bluuebunny/crossref_metadata_2025 huggingface dataset:
Reservoir characterization of a shallow marine sandstone; the Lower Cretaceous Sandringham Sands (Leziate Beds) and Carstone formations, eastern England
Authors: Thomas C. J. S.
Published: November 2010

An onshore shallow marine sandbody has been investigated in several extensive quarry outcrops in the Norfolk area of eastern England in terms of its sedimentology (sedimentary structures, geometry and architecture), sequence stratigraphy and reservoir-scale heterogeneity. In addition to conventional sedimentological logging techniques, vertical profiles were analysed using a steady-state electronic probe permeameter to investigate permeability heterogeneity. Permeability analysis was also complemented by spectral gamma ray profiles, which were used to characterize facies associations in terms of their total radioactivity and relative proportions of potassium, uranium and thorium. It was found that lithofacies type and bounding surface have the dominant control on permeability heterogeneity and thus flow unit compartmentalization. This study aims to complement pre-existing outcrop analogue datasets which attempt to model fluid flow more accurately in analogous subsurface reservoirs. It also serves to highlight the difficulty in accurately identifying and modelling subsurface shallow marine/estuarine tidal channel depositional systems for well/drainage and or production strategies.
Hydrocarbon filling history and reservoir continuity of oil fields evaluated using
87
Sr/
86
Sr isotope ratio variations in formation water, with examples from the North Sea
Authors: Mearns E. W. , McBride J. J.
Published: November 2010

This paper describes how
87
Sr/
86
Sr ratios in formation waters are used to evaluate compartmentalization of hydrocarbon reservoirs. Strontium Isotope Residual Salt Analysis (SrRSA) of core samples provides a means of measuring
87
Sr/
86
Sr ratios in formation water from hydrocarbon columns and aquifers. Smooth SrRSA profiles suggest progressive, uninterrupted, filling and the absence of sealed barriers, while a step change in a profile normally suggests a barrier sealed up-dip from the well penetration. Inferences about lateral connectivity are made by comparing SrRSA profiles from neighbouring wells at TVD. Profiles that are superimposed when plotted at TVD suggest the well sections share a common filling history and lie in the same flow unit. Neighbouring SrRSA profiles that are not superimposed normally suggest segmented compartmentalization of the reservoir. Post-fill structural tilting of reservoirs and hydrodynamism synchronous with filling are processes which complicate data interpretation. Drilling mud contamination of core water is the most serious technical limitation of the SrRSA technique.
Barnowko-Mostno-Buszewo (BMB); the largest crude oil deposit in Poland
Authors: Gorski Maciej , Wojtkowiak Zofia , Radecki Stanislaw
Published: November 2010

In the 1970s and 1980s exploration performed within the Polish part of the Permian Basin, particularly in the Gorzow region, found the Main Dolomite (the Upper Permian-Zechstein) formation to be very prospective, as proved by the discovery of many oil and gas fields. In the early 1990s exploration based on 2D seismic intensified and resulted in the definition of three separate structures: Barnowko, Mostno and Buszewo. The exploration wells located on these structures found the first two to be gas-bearing and the third to be oil-filled. Subsequent interpretation of the 3D seismic showed that, in reality, the three discoveries are a single field. This conclusion was based on the analysis of geometry and distribution of the reservoir parameters. It has been proved by the results of eleven consecutive wells (since writing this paper a further 6 wells have been drilled which confirm the interpretation). All of the above shows this field to be the largest oil field of the Polish part of the Permian Basin, as well as the largest in Poland.
Seismic imaging of a carbonate reservoir; the Dogger of the Villeperdue oil field, Paris Basin, France
Authors: Mougenot D.
Published: November 2010

The Villeperdue field produces oil from a thin and heterogeneous carbonate reservoir of middle Jurassic age. Despite the presence of 150 wells, the production of this field (about 9000 bbl/day) is decreasing continuously and forecasting the productivity of new wells remains hazardous. In a joint effort by four operators, a contractor and a research institute, advanced seismic methods including 3D, 2D-3c (3 components), 2D-HR (High Resolution) and 3c-VSP (borehole seismic) were combined to improve reservoir characterization and define methods for revitalizing exploration in the Paris Basin. The combination of continuous spatial sampling, such as that obtained in 3D, and a Vibroseis emission adapted to the high-frequency attenuation, such as that used in 2D-HR, supplied useful information about the reservoir heterogeneities which cannot be provided by correlation of the well data. In this way thickness, lateral porosity variations and small faults (throw <10 m) were successfully detected, making it easier to select the locations of new production wells.
The Matzen Project; rejuvenation of mature field
Authors: Hamilton W. , Johnson N.
Published: November 2010

The giant oil field Matzen, located in the Vienna Basin, Austria is subject to a modern geological and geophysical re-examination. Almost 50 years of production make this field a mature asset in traditional terms. 3D seismic and applied sequence stratigraphy are being used to re-assess the geological architecture and the depositional setting of the field. An integrated project approach (quick review-early results, Integrated Petroleum Engineering Studies and a Field Development Plan) is taken to identify and quantify the remaining oil and gas reserves and to assess the most economic and cost-effective production of these reserves. First results reveal a more complex geology than previously recognized--both structurally and stratigraphically--which, in combination with existing production data, will lead to new exploitation opportunities. The future implementation phase--drilling, re-completions, etc--will be based on the findings of the ongoing project.
Unlocking the potential of the Schrader Bluff Formation, North Slope Alaska
Authors: Croft M. D. , Bidinger C. R. , Vandergon M. A.
Published: November 2010

