Facies Description Research Articles

Dealing with spatial heterogeneity

Heterogeneity can be dealt with by defining homogeneous equivalent properties, known as averaging, or by trying to describe the spatial variability of the rock properties from geologic observations and local measurements. The techniques available for these descriptions are mostly continuous Geostatistical models, or discontinuous facies models such as the Boolean, Indicator or Gaussian-Threshold models and the Markov chain model. These facies models are better suited to treating issues of rock strata connectivity, e.g. buried high permeability channels or low permeability barriers, which greatly affect flow and, above all, transport in aquifers. Genetic models provide new ways to incorporate more geology into the facies description, an approach that has been well developed in the oil industry, but not enough in hydrogeology. The conclusion is that future work should be focused on improving the facies models, comparing them, and designing new in situ testing procedures (including geophysics) that would help identify the facies geometry and properties. A world-wide catalog of aquifer facies geometry and properties, which could combine site genesis and description with methods used to assess the system, would be of great value for practical applications.

Facies analysis of the Codó Formation (Late Aptian) in the Grajaú Area, Southern São Luís-Grajaú Basin

Facies descriptions of the Codó Formation in the Grajaú area are provided for the first time, and its sedimentary characteristics compared to those from the Codó area to allow paleoenvironmental reconstructions. Deposits in the Grajaú area include evaporites, limestones and argillites bearing features indicative of a shallow, low energy, subaqueous, saline environment exposed to meteoric and/or capillary conditions. Flooding-evaporative concentration-desiccation cycles suggest a saline pan complex surrounded by extensive evaporitic mudflats. The location of the system, whether coastal or inland, is a matter open for debate. However, the later hypothesis is favored considering: 1. Sr isotopic data, with values higher than those expected for Late Aptian marine waters; 2. calcitic composition of limestones (instead of dolomitic and/or magnesitic as expected in coastal settings); and 3. presence of continental ostracods and lack of marine fauna. This interpretation is consistent with that proposed for UpperAptian deposits of the Codó area, but the depositional system there was one dominated by more stable, well-stratified, anoxic waters and evaporite precipitation in central lacustrine areas, while in the Grajaú area the salt pan was more oxygenated and ephemeral, with salt precipitation mainly in marginal areas or along surrounding mudflats.

Sequence Stratigraphy and Depositional Dynamics of Carbonate Buildups and Associated Facies from the Lower Mississippian Fort Payne Formation of Southern Kentucky, U.S.A.

Abstract Carbonate buildups are a common feature in Mississippian sections worldwide. Yet despite intense study, questions remain about depositional processes that form such structures and their interrelations, if any, to each other. Carbonate buildups located in siliciclastic basins are particularly understudied and poorly understood. This study focuses on a new exposure of buildups in the siliciclastic-dominated Fort Payne basin (Osagean) of south central Kentucky. It represents a first attempt to combine field and petrographic descriptions of facies in the buildup interval of the Fort Payne with the concepts of sequence stratigraphy to gain better insight into their depositional histories. The buildup interval is composed of five distinct facies. Two of these, the fossiliferous green shale and the tabular crinoidal packstone-grainstone, represent the background sedimentation during buildup nucleation and growth. The remaining three facies make up the buildups themselves. The shaly packstone marks the inception of buildup growth, the massive wackestone represents the core of the buildups, and the crinoidal grainstone is a buildup-flank facies deposited near the end of buildup growth. The buildups of the Fort Payne Formation grew during the transgressive phase of one third-order sequence in the early Osagean. The time at which buildup growth ceased cannot be determined precisely with available data but likely occurred either at the maximum flooding surface or during the early highstand. Three commonly used depositional models, abbreviated as the lithoherm model, the baffling model, and the microbial model, are evaluated with respect to the Fort Payne buildups. None of the models is deemed adequate to explain all of the features of the buildups. Rather, a combination of all three seems to be required to account fully for all of the characteristics noted in this study. This multi-faceted depositional model compares favorably with other Carboniferous buildups worldwide, suggesting commonalities that transcend the properties of the basins in which they grew.

