdigalian to Langhian. These cycles are interpreted to be eustatic in nature and driven by the long-term 400-Ka orbital eccentricity-cycle-changing ice volumes in the nascent Antarctic icecap. We propose that the Mut Basin is an exemplary case study area for guiding lithostratigraphic predictions in early Miocene shallow-marine carbonate and mixed environments elsewhere in the world. The Late Burdigalian in the Mut Basin was a time of relative tectonic quiescence, during which a complex relict basin topography was flooded by a rapid marine transgression. This area was chosen for study because it presents extraordinary large-scale 3D outcrops and a large diversity of depositional environments throughout the basin. Three study transects were constructed by combining stratal geometries and facies observations into a high-resolution sequence stratigraphic framework. 3346 m of section were logged, 400 thin sections were studied, and 145 biostratigraphic samples were analysed for nannoplankton dates (Bassant, P., 1999. The high-resolution stratigraphic architecture and evolution of the Burdigalian carbonate-siliciclastic sedimentary systems of the Mut Basin, Turkey. PhD Thesis. GeoFocus 3. University of Fribourg, 277 p.). The first transect (Alahan) is on the northwestern basin margin. Here, the siliciclastic input is high due to the presence of a river system. The siliciclastic depocentre migrates landwards during transgressions, creating an ecological window allowing carbonates to develop in the distal part of the delta. Carbonate production shuts down during the regression when siliciclastics return. The second transect (Pirinç) is also situated on the northern basin margin 12 km to the east of the Alahan section. It shows a complete platform-to-basin transition. An isolated carbonate platform complex develops during the initial flooding, which is drowned during a time of rapid sea-level rise and environmental stress, associated with prograding siliciclastics. The shelf margin then retrogrades forming large-scale clinoform geometries and progrades before a major sea-level fall provokes slumping collapse, followed by rebuilding of the shelf margin as sea level rises again. The third transect (Silifke) has a steep asymmetric Pre-Miocene valley-topography, forming a narrow strait, linking the Mut Basin to the Mediterranean. Strong tidal currents are generated in this strait area. Siliciclastic input is low and localised. Eighty metres of cross-bedded bioclastic sands are deposited in a tidal regime at the base. Subsequently, carbonate platforms backstep against the shallow-dipping northern flank, while platforms only develop on the steep southern flank when a firm wide shallow-marine substrate is provided by a bench on the footwall block. The energy of the environment decreases with increased flooding of the strait area. Third-order sequences and higher-order parasequences have been identified in each transect and correlated between transects. Correlations were made using biostratigraphic data and high-resolution sequence stratigraphy in combination with the construction of the relative sea-level curve for each site. The third-order highstands are stacked in a proximal position and separated by exposure surfaces, while the lowstands, deposited in a distal setting, are separated by deep-marine (offshore or subphotic) deposits. The parasequences produce dominantly aggradational and progradational geometries with transgressive ravinement surfaces and exposure surfaces developing at times. Reconstruction of the depositional profile shows that the third-order sequences are driven by relative sea-level oscillations of 100–150 m, and that these may be attributed to 400-Ka orbital eccentricity cycles. The parasequences are driven by eustatic 20–30 m sea-level oscillations, which may be attributed to the 100-Ka orbital eccentricity cycles. The isolated carbonate build-ups in the Pirinç and Alahan transects develop at the same time as bioclastic tidal deposits in the Silifke area during the transgression of sequence 1. This is caused by a difference in hydrodynamic regime: a direct result of basin morphology funneling tidal currents in the Silifke area. We also demonstrate how during the highstands a siliciclastic delta system progrades in the Alahan area, while only 12 km to the east, a fringing carbonate platform develops, showing how siliciclastic input can have a very localised effect on carbonate environments. The exceptional quality of the outcrops with its variety of environments and its location at the Tethyan margin make this site a good candidate for a reference model for Burdigalian reef and platform architectures.

Sequence stratigraphy in a marine moraine at the head of Hardangerfjorden, western Norway: evidence for a high-frequency relative sea-level cycle

The depositional architecture and stratigraphy of the Hæreid moraine, a sedimentary ridge ca. 1.5 km long and up to 113 m in height at the head of Hardangerfjorden, West Norway, have been reconstructed in a high-resolution sequence stratigraphic framework. Information from ground-penetrating radar (GPR) profiles, outcrop sections and borehole data have been used in the analysis. The basal, forced regressive deposits comprise relicts of a Gilbert-type delta that commenced its development at the front of a grounded glacier. On the seaward (distal) side of the ridge, there is a major channel-fill/mouth-bar complex covering large parts of the delta's former frontal slope and prodelta zone. The complex occurs in the seaward lengthening of a fluvially incised channel and is interpreted as a lowstand to early transgressive succession of fluvial and fluvial-estuarine facies. The channel-fill/mouth-bar complex and the dissected delta top have been planed off through transgressive ravinement and the delta top is overlain by an upvalley-thinning sedimentary wedge, 3–8 m thick and with a general landward onlapping and propagating internal bedform geometry. This wedge is thought to be composed mainly of transgressive, marine (estuary–mouth barrier) facies. On the landward (proximal) side of the ridge, the transgressive deposits include a retrograding landward-dipping foreset interpreted as relicts of a flood-tidal delta overlain by possible washover fan deposits. These deposits are again conformably overlain by laminated clay, interpreted as the remains of a highstand mud drape. The depositional sequence delineated in this study, up to 20 m thick and comprising deposits of a lowstand-wedge, a transgressive and a highstand systems tract, developed in response to a relative sea level (RSL) rise of 12–15 m. This RSL rise, which interrupted the general RSL fall following the deglaciation, is correlated with the Younger Dryas transgression, a regionally recorded sea-level event. The highstand mud drape was deposited as the rising RSL ultimately led to drowning of the moraine. The highstand and transgressive deposits are erosively truncated by a thin gravelly lag, deposited during final emergence in the early Holocene.

