Reservoir Analogue Research Articles

Modes and timing of fracture network development in poly-deformed carbonate reservoir analogues, Mt. Chianello, southern Italy

Structural and paleostress analyses carried out on a kilometre-sized outcrop of allochthonous shallow-water carbonate units of the southern Apennines allowed us to unravel a superposed deformation pattern associated with plate convergence. The reconstructed tectonic evolution involves: (i) early extensional faulting and fracturing associated with bending of the foreland lithosphere during forebulge and foredeep stages (including the development of both ‘tangential’ and ‘radial’ normal fault and tensile fractures; Early-Middle Miocene); (ii) large-scale thrusting and folding (Late Miocene); (iii) transcurrent faulting (including two distinct sub-stages characterized by different remote stress fields; Pliocene-Early Pleistocene), and (iv) extensional faulting (late Quaternary). Stage (i) normal faults – generally occurring as conjugate sets – and related fractures and veins are variably deformed and overprinted by later horizontal shortening. Despite having experienced such a long and complex structural history, the studied carbonates are characterized by a ‘background’ fracture network – including two joint/vein sets orthogonal to each other and to bedding – that appears to be associated with the early fault sets that formed during the first (foredeep/forebulge-related) deformation stage. Therefore, away from younger (Late Miocene to Quaternary) fault zones, the permeability structure of the studied carbonates appears to be essentially controlled by the early, inherited fracture network. As a similar fracture network is likely to characterize also the buried Apulian Platform carbonates, representing the reservoir units for major oil fields in southern Italy, our results also bear possible implications for a better understanding of fluid flow in the subsurface and related hydrocarbon production.

Upper Albian rudist buildups of the Edwards Formation in central Texas: A GPR-assisted reservoir analog study

Albian rudist-associated shallow water carbonates form important hydrocarbon reservoirs in the Middle East, Mexico, and the United States. Outcrops of rudist-bearing shallow water carbonates are common across parts of central Texas, USA, and in places display lateral and vertical relationships that form important analogs for the subsurface distribution and heterogeneity of hydrocarbon reservoirs and seals. In particular, the walls and spillways of several lakes in central Texas provide ideal conditions for the investigation by ground-penetrating radar (GPR) of the three-dimensional geometries of platform interior rudist lithofacies belts.This study integrates outcrop studies and GPR surveys to clarify lateral and vertical facies relations of rudist-bearing lithofacies in the Cretaceous Edwards Formation (Fredericksburg Group) that are partially exposed in spillways and gullies near Lake Georgetown and Belton Lake in central Texas, USA. GPR data illuminated four types of mounds that have distinct three-dimensional geometries, lithofacies, and biota and that record both seaward to leeward changes and vertical changes from below wavebase to within wavebase. The lowermost mounds are high relief circular caprinid mounds that mark the aggradational part of the Edwards lithostratigraphic unit at our study locality. Well cemented, low relief toucasid–foraminiferal mounds and grainstones cap these caprinid-dominated buildups. Weakly cemented, circular, flat-topped radiolitid–caprinid–toucasid mounds developed above the toucasid mounds and low relief, often sucrosic-dolomitized mounds constitute the most shallow water rudist accumulations. Stromatolitic dolomites record final filling of accommodation space on the Edwards platform. GPR provides an unparalleled view of the three-dimensional growth, vertical accretion, and progradation of these mounds and lithofacies through time, and the geoelectrical signatures provide insight on porosity and permeability of the lithofacies in outcrop.

Incised valleys in marginal-lacustrine depositional environments: a new reservoir analogue from Lake Eyre, central Australia