Seismic geomorphology-based facies classification

Seismic facies analysis is a powerful, yet largely subjective, methodology for hydrocarbon exploration and development. The term “seismic facies” means different things to different people. For this study, however, seismic facies is defined as a seismic description of depositional facies confined in a seismically thin bed at a normal seismic sampling rate (e.g., 4 ms), making this study's seismic facies analysis different from classical seismic facies analysis of much thicker depositional sequences. As a subjective interpretation of seismic attributes, seismic facies analysis is often laborious and inconsistent, especially if multiple mapping units are involved. How to automate the process via computer pattern recognition so that consistency could be improved and the 3D cycle time reduced has been a hot topic in recent years.

Three-dimensional architecture of a coalesced, collapsed-paleocave system in the Lower Ordovician Ellenburger Group, central Texas

The three-dimensional, interwell-scale architecture of a Lower Ordovician Ellenburger coalesced, collapsed-paleocave system was constructed through the integration of ground-penetrating radar (GPR), shallow-core, and outcrop data. The data were collected near Marble Falls in central Texas over an area (800 1000 m [2600 3300 ft]) that could cover several oil-well locations (160 ac; 0.65 km2) typical of a region such as west Texas. Integration of core-based facies descriptions with GPR-reflection response identified several paleocave facies that can be recognized and mapped with GPR data alone: (1) continuous reflections image the undisturbed strata, (2) relatively continuous reflections (over tens of meters) characterized by faults and folds image the disturbed strata, and (3) chaotic reflections having little to no perceptible continuity image heterogeneous, cave-related brecciated facies recognized in core that cannot be individually resolved with the GPR data. These latter facies include the highly disturbed strata, coarse-clast chaotic breccia, fine-clast chaotic breccia, and sediment fill.The three-dimensional architecture of the coalesced, collapsed-paleocave system based on core and GPR data indicates that there are trends of brecciated bodies that are as much as 350 m (1100 ft) wide, greater than 1000 m (3300 ft) long, and tens of meters high. These brecciated bodies are coalesced, collapsed paleocaves. Between the brecciated bodies are areas of disturbed and undisturbed host rock that are jointly as much as 200 m (660 ft) wide.As a cave system is buried, many structural features form by mechanical compaction. These features include folds, sags, and faults. The folds and sags measure from a few meters to several hundred meters wide. The collapse-related faults are numerous and can have several meters of displacement. Most are normal faults, but reverse faults also occur.

Reservoir characteristics of intracontinental carbonate ramp deposits-Upper Muschelkalk, Middle Triassic, NE Netherlands

AbstractThe Upper Muschelkalk is an unusual reservoir in NW Europe, producing only in the Coevorden Muschelkalk field, onshore the Netherlands. Origin and nature of the gas producing intervals were poorly known. The objective of the paper is to provide a comprehensive description of facies, cyclicity and petrophysical characteristics. From this description a depositional and sequence stratigraphic model is proposed, which explains why there is gas production only from certain intervals of the sequence. Our investigation is based on seismic, core and open hole log data. It indicates that the reservoir consists of dolomites, which are either muddy lagoonal to sabkha, or grainy backshoal deposits. The best reservoir quality is encountered in peloidal-oolitic packstones to grainstones. These represent storm-dominated backshoal deposits and constitute the inner part of a homoclinal carbonate ramp. The succession shows a conspicuous hierarchical cyclicity. Porous backshoal deposits form during maximum transgression and early regression. However permeable, gas producing backshoal deposits only occur in the upper 15 to 20 m, which forms the large-scale regressive hemi-cycle of the Upper Muschelkalk. Better reservoir quality in the upper hemi-cycle is due to changes in grain type and early diagenesis. The investigation might serve as calibration point for further exploring the Upper Muschelkalk reservoir and its facies pattern in the NW European basin.

Sediment facies and hydrodynamic setting: a study in the south western Baltic Sea

