Jean Borgomano

Critical porosity and elastic properties of microporous mixed carbonate-siliciclastic rocks

By integrating elastic-property measurements and quantitative mineralogic and petrographic analyses of 45 mixed carbonate-siliciclastic samples from two wells drilled in Late Cretaceous rock of the South Provence Basin (southeast France), we can (1) identify and quantify the parameters controlling elastic properties; (2) demonstrate that micrite can be considered as a porous medium with a low critical porosity, averaging 18%; and (3) relate diagenetic transformations, pore-structure modifications, and elastic-property changes. Microporous carbonates with compact anhedral and euhedral microrhombic micrites display a steeper decrease in compressional and shear velocities with increasing porosity than do carbonate rocks with moldic, intergranular, or intercrystalline macroporosity. The low value of critical porosity estimated in micrites (18%), as well as the steep slopes of velocity-porosity relationships at low porosity, is believed to result from a pore-network geometry characterized by very flat, thin pores bounded by planar faces of micrite crystals. Cementation of microrhombic micrite steeply increases elastic moduli, whereas dissolution processes significantly increase porosity with low variations of elastic moduli. Thus, critical-porosity concepts can help describe and model elastic properties of micritic microporous carbonate.

Stratigraphic well correlations for 3-D static modeling of carbonate reservoirs

The principles and purposes of stratigraphic well correlation in carbonate sedimentary systems are defined and discussed within the context of static reservoir modeling. The challenge of well correlations is to relate the heterogeneities measured at core and well scales to the spatial heterogeneities at reservoir and flow unit scales. The introduction of a priori knowledge in the process of stratigraphic well correlation is critical to support the stratigraphic rules and to establish a coherent geological and petrophysical concept. The links between well correlation and geostatistics are discussed with regard to the stationarity hypothesis and property trend analysis. We stress that wells are incomplete and biased samples of the geological reality, which is not dependent, unlike the dynamic reservoir behavior, on the well numbers, location, and spacing. Stratigraphic rules are applied as a function of the well spacing relative to the geological reality. A simple trigonometric method, combining angle of base profile, paleobathymetry, and well spacing, is introduced to check the validity of the well correlation in carbonate ramp-like systems. Two models, based respectively on outcrop and subsurface with seismic data, are discussed in detail to show the combined influence of the data set, sedimentary systems, and diagenetic transformations on stratigraphic well correlations.

Characterization of karstic networks by automatic extraction of geometrical and topological parameters: comparison between observations and stochastic simulations

Abstract Although karstic networks may have a major impact on fluid flow in reservoir characterization, they exhibit great intrinsic heterogeneity that makes their characterization very complex. This work proposes an integrated workflow to study and stochastically simulate karstic networks. This approach is based on the study of outcropping caves. Topological and geometrical parameters are automatically extracted from cave surveys. The extracted geometrical parameters are used to determine the input parameters of the stochastic simulations. These simulations utilize a structure-based, pixel-based and geostatistical approach. To check for consistency, a procedure is proposed to compare the topological and geometrical parameters of observed and simulated karst networks using multivariate analyses. The proposed integrated workflow has been successfully applied to a real case study involving karsts in Jurassic limestone from the south of France. The obtained karstic networks reproduce observed topological and geometrical parameters even when the employed simulation approach relies solely on geometrical parameters.

Three‐dimensional structural modeling of an active fault zone based on complex outcrop and subsurface data: The Middle Durance Fault Zone inherited from polyphase Meso‐Cenozoic tectonics (southeastern France)

The objective of this study was to realize a three-dimensional (3-D) geological model of the deep basin structure of the Middle Durance region (of folds and faults) by integration of geological and geophysical data, and to evaluate its fault geometry and tectonic history. All of the available geophysical and geological data were compiled in three dimensions using the gOcad geomodeler. The geological and geophysical data were used to build a 3-D geological model of the Middle Durance region. The data on the 3-D geometry of fault surfaces and stratigraphic horizons and the thickness maps of the main stratigraphic units are supported by the 3-D geological model. We show that the Middle Durance Fault cannot be interpreted as a single fault plane that affected the entire Meso-Cenozoic sedimentary layers and the Paleozoic basement but as a listric segmented faulting system in sedimentary layers, rooted in Triassic evaporites and a normal block faulting system in the basement. This decoupling level in the Triassic layers reveals thin-skin deformation, formed by strong mechanical decoupling between the Mesozoic sedimentary cover and the Paleozoic basement. This study also confirms that the Provence geological structure has resulted mainly from Pyrenean deformation, which was partly reactivated by Alpine deformation. We demonstrate that the Middle Durance Fault Zone is a transfer fault that accommodates deformation of the sedimentary filling of the South-East Basin through modified fold geometry over a zone of 7 km to 8 km around the main segment of the fault zone.