Incised-valley fill deposits can form important hydrocarbon reservoirs and provide pathways for hydrocarbon migration. Incised-valleys formed in marginal-marine environments are well described, however, marginal-lacustrine incised-valleys have been the focus of extremely few investigations and are poorly understood. This paper provides a new description of incised-fluvial systems that are presently constructing terminal deposits in embayments around the shoreline of Lake Eyre, central Australia. It is anticipated that better awareness of such deposits will assist in the recognition of these depositional environments in the rock record, which should be useful for exploration purposes and for the generation of improved models for continental dryland fluvial-lacustrine reservoir deposits. A classification of all significant river mouth deposits around Lake Eyre (width >300 m; n = 104), from topographic map and satellite image data, found that 54% are incised-valleys presently accreting a terminal deposit in a shoreline embayment (playa lake estuary). The depositional elements of three incised-valley systems have been mapped using satellite imagery in a GIS platform, from which element geometries are described. Controls on incised-valley formation are investigated by comparing these observations with evidence for past lake highstands and neotectonics and observations from satellite images, geological map data, and digital elevation model data. The terminal splay deposits of rivers around Lake Eyre are well-used analogues for dryland reservoirs; however, the focus has been on deposits accreting directly onto the playa. It is likely the incised-valleys and terminal deposits in the embayments described here will be of interest to companies exploring in, and producing from, ancient drylands and other lacustrine depositional environments.

A new workflow for carbonate reservoir modelling based on MPS: shoal bodies in outcrop analogues (Triassic, SW Germany)

Abstract This study presents a workflow for 3D modelling of carbonate reservoirs using multiple-point statistics (MPS) in the framework of a pre-existing model. It consists of the following steps: (1) applying a hierarchical classification scheme for carbonate geobodies; (2) based on this classification, retrieval of relevant data from Carbdb, a novel software to manage a database of analogue studies; (3) construction of training images based on the retrieved data from Carbdb; and (4) using the training images when building a 3D reservoir model with MPS. MPS makes use of training images to capture depositional patterns, which will then be reproduced during the stochastic simulations. Carbdb provides a library of quantitative data such as dimensions, geometries and the distribution pattern of geobody analogues necessary for building training images. The MPS workflow was applied to carbonate shoal bodies from a reservoir analogue, the Muschelkalk in SW Germany. Present-day shoal bodies from the Arabian Gulf were retrieved from Carbdb as possible modern analogues to generate training images. The realizations of this MPS approach are compared with a previously established 3D geocellular model that was built deterministically by interactive facies modelling. The MPS simulations produced geologically more realistic facies distributions with higher facies heterogeneity, similar to the depositional patterns observed in modern analogues.

CARBONATE GEOBODIES: HIERARCHICAL CLASSIFICATION AND DATABASE – A NEW WORKFLOW FOR 3D RESERVOIR MODELLING

Quantitative data on geobodies are crucial for reservoir modelling. Although abundant quantitative data are available in the literature for siliciclastic depositional systems, equivalent data for carbonate systems are scarce. In this paper we introduce a new approach to the management of quantitative data on carbonate geobodies which is based on a hierarchical classification scheme. The classes to which a carbonate geobody are assigned are: (1) depo‐time (i.e. geological age); (2) depo‐system (i.e. type of carbonate platform); (3) depo‐zone (i.e. facies belt or zone); (4) depo‐shape (i.e. geometry of the geological body); (5) depo‐element (i.e. architectural elements present); and (6) depo‐facies (litho‐ and biofacies). This hierarchical classification is complemented by a set of rules for modifying depo‐shapes which refer to their spatial distribution and patterns of interaction.Based on this classification, an extensive database has been developed which can be used for 3D reservoir modelling. The database holds more than 600 case studies from outcrop analogues and the subsurface and also from satellite images of modern carbonate settings. The database can be used as the basis for a new workflow for reservoir modelling which uses multiple‐point statistics (MPS). MPS makes use of training images to capture and reproduce facies patterns and geometries during stochastic simulations.The application of this new approach is demonstrated by modelling a Cretaceous outcrop reservoir analogue from southern France. The use of MPS allows the generation of geologically realistic and complex facies distributions in the model based on the simplified training images.

FACIES ARCHITECTURE OF KOOKFONTEIN SHELF EDGE DELTA, TANQUA-KAROO BASIN (SOUTH AFRICA): IMPLICATIONS FOR FACIES ANALYSIS AND MODELLING

