The Homerian (Silurian) stratigraphy of the May Hill and Gorsley inliers of England, UK: integration of carbon isotope data, sedimentology, and sequence stratigraphy

Biostratigraphy is routinely run on most wells in the Malay Basin, but it’s value in interpreting sequence stratigraphic succession has not been fully assessed. For the first time, biostratigraphy has been fully integrated with seismic to construct a regional sequence stratigraphic succession of the Oligocene to Pliocene sediments of the basin. A comprehensive biostratigraphic database from over 40 wells has been reviewed within a regional seismic grid. The data shows that most of the biostratigraphic assemblages are driven by sequence stratigraphic processes that are largely attributed to sea level and climatic changes. The lowstand systems tract can be differentiated from the transgressive and highstand systems tracts by the low proportion of mangrove-derived pollen (especially Rhizophora type), the high represenation of dry-cool palynomorph elements, and in many instances pollen the presence of acmes of pollen from an unusual type of peat swamp, termed ‘Kerapah’ swamp. The transgressive surface is often marked by an increase in foraminiferal abundance, and coincides at the onset of increasing mangrove-derived pollen. The transgressive systems tract is generally characterized by the increased abundance of mangrove-derived pollen coinciding with the main period of sea level rise. The maximum flooding surface is often differentiated by an acme of foraminifera and nannofossils. In outer shelf and upper bathyal environments, the maximum flooding surface is often indicated by an acme of deep and/or cold water of foraminifera. Within the highstand systems tract, pollen suggesting a warm and wet climate tends to dominate, and benthic milioliid foraminifera may be common. Through properly assessing the above biostratigraphic parameters, major sequence stratigraphic stratal surfaces and their associated system tracts can be recognized on Biostratigraphic data alone. These surfaces are positioned into a seismic framework by determining their fit with stratal termination patterns of onlap and downlap. By holding a workshop session in a workstation environment, horizons with anomalies between seismic and biostratigraphy can be adjusted iteratively. Typically, both disciplines contribute more or less equally to positioning stratal surfaces and constructing the sequence stratigraphic model. Currently 21 sequences (third and fourth order) are recognised in the Malay Basin based on the strengths of both seismic and biostratigraphy. This review demonstrates that the sequence biostratigraphigraphic approach, integrated with seismic sequence stratigraphy provides a more robust sequence stratigraphy than that obtained when using either discipline on its own. It is strongly recommended that future Malay Basin sequence interpretation should be conducted as a joint process with respect to the interpretation of sequence stratigraphic surfaces; with the integration of biostratigraphic and seismic data taking place in a workstation environment. Both disciplines can add value to the other if used together.

Study of a portion of the Upper Cretaceous Mancos Shale in the San Juan Basin of New Mexico shows that organic facies deposited on the shelf change noticeably at surfaces that have sequence stratigraphic significance. Shelf sediments below transgressive surfaces contain abundant, well-preserved terrestrial organic matter (phytoclasts) whereas sediments above transgressive surfaces contain sparse and highly degraded phytoclasts and more hydrogen-rich organic matter. Shelf sediments associated with the maximum flooding surface typically contain the least terrestrial organic matter. These results indicate that the type and preservation of organic matter is related to both the rate of terrigenous sediment supply to the shelf and the bottom water oxygen conditions present on t e shelf. Variations in the amount and type of organic matter (organic facies) preserved in shelf sediments are predictable within a sequence stratigraphic framework. Each systems tract has a distinctive depositional style that affects the amount of terrigenous sediment influx to the shelf and, consequently, the type and preservation of organic matter that is deposited on the shelf. Fine-grained marine sediments in transgressive systems tracts possess high total organic carbon and yield relatively high amounts of hydrocarbons during pyrolysis. Petrographically, this organic matter is composed primarily of amorphous nonstructured protistoclasts. Phytoclasts in the transgressive systems tract are highly degraded. In contrast, progradational marine depositional systems of both the lowstand and hig stand systems tracts contain End_Page 221------------------------ less total organic carbon and less pyrolyzable hydrocarbons. Petrographic analysis of organic matter in these rocks reveals abundant macerals of terrestrial origin. Phytoclasts are especially well preserved in the lowstand systems tract. Integration of data from the characterization of organic matter with sedimentologic and regional stratigraphic information provides greater precision in locating surfaces that bound systems tracts within the depositional sequence. An example of this approach is presented for a part of the Upper Cretaceous Mancos Shale of the San Juan Basin, New Mexico. Organic matter data not only improve systems tract identification in fine-grained, basinward facies but also demonstrate that the predictive capabilities of sequence stratigraphy are applicable to marine petroleum source rocks. These results indicate that optimum source rock potential is found in the transgressive systems tract below the condensed section facies that contains the downlap surface.