Insights of 3D Geological Modelling in Distributed Hydrogeological Models of Karstic Carbonate Aquifers

Flow simulation in karstic aquifers with distributed hydrogeological models may be used to numerically model the spatial distribution, the connectivity and the geometry of the karstic network. A new approach is proposed to characterize the karstic network and to reproduce it by the use of 3D geological modelling. The observed karstic network is first decomposed into sets of unidirectional elements which are analysed in 3D with variograms in term of dimension and distribution. These sets of karst directions are then stochastically simulated in 3D in a curvilinear grid that is consistent with the orientation of inception horizons. Several probability maps or 3D probability fields can be added as secondary data in order to constrain the distribution and the connectivity of the simulated karstic network.

Relevance of the stochastic stratigraphic well correlation approach for the study of complex carbonate settings: application to the Malampaya buildup (Offshore Palawan, Philippines)

Abstract The stochastic stratigraphic well correlation method considers the stratigraphic correlation of well data as a set of possible models to sample and manage uncertainty in subsurface studies. This method was applied to the Malampaya buildup (a well documented offshore gas field located NW of the Palawan Island, Philippines), aged upper Eocene to lower Miocene. Previous studies highlight that rock petrophysical properties are mainly controlled by diagenesis. Correlation rules are thus developed in order to adapt the stochastic stratigraphic well correlation method to the study of diagenetic units. These rules are based on wireline log shape and diagenetic units types. Four stratigraphic correlation models are generated using the proposed correlation method: a deterministic one corresponding to the most probable model considering only well data and three stochastic ones. These correlation models are bound with geostatistical methods to build static reservoir models. Synthetic seismic profiles are computed from facies models conditioned to acoustic impedance models. It leads to comparable seismic amplitude images, highlighting the importance of considering several well correlation models for one given seismic survey. Stochastic stratigraphic correlations are shown to have a first-order impact on reservoir unit characterization, rock volumes and fluid flow response on the reservoir model.

Three-dimensional structural model of composite dolomite bodies in folded area (Upper Jurassic of the Etoile massif, southeastern France)

The three-dimensional (3-D) geometry of fractures and fault-related dolomite is difficult to access with classical subsurface prospection tools. Therefore, we have investigated an outcrop to improve the subsurface prediction for complex dolomite bodies. This outcrop is located in the Etoile massif (southeastern France) within a fault-bend anticline. The sedimentary units are of Upper Triassic to lower Barremian age. The fold results from the Pyreneo-Provencal shortening during the Late Cretaceous to the Eocene. The anticline hosts three types of dolomite bodies: (1a) massive dolomite of middle to late Oxfordian age, (1b) syndepositional stratabound dolomite of Tithonian age, and (2) isolated dolomite bodies associated with fractures and faults. Large-scale geometries of fault-related dolomite bodies have been modeled in 3-D. The 3-D geometries of these bodies show diapir-, finger- and wall-like structures. These bodies are located close to the main thrusts, in strata of middle Oxfordian to early Barremian age and are linked to the compressive fold-bending phase during the Late Cretaceous. Fault-related dolomitization occurred because of magnesium removal from the hydraulic brecciation and the pressure solution of type 1 dolomite with overpressured fluids. These fluids flushed upward along the main thrust and laterally by following the reservoir property contrasts in the host rocks. Fault-related dolomite bodies are either spread far apart from faults in grainy limestones with good initial reservoir properties or are restricted to fault vicinity in muddy limestones with poor initial reservoir properties. The study of the structural and stratigraphic framework was essential in the understanding of the dolomitization process.