In recent years, the construction of accurate geological models and subsequent upscaling for reservoir simulation are commonly built from an integration of subsurface and surface datasets. Surface data can supply additional information on facies variability and small scale heterogeneity needed for a robust reservoir model, yet impossible to attain from subsurface data. This study therefore presents an outcrop characterisation study of the Permian Kookfontein deltaic succession using a combination of detailed sedimentary log, gamma-ray log and photopanel analysis. Based on texture and sedimentary structures, twelve depofacies are recognised which are broadly grouped into four lithofacies associations i.e. sandstone facies, heterolithic facies, mudstone facies and soft-sediment deformation facies. Following a hierarchical procedure, these depofacies and lithofacies form the basic building blocks for the flooding surface-bounded facies succession (i.e. cycle). Lateral juxtaposition of observed vertical facies variations across each cycle in an inferably basinwards direction exhibits upward change in features, i.e. decrease in gravity effects, increase in waves and decrease in slope gradient of subsequent cycles. This systematic upward transition in features, grading vertically from distal to proximal, represents a deposition of mid-slope to shelf-margin succession exhibiting an overall upward thickening and coarsening with progradational stacking pattern typical of a normal regressive prograding delta. However, in detail, cycles show some anomalies from a purely thickening and coarsening upward succession. Deposition of each cycle is believed to result from: 1. primary deposition by episodic and probably sporadic mouthbar events governed by stream flow dynamics; and 2. secondary remobilisation of sediments under gravity. The architecture and geometry of the ensuing depo-system is interpreted to have been a river-dominated, gravitationally reworked and wave-influenced shelf edge Gilbert-type delta. Widespread distribution of soft-sediment deformation structures, their growth-style and morphology within the studied succession are empirically related to progradation of Gilbert-type mouthbars over the shelf break as well as the slope gradients of the Kookfontein deltaic clinoformal geometry. Apparently, low-slope gradients may have favoured mostly loading and dewatering structures rather than large-scale slumps. Although shale content (shaliness) estimation from gamma-ray logs offers a quick and straightforward way for assessing reservoir potentiality of encountered facies in the field, this is rather crude and therefore its reliability requires detailed petrographic characterisation for confirmation. The described internal heterogeneity in this work is below the resolution (i.e. mm-scale) of most conventional well-logs, and therefore could supplement well-log data especially where there is no borehole image and core data. The combination of ‘descriptive’ facies model and schematic geological model for our specific delta make the results of this study applicable to any other similar ancient depo-system and particularly subsurface reservoir analogue.

Seismic Stratigraphy and Seismic Geomorphology: Insights on Characterization of a Carbonate Reservoir

Seismic stratigraphy and seismic geomorphology provides an indication of a carbonate platform’s internal and external architecture. High quality 3D seismic data integrated with wireline logs and core materials furthers detailed depositional element analysis, lithology prediction and diagenetic modification of the stratigraphic section, which help to build a depositional model, sequence stratigraphy framework and enhance the evaluation of the reservoir potential of this unit and a prediction of fluid flow during hydrocarbon production. This study mainly focus on using 3D seismic data calibrated with core and logs from oil field A to characterize the stratigraphy and geomorphology of the depositional elements of the carbonate reservoir (Aptaian Stage) and infer the process of the deposition where appropriate. Integration of seismic data with well data provides the frame work for reconstruction depositional evolution history the reservoir. The high seismic resolution of the A reservoirs also provides useful analogs for other subsurface reservoirs from similar depositional environments.

Modeling 3D porosity and permeability from GPR data in the Ellenburger Dolomite, central Texas

Three-dimensional porosity and permeability were modeled in an Ellenburger carbonate reservoir analog from 2D crosshole and 3D surface survey ground-penetrating radar (GPR) data. Two-dimensional GPR crosshole velocity tomography, 3D migration of the GPR surface data, and porosity and permeability calibration to GPR attributes results in 3D porosity and permeability predictions that provide a consistent model of the paleocave structures and facies distributions. Picking the maximum instantaneous amplitude of the direct arrival wavelet for velocity tomography reduces uncertainties caused by a low signal-to-noise ratio, uncorrelated noise, and the interference between reflections and critical refractions at the earth/air interface. The GPR velocity is anisotropic with an average vertical to horizontal velocity ratio of 0.93, which is attributed to the dominance of the relatively horizontal orientation of the maximum porosity and permeability. Porosity and permeability trends are influenced by regional northeast-southwest and northwest-southeast striking conjugate fractures associated with the Pennsylvanian Ouachita orogeny and breccia facies generated by three episodes of burial and the resulting paleocave collapses. At depths [Formula: see text] from the present surface, large brecciated dolomite and limestone blocks have low porosity and low permeability. Between a depth of [Formula: see text] and [Formula: see text] irregular fracture orientations and distributions associated with collapse breccias have a higher average porosity and permeability. A deeper zone ([Formula: see text] to [Formula: see text] in depth), has intermediate permeability and porosity. Porosity and permeability could not be calibrated in open voids. Thus, the predictions are applicable to the core-scale to which they were calibrated, but are lower bounds for the whole volume, which contains breccias, karst, and fractures that increase both porosity and permeability at larger scales.