The Milne Point Unit, North Slope Alaska, contains 2X10
9
BBL STOOIP, in the Late Cretaceous Schrader Bluff Formation. This resource is part of a larger viscous oil accumulation in excess of 26X10
9
BBL STOOIP. Exploitation of the Schrader Bluff commenced in 1991 with an initial 22 well development. Resulting capital and operating costs gave the basis for the larger planned development. These cost projections, coupled with low flow rates--350 BBL oil per day (BOPD)--rendered the project uneconomic and drilling ceased in 1992. BP Exploration (Alaska) Inc. (BPXA) acquired Milne Point in 1994 and laid plans to develop the Schrader Bluff and two deeper reservoirs. Most of the current production comes from two deeper reservoirs, however, work on the problematic Schrader Bluff has continued. Learning through innovative drilling and completion programmes, plus additional technological and contractual innovations, are considered the keys to unlocking the value of this vast viscous oil resource.
Upper Palaeozoic carbonate reservoirs on the Norwegian arctic shelf; delineation of reservoir models with application to the Loppa High
Authors: Stemmerik Lars , Elvebakk Geir , Worsley David
Published: November 2010

The reservoir potential of the Upper Palaeozoic carbonates in the Barents Sea area is primarily controlled by early diagenetic processes. Upper Bashkirian to Asselian shallow platform carbonates deposited in warm, arid to semi-arid climates were dominated by aragonitic organisms and mineralogically unstable aragonite and high-Mg calcite cements and mud. A reservoir model for these carbonates involves extensive dolomitization and dissolution of metastable carbonate during repeated subaerial exposure. The reservoir model is confirmed by drilling and is accordingly regarded as low risk. Artinskian and Upper Permian shallow water carbonates deposited in a cold temperate climate were dominated by calcitic organisms and silica sponges, and associated with calcite cements and mud and chert. A reservoir model for these carbonates involves either preservation of primary porosity in carbonate build-ups or extensive dissolution of build-up marine cement during prolonged subaerial exposure. This model is not confirmed by drilling and is regarded as high risk.
Late Permian (Zechstein) rifting in the Netherlands; models and implications for petroleum geology
Authors: Geluk Mark
Published: November 2010

Multidisciplinary studies in the Netherlands have revealed two new phases of late Variscan extensional faulting during the Late Permian. The names Tubantian I and II are proposed in this paper. Tubantian I movements were triggered by rapid deposition and loading of anhydrite upon a differentiated basement, in combination with mild E-W extension. A series of small pull-apart basins and tilted fault blocks formed and local collapse occurred of the Variscan Front. The relief was subsequently filled with carbonates and evaporites of the Z1 (Werra) Formation. Fault movements stopped prior to deposition of the Z2 (Stassfurt) Formation. Tubantian II movements caused uplift and erosion, especially in the southern onshore Netherlands. Contemporaneously, sandy erosional products were deposited in the southwestern offshore area of the Netherlands and the adjacent UK sector and playa-type halites and claystones accumulated in the central parts of the basin. Three features have implications for hydrocarbon exploration: the early formation of fault/dip closed structures shortly after deposition of the Upper Rotliegend; the reorganization of the fluid-flow system and the deposition of contemporaneous sandy deposits.
Estimation of critical gas saturation during pressure depletion in virgin and waterflooded reservoirs
Authors: McDougall Steven R. , Sorbie Kenneth S.
Published: November 2010

An important issue in petroleum engineering is the prediction of gas production during reservoir depletion--either following conventional waterflooding operations or in the early stages of hydrocarbon production. The estimation of critical gas saturation for use in corresponding simulation studies is clearly a primary concern. To this end, a 3D, three-phase numerical pore-scale simulator has been developed that can be used to estimate critical gas saturations over a range of different length scales and for a wide range of fluid and rock properties. The model incorporates a great deal of the known physics observed in associated laboratory micromodel experiments, including embryonic nucleation, supersaturation effects, multiphase diffusion, bubble growth/migration/fragmentation, oil shrinkage, and three-phase spreading coefficients. The precise pore-scale mechanisms governing gas evolution have been found to be far more subtle than earlier models would suggest because of the large variation of gas/oil interfacial tension (IFT) with pressure. This has a profound effect upon the migration of gas structures during depletion. In models pertaining to reservoir rock, the process of gas migration is consequently much slower than predictions from more simplistic models would imply. This is the first time that bubble fragmentation and IFT variations have been included in a model of gas evolution at the pore-scale and the implications for production forecasting are expected to be significant. In addition, novel scaling groups have been derived for a number of different facies under both virgin and waterflooded conditions. One future application of these groups would be to scale S
gc
values obtained from high rate depressurization experiments to the low rate conditions more characteristic of field operations.
Wellbore failure induced by formation testing
Authors: Hillis Richard R. , Thomas Simon D.
Published: November 2010