The Apulia Carbonate Platform—Gargano Promontory, Italy (Upper Jurassic–Eocene)

The Upper Jurassic to Eocene carbonate rocks of the Gargano Promontory belong to the Apulia Carbonate Platform (ACP) and provide a spectacular and complete succession of slope and base-of-slope resedimented gravity flow carbonates with preserved reservoir properties and, with its coeval carbonate platform, displaying various tectonostratigraphic architectures. The ACP margin is characterized by an overall aggrading architecture, and different geometric and depositional features. Facies types and sedimentary dynamics of the carbonate slope and gravity deposits can be analyzed with respect to the stratigraphic architecture of the platform-to-basin transition. These outcrops are the only analogs of some important oil reservoirs and plays present in the equivalent slope to basin succession in the Adriatic offshore and elsewhere.

Characterization of the Devonian Kharyaga carbonate platform (Russia): Integrated and multiscale approach

ABSTRACT The Devonian carbonate platform (Obj-2) of the Kharyaga field (Russia) has been operated by Total since 1999 and produces 42° API oil, rich in H2S. A multidisciplinary (sedimentological, structural, stratigraphic, and geomechanical modeling) and multiscale study was made of the field, integrating seismic, micro-resistivity log, and core data to characterize the reservoir. The Kharyaga carbonate platform is characterized by complex relationships among sea-level variations, subsidence, and sedimentation rates. The field is divided into a platform edge (barrier zone) in the southern area, and back barrier and lagoon environments to the north, each characterized by different facies distribution and dynamic behavior. The platform shelf and the reef flat show dome-shaped thrombolites; the back barrier is characterized by grainstone shoals associated with columnar stromatolites, whereas the lagoon comprises peloidal wackestones and packstones associated with laminated fenestral stromatolites. Significant and prolonged subsidence, in both the lagoon and the platform edge, is associated with partial emergence of the platform reef, as shown by karst development. Seismic interpretation highlighted both underlying north-south structures and syndepositional east-west collapse faults along the southern barrier edge. Two-dimensional and three-dimensional sedimentological modeling of the Obj-2, calibrated by well data and core analyses, allowed the simulation of alternative scenarios to explain the evolution of the carbonate platform during the Devonian and suggested the observed facies distribution is compatible with the presence of a fixed outer platform edge represented by east-west faults. The carbonate platform of the Kharyaga field exhibits complex behavior; hydrocarbon (HC) accumulation and flow is controlled by the interplay of primary porosity, karst distribution, and structural discontinuities (faults and fractures). Besides the role of the karstification, this paper mainly focuses on the role played by tectonic structures on the evolution of the carbonate platform and on the HC flow. From drill stem test data, east-west faults and karsts are considered as major permeability heterogeneities, but interference tests showed more complex fluid pathways at the smaller scale. Microresistivity images show dominant northeast-southwest and northwest-southeast fracture sets in the central barrier, forming an interconnected flow network with the seismic faults. Geomechanical modeling suggests that these fractures are subseismic structures linked to inherited, deep-seated faults active at the time of fracturing, in addition to the listric reservoir faults.

A Transition from a Passive to a Tectonically Active Margin and Foreland Basin Development in the Late Cretaceous of the Fars Area and Offshore (Zagros)

The northeastern margin of the Arabian plate in the Fars Area was influenced by a series of tectono-sedimentary events during the Late Cretaceous. These events are well documented by significant variations in sedimentary facies and sedimentation patterns and thickness. The presence of igneous dikes is another significant phenomenon at the top of Cenomanian platform. Nine regional transects parallel and perpendicular to the Zagros trend were prepared. These transects vertically contain three tectono-sedimentary phases: Phase I (Late Albian to Turonian), Phase II (Coniacian to Late Campanian) and Phase III (Late Campanian to Maastrichtian). Phase I is characterised by shallow-water carbonate platforms bordering intrashelf basins. Eustatic sea-level variations can be the main factor controlling the accommodation space in parts of the area, whereas to the southeast the role of the regional and salt tectonic are more dominant. Phase II is marked by major changes in the depositional environments and sedimentary facies, as a result of obduction and foreland basin creation. The pelagic marls host large volumes of carbonate and siliciclastic gravity flows and far-traveled radiolarites and ophiolites as well as thrust slices of older carbonates. Phase III is dominated by pelagic facies interfingering with shallow-water Omphalocyclus and Loftusia-bearing facies.