This study aims at investigating the relationship between sedimentary facies and hydrodynamic setting by applying statistical analysis of sedimentological data and hydrodynamic modelling. The facies description bases on a dataset of grain-size analysis of surface sediments of the southwestern Baltic Sea. The facies is described by the grain-size parameters median, sorting, and skewness – parameters of a distribution function fitting the grain-size data. The function was derived from a formula proposed by Tauber (1995). The three grain-size parameters were mapped for the southwestern Baltic Sea area applying ordinary kriging (Journel and Huijbregts 1978). The study area was subdivided into uniform facies regions using the concept of regionalized classification after Harff and Davis (1990). The near-bottom hydrodynamic conditions controlling sediment deposition are represented by the average kinetic current energy, the average kinetic wave energy, and the average current vector derived from results of numerical modelling covering a period of 1 year (Rietz et al. 2000). Transport pathways in the southwestern Baltic Sea were postulated based on the directions of the average current vectors which are assumed to be the preferred directions for clastic material transport. A comparison of the hydrodynamic conditions at selected test locations along the preferred transport pathways with the granulometric facies reveals the common case of a direct genetic dependency between the surface sediment facies and the recent hydrodynamic setting. An exception occurs within the Pomeranian Bight. Results indicate that the sediments of this area have not been accumulated under the present-day conditions which supports the findings of Wehner (1990) reporting a glacio-fluviatile late Pleistocene genesis of the sediments there.

Stratigraphy and sedimentology of shoreface and fluvial conglomerates: insights from the Cardium Formation in NW Alberta and adjacent British Columbia

ABSTRACT In this paper we describe little-studied exposures of the Upper Cretaceous Cardium Formation in the northern Foothills and Peace River Plains, located north of Twp. 58. We correlate sixteen principal outcrop sections along the Foothills and across the northern escarpment of the Cardium as far east as the Smoky River. Correlations are based on tracing bounding erosion surfaces, initially observed in well logs and cores, and later extended into outcrop. The Kakwa Member is conglomeratic in many of these sections. The member displays a spectrum of conglomerate types, of both shallow marine and fluvial origin. Depositional environments are differentiated on the basis of stratigraphic context, conglomerate texture, sedimentary structures, stratification style and paleogeographic setting. We describe in detail four localities exemplifying the main paleoenvironments. At Bay Tree, a 12 m thick section consists primarily of clast-supported conglomerates representing a wave-dominated shoreface and beachface. This environment is dominated by broadly horizontal stratification with horizontal facies heterogeneity on a metre scale. At Cutbank Lake, swaley-stratified shoreface sandstones contain pebble-lined scours that show an upward increase in thickness and lateral continuity and represent rip current deposits. At Mount Niles, conglomerate forms a 2-6 m thick, >200 m wide, channelized body consisting of heterolithic matrix-supported conglomerates and pebbly sandstones capped by gravel wave ripples. Deposition may have been in a river-mouth setting. At 'Horseshoe Mountain', the upper part of the Kakwa Member consists of metre-scale crossbedded pebbly sandstone and matrix-supported conglomerate deposited in a pebbly fluvial system lacking marine influence. For the entire study area, paleocurrent observations indicate a strong NW to SE alongshore transport of gravel, with storm waves approaching from the NE. Fluvial crossbedding is directed towards the NE. Some of the outcrop facies can also be recognized in core from the adjacent subsurface. Our descriptions of conglomerate facies in outcrop facilitate interpretation of the depositional environment of comparable units in subsurface. Unfortunately, the limited extent of exposures does not allow us to determine with precision the geometry of conglomeratic units. However, a broad conglomerate-rich zone >90 km in dip extent and 10-20 km in strike extent can be traced across the northern outcrop belt and probably records the position of a major and long-lasting pebbly fluvial system. Subsurface analogs would be exploration fairways. At the reservoir scale, conglomerate bodies showing greater influence of wave reworking would tend to be more elongate, and have greater facies continuity/permeability, in a shore-parallel direction. The outcrops display lateral textural heterogeneity at scales of metres to 10s of metres. This heterogeneity would affect reservoir performance, but could not be captured (for reservoir modeling) using typical development well spacing. End_Page 437------------------------

Signatures paléoclimatiques des échinides du Néogène final atlantique à faciès redonien

Palaeoclimatic signifiance of the Redonian echinoids from the Late Atlantic Neogene. The Redonian “faluns” outcropping in numerous localities of the North-Western France provides special echinoid faunas containing marsupiate echinoids. The Redonian notion is redefined according to unpublished observations realized on the stratotype outcropping in the Rennes area. Lithological descriptions of the stratotypical facies are given. New datations realized on the Rennes area and on different Redonian localities of Western France show that several Redonian outcrops, and so the marsupiate echinoids that they contain, are Messinian in Brittany, and Pliocene in Vendée, in Loire-Atlantique and in Manche. The presence of such marsupiate species in North-Western France at the end of the Neogene is interpreted as a phenomenon induced by temperature and stream perturbations of the water with input of cold water via the East Armorican strait at the Middle-Late Miocene and during the Pliocene, and by a more general cooling during the Messinian.