Five formation tests were undertaken in well 110/8A-5 in the Irish Sea. Pressures within the tested intervals were reduced from 16-17 MPa to c. 10 MPa. The tested intervals, which were subsequently logged by an electrical imaging tool, exhibit zones of low resistivity on opposite sides of the wellbore wall. These zones are restricted to the tested intervals and interpreted as borehole breakouts. It is inferred that the reduction in wellbore pressure associated with testing increased the stress acting on the wellbore wall, leading to failure. This confirms that such wellbore failure can be induced by reducing mud weight. Maximum horizontal stress is inferred to be orientated east-west which has implications for reservoir development, because natural and induced fluid flow will tend to be focused in that direction. With regard to the formation tests, near wellbore fracturing may result in modelled permeabilities exceeding those associated with intact reservoir rocks.
Overpressured Cenozoic shale mapped from velocity anomalies relative to a baseline for marine shale, North Sea
Authors: Japsen Peter
Published: November 2010

A study of interval velocities from almost a thousand wells reveals basinwide differences in physical properties of the Cenozoic deposits of the North Sea Basin. These differences relate primarily to the sediments below the mid-Miocene unconformity as testified by a subdivision of a subset of these wells. Velocity-depth anomalies are mapped relative to a constrained, normal velocity-depth trend derived for marine Jurassic shale: tt = 465.e (super -z/2435) +180, where tt is transit time in mu s m (super -1) , and z is depth in metres below sea bed. The upper Cenozoic deposits are close to normal compaction, whereas anomalies for the lower Cenozoic sediments outline a zone of undercompaction in the Central North Sea that corresponds to the overpressure in the Upper Cretaceous-Danian Chalk. The overpressure results from a balance between the load of the upper Cenozoic deposits, and the draining determined by the thickness and sealing quality of the lower Cenozoic sediments. The shale trend may be more widely applicable to marine shale dominated by smectite/illite. This suggestion is based on the observed correspondence between velocity anomalies and pressure data, and due to the match between trends for marine shale of different ages in the North Sea and in the US Gulf Coast area over a significant velocity range.
Variations in fracture system geometry and their implications for fluid flow in fractures hydrocarbon reservoirs
Authors: Odling N. E. , Gillespie P. , Bourgine B. , Castaing C. , Chiles J. P. , Christensen N. P. , Fillion E. , Genter A. , Olsen C. , Thrane L. , Trice R. , Aarseth E. , Walsh J. J. , Watterson J.
Published: November 2010

Studies assembling high quality datasets of fracture systems (joints and faults) from four reservoir analogues are described. These comprise limestones (Ireland), sandstones (Norway and Saudi Arabia) and chalk (Denmark). These are used with existing information from the literature to review the major controls and scaling behaviour of fracture systems expected in reservoir rocks. Lithological layering was found to be important and two end-member fracture systems have been identified. In "stratabound" systems, fractures are confined to single layers, sizes are scale restricted, and spacing is regular. In "non-stratabound systems", fractures show a wide range of sizes (often power-law), are spatially clustered and vertically persistent. In nature, variations between and combinations of these systems exist. These end-member systems have contrasting implications for fluid flow, including the scale of fracture that controls flow and the existence of a representative elementary volume, and thus on appropriate modelling approaches.
Nang Nuan oil field, B6/27, Gulf of Thailand: karst reservoirs of meteoric or deep-burial origin?
Authors: Heward Alan P. , Chuenbunchom Supamittra , Mäkel Gerard , Marsland David , Spring Laurent
Published: November 2010

Karst reservoirs in the Chumphon Basin of the Gulf of Thailand have produced oil at well rates exceeding 10 000 BBL/d. Meteorically karstified buried hills were recognized as a potential exploration play. The Nang Nuan discovery well appeared to confirm such a play, and the concept prevailed despite the accumulation of contrary and unusual data. By the time a subsequent well had produced nearly 4 × 10
6
BBL oil, there was a desire to better understand the prospectivity of the concession. The accumulated data indicate that the highs are probably syn-rift horsts and inversion features. Karst reservoirs occur in Ratburi carbonates, and Mesozoic and Tertiary clastics, apparently unrelated to subaerial exposure. The karstification appears to be primarily of deep-burial origin, as indicated by the nature of the karst, substantial pore volumes that are difficult to account for, and temperature and flow anomalies consistent with active geothermal circulation. There are granites and hot springs in the vicinity, and abundant CO
2
in this and neighbouring basins. Such deep-burial karst reservoirs have different implications for reserves estimation, prospect ranking and well completions.
Uncertainties associated with fault sealing analysis
Authors: Hesthammer Jonny , Fossen Haakon
Published: November 2010