Carbon Isotopic Fractionation Across A Late Cambrian Carbonate Platform: A Regional Response To The SPICE Event As Recorded In The Great Basin, United States by Jonathan Lloyd Baker Dr. Ganqing Jiang, Examination Committee Chair Associate Professor of Geoscience University of Nevada, Las Vegas Geochemical models have suggested that the late Cambrian was characterized by a greenhouse climate with high pCO2. Furthermore, stableisotope analyses within the Great Basin have documented a large carbonate isotope (δ13Ccarb) excursion, known as the Steptoean Positive Carbon Isotope Excursion (SPICE). This event has been documented globally, and is interpreted as having resulted from enhanced organic carbon burial. Unless the size of carbon reservoirs in the Cambrian ocean was significantly different from those of the Cenozoic, this forcing should have resulted in a comparable carbon-isotope excursion in organic matter (δ13Corg). It is also predicted that increased organic carbon burial would lower atmospheric CO2, which may cause global cooling and a reduction in carbonate-organic carbon isotope fractionation. To test these predictions, paired carbonate and organic carbon isotope data are reported here from carbonate stratigraphic sections at Shingle Pass, Nevada and in House Range, Utah. At Shingle Pass, δ 13Corg values record a positive excursion that roughly mirrors δ 13Ccarb values at a similar magnitude, suggesting an oceanographic control on the carbon isotope trend. In the House Range section, iii although δ 13Corg values show a rough positive shift associated with positive δ13Ccarb, the magnitude is smaller and values show minor shifts across the excursion. However, constructing a time-equivalent overlay of data from both sections using key stratigraphic boundaries resolved apparent discrepancies, suggesting a regional control on carbon isotopic fractionation. The difference between carbonate and organic carbon isotope values (Δ13C = δ13Ccarb – δ13Corg) averages 27‰ to 28‰ in both sections, but increases to 30‰ at the peak of the excursion and falls to as low as 25‰ immediately after the Sauk II/III sequence boundary. Temporal variations in Δ 13C do not follow the predicted atmospheric CO2 changes before the δ13Ccarb peak of the SPICE, as might have been derived from the increased organic carbon burial model for the origin of the SPICE event, and indicates that the carbon isotope fractionation was less sensitive to atmospheric CO2 changes when ambient CO2 was high. The abrupt drop in Δ13C after the δ13Ccarb peak of the SPICE is consistent with low atmospheric CO2 and the potential evolution of photosynthetic organisms in adapting to CO2-limited environments with stronger bicarbonate uptake during carbon fixation.