Sedimentary facies and radiocarbon dates of the Nam Dinh-1 core from the Song Hong (Red River) delta, Vietnam

The Song Hong (Red River) delta, which is located on the western coast of the Gulf of Bac Bo (Gulf of Tonkin) in the South China Sea is characterized by three morphological systems that are clearly distinguished spatially: fluvial-, tidal-, and wave-dominated. We obtained a 70-m-long core of sediments (the Nam Dinh-1 core) from the central part of the delta in 1999. This paper presents the first detailed description of sedimentary facies with high-resolution radiocarbon dating for the latest Pleistocene–Holocene sediments of the Song Hong delta. The core sediments were divided into three units on the basis of the sediment facies: in ascending order, Unit 1, fluvial sediments consisting of fining-upward gravels to clay; Unit 2, coarsening-upward marine clay to shelly sand; and Unit 3, coarsening-upward marine clay and laminated sand. Twenty-one radiocarbon dates showed that the core succession was deposited after the Last Glacial Maximum (LGM); the ages were 15–11 cal. kyr bp for Unit 1, 11–9 cal. kyr bp for Unit 2, and 8–0 cal. kyr bp for Unit 3. These data indicate that sediments were deposited in transgressive fluvial/estuarine to regressive deltaic environments formed in the central delta plain of the Song Hong after the LGM in response to sea-level changes.

SEISMIC TO SIMULATION: INTEGRATED RESERVOIR MODEL FOR THE PATRICIA BALEEN GAS FIELD

The Patricia and Baleen offshore gas fields are located in the northeastern part of the Gippsland Basin in southeast Australia. Although discovered by two exploration wells almost a quarter of a century ago, the two gas fields only recently have again become the focus of appraisal and subsequent development activity through OMV’s acquisition of Cultus in 1999.After the drilling of a successful appraisal well in late 1999, a high resolution 3D seismic survey was acquired in early 2000. No further data acquisition will be undertaken. Special emphasis was therefore put on maximising the value of the 3D dataset by integrating the PreSTM (Pre. Stack Time Migration) seismic and several Elastic Impedance attributes with all other available subsurface data prior to building a sophisticated stochastic reservoir model for simulation.This paper describes how the integration of leading edge seismic technology with unconventional geological modelling was used to overcome a number of major challenges in order to build a coherent static reservoir model and constrain resource uncertainty given the limited amount of wireline and core data:A large proportion of the gas fields is strongly affected by seismic tuning which would introduce significant uncertainties on GRV and GWC estimations from seismic, if not accounted for properly. Likewise all seismic and to a somewhat lesser extent basic inversion based attributes used for reservoir property determination are strongly affected by this geophysical artefact: These challenges (and seismic pitfalls) were met by inverting the conventional 3D seismic for Pand S- wave impedances and generating a set of Elastic Impedance Cubes, difference cubes and LRM Cubes (standing for the elastic constants Lambda (λ), Rho (ρ) and Mhu (μ)), defining petroacoustic properties of the reservoir rocks. These cubes were tested for mathematical dependency and used for the conditioning of the facies and porosity models.The glauconitic Gurnard reservoir contains a high fraction of conductive minerals and is almost completely bioturbated. Conventional saturation estimations based on wireline-logs and conventional sequence stratigraphic facies description did not deliver a reliable picture: Instead a facies model based on ichnofabric analysis was built and constrained with data available at the three well locations. Saturation height functions were applied separately for each facies type. The Rho-Lambda (ρλ) cube was used to condition facies distribution away from the wells.More specifically, the results presented in the paper are:Elastic Impedance inversion provided vertical seismic resolution in the order of 4 m to 10 m, thereby allowing a more accurate seismic estimation of GRV and the GWC. Lamesf Constants were extracted from seismic in order to classify lithology.A realistic facies model was built utilizing the Rho- Lambda (ρλ) cube combined with ichnofabric analysis tied to permeability and water saturation distributions.Elastic Impedance Difference cubes were successfully calculated to eliminate tuning even further and condition the stochastic porosity model.Connected volume maps were used to optimise the production well pathsThe GIIP upside volume has been upgraded compared to that based on an earlier simplistic geological reservoir model used for simulation. A more realistic P10/P90 reserves range is now supported by a number of deterministic and stochastic reservoir models.