Recent advances in understanding how faults restrict fluid flow in sandstone reservoirs have led to improved models for reservoir simulation. Nevertheless, there are still many uncertainty factors that can render even the most detailed simulation model useless. On a detailed scale, these uncertainties include variations in lateral continuity of faults, properties and thickness of fault zones, and the influence of deformation bands within and outside damage zones. Subseismic features such as small-scale relay zones, drag features and frequency and distribution of small faults around the fault zone further decrease the confidence level of simulation modelling results. Detailed analyses of seismic and well data from the Gullfaks Field, Northern North Sea, have helped understand the detailed structural reservoir characteristics. The results from these analyses can, in many cases, be used as input to further enhance models for reservoir simulation in order to increase the validation of the models. Furthermore, the studies carried out on the Gullfaks Field demonstrate that a sound approach to knowledge management for increased oil recovery based on fault seal analysis requires sharing of gained knowledge from many oil and gas fields rather than monopolizing information that cannot be fully utilized by studies from a single field.
Reservoir identification and characterization through sequential horizon mapping and geostatistical analysis: a case study from the Gulf of Thailand
Authors: Kongwung B. , Ronghe S.
Published: November 2010

The integration of sequential horizon slicing, attribute extraction, seismic facies characteristics, and wireline information from a Gulf of Thailand dataset enabled reconstruction of the depositional sequence, identification of reservoir units, and the analysis of reservoir geometry within an approximately 50 ms thick interval of seismic data. The depositional environment was verified to be fluvio-deltaic, with potential reservoirs comprising channel sands, associated point bars, thin crevasse splays and thin sand bars. Channel geometries were measured for five main channels using width/thickness ratios and sinuosity. Areal distributions of porosity, net sand thickness, gas saturation and hydrocarbon pore meter were predicted through geostatistical modelling. Collocated cokriged maps revealed high porosity and high sand thickness trends to relate to the main channel geometries. Collocated cokriged predictions of gas saturation and HPM distributions showed four potential areas of hydrocarbon accumulations where sand channels terminating against fault planes formed dip closures in structural highs.
Evolution and hydrocarbon habitat of the South Turgay Basin, Kazakhstan
Authors: Moseley B. A. , Tsimmer V. A.
Published: November 2010

The South Turgay Basin is a Mesozoic intracontinental rift with a Lower Jurassic to Lower Cretaceous fill. It is underlain by a basement complex comprising Precambrian metamorphics and Palaeozoic carbonates and clastics, and was formed as a result of right lateral movement on the Karatau–Talasso–Fergana Fault. Four principal graben systems are found in the basin. These are the Ariskum, Akshabulak, Sarylan and Bozingen grabens. The graben fill is represented by up to 5 km of dominantly continental sediments, with lacustrine, alluvial and fluvial units, with a series of gross fining-upwards sequences in the Lower to Middle Jurassic (syn-rift) and Upper Jurassic to Lower Cretaceous (post-rift). Marginal marine conditions began to become established during the Apto-Albian with a marine transgression from the west. Tertiary regional uplift resulting from the India–Eurasia collision stripped off later deposits. Recoverable hydrocarbons in the order of 1 billion barrels of oil equivalent have been proven to date in the large Kumkol Field and a number of smaller pools.
Developing and managing turbidite reservoirs – case histories and experiences: results of the 1998 EAGE/AAPG research conference
Authors: Dromgoole Peter , Bowman Mike , Leonard Andrew , Weimer Paul , Slatt Roger M.
Published: November 2010

This paper summarizes the results of a joint EAGE/AAPG research conference that was convened in Almeria, Spain in October 1998. The theme of the conference was how to better produce deep-water reservoirs based on lessons learned from the past 25 years. A repeated message at the conference was that there is more complexity than anticipated in turbidite reservoirs, contrary to the expectations of many geoscientists. Such complexity may go unnoticed during initial depletion, and only be observed during secondary injection of fluids. Early recognition of shale occurrences and geometries, bed continuity, and stratigraphic variations in net-to-gross ratios appear to be the main issues related to maximizing well performance.
Synthetic seismic modelling of a large-scale geological cross-section from the Book Cliffs, Utah, USA
Authors: Hodgetts David , Howell John A.
Published: November 2010

Synthetic seismic sections have been generated from a 125 km long, depositional dip orientated cross-section compiled from outcrop data from the Book Cliffs of Eastern Utah, USA. These data are used to define the earth filter for a synthetic seismic section. An outcrop-based dataset has been used in preference to well data (though well data have been incorporated into the study section) because of the high confidence in the lateral continuity of data. The regional cross-section is modelled at 20, 50 and 100 Hz seismic source frequencies. As resolution increases, more laterally discontinuous reflections relating to facies terminations are imaged. Particularly important is the increase in internal reflections within each of the stratigraphic members (particularly the Sunnyside Member). These low angle clinoform events are imaged in low-resolution data but constructively interfere to form a lower number of more continuous looking events.
Aeolian grain flow architecture: hard data for reservoir models and implications for red bed sequence stratigraphy
Authors: Howell John , Mountney Nigel
Published: November 2010