Constructing hydrocarbon reservoir analogues of aeolian systems using ground penetrating radar

Abstract This paper presents a three-dimensional ground penetrating radar (GPR) case study of contemporary dunes from southern Libya that may serve as an analogue for oil and gas reservoirs in aeolian systems. A 30 MHz inline GPR system was used to image an undulating region 260 m wide × 480 m long in less than 4 h, with a line spacing of approximately 1 m at survey speeds of over 30 km/h. The internal aeolian architecture was imaged to a depth of about 40 m. Complex three-dimensional cross-stratification is evident within the resultant 3D data cube. A full range of dune heterogeneity is inferred: facies interaction between lake and dune environments, the course of ancient streams, dune field/sand sheet relationships, bounding surface geometry and primary strata type distribution. Different dune generations are perceived within the survey, with complex superimposed relationships apparent. Near-surface sand sheet and deeper linear dune/barchanoid ridge geometries are revealed. However, it is recognised that the complex pattern of contemporary dune formations in the area may indicate alternative interpretations. Finally, the distribution of appropriate reservoir properties is discussed.

Hydrothermal dolomitization in platform and basin carbonate successions during thrusting: A hydrocarbon reservoir analogue (Mesozoic of Venetian Southern Alps, Italy)

The Early Jurassic dolomitized carbonates in the Venetian Alp, represent a surface analogue of the hydrocarbon exploration targets in Adriatic offshore and Po Plain, Italy. Dolomitization affected the carbonate platform of Monte Zugna Formation (Lower Jurassic) and the Neptunian dikes breccia in the pelagic Maiolica Formation (Uppermost Jurassic–Lower Cretaceous) improving the poro-perm characteristics. Petrography, stable isotope, strontium isotope ratio, trace element and fluid inclusion analyses were carried out on samples from the Monte Grappa Anticline, which is the direct analogue for subsurface. The petrographic analyses showed a first pervasive, replacement dolomitization phase (D1) followed by volumetrically less important dolomite cement precipitation phases (D2, D3, DS). The same, quite wide range of oxygen isotope (−9 to −2‰ V-PDB) is observed in all dolomite types. The δ 13C range is in the positive field of marine derived carbonate (from +0.5 to +3.2‰ PDB). The trace element analysis showed a slight enrichment in Fe and Mn contents in the Monte Zugna dolostones with respect the original limestone. The same dolomite precipitation temperature (up to 105 °C Th) was observed in the replacement and cement dolomites, suggesting a unique dolomitization event. This temperature, largely higher than the maximum burial temperature (about 50 °C), supports a hydrothermal origin of the dolomitizing fluids, which had a seawater to brackish composition. The data collected suggest a hydrothermal dolomitization occurring during to the South Alpine thrusting according to the “squeegee model”. The interpretation is consistent with the dolomitization model proposed for similar Jurassic successions in the Central Southern Alps. This study indicates that the deformed foreland and thrust fold belts carbonates in Po Plain and Adriatic offshore are suitable to be dolomitized, and therefore reflect an efficient hydrocarbon exploration play.

Imaging and characterization of a carbonate hydrocarbon reservoir analogue using GPR attributes

Abstract We adapt and test seismic attributes techniques on a 2-D and 3-D multi-frequency GPR dataset recorded in an abandoned limestone quarry, analogous to a specific set of hydrocarbon reservoirs. Our main objective was to image the vertical and lateral lithological variations, the network of stratigraphic joints and fractures and to characterize the rock mass based on the radar response. We apply semi-automatic horizon mapping techniques using manually picked seeds (control points) on selected attributes, and automatic extrapolation both on in-line and cross-line, starting from seed positions. We also apply Principal Component Analysis (PCA) and cluster analysis on group data with similar multi-attribute response to reduce the total number of calculated attributes by minimizing the interpreter's bias. We compare and validate the results with direct outcrop measures, imaging a hydrocarbon reservoir analogue in 3-D to over 10 m beneath the topographic surface.