Sedimentary facies, diatom and foraminifer assemblages in a late Pleistocene–Holocene incised-valley sequence from the Mekong River Delta, Bentre Province, Southern Vietnam: the BT2 core

A detailed description of sediment facies, diatom, mollusca and foraminifer assemblages, and 14C ages of the Mekong River Delta, Southern Vietnam, is presented in this paper. A 71 m long core, recovered in 1997 at the Bentre province in the eastern part of the Mekong River Delta, is divided into eight units and nine sediment facies on the basis of sedimentary properties, diatom and foraminifer assemblages, and 14C ages. These units show facies changes from transgression to regression in relation to the late Pleistocene–Holocene sea-level changes. The Postglacial transgression caused by a sea-level rise led to infilling of the incised valley and formation of estuarine sediments and open bay muddy sediments in ascending order. Estuarine sediments consist of slightly oxidized yellowish–grey silty sand and intercalated greenish–grey and stiffly brownish–grey sandy silt and silty clay. The muddy facies, 13.5 m thick, is characterized by abundant marine planktonic diatoms and open-sea foraminifers. This facies indicates the maximum Holocene marine influence was around 5300 cal yr BP at the BT2 site. The regressive succession is composed of deltaic sediments from prodelta, delta front, sub- to inter-tidal flat and beach ridge in ascending order. 14C ages indicate that the delta front passed the core site at approximately 4000–3000 cal yr BP. The coastal progradation rate was 17–18 m yr −1 during the 5300–3500 cal yr and decreased to 13–14 m yr −1 during the last 3500 cal yr.

Description and numerical model of Pleistocene iceberg scours and ice‐keel turbated facies at Toronto, Canada

Near Toronto, in Southern Ontario, Canada, glaciolacustrine muds and shoreface sands of Late Pleistocene age (Early Wisconsin glaciation; ≈45 ka) were deformed by icebergs ploughing the floor of an ancestral ice‐dammed Lake Ontario. Outcrop mapping and a ground‐penetrating radar survey identify ice scour structures up to 4 m deep, up to 10 m wide and at least several hundred metres long with high‐standing lateral margins (berms). Ploughing of lake‐floor sediment is also recorded by ice‐keel turbated facies in which storm‐deposited shoreface sands have been mechanically mixed with underlying muds. Palaeoenvironmental information for one prominent scour, such as water depths, estimates of the mass and draft of the ice mass and scouring forces, can be determined using a simple finite element numerical model. A mass of 0·04 million tonnes, a keel draft of between 10 and 30 m and a scouring force of 5 × 103 kN is consistent with scouring by a small iceberg (‘bergy bit’) or pressure‐ridged lake ice; the former is preferred because of the considerable depth of the scour and the overall glacial depositional setting. Estimates of ice‐mass dimensions agree with independent reconstructions of palaeobathymetry (no greater than 20 m) derived from storm‐deposited hummocky and swaley cross‐stratified facies that fill the scour. Data presented here aid the identification of ice‐scour structures and turbated sediment in the ancient record; despite being a common process on modern high‐latitude shelves, descriptions of ancient structures and facies are few.

FUZZY PARTITIONING SYSTEMS FOR ELECTROFACIES CLASSIFICATION: A CASE STUDY FROM THE MARACAIBO BASIN

This paper describes a method of advanced data processing for the inverse problem of lithofacies prediction from well logs using fuzzy partitioning systems. A fuzzy partitioning system consists of a set of fuzzy If‐Then rules of the form “If bulk density (pb) is low and neutron porosity (øCNL) is high Then classify pattern x=(pbøCNL) as Fades Fi”. In this paper, we introduce an intelligent method for the problem of fuzzy rule generation based on fuzzy clustering. Fuzzy clustering is used to detect structures in the multidimensional space of the available well log readings. Each cluster detected is a potential fuzzy classification rule. By applying fuzzy validity measures an optimum number of fuzzy clusters can be found. Using this approach, the number of rules, the antecedent membership functions and other parameters that constitute the fuzzy partitioning system are derived in an automatic way.The aim is to find a minimum set of fuzzy classification rules that can correctly classify all log training patterns. Unlike traditional methods of predicting lithofacies, this approach does not require prior knowledge about the partitioning of the well log readings or any assumption of the facies probability densities. Computer simulations using selected well log responses and facies description from a clastic and carbonate sequence in the Maracaibo Basin (western Venezuela) examine the performance of the fuzzy rule‐based classification approach. The performance of the fuzzy classification method is evaluated against the fades classification results using conventional statistical analysis.