This paper introduces the Cretaceous Etjo Formation of NW Namibia as a sedimentological analogue for the Leman Sandstone, the principal gas reservoir of the UK Southern North Sea. Special reference is made to the documentation of hard knowledge from the analogue for input into very fine-scale reservoir models suitable for upscaling. The data presented address the sedimentary aspects of reservoir heterogeneity in aeolian sandstones providing size populations for grain flow laminae which typically exhibit permeability of an order of magnitude better than the grain fall and wind-rippled strata which encase them. The results also have significant and more general implications for existing models of aeolian sequence stratigraphy. The data collected are used to demonstrate that there is no link between preserved bedform thickness and original dune height. This has implications for the role of subsidence in controlling preserved bedform thickness.
The Cretaceous post-rift basin configuration of the northern North Sea
Authors: Gabrielsen Roy H. , Kyrkjebø Rune , Faleide Jan Inge , Fjeldskaar Willy , Kjennerud Tomas
Published: November 2010

The present analysis suggests that three stages can be identified in the post-rift Cretaceous development of the northern North Sea, namely the incipient (Ryazanian–latest Albian), the middle (Cenomanian–late Turonian) and the mature (early Coniacian–early Palaeocene). The transition from syn-to post-rift configuration was strongly diachronous, suggesting that the thermal state of the system was not homogeneous at the onset of the post-rift stage. This is supported by observed differences between the early post-rift subsidence histories of the southern Viking Graben, the Stord Basin and the Sogn Graben.

The incipient post-rift stage was characterized by diverse subsidence. The major structural features inherited from the syn-rift basin (e.g. crests of rotated fault blocks, relay ramps and sub-platforms) had a strong influence on the basin configuration and, therefore, the sediment distribution. In the middle stage the internal basin relief became gradually drowned by sediments. This is typical for basins where sediment supply outpaces or balances subsidence, as was the case in the northern North Sea. Thus, the influence of the syn-rift basin topography become subordinate to the subsidence pattern which was determined by the crustal thinning profile which, in turn, relies on thermal contraction and isostatic/elastic response to sediment loading. The mature post-rift stage was characterized by the evolution into a wide, saucer-shaped basin where the syn-rift features finally became erased. Since thermal equilibrium was reached at this stage, subsidence ceased, and the pattern of basin filling became, to a larger degree, dependent on extra-basinal processes. This simple pattern was influenced by the structural inhomogeneity of the basin. This inhomogeneity may have included the graben units, in turn related to contrasting geometries of the lithospheric structure.

The incipient stage of post-rift development was halted by relative uplift/deceleration of subsidence, locally corresponding to 200 m. This is ascribed to a hitherto undescribed thermo-tectonic event. The mechanism of this event is not yet known.
Regression analysis and C
7+
description for accurate PVT data calculations with equations of state
Authors: Nichita Dan Vladimir , Minescu Florea , Cretu I.o.n.
Published: November 2010

Simulation of improved recovery processes from gas condensate and volatile oil reservoirs is significantly affected by the match of experimental PVT data. Therefore, a proper characterization of the mixture composition and tuning of the equation of state used are crucial for the accuracy of the reservoir model. This paper presents an efficient method for phase behaviour matching by non-linear regression. The constraints introduced by the boundaries of the regression variables are eliminated by a suitable change of variables. This leads to an unconstrained optimization problem, solved by an original implementation of the Levenberg–Marquardt algorithm. The C
7+
fraction is described by a continuous (semi-infinite or truncated) distribution function. A new, rigorous generalized quadrature method is developed for the characterization of the continuous portion of the mixture, which can be applied to any distribution function.

The regression was applied to PVT data for several gas-condensate, including near-critical, and volatile oil systems subjected to different types of expansion and swelling tests, as well as multistage separation processes. The calculated results indicate very good agreement with experimental values. The regression algorithm proves to be robust and efficient.
Geochemistry and thermal maturation of Triassic to Eocene source rocks in the Central Taurus Belt, SW Turkey
Authors: Sari A. , Sonel N. , Albayrak M.
Published: November 2010

Triassic–Middle Eocene sedimentary sequences in the Central Taurids contain sufficient organic matter to constitute potential source rocks. Geochemical data are used to examine the amount, type and maturation of organic matter and the hydrocarbon potentials of the Triassic Tarasci Fm Limestone, the Late Jurassic–Early Cretaceous Akkuyu Fm limestones and shales and the Middle Eocene Gumusdamla Fm shales. During the extensive Senonian and Lutetian horizontal movements, sub-thrust units of these formations attained higher maturity values in the north (Seydisehir) than in the south (Akkuyu) of the study area. The TOC, S
2
, and HI values decrease with increasing thermal maturity (365–569°C). Therefore, the geochemical data indicate that the formations are gas and oil source rocks and may produce gas with some oil.
Sequential dip-slip fault movement during rifting: a new model for the evolution of the Jurassic trilete North Sea rift system
Authors: Davies R. J. , Turner J. D. , Underhill J. R.
Published: November 2010

Controversy has long surrounded the kinematics of faulting in the Middle–Late Jurassic North Sea trilete rift system. Integration of structural styles and subsidence analysis derived from well-constrained seismic interpretation enables a new, unified model to be proposed in which strike-slip was negligible, dip-slip extension predominated throughout the rifting episode and normal faults were active sequentially not synchronously. Extension was initiated on N–S and NNE–SSW trending faults during the Bathonian and Callovian, NE–SW and E–W structures during the Oxfordian and NW–SE faults during the Kimmeridgian and Volgian. The results allow us to speculate that fault activity was driven by variations in the prevailing far-field stress regime that were superimposed upon a trilete junction that formed as consequence of Middle Jurassic thermal doming. Significantly, rotation of the stress field during rifting is similar in other rifts, such as the Afro-Arabian system.
Gradual deformation and iterative calibration of truncated Gaussian simulations
Authors: Hu Lin Y. , Le Ravalec Mickaële , Blanc Georges
Published: November 2010