Simulating the effect of subseismic fault tails and process zones in a siliciclastic reservoir analogue: Implications for aquifer support and trap definition

Subsurface, intra-reservoir faults have subseismic portions (the fault tail) and process zones that must be considered for a complete evaluation of their role in a reservoir setting. In this paper we show that this subseismic fault domain, generally associated with all seismically mappable faults, may extend several hundred meters beyond the seismically mapped tip point, depending on vertical seismic resolution and fault displacement gradients along strike. We use reservoir modelling and fluid flow simulation of a sandstone reservoir analogue to demonstrate how a low-permeable process zone may generate steep pressure gradients in the reservoir and affect the tortuosity of reservoir fluid flow. Results and examples combined show how small adjustments in fault interpretations in the subseismic domain may significantly affect trap definition, prospect volumes, project economics and selection of exploration well locations. For production settings, we demonstrate how low-permeable fault tails and process zones may increase flow tortuosity and delay water breakthrough, thereby enhancing sweep efficiency and recovery from otherwise bypassed pockets of hydrocarbons in the reservoir. The results also indicate that process zones may contribute to pressure compartmentalization. Finally, a simple methodology for the estimation of subseismic fault continuity is presented.

Quantitative shale characterization of the tidally influenced Sego Sandstone

Vertical permeability is a critical parameter to estimate when modeling tidally influenced deltaic successions. The Campanian Sego Sandstone, in the Book Cliffs of Utah, is an outcrop analog for tidal systems with primary reservoirs being deposited as tidal bars in both confined and unconfined settings. A simple sand-shale model was used to quantify the effective vertical permeability using the shale character of the Sego Sandstone. Shale lengths, widths, thicknesses, and frequencies were measured from high-resolution light detection and ranging point clouds. Shales in confined tidal bars are approximately three times as long (mean, 16.3 m [53.5 ft]) and as wide (mean, 5.52 m [18.1 ft]). Within unconfined tidal bars, shales are roughly equidimensional (mean length, 18.6 m [61.0 ft]; mean width, 18.3 m [60.0 ft]). The different shale dimensions of confined and unconfined tidal bars result in different effective vertical permeability distributions, indicating that these two bar types behave differently under conditions of fluid flow. In analogous reservoirs, composed primarily of tidal bars, it is essential to differentiate and map confined and unconfined tidal environments.

Static connectivity of fluvial sandstones in a lower coastal-plain setting: An example from the Upper Cretaceous lower Williams Fork Formation, Piceance Basin, Colorado

This study addresses the field-scale architecture and static connectivity of fluvial sandstones of the lower Williams Fork Formation through analysis and reservoir modeling of analogous outcrop data from Coal Canyon, Piceance Basin, Colorado. The Upper Cretaceous lower Williams Fork Formation is a relatively low net-to-gross ratio (commonly 30%) succession of fluvial channel sandstones, crevasse splays, flood-plain mudstones, and coals that were deposited by meandering river systems within a coastal-plain setting. The lower Williams Fork outcrops serve as proximal reservoir analogs because the strata dip gently eastward into the Piceance Basin where they form natural gas reservoirs. Three-dimensional architectural-element models (3-D reservoir models) of the lower Williams Fork Formation that are constrained to outcrop-derived data (e.g., sandstone body types, dimensions, stratigraphic position) from Coal Canyon show how static sandstone body connectivity is sensitive to sandstone body width and varies with net-to-gross ratio and well spacing. With a low well density (e.g., 160-ac well spacing), connectivity is low for net-to-gross ratios less than 20%, connectivity increases between net-to-gross ratios of 20 to 30%, and levels off above a net-to-gross ratio of 30%. As well density increases, static connectivity increases more linearly with an increasing net-to-gross ratio. For a 20-ac well spacing, static connectivity can range from approximately 35 to 75% and 45 to 80% for net-to-gross ratios of 10 and 15%, respectively, depending on sandstone body width. Given the lower net-to-gross ratio and continuity of lower Williams Fork deposits, this underscores the importance of representative sandstone body statistics (e.g., sandstone body type, dimensions) to aid in subsurface correlation and mapping and to constrain reservoir models.