Short- and long-term sedimentation on Montportail–Brouage intertidal mudflat, Marennes–Oléron Bay (France)

The intertidal mudflat of Montportail-Brouage is 4 km wide and extends over about 30% of intertidal area of the Bay of Marennes-Oléron. The sampling area was a cross-shore transect (east–west) in the mid-part of the mudflat, so as to overlap the different geomorphological features, from the shore to the central channel. Particularly distinctive were zones of shore-oblique ridges and runnels, and small channels. The short-term erosion-sedimentation processes related to these bedforms, and their effects on the long-term stability of these structures are poorly known. Thus, sediment budget is difficult to assess in the long term, due to temporal variations. Monthly sedimentological surveys were performed from March 1997 to May 1998. Six stations were sampled by coring for determination of water content, dry density, grain size and carbonate content of the sandy fraction, measured on the topmost 5 cm. Within the ridge and runnel zone, this sampling was done on both structures along with the determination of depth profiles of macrofauna species. Radiographic profiles to a depth of 50 cm were made at each of the 6 stations for description of the sedimentary facies, and radioisotope profiles ( 7 Be, 210 Pb exc ) were made at four stations. Wet bulk density appeared to be roughly constant (1.39–1.44 kg m −3) over the whole mudflat below 2 or 3 cm. For the levels 0–1 and 1–2 cm, the bulk density showed much more variation, in particular in the runnels. These variations were due to episodic deposits of fluid mud (wet bulk density <1.25 kg m −3). The sand content decreased from the lower part of the mudflat to the upper part, particularly in the fluid mud. On the contrary, the carbonate content of the sand fraction increased in the upper part by accumulation of foraminifera associated with shell lag deposits. 7 Be measurements revealed a short-term sedimentation of fluid mud (up to 21.04 cm yr −1), particularly in runnels from the upper mudflat, thus indicating a temporary deposit, easily resuspended by wave action. 210 Pb exc measurements showed a long-term sedimentation rate which was 4 times higher in the lower part (0.97 cm yr −1) of the mudflat (near oyster reefs and mussel “bouchots”) than in the upper part (0.26 cm yr −1). In the middle mudflat, ridges and runnels exhibited a large difference of the long-term sedimentation rates, 0.70 cm yr −1 on ridges and only 0.07 cm yr −1 in runnels, that could be considered as a passageway for fluid mud transport. In the middle mudflat, where ridges and runnels occured, synopsis of observations indicated that a 30 yr old and 18 cm thick ridge layed on a more than 100 yr old basement mudflat. This bedform is maintened through short- and long-term sedimentations. In the runnels, always flooded by water even at low tide, the short-term sedimentation was 21.04 cm yr −1, but these sediments can be easily resuspended by tidal currents, inducing a weak long-term sedimentation (0.07 cm yr −1). In the ridges, the short-term sedimentation was 7.27 cm yr −1; however, due to potential impacts of drying processes, along biostabilization by epipelic diatoms during subaerial exposure at low tide, the short-term sedimentation contributed to a long-term sedimentation of 0.70 cm yr −1.

