Bruno Caline

3D modeling of the Arab Formation (Maydan Mahzam Field, Offshore Qatar): an integrated approach

The Late Jurassic Arab Formation consists of complex carbonate and evaporite facies associations deposited along ramps and intra-shelf Arabian basins, which form large hydrocarbon fields. Most of the time, the 3D reservoir characterization of such reservoirs is challenging, due to superimposed diagenetic overprints. The aim of this paper is to present an integrated approach using original rock-typing and modeling methods for the characterization of the four main reservoirs of the Arab Formation in Maydan Mahzam Field (Qatar). A sedimentological study was conducted on cores, and a sequence stratigraphy framework was developed. Three depositional models are proposed to illustrate the progradation of the Arab D carbonate platform toward the Southeast and the deposition of inner ramp/sabkha facies of the Arab A, Arab B and Arab C reservoirs. Rock-types that are characterized by specific geological, petrophysical and Kr/Pc properties have been defined from cores and thin sections, taking into account log response and SCAL measurements. These rock-types have been extended to all the wells by mean of a semi-interactive statistical classification applied on log data. They have been propagated in a 3D grid using a non-stationary geostatistical approach guided by 3D probability cubes. The probability cubes calculation is based on local vertical proportion curves determined from well sets and from the sedimentological models which cover undrilled areas. This paper contributes to a better understanding of the sedimentology of the Arab Formation in Qatar and helps to refine the regional distribution of the Arab D reservoir facies. It demonstrates that an accurate rock-typing scheme combined with the definition of a sequence stratigraphy framework are of prime importance for building 3D static models, which honor geological concepts for carbonate reservoir simulation.

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.

Interplay between fracturing and hydrothermal fluid flow in the Ason Valley hydrothermal dolomites (Basque-Cantabrian Basin, Spain)

Abstract In Asón Valley hydrothermal dolomite area (Basque–Cantabrian Basin, northern Spain), an overlapping stepover area between two major basement faults, the Cabuerniga and Ruahermosa transtensional faults, was the location for different scales and types of extensive fractures. This fracture mesh affected the Albian Ranero limestone and was formed in a dilational jog, a regional fluid throughflow area. It acted as pathway for overpressured fluids that controlled the dolomite mineralization in the Ranero massif area. The study of synchronous structural features, fluid flow channelling and dolomitization processes indicated their tectonic control. The fluid circulated and concentrated preferentially in more fractured areas with increased permeability, such as extensional chimneys, creating dolomite bodies. Repeated extensive tectonic activity enhanced fracture porosity, promoting overpressured fluid migration and cyclical dolomitization events. The studied fracture pattern suggests the presence of sinistral transtension during the formation of extensional joint-sets that channellized the mineralizing fluid-flow. A gradation in structural features and dolomite facies and textures is visible from the main Pozalagua fault dolomite body to peripheral dolomite bodies as the Breccia body and Ranero megajoints. These differences could reflect a proximal–distal trend from the main fluid-flow area along the Pozalagua fault to the Ranero megajoints.

The carbonate-evaporite lagoon of Al Dakhirah (Qatar): an example of a modern depositional model controlled by longshore transport

Abstract The southern coast of the Arabian Gulf is considered a good example of an arid carbonate depositional system. The objective of this field investigation is to better elucidate the dynamic controls on the character and pattern of the depositional belts in a carbonate-evaporite lagoonal setting. The interpretation of this lagoon is based on combined field examination and laboratory analyses of surface samples, and this has resulted in an updated depositional model for carbonate-evaporite lagoonal settings. This study highlights the effects of sediment transport by longshore currents, with the formation of sand spits that gradually closed the lagoon during their southwards migration. The associated narrow and elongated back-barrier settings consist of tidal-dominated muddy sediments affected by a network of tidal channels. This wave-dominated high-energy system has generated several carbonate barrier and back-barrier units that migrated southwards and seawards during the last few thousands of years. This updated depositional model significantly differs from shoreline-parallel facies tracts of the classical Trucial Coast model, where the dominant wind is orientated perpendicular to the coastline. Conversely to the sediment belts of the Trucial Coast, the Al Dakhirah lagoon displays a strongly asymmetrical pattern of the sediment belts, marked by a southwards and seawards migration.

Tight Chalks - How Does Microtexture Affect Petrophysical and Geomechanical Properties?

High porosity chalks have been extensively studied over the past decades. Only recently, there has been an increasing interest in the understanding of low permeability chalks, forming potential unconventional reservoirs or intra-reservoir seals. In order to better understand the properties of those tight chalks, an integrated petrographical, petrophysical and geomechanical study was carried out on a set of 35 carefully selected outcrop samples, covering a wide range of lithotypes. The dataset gathered covers a broad spectrum of values with regards to determined petrophysical (e.g.porosities from 15 to 45%, pore throat diameters from