Understanding the stratigraphic framework of Oleum field is critical to hydrocarbon exploration and production success, owing to the alternating nature of organic-rich shale envelopes and porous sand sheets of the field. This research is aimed at studying the sequence stratigraphic framework and depositional environments of sedimentary facies of Oleum field, onshore (swamp) Niger Delta. This aim was achieved using sequence stratigraphic principles based on the integration of biostratigraphic, paleobathymetric, seismic and wireline log data of two wells (i.e. Oleum-001 and Oleum-002). This has led to the delineation of two maximum flooding surfaces (? Ma MFS and 13.6 Ma MFS) at 8182 ft and 9080 ft respectively. Each MFS is associated with depositional sequence and systems tracts. The first depositional sequence consists of two systems tracts; transgressive system tract (TST) and highstand system tract (HST), while the second depositional sequence consists of all the three systems tracts; lowstand system tract (LST, TST and HST). The 13.6 Ma MFS was delineated based on the occurrence of Bolivina 29a / Cassidulina 7 fossils. Additionally, the well logs sequence stratigraphy revealed two sequence boundaries which occur at 7255 ft and 8865 ft of Oleum-001, and 7033 ft and 8770 ft of oleum-002. The lithofacies are predominantly sand and shale displaying different kinds of log motifs. The sedimentological log motif shows a coarsening upward and blocky sands of the HST delineated as the system tract with the best reservoir properties. Fining upward and serrated/saw tooth motif of the TST is delineated as the facies with the best seal properties. The result indicates that the stratigraphic framework of Oleum Field is fluvio-deltaic to marine setting.

The type and preservation of organic matter is related to the depositional systems tract in which the sediments were deposited. Shelf sediments in the transgressive systems tract contain sparse, highly degraded phytoclasts whereas organic matter in the highstand systems tract is dominated by well preserved phytoclasts introduced to the shelf during progradation. Because of this relationship, integration of data from organic petrology with sedimentologic and biostratigraphic results provides greater resolution in locating critical surfaces (sequence boundaries, transgressive surfaces, and surfaces of maximum starvation) that bound depositional systems tracts within the depositional sequence. The Eocene-Oligocene shelf sediments exposed in St. Stephens Quarry, Alabama provide an excellent example of the relationship between depositional systems tract and organic matter deposition. Deposition of the Shubuta Clay in the transgressive systems tract terminated with the surface of maximum starvation. This surface is marked by a thin (<2 cm), laterally extensive, phosphate-rich shell hash that contains only minor amounts of highly degraded phytoclasts. Graphic correlation of biostratigraphic data from six microfossil groups and pectinid mollusks indicates that the shell hash represents a hiatus of about 0.29 million years. Deposition in the subsequent highstand systems tract resulted in an increase in well preserved phytoclasts in the overlying Red Bluff Clay/Bumpnose Limestone. A transgressive surface forms the contact between the Red Bluff Clay and a thin tongue of the Mint Springs Marl. Phytoclasts are much less common in the Mint Springs above the transgressive surface than in the Red Bluff below. No hiatus is recorded at this surface suggesting that the type 2 sequence boundary is conformable at this section and may exist in the Red Bluff below the transgressive surface. This integrated approach confirms and refines previous sequence stratigraphic work performed on this important Gulf Coast section.

The type and preservation of organic matter is related to the depositional systems tract in which the sediments were deposited. Shelf sediments in the transgressive systems tract contain sparse, highly degraded phytoclasts whereas organic matter in the highstand systems tract is dominated by well-preserved phytoclasts introduced to the shelf during progradation. Because of this relationship, integration of data from organic petrology with sedimentologic and biostratigraphic results provides greater resolution in locating critical surfaces (sequence boundaries, transgressive surfaces, and surfaces of maximum starvation) that bound depositional systems tracts within the depositional sequence. The Eocene Oligocene shelf sediments exposed in St. Stephens Quarry provide an excellent example of the relationship between depositional systems tract and organic matter deposition. Deposition of the Shubuta Clay in the transgressive systems tract terminated with the surface of maximum starvation. This surface is marked by a thin (<2 cm), laterally extensive, phosphate-rich shell lag that contains only minor amounts of highly degraded phytoclasts. Graphic correlation of biostratigraphic data reveals a marine hiatus (120,000 years) within the shell lag. Deposition in the subsequent highstand systems tract resulted in an increase in well-preserved phytoclasts in the overlying Bumpnose Limestone and Red Bluff Clay. A transgressive surface forms the contactmore » between the Red Bluff Clay and the Mint Springs Marl. Phytoclasts are less common and more degraded in the Mint Springs above the transgressive surface than in the Red Bluff below. No hiatus is observed at this surface, suggesting that the type 2 sequence boundary is conformable at this section and may exist in the Red Bluff below the transgressive surface. This integrated approach confirms and refines previous sequence stratigraphic work performed on this important Gulf Coast section.« less