A sedimentological approach to refining reservoir architecture in a mature hydrocarbon province: the Brent Province, UK North Sea

Improved reservoir characterisation in the mature Brent Province of the North Sea, aimed at maximising both in-field and near-field hydrocarbon potential, requires a clearer understanding of sub-seismic stratigraphy and facies distributions. In this context, we present a regional, high-resolution sequence stratigraphic framework for the Brent Group, UK North Sea based on extensive sedimentological re-interpretation of core and wireline-log data, combined with palynostratigraphy and published literature. This framework is used to place individual reservoirs in an appropriate regional context, thus resulting in the identification of subtle sedimentological and tectono-stratigraphic features of reservoir architecture that have been previously overlooked. We emphasise the following insights gained from our regional, high-resolution sequence stratigraphic synthesis: (1) improved definition of temporal and spatial trends in deposition both within and between individual reservoirs, (2) development of regionally consistent, predictive sedimentological models for two enigmatic reservoir intervals (the Broom and Tarbert Formations), and (3) recognition of subtle local tectono-stratigraphic controls on reservoir architecture, and their links to the regional, Middle Jurassic structural evolution of the northern North Sea. We discuss the potential applications of these insights to the identification of additional exploration potential and to improved ultimate recovery.

High resolution sequence stratigraphic architecture of a transgressive coastal succession: Albian Bow Island Formation, southwestern Alberta

ABSTRACT We here present the first detailed published sequence stratigraphic study of the Lower Cretaceous Bow Island Formation. Two orders of sequences are identified, based on the integration of sedimentology, micropaleontology, ichnology and petrophysical characteristics. The studied interval encompasses two lower-order sequences. Shelf, shoreface, and coastal plain deposits of the lower and middle members of the Bow Island Formation form the transgressive and highstand systems tracts of the basal sequence. A major relative sea level fall caused a prolonged period of sub-aerial exposure and weathering of the deposits of the middle member of the Bow Island Formation, and farther to the east and northeast, incision of deep valleys into shoreface deposits of the Viking Formation. An overlying complex succession of tidal flat, estuarine, shoreface, and shelf deposits of the upper member of the Bow Island Formation and marine shales of the Westgate Formation represent the transgressive systems tract of the younger low-order sequence. Within the transgressive succession of the upper member of the Bow Island Formation and Westgate Formation, five higher-order sequences are identified. The high-order sequence boundaries are marked by basinward shifts of facies, incision of up to 15 m deep valleys and soil development on intervalley areas. This demonstrates that this period of overall sea level rise was punctuated by relative sea level falls, justifying subdivision into sequences rather than parasequences. Transgressive surfaces, often developed as prominent, pebble-mantled ravinement surfaces, subdivide the individual highorder sequences into lower and upper units. The lower units are comprised of tidal influenced incised valley fill, forming the main reservoirs, and tidal and storm influenced back-barrier lagoons deposited during lowstand and early transgressive periods. Foraminiferal assemblages were critical in distinguishing between these lagoonal deposits and open marine shoreface deposits. Deposits of the basal part of the upper units are characterized by a stepwise change towards more open marine conditions following each transgression, from marginal marine tidal flat and lagoonal deposits to shoreface and finally to shelf deposits of the Westgate Formation. This demonstrates the stacking in a retrogradational sequence set of the high-order sequences of the upper member of the Bow Island Formation and Westgate Formation. Erosion associated with the transgressions increases upward in intensity with each successive transgression with the greatest depth of erosion associated with the Westgate transgression. This reflects an upward increase in energy regime of the sedimentary environments that bypassed the area during the transgression. Within the overall transgressive upper member of the Bow Island Formation, an upward increase in the depth of incised valleys with each successive incision event likely reflects an upward increase in depositional relief due to the development of more open marine conditions and to the retrogradational and aggradational character of the upper member of the Bow Island Formation. The Westgate transgressive surface is a complex ravinement surface characterized by a westward, stepwise rise, indicating that it was formed during a period of gradual relative sea level rise, interrupted by phases of more rapid sea level rise. Establishment of this high-resolution sequence stratigraphic framework allows differentiation between these various generations of incision and thereby the mapping of the individual valleys and reservoirs associated with them. * Current address: Petroleum Geology, Saskatchewan Industry and Resources, 201 Dewdney Ave East, Regina, SK, Canada, S4N 4G3; E-mail: ppedersen@ir.gov.sk.ca End_Page 441------------------------