Understanding the evolution of syn-depositional folds: Coupling decompaction and 3D sequential restoration

The analysis of basin dynamics and burial evolution requires a good understanding of sediment compaction. Classically, decompaction of sediments is performed in one dimension at a well location, using either a simple compaction/depth relationship or more complex elasto-plastic models. This paper presents a new approach combining sequential decompaction with 3D restoration to allow for a true 3D basin analysis. Decompaction is performed in 3D after each restoration step, thus taking into account possible tectonic events and lateral thickness variations. Care is taken to apply decompaction to ensure volume continuity especially around faults. This approach is particularly suitable for syn-depositional folds whose growth strata constrain tectonic evolution through time. The proposed approach is applied to the sand-rich turbiditic reservoir analogue of Annot (SE France) where two fictitious wells are used to compare the new 3D technique to a well decompaction analysis. Coupling restoration and decompaction leads to an improved assessment of the basin history: an uplift of the underlying units is identified, which was not detected using decompaction on wells only. Such differences may have a significant impact on possible hydrocarbon maturation models of the basin. Moreover, the geometry of the restored and decompacted models can better constrains the basin history, and influence our understanding of potential hydrocarbon migration pathways.

Characterization of stratigraphic architecture and its impact on fluid flow in a fluvial-dominated deltaic reservoir analog: Upper Cretaceous Ferron Sandstone Member, Utah

Fluviodeltaic stratigraphic architecture and its impact on fluid flow have been characterized using a high-resolution, three-dimensional, reservoir-scale model of an outcrop analog from the Upper Cretaceous Ferron Sandstone Member of central Utah. The model contains two parasequence sets (delta complexes), each with five or six parasequences, separated by an interval of coastal plain strata. Each parasequence contains one or two laterally offset teardrop-shaped delta lobes that are 6 to 12 km (4–7 mi) long, 3 to 9 km (2–6 mi) wide, 5 to 29 m (16–95 ft) thick, and have aspect ratios (width/length) of 0.4 to 0.8. Delta lobes have a wide range of azimuthal orientations (120) around an overall east-northeastward progradation direction. In plan view, delta lobes in successive parasequences exhibit large (as much as 91) clockwise and counterclockwise rotations in progradation direction, which are attributed to autogenic lobe switching. In cross-sectional view, parasequence stacking is strongly progradational, but a small component of aggradation or downstepping between parasequences reflects relative sea level fluctuations. We use flow simulations to characterize the impact of this heterogeneity on production in terms of the sweep efficiency, which is controlled by (1) the continuity, orientation, and permeability of channel-fill sand bodies; (2) the vertical permeability of distal delta-front heteroliths; (3) the direction of sweep relative to the orientation of channel-fill and delta-lobe sand bodies; and (4) well spacing. Distributary channel-fill sand bodies terminate at the apex of genetically related delta lobes and provide limited sand body connectivity. In contrast, fluvial channel-fill sand bodies cut into, and connect, multiple delta-lobe sand bodies. Low, but non-zero, vertical permeability within distal delta-front heteroliths also provides connectivity between successive delta-lobe sand bodies.

Scaling and geometric properties of extensional fracture systems in the proterozoic basement of Yemen. Tectonic interpretation and fluid flow implications

Multi-scale mappings of fracture systems in the crystalline basement of Yemen are presented. Fracture datasets are described through statistical analyses of direction, length, spacing, density, and spatial distribution. Results are combined with field observations and can be directly used to model the geometry of the fracture networks in analog basement rocks, from multi-kilometric to decametric scales. The fractured reservoir analog is defined with a dual porosity model in which tectonic and joint systems correspond to the basement reservoir “backbone” and “matrix” respectively. These two end-members reveal contrasting geometrical, reservoir, and scaling properties. In tectonic systems, multi-scale geometries are “self-similar”, the fracture network shows fractal behavior (power-law length distribution and clustered spacing), and fault zones show hierarchical organization of geometrical parameters such as length, thickness, and spacing. In joint systems, the fracture network is scale dependent with exponential length distribution, and shows anti-clustered spacing. However, these two end-members have both well-connected properties, with fault zones acting as main drain and joint systems acting as the fluid supply.