Recently, we proposed the gradual deformation approach for constraining stochastic models to dynamic data (well-tests and production history). In this paper, we review the basic gradual deformation algorithm and extend its application to different types of truncated Gaussian simulations (including non stationary truncated Gaussian and truncated pluri-Gaussian simulations). A case study on the calibration of a reservoir lithofacies model to well-test pressure data illustrates the efficiency of the gradual deformation approach.
Modelling of stochastic faults and fault networks in a structural uncertainty study
Authors: Lecour Magali , Cognot Richard , Duvinage Isabelle , Thore Pierre , Dulac Jean-Claude
Published: November 2010

Modelling faults from seismic data for a 3D depth model is a difficult task because of the multiple sources of uncertainty. The uncertainty may be attributed to migration velocities, picking of faults and organization of the fault network in 3D. Faults are generally not migrated from time to depth domain like horizons are, but modelled in the depth domain from the depth migrated horizons. For this reason, a new data structure has been designed that is targeted for fault modelling. Taking uncertainties into account, this structure allows for rapid modelling of faults from depth migrated horizons. The input data and the parameterization of the new data structure will be described. Following this, a way to incorporate uncertainties during the interpretation process is proposed and a description of different stochastic methods used to compute new shapes and locations inside a given uncertainty volume will be made. Finally, the method and the results obtained will be described while studying uncertainties on more complex fault networks. The influence of fault uncertainties on the reservoir volumetric estimates will be shown as one possible result of the simulation process.
Integration of production data into reservoir models
Authors: Oliver Dean S. , Reynolds Albert C. , Bi Zhuoxin , Abacioglu Yafes
Published: November 2010

The problem of mapping reservoir properties, such as porosity and permeability, and of assessing the uncertainty in the mapping has been largely approached probabilistically, i.e. uncertainty is estimated based on the properties of an ensemble of random realizations of the reservoir properties all of which satisfy constraints provided by data and prior geological knowledge. When the constraints include observations of production characteristics, the problem of generating a representative ensemble of realizations can be quite difficult partly because the connection between a measurement of water-cut or GOR at a well and the permeability at some other location is by no means obvious. In this paper, the progress towards incorporation of production data and remaining challenges are reviewed.
The structure of western Sicily, central Mediterranean
Authors: Catalano R. , Merlini S. , Sulli A.
Published: November 2010

Western Sicily is part of the Sicilian chain, a sector of the SE-verging Alpine orogenic belt in the central Mediterranean. Interpretation of seismic reflection profiles, boreholes and recent inland geological data, have enabled us to assess the deep structural grain. A wedge of flat-lying Mesozoic–Miocene carbonate and terrigenous rocks (pre-Panormide nappes) is superimposed on NW-trending, 7–8 km thick, Mesozoic–Paleogene carbonate thrust ramps (Trapanese units), arranged in two structural levels extending from the Tyrrhenian coast to western offshore Sicily. Upper Miocene to Pleistocene terrigenous strata, often deformed, fill syntectonic basins above the thrust pile. The main tectonic transport of the thrust pile, developing from Early Miocene to Early–Middle Pleistocene times, was towards the east and southeast.

Initial stacking and deformation of the pre-Panormide allochthon is bracketed between Early and Late Miocene. The Late Miocene–Early Pleistocene underthrusting of the Trapanese–Saccense units, that acted through more recent deep-seated thrusts in the carbonate platform layer, induced late stage refolding and further shortening in the early emplaced pre-Panormide nappe. Previously formed structures appear to have been dissected or reactivated by a right oblique transpression during the Late Pliocene–Pleistocene. The geometry of the carbonate bodies opens new potential perspectives on the existence of structural traps, but the uncertainties of source rock occurrence remain.
Influence of fine-scale heterogeneity patterns on the large-scale behaviour of miscible transport in porous media
Authors: Elfeki A. M. M. , Dekking F. M. , Bruining J. , Kraaikamp C.
Published: November 2010

An extensive series of numerical simulations on two-dimensional flow and miscible transport are carried out. The purpose of performing these simulations is to study the influence of fine-scale heterogeneity patterns (i.e. horizontal laminations, cross-bedding at 45°and 135°) with short range and long range correlation structure on large-scale behaviour of miscible transport in porous media. Synthetic heterogeneous structures have been generated using newly developed stochastic techniques (e.g. the coupled Markov chain method) to model the subsurface formations in various configurations, using realistic characteristics, and the tree-indexed Markov chain method to merge these heterogeneities at various scales. The results of the simulation are compared with simulations on a reference model of heterogeneity where there is no fine-scale heterogeneity. The simulations show that the variation in the fine-scale heterogeneity inside the large-scale lithological units has considerable impact on concentration distribution and the spreading of miscible plumes. The combination of the two stochastic techniques (the coupled Markov chain model and the tree-indexed Markov chain) is a useful tool to study multi-scale transport behaviour in heterogeneous media. The fine-scale heterogeneity enhances the mixing process, but the definition of an asymptotic giga-scopic dispersion at field scale is still questionable.
Determination of facies from well logs using modular neural networks
Authors: Bhatt Alpana , Helle Hans B.
Published: November 2010