Geochemical expression of sequence stratigraphic surfaces: A case from Upper Cretaceous shallow-water carbonates of southeastern Neo-Tethys margin, SW Iran

Impedance models should be more than just the inversion of seismic data, they should result from the integration of data from diverse sources. This integration adds value to the impedance model by increasing the information content and interpretability of the various data. The integration of geological, geophysical and other data measured in the different domains of time and depth is often not straightforward. One solution is to integrate the data within a common sequence stratigraphic framework. A case study from a maturing oil field shows how this approach can lead to the improved understanding of the distribution of fluids and reservoir properties. An initial sequence stratigraphic framework was derived from the best quality well log data and preliminary seismic inversion results. This framework was used to guide the conditioning and integration of the all the well log data. As more well log data were integrated, improvements in wavelet estimation and seismic inversion were achieved. The initial framework was refined as the data demanded. The final result was an impedance model in time and depth consistent with the seismic data, the well log data and the geological interpretation. The development of the most productive interval in the field had previously been based on the assumption that vertical connectivity existed between the different sands within it. Although recent drilling has disproved this assumption and indicated vertical barriers to fluid flow, these could not be imaged using conventional analysis of reflection seismic data. Using the sequence stratigraphic framework to extract impedance values, the separate sand layers could be imaged. These extractions also confirmed that hydrocarbons in an unperforated sand had not yet been depleted and allowed new development drilling locations to be selected.

This paper presents an integrated rock-typing workflow leading to enhanced 3D static models. The work is based on the integration of several tools which optimize the contribution of all the available data : a specific thin-section description methodology sophisticated log-derived electrofacies calibration approaches, incorporating sequence stratigraphy rules; an enhanced calibration approach based on dynamic data. It is illustrated by an application to the lower cretaceous carbonate reservoir in offshore Abu Dhabi. The different steps of the methodology and their mutual interaction are detailed. This integrated work establishes a consistent way to fill the gap between core and production scales, using log-derived electrofacies extendable to all the logged wells. It is shown first how sequence stratigraphy can provide a global framework, common to the different scales that ensure the consistency of the whole work. Then, emphasis is put on the sophisticated thin-section description methodology, based on facies association identification and sequence stratigraphy, which facilitates the further electrofacies calibration. In a third step, we detail the log-derived electrofacies determination and calibration methodology, which takes into account thin-section description, core descriptions, sequence stratigraphy analysis, CCAL data, and SCAL data in order to provide consistent rock-types in uncored wells. In the end, it is shown how the integration of dynamic data in a well by well QC can significantly enhance the prediction of high permeability drains. Modeling issues are then discussed, focus being put on the relationship between the various scales, on the geological control and robustness of the final 3D model that are enhanced by the large number of control points provided by the extension of rock-types to non-cored wells. The impact on dynamic modeling is shown as a conclusion.

A super-giant carbonate field in Abu Dhabi has most of its remaining reserves in carbonate build-up and prograding basin-margin deposits of Lower Cretaceous age (Shuaiba Formation). To guide further field production, a sequence stratigraphic framework was developed based on integration of core, log and seismic data. This framework is the cornerstone for building a new reservoir model and provides the key for a better understanding of facies and flow unit continuity guiding present and future field production and performance. Approximately 730 wells, wireline logs and the latest core descriptions were integrated for this study. Another key element was the incorporation of 3D seismic data coupled with several iterations between well log and seismic picking. Detailed seismic interpretation led to the delineation of 3rd and 4th order sequences. The picking of higher order sequences was based on well data guided by the seismic surfaces. This study provides an excellent example of extracting maximum information from seismic and the full integration of geoscience and production data to provide a new 3D framework. The sequence framework uses a consistent nomenclature based on the Arabian Plate Standard Sequence framework for the Aptian (van Buchem et. al., 2010). The Shuaiba is subdivided into six 3rd order sequences (Apt 1, 2, 3,4a, 4b, and 5) which, based on stacking patterns, record a complete 2nd order cycle of Transgressive, Highstand, and Late Highstand systems tracts (Apt 1–4b). The Bab Member (Apt 5) and Nahr Umr Shale form the Lowstand to Transgressive systems tracts of the next Super-sequence. The third order Apt 1 sequence and the Apt 2 TST form the 2nd order transgressive systems tract, characterized by back-stepping and creation of differential relief between the Shuaiba shelf and Bab intra-shelf basin. These sequences are dominated by Orbitolina and algal/microbial Lithocodium/Bacinella fossil associations. The Apt 2 HST and Apt 3 Sequence form the 2nd order early highstand systems tract during which the platform area aggraded and the topographic split into platform, slope and basin became most pronounced. Sediments are extremely heterogeneous and varying properties introduce significant problems in understanding fluid flow. During the regressive part of the Apt 3 sequence accommodation space was limited and deposition switched to progradation at the platform margin. The platform top is characterized by thin cycles of rudist floatstones/rudstones separated by thin cemented flooding and exposure horizons, whilst the platform margin received large quantities of rudstones, grain and packstones organized in clinoform sets. Clinoforms are separated by thin stylolitic cemented layers, which are transparent on seismic. The Second Order late highstand systems tract is composed of 3rd order cycles Apt 4a and Apt 4b. These are detached from the main buildup, which probably stayed largely exposed, and form strongly prograding slope margin wedges composed of alternating dense mudstones (TST) and grainstone/packstone sequences with coarse grained top-sets which formed during highstand phases. Lowstand deposits of the Apt 5 cycle (Bab Member) are dominated by fine-grained siliciclastics capped by thin oolitic carbonate facies which are isolated from the main part of the field and are not hydrocarbon charged.

Sequence stratigraphic analysis subdivides stratal packages into chronostratigraphic units composed of genetically related facies. Sequences are composed of stratal units that develop in response to changes in shelfal accommodation. Carbonate platform successions develop a hierarchy of sequences and cycles ranging from high (10,000 yrs.) to low (10-20 My supersequences) frequency. This stratigraphic hierarchy controls the facies distribution during long-term platform development. Due to the dominant organic origin of sediments, important differences exist between carbonates and siliciclastics that must be taken into account in a sequence analysis. Eustasy and tectonic subsidence control accommodation, and the health of the carbonate controls sediment supply. Generally, the bulk of deposition occurs during sea level highstands. Early marine cementation is not equal for all platforms. Platforms with steep foreslopes or platforms facing restricted basins will have long residence time in an active cementation environment, and are cement-rich. Highly productive platforms facing shallow basins will fill accommodation space rapidly, have a short residence time, and will be cement-poor. In general, sequence boundaries are regional onlap surfaces. Submarine erosional truncation commonly occurs at platform margins and on the slope. Abrupt facies truncation or dislocation is commonly present at sequence boundaries. The degree of subaerial alteration during sequence boundary formation will vary depending on the climate, the original mineralogy of the underlying highstand platform, and time. If the original mineralogy of a platform is dominantly aragonite and hi-Mg calcite the degree of alteration can be extensive. If the lowstand climate is relatively humid, platform-wide solution occurs that may extend deep into the highstand depending on the magnitude and duration of the sea level fall. If the climate is arid to semi-arid, only relatively minor karstification is predicted to occur. Low-Mg calcite-dominated systems show extensive karstification only during major multi-million year periods of subaerial exposure (i.e., 2nd-order sea level falls). Depositional slope angle and the degree of early cementation play a critical role in the development of lowstand systems tracts. In-situ, lowstand platforms and banks can develop in Type-1 sequences (1) in down ramp positions, and (2) on the slope and toe-of-slope of low-angle platforms. Where platform margins are steeper and well-cemented, lowstand deposition is characterized by abundant coarse debris eroded from the platform margin and slope areas. Steep, by-pass margins present a special case, as both transgressive and lowstand sedimentation may develop toe-of-slope onlap geometries. Significant transgressive carbonates will develop where paleoceanographic conditions permit the factory to keep-up with sea level rise. Well-circulated, shallow water conditions over a wide area (i.e., low slope or broad shelf) will allow a significant transgressive systems tract to develop. Integration of seismic, well log, and core data, paleontology, strontium age dating, and velocity analysis enabled construction of a sequence stratigraphic framework for the Gulf of Papua case study area. Rapid subsidence during early foreland development in the Gulf allowed development of thick Miocene platforms on isolated paleo-highs and hinged to the basin margin. Onlap above and erosional truncation below define sequence boundaries. Pervasive dolomitization and subaerial vuggy to cavernous porosity, extends below sequence boundaries for tens to hundreds of meters. Highstand systems tracts are characterized by mounded to chaotic seismic facies at platform margins. Platform interior seismic facies vary between parallel, concordant and mounded facies. Mounded facies are interpreted to be reefal buildups and parallel facies are interpreted to be flat lying lagoonal sediments. Platform foreslopes have gentle to steep dips depending on platform margin relief at basin margin positions. Lowstand systems tracts are observed at platform margins and comprise in-situ shallow water platform facies, and allochthonous debris. The Neogene comprises three 2nd-order supersequences, Lower Miocene, upper Lower to Middle Miocene, and Upper Miocene-Recent. These supersequences are divided into six Miocene and two Pliocene 3rd-order sequences. The Lower Miocene 2nd-order sea-level rise, combined with rapid subsidence, initiated platform growth. Reefal platforms kept pace with sea level rise and comprise the bulk of growth over isolated paleohighs. Although the western basin margin, Borabi platform trend kept pace with subsequent relative rises in sea level, rapid subsidence due to initial thrust sheet loading combined with an early Middle Miocene 2nd-order sea level rise drowned isolated platform growth centers in the Gulf basin area. Later forebulge development in the Middle-Late Miocene resulted in prolonged subaerial exposure of these drowned platforms. Renewed thrust sheet emplacement combined with the 2nd-order eustatic sea level rise during the latest Miocene and early Pliocene, drowned platforms throughout the Gulf and caused a major backstepping of the Borabi trend platforms. During the Pliocene to Recent, rapid influx of siliciclastics from the north and west onlapped and covered most reef platforms and deposition became restricted to the southern portion of the Borabi trend.

Variations in the amount and type of organic matter preserved in shelf sediments are predictable within a sequence stratigraphic framework. These variations can be documented using routine petroleum source rock evaluation techniques. The type and preservation of organic matter is related to the rate of allochthonous shelf sedimentation. Each depositional systems tract in a sequence has a distinct depositional style that affects changes in the amount of terrigenous influx. Therefore, integration of source rock data with sedimentologic and regional stratigraphic results provides greater resolution in locating the critical surfaces that bound depositional systems tracts within the depositional sequence. This integrated sequence stratigraphic approach has been applied to conventional cores of Upper Cretaceous strata in the San Juan basin of New Mexico. Fine-grained marine sediments in transgressive systems tracts possess high total organic carbon and yield relatively high amounts of hydrocarbons during pyrolysis. Petrographically, this organic matter is composed primarily of amorphous macerals. Both the lower Juana Lopez and the Mancos Shale above the Tocito Sandstone provide examples of organic matter deposited in the transgressive systems tract. In contrast, marine depositional systems of both the lowstand and highstand systems tracts contain less total organic carbon and less pyrolyzable hydrocarbons. This methodologymore » not only improves systems tract identification in fine-grained, basinward intervals but also reveals those portions of the depositional sequence that are most favorable for marine petroleum source rock formation.« less

Depositional architecture of the late Ordovician drowned carbonate platform margin and its responses to sea-level fluctuation in the northern slope of the Tazhong region, Tarim Basin

For much of the Mesozoic record there has been an inconclusive debate on the possible global significance of isotopic proxies for environmental change and of sequence stratigraphic depositional sequences. We present a carbon and oxygen isotope and elemental record for part of the Early Jurassic based on marine benthic and nektobenthic molluscs and brachiopods from the shallow marine succession of the Cleveland Basin, UK. The invertebrate isotope record is supplemented with carbon isotope data from fossil wood, which samples atmospheric carbon. New data elucidate two major global carbon isotope events, a negative excursion of ∼2‰ at the Sinemurian–Pliensbachian boundary, and a positive excursion of ∼2‰ in the Late Pliensbachian. The Sinemurian–Pliensbachian boundary event is similar to the slightly younger Toarcian Oceanic Anoxic Event and is characterized by deposition of relatively deepwater organic‐rich shale. The Late Pliensbachian strata by contrast are characterized by shallow marine deposition. Oxygen isotope data imply cooling locally for both events. However, because deeper water conditions characterize the Sinemurian–Pliensbachian boundary in the Cleveland Basin the temperature drop is likely of local significance; in contrast a cool Late Pliensbachian shallow seafloor agrees with previous inference of partial icehouse conditions. Both the large‐scale, long‐term and small‐scale, short‐duration isotopic cycles occurred in concert with relative sea level changes documented previously from sequence stratigraphy. Isotope events and the sea level cycles are concluded to reflect processes of global significance, supporting the idea of an Early Jurassic in which cyclic swings from icehouse to greenhouse and super greenhouse conditions occurred at timescales from 1 to 10 Ma.

Calcite cemented sandstone layers are common heterogeneities in shallow marine reservoirs where they cause significant flow barriers. Field analogue studies indicate that the most laterally persistent cemented layers are associated with sequence stratigraphic bounding surfaces where the cementation forms a complex network of beds concentrated around both maximum flooding surfaces and sequence boundaries. Although individual calcite cemented beds are thin, they are associated with very high acoustic impedances and concentration of these thin, high impedance beds around bounding surfaces produces a significant seismic response which can be used to provide information on the spatial distribution of flow barriers. This information along with a sequence stratigraphic interpretation of the reservoir and geometrical data extracted from field analogues provides the input for an integrated reservoir description of calcite cemented barriers using a stochastic modelling approach. The stochastic model is a non-stationary indicator field with an external trend in the indicator proportions. Variograms are used to control the geometry of individual cemented beds. Sequence stratigraphy and seismic data are used to define spatial trends in the proportion of cemented beds; sequence stratigraphy provides the vertical constraints, and seismic data provide lateral constraints. The modelling approach has been tested using data from the TOGI area of the Troll gas field in the Norwegian North Sea. A controlled (verifiable) test has been carried out using synthetic seismic data based on a realistic, heterogeneous, 3D acoustic model of TOGI. These data have been inverted using a constrained sparse-spike seismic inversion technique. The test demonstrated that the prototype modelling procedure functioned satisfactorily. The integration of data from several sources contributed to the generation of realistic heterogeneity models constrained by a maximum amount of information. A test using real seismic data from TOGI has been initiated. The results of the sparse-spike inversion are similar to those obtained in the synthetic test. These inverted data are presently being depth converted and prepared for use in stochastic heterogeneity modelling.