Geologically based model of heterogeneous hydraulic conductivity in an alluvial setting

Information on sediment texture and spatial continuity are inherent to sedimentary depositional facies descriptions, which are therefore potentially good predictors of spatially varying hydraulic conductivity (K). Analysis of complex alluvial heterogeneity in Livermore Valley, California, USA, using relatively abundant core descriptions and field pumping-test data, demonstrates a depositional-facies approach to characterization of subsurface heterogeneity. Conventional textural classifications of the core show a poor correlation with K; however, further refinement of the textural classifications into channel, levee, debris-flow, and flood-plain depositional facies reveals a systematic framework for spatial modeling of K. This geologic framework shows that most of the system is composed of very low-K flood-plain materials, and that the K measurements predominantly represent the other, higher-K facies. Joint interpretation of both the K and geologic data shows that spatial distribution of K in this system could not be adequately modeled without geologic data and analysis. Furthermore, it appears that K should not be assumed to be log-normally distributed, except perhaps within each facies. Markov chain modeling of transition probability, representing spatial correlation within and among the facies, captures the relevant geologic features while highlighting a new approach for statistical characterization of hydrofacies spatial variability. The presence of fining-upward facies sequences, cross correlation between facies, as well as other geologic attributes captured by the Markov chains provoke questions about the suitability of conventional geostatistical approaches based on variograms or covariances for modeling geologic heterogeneity.

Integrated Reservoir Characterization Study of a Carbonate Ramp Reservoir: Seminole San Andres Unit, Gaines County, Texas

Summary One of the important issues in constructing geologic and reservoir models is to define geologic frameworks. A geologic framework is fundamental to defining flow units, to interpolating well data, and thereby to modeling fluid flow. For the Seminole San Andres Unit (SSAU), the high-frequency cycles (HFC's) and rock-fabric facies identified on outcrop analogs and cores were used to correlate wireline logs. Reservoir and simulation models of the outcrop and a two-section area of SSAU were constructed with rock-fabric units within the HFC's as a geologic framework. Simulations were performed using these models to investigate critical factors affecting recovery. HFC's and rock-fabric units are the two critical scales for modeling shallow-water carbonate ramp reservoirs. Descriptions of rock-fabric facies stacked within HFC's provide the most accurate framework for constructing geologic and reservoir models, because discrete petrophysical functions can be fit to rock fabrics and fluid flow can be approximated by the kh ratios among rock-fabric flow units. Permeability is calculated using rock-fabric-specific transforms between interparticle porosity and permeability. Core analysis data showed that separate-vug porosity has a very strong effect on relative permeability and capillary pressure measurements. The effect of stratigraphic constraints on stochastic simulation was studied. Geologic models generated by a conventional linear interpolation, a stochastic simulation with stratigraphic constraints, and a stochastic simulation without stratigraphic constraints were compared. The stratigraphic features of carbonates can be observed in stochastic realizations only when they are constrained by rock-fabric flow units. Simulation results from these realizations are similar in recovery but different in production and injection rates. Scale-up of permeability in the vertical direction was investigated in terms of the ratio of vertical permeability to horizontal permeability (kvh). This ratio decreases exponentially with the vertical gridblock size up to the average cycle size of 20 ft (6.1 m) and remains at a value of 0.06 for a gridblock size of more than 20 ft (&amp;gt;6.1 m), which is the average thickness of HFC's. Simulation results showed that the critical factors affecting recovery efficiency are stacking patterns of rock-fabric flow units, kvh ratio, and dense mudstone distribution.

97/02520 Maceral/microlithotype analysis of the Hard-grove grindability of lithotypes from the Phalen coal bed, Cape Breton, Nova Scotia