Zonation of well logs and the correlation of zones between wells are primary tasks in sub-surface geological and engineering analysis. We propose in this paper an artificial neural network (ANN) approach for objective clustering and identification of facies from well logs. The method relies upon combining back-propagation neural networks in ensembles and modular systems, where the multi-class classification problem of facies identification has effectively been reduced to a number of two-class problems.

Based on the neural network responses using synthetic logs from a realistic model, we optimized the architecture and training procedure of the component networks in the modular system, where the building blocks are simple three-layer back-propagation ANNs. Ensembles of ANNs are trained on disjoint sets of patterns using soft overtraining to ensure diversity and generalization. Recurrent ANNs are shown to enhance the facies continuity by effectively removing ambiguous or spurious classifications.

The performance of the technique was demonstrated using synthetic data and it was then used to detect four different facies within the Ness Formation in the North Sea. An average hit rate of above 90% in wells not used for training the network is slightly to significantly better than the performance published for similar classification experiments.
Kadanwari Gas Field, Pakistan: a disappointment turns into an attractive development opportunity
Authors: Ahmad Nasir , Chaudhry Siddique
Published: November 2010

Kadanwari Gas Field, located in the Middle Indus Basin of Pakistan, was discovered in 1989. Lower Goru sands of Cretaceous age are the producing reservoir in this field. Initially, the structure was considered a relatively simple four-way closure with continuous sand. During appraisal, three wells were drilled and each of these tested gas. On the basis of these results 728×10
9
SCF of sales gas reserves were estimated and a processing facility was designed accordingly. Due to the corrosive and sour nature of Kadanwari gas, 22% chrome alloy was used in the well completion and surface facilities. Additional development wells and early production data indicated that the reserves were much smaller than originally estimated. After further studies, including reprocessing of seismic data, the reserves were revised downward to less than 200×10
9
SCF; by that time a total of nine wells had been drilled. Although the field was considered to be a disappointment, the subsurface studies continued and, as a result, the tenth well tested a new fault compartment, proving an accumulation of considerable reserves. As a result of detailed studies of the field, a number of other opportunities were also identified. Presently, the sales gas reserves are estimated at approximately 300×10
9
SCF and this has given a new life to the field. Some other independent fault-bounded structures in the field are now considered prospective and these have the potential to add sales gas reserves ranging from 100–500 bcf.
Well-bore reservoir evaluation technologies to optimize field revitalization
Authors: Bryant I. D.
Published: November 2010

The economic success of field revitalization projects depends upon draining reservoir compartments that frequently contain smaller reserves volumes than those targeted by the initial field development, in a cost-effective manner. Well-bore measurements can contribute to risk management of redevelopment by identifying and monitoring the drainage of remaining hydrocarbons. Applications of cased-hole and open-hole measurements to optimizing field redevelopment are illustrated using case studies from the Brent Field, UK; Block IV, Venezuela and the T&J Ashworth Lease, USA.

Cased-hole logging using nuclear tools has evolved from time-lapse monitoring to detect changes in saturation to also include through-casing formation evaluation. Where deep invasion prevents the use of these nuclear methods, through-casing resistivity tools can successfully detect hydrocarbons.

Open-hole formation pressures can significantly impact redevelopment strategies, as can evaluation of filtrate invasion using open-hole array resistivity tools. Emerging permanent sensor technologies enable continuous monitoring of both water saturation and formation pressure, thereby offering the potential to improve the performance of future field revitalization projects.
Balder and Jotun – two sides of the same coin? A comparison of two Tertiary oil fields in the Norwegian North Sea
Authors: Bergslien D.a.g.
Published: November 2010

The Balder and Jotun fields are located on the western flank of the Utsira High, close to the eastern pinch-out of a Tertiary submarine fan system. Although similar in many aspects, the fields display important depositional, structural and stratigraphic differences which influence the choice of development strategy. The subsurface development strategy for the fields has been designed to optimize oil capture and minimize risk based on the interpreted reservoir geology. Therefore, differences between the exploration histories and reservoir geology are reflected in the development strategy of the two fields.