ABSTRACT: Porosity Preservation in Deeply Buried Chlorite-Coated Sandstones of the Norwegian Sea: Understanding Early Diagenetic Processes in a High Resolution Sequence Stratigraphic Framework

ABSTRACT: Porosity Preservation in Deeply Buried Chlorite-Coated Sandstones of the Norwegian Sea: Understanding Early Diagenetic Processes in a High Resolution Sequence Stratigraphic Framework

Sequence Stratigraphy of the Arab A to C Members and Hith Formation, Offshore Abu Dhabi

ABSTRACT The Upper Jurassic Hith Formation and Arab members A, B and C, in central and western offshore Abu Dhabi, consist of 450 to over 600 feet of massive to interbedded anhydrites with varying proportions of limestones and dolomites. A high resolution sequence stratigraphic framework for this important petroleum reservoir interval was developed from core and well log data, and various inorganic geochemical analyses. This data was acquired from wells located at 3 locations spread over 100 kilometers. Nineteen shallowing-upward parasequences, corresponding to fourth and possibly fifth-order cycles, were recognized for the Arab members as follows: A (7 cycles), B (5 cycles), and C (7 cycles). Five parasequences were recognized for the Hith Anhydrite Formation. The Arab parasequences are arranged in a layer-cake stacking pattern and vary in thickness from 6 to 30 feet. These are interpreted to correspond to transgressive-regressive episodes which are driven by low-amplitude sea-level fluctuations (eustacy). The typical parasequence consists of shoal grainstones, representing transgressive system tracts, that pass upward into thin-bedded lagoonal burrowed mud/wackestones, representing the maximum flooding surface. These are overlain by coarse bioclastic grainstones capped by algal laminites and culminate into supratidal anhydrites, which pinchout eastwards. In the west offshore Abu Dhabi the parasequences are thicker and consist of intertidal pack/grainstones overlain by anhydrites.

The Application of a High Resolution Sequence Stratigraphic Framework to Underexplored Paleogene Plays in the Northern North Sea  :ABSTRACT

The Application of a High Resolution Sequence Stratigraphic Framework to Underexplored Paleogene Plays in the Northern North Sea  :ABSTRACT

Integrated Geologic and Engineering Reservoir Characterization of the Hutton Sandstone, Jackson Region, Australia: ABSTRACT

An integrated geologic and engineering reservoir characterization study of the Hutton Sandstone was completed for the Jackson region, Eromanga Basin, Australia. Our approach involves four principal steps: (1) determine reservoir architecture within a high-resolution sequence stratigraphic framework, (2) investigate trends in reservoir fluid flow, (3) integrate fluid flow trends with reservoir architecture to identify fundamental reservoir heterogeneities, and (4) identify opportunities for reserve growth. Contrary to the existing perception, the Hutton Sandstone, a continental-scale bed-load fluvial system, does not behave as a large, homogeneous tank in which pistonlike displacement of produced oil occurs unimpeded by vertical migration of the aquifer. The sequence stratigraphic analysis identified numerous thin but widespread shale units, deposited during lacustrine flooding events that periodically interrupted episodes of coarse clastic Hutton deposition. These shales represent chronostratigraphically significant surfaces. More importantly, the trends established in reservoir fluid flow from monitoring aquifer encroachment, production response to water shut-off workovers, and differential depletion in Repeat Formation Tests indicate that these shale units act as efficient barriers to vertical fluid flow. Erosion of the upper part of the Hutton reservoir by the younger Birkhead mixed-load fluvial system caused further stratigraphic complexity and introduced additional barriers to vertical and lateral migration ofmore » mobile oil and aquifer encroachment. This integrated characterization targeted strategic infill and step-out drilling and recompletion candidates.« less

Sequence stratigraphy of a Pliocene delta complex deposited in an active margin setting, Etchegoin and San Joaquin gas sands, San Joaquin basin, California: ABSTRACT

Prolific gas sands of the Pliocene Etchegoin and San Joaquin formations of the southern San Joaquin basin, California, are part of a 1300-m thick succession of deltaic sediments that record the final regression of the Pacific Ocean from a tectonically active, restricted basin associated with the California transform margin. Individual field studies, lacking a regional framework and based primarily on electric log data, correlate these gas sands to the extent that individual sands maintain the same stratigraphic level within the succession. However, a high-resolution sequence stratigraphic framework, constructed from recent 3D-seismic data and detailed well log correlations on the Bakersfield Arch area of the basin, indicates that the Pliocene succession is part of a south/southwest prograding delta complex. Therefore, sands climb up-section in the landward direction and grade laterally from deep-water to shallow-water facies. Because lithofacies boundaries cross chronostratigraphic surfaces, previous interpretations of the reservoir architecture are inaccurate. This model increases predictability of reservoir facies by constraining lithofacies mapping and enables interpretation of the effects on deposition of the integrated and inter-related controls of tectonics, eustatic sea-level change, and sediment supply. With this understanding, a well-defined model of the stratal architecture of the Pliocene succession of the southern San Joaquinmore » basin is now possible.« less