An outcrop-based comparison of facies modelling strategies in fan-delta reservoir analogues from the Eocene Sant Llorenç del Munt fan-delta (NE Spain)

ABSTRACT Sedimentary facies is a key control on petrophysical properties within subsurface reservoirs and facies modelling is a critical aspect of reservoir modelling. Several modelling methods exist and selecting the best approach for a specific case is challenging and time-consuming. Outcrop analogues provide detailed information on architecture, geometry and facies connectivity that is not directly available in the subsurface. By modelling outcrop data it is possible to test and compare different modelling strategies systematically in a case where the geology is well constrained. The Eocene aged, Sant Llorenc del Munt fan-delta complex (NE Spain) is a well exposed, transgressive–regressive fan-delta. Outcrop data were used to test a variety of modelling strategies in which the density of conditioning wells, stratigraphic subdivision, modelling algorithm and trends were all varied. The results of these modelling exercises were compared against themselves and against a close-to-deterministically built Base Case reconstruction using a series of static measures including the distribution of fan-delta front reservoir facies, directional connectivity and reservoir-to-well connectivity. The results highlight the following: (a) the impact of the conditioning well density on improving the stratigraphic architecture reproduction in the different modelling approaches; (b) that surface-based modelling subdivisions including the maximum flooding surface to separate independent grids for modelling the transgressive and regressive sequence sets can be detrimental when compared to using only the top and base of the composite sequence unless additional constraints are included; (c) that an algorithm combining a linear trend and a Gaussian field is the most suitable algorithm for reproducing this type of architecture, but requires defining a 3D trend; and (d) the need for using trends to reproduce the architecture when well data are sparse. These results provide guidelines for modelling analogue fan-delta reservoirs in the subsurface.

Improved statistical multi-scale analysis of fractured reservoir analogues

This paper includes the results of the application of novel methodologies for the statistical analysis of tensile fracture attributes (spacing, density, and aperture). The statistical methods have been applied to a fractured Lower Cretaceous carbonate succession cropping out in the Sorrento Peninsula (Naples area, Italy), representing a geological analogue of buried reservoirs of southern Apennines major oil fields. As fracture networks (observable from outcrop to the crystal scale) can significantly affect the hydraulic behavior of a fractured reservoir, the definition of appropriate models of fracture spacing and aperture probability distribution at various scales represents an important goal of structural analysis. In order to achieve such an objective, sampling has been carried out at different scales, by means of traditional scan lines at outcrop, as well as micro-scan lines carried out both by a digital micro-camera (50×) and by the optical microscope (200×). Fracture spacing and density analysis are mainly aimed at establishing the characteristics of joint spatial distribution over a range of scales. Aperture analysis is aimed at verifying that the aperture cumulative frequency is described by a power law and, in the latter instance, to provide an effective method for a more precise determination of the exponent of the power law. Finally, new expressions are provided, in closed form, in order to calculate the confidence interval of the power-law exponent. The proposed criteria provide handy and effective methods for a significantly improved statistical analysis of fracture attributes.

Seismic interpretation of the Laga basin; constraints on the structural setting and kinematics of the Central Apennines

Abstract: The Messinian Laga basin is the largest foreland basin within the Central Apennines fold and thrust belt (Italy). This area, actively investigated in the 1980s and 1990s for hydrocarbon resources, is considered a valuable analogue for clastic reservoirs developed in confined structural settings. Furthermore, it represents a key area for understanding the evolution of the Apennines, as it links the internal, structurally uplifted Early Miocene fold and thrust belt of the western Central Apennines with the more external and recent belt to the east. Despite several papers published on this area, the only reconstruction of the substratum structure is an internal and classified industry report. During the present study, we had access to a seismic database comprising 200 km of seismic profiles that were collected between 1983 and 1990. These data allowed us to reconstruct the structural setting of the Laga basin substratum, define the lateral continuity of the main compressional structures within the basin, construct a balanced cross-section, and define the shortening values.