Both fields comprise Tertiary reservoir sands shed from the East Shetland Platform and transported across the Viking Graben area onto the Utsira High by sandy debris flows and turbidites. These distal gravity flow deposits display both thin-bedded sands and thicker more massive sandstones (>100 m). In the Balder Field, an intricate interaction between deposition and soft sediment deformation processes generated a complex network of reservoir compartments with common fluid contacts. In the Jotun Field, the oil–water contact is also common between all three structures, but a gas cap is restricted to one of the structures.
Microstructural and petrophysical characterization of Muderong Shale: application to top seal risking
Authors: Dewhurst David N. , Jones Richard M. , Raven Mark D.
Published: November 2010

Analysis of the Muderong Shale from the Carnarvon Basin suggests the shale is dominated by interstratified illite–smectite with a high percentage of illite interlayers. Capillary pressure measurements indicate that gas columns of
c
. 250 m could be sealed by such shale, although the choice of drying method used does influence the accuracy of this calculation. Freeze drying yielded the most consistent threshold pressure results, whereas air drying and vacuum drying showed a greater range of values. Similar calculations in regard to carbon dioxide sequestration indicate column heights of between 550 m and 750 m could be retained. Column height variation is primarily dependent on the contact angle of supercritical carbon dioxide with shale. Microstructurally, the shale is clay supported, exhibiting differential compaction of clays around more rigid grains and containing numerous high aspect ratio discontinuous fractures. These fractures do not affect the capillary properties of the shale, even when injection is fracture-parallel, suggesting they are unlikely to influence reservoir-scale fluid-flow properties. Comparison of the Muderong Shale laboratory data with hydrocarbon column heights from Carnarvon Basin discoveries indicate that top seal failure by capillary breakthrough is unlikely given the maximum lengths of hydrocarbon columns encountered to date. Potential for top seal failure is more likely to be influenced by formation integrity, pore pressure and
in situ
stress conditions.
Snail1 transcription factor is a critical mediator of hepatic stellate cell activation following hepatic injury
Authors: Scarpa Melania , Grillo Alessia R. , Brun Paola , Macchi Veronica , Stefani Annalisa , Signori Sara , Buda Andrea , Fabris Paolo , Giordani Maria Teresa , De Caro Raffaele , Palù Giorgio , Castagliuolo Ignazio , Martines Diego
Published: November 2010

Following liver injury, the wound-healing process is characterized by hepatic stellate cell (HSC) activation from the quiescent fat-storing phenotype to a highly proliferative myofibroblast-like phenotype. Snail1 is a transcription factor best known for its ability to trigger epithelial-mesenchymal transition, to influence mesoderm formation during embryonic development, and to favor cell survival. In this study, we evaluated the expression of Snail1 in experimental and human liver fibrosis and analyzed its role in the HSC transdifferentiation process. Liver samples from patients with liver fibrosis and from mice treated by either carbon tetrachloride (CCl4) or thioacetamide (TAA) were evaluated for mRNA expression of Snail1. The transcription factor expression was investigated by immunostaining and real-time quantitative RT-PCR (qRT-PCR) on in vitro and in vivo activated murine HSC. Snail1 knockdown studies on cultured HSC and on CCl4-treated mice were performed by adenoviral delivery of short-hairpin RNA; activation-related genes were quantitated by real-time qRT-PCR and Western blotting. Snail1 mRNA expression resulted upregulated in murine experimental models of liver injury and in human hepatic fibrosis. In vitro studies showed that Snail1 is expressed by HSC and that its transcription is augmented in in vitro and in vivo activated HSC compared with quiescent HSC. At the protein level, we could observe the nuclear translocation of Snail1 in activated HSC. Snail1 knockdown resulted in the downregulation of activation-related genes both in vitro and in vivo. Our data support a role for Snail1 transcription factor in the hepatic wound-healing response and its involvement in the HSC transdifferentiation process.
Diet-induced impaired glucose tolerance and gestational diabetes in the dog
Authors: Moore Mary Courtney , Menon Renuka , Coate Katie C. , Gannon Maureen , Smith Marta S. , Farmer Ben , Williams Phillip E.
Published: November 2010

Glucose metabolism was compared in dogs consuming a chow/meat diet throughout pregnancy (P group, n = 6) and dogs switched to a high-fat/high-fructose (HFF) diet during the 4th–5th gestational week (gestation ≃9 wk; P-HFF group; n = 6). An oral glucose tolerance test (OGTT; 0.9 g/kg) was administered in the 6th–7th gestational week, and a hyperinsulinemic [0–120 min: 1.8 pmol·kg−1·min−1 (low insulin); 120–240 min: 9 pmol·kg−1·min−1 (high insulin)] euglycemic clamp was performed the following week. Nonpregnant (NP) female dogs underwent OGTTs but not clamp studies. All P-HFF dogs exhibited impaired glucose tolerance (IGT) or gestational diabetes (GDM), but only one P dog had IGT. Insulin concentrations in P and P-HFF dogs were significantly lower than in NP dogs 30 and 60 min after the OGTT. Therefore, mean islet size and area were evaluated in P and NP dogs. These values did not differ between groups, and proliferating endocrine cells were rare in pregnancy. During exposure to high insulin, glucose infusion rate and hindlimb glucose uptake were ∼30% greater ( P < 0.05) and net hepatic glucose output was more suppressed (−5.5 ± 6.1 vs. 7.8 ± 2.8 mg·100 g liver−1·min−1, P < 0.05) in P than in P-HFF dogs. In conclusion, in the 2nd trimester the canine pancreas does not exhibit islet hypertrophy, hyperplasia, or neogenesis. Combined with the lack of pancreatic adaptation, a HFF diet during late pregnancy produces a canine model of IGT and GDM without hyperinsulinemia but exhibiting liver and muscle insulin resistance.