The coal petrologist seeks to determine the petrographic characteristics of organic and inorganic coal constituents and their lateral and vertical variations within a single coal bed or different coal beds of a particular coal field. Definitive descriptions of coal characteristics and coal facies provide the basis for interpretation of depositional environments, diagenetic changes, and burial history and determination of the degree of coalification or metamorphism. Numerous coal core or columnar samples must be studied in detail in order to adequately describe and define coal microlithotypes, lithotypes, and lithologic facies and their variations. The large amount of petrographic information required can be obtained rapidly and quantitatively by use of an automated image-analysis system (AIAS).An AIAS can be used to generate quantitative megascopic and microscopic modal analyses for the lithologic units of an entire columnar section of a coal bed. In our scheme for megascopic analysis, distinctive bands 2 mm or more thick are first demarcated by visual inspection. These bands consist of either nearly pure microlithotypes or lithotypes such as vitrite/vitrain or fusite/fusain, or assemblages of microlithotypes. Megascopic analysis with the aid of the AIAS is next performed to determine volume percentages of vitrite, inertite, minerals, and microlithotype mixtures in bands 0.5 to 2 mm thick. The microlithotype mixtures are analyzed microscopically by use of the AIAS to determine their modal composition in terms of maceral and optically observable mineral components. Megascopic and microscopic data are combined to describe the coal unit quantitatively in terms of (V) for vitrite, (E) for liptite, (I) for inertite or fusite, (M) for mineral components other than iron sulfide, (S) for iron sulfide, and (VEIM) for the composition of the mixed phases (Xi) i = 1,2, etc. in terms of the maceral groups vitrinite V, exinite E, inertinite I, and optically observable mineral content M. The volume percentage of each component present is indicated by a subscript. For example, a lithologic unit was determined megascopically to have the composition (V)13(I)1(S)1(X1)83(X2)2. After microscopic analysis of the mixed phases, this composition was expressed as (V)13(I)1(S)1(V63E19I14M4)83(V67E11I13M9)2. Finally, these data were combined in a description of the bulk composition as V67E16I13M3S1. An AIAS can also analyze textural characteristics and can be used for quick and reliable determination of rank (reflectance).Our AIAS is completely software based and incorporates a television (TV) camera that has optimum response characteristics in the range of reflectance less than 5%, making it particularly suitable for coal studies. Analysis of the digitized signal from the TV camera is controlled by a microprocessor having a resolution of 64 gray levels between full illumination and dark current. The processed image is reconverted for display on a TV monitor screen, on which selection of phases or features to be analyzed is readily controlled and edited by the operator through use of a lightpen.We expect that automated image analysis, because it can rapidly provide a large amount of pertinent information, will play a major role in the advancement of coal petrography.

Facies deposicionales Holocenas de la Costa de Huelva: propuesta de nomenclatura para litofacies estuarinas

Depositionail holocene facies identified along the Huelva coast, southwestern Spain, are joined mb nine sets: (1.) lateral-fluvial bars, (2> fluvial flood plain, (3> estuarine channel, (4> tidal channel, channel-margin, (6> tidal fiat, (7> tidal delta, (8> salt-marsh and (9) sandy spit. A nomenclature of estuarine lithofacies, descriptive terrninology, as identified in different and rdated coastal environments is proposed. Estuarine lithofacies can be classified according to capital letters to represent lit.hology, small letters for physical sedimentary structures, a Greek letter for burrowing type ane, finally, a number to indicate trw burrowing degree. Nine estuarine lithofacies groups with vanous assoeiations of individual litliofacics aire distinguished: (1) gravels, (2) plant-derived organic accumulations, (~> shell accumulations, (4> burrowed clean sands, (5) unburrowed clean sands, (6> muddy sands, (7> sandy muds, (8> unburrowcd muds and (9> burrowed muds. Depositional facies occurred along the Huelva coast, with indication of every associated estuarine lithofacies group, are interpreted showing their lateral, vertical and longitudinal variability as occurred along the different estuarine domains. The application of the proposed nomenclature contribute to: (1> make the synthesis of the facies showed on the modem estuaries and (2) to facilitate the facies description in the oid estuaries as well as its comparison with thc modern ones.

The Application of Seismic Stratigraphic Methods on Exploration 3D Seismic Data to Define a Reservoir Model in OPL 210, Deepwater Nigeria: ABSTRACT

OPL 210 lies in deepwater on the northwestern flank of the Niger Delta. The partners in this block are Allied Energy and The Statoil and BP Alliance. The license has a 5 year initial exploration phase and carries a 2 well commitment. At present the database comprises a 1 x 1 km grid of 2D seismic across the block, and 450 sq. km of 3D in an area of special interest. A larger 3D survey is planned for 1995. Little is known about the reservoir in the deep water, but we expect our main target to be ponded slope and basin turbidites. As such the bulk of the shelf well data available has little or no relevance to the play type likely to be encountered. Prior to drilling, seismic stratigraphy has been one of several methods used to generate a consistent predictive reservoir model. The excellent quality and high resolution of the 3D data have allowed identification and detailed description of several distinctive seismic facies. These facies are described in terms of their internal geometries and stacking patterns. The geometries are then interpreted based on a knowledge of depositional processes from analog slope settings. This enables a predictive model tomore » be constructed for the distribution of reservoir within the observed facies. These predictions will be tested by one of the first wells drilled in the Nigerian deepwater in mid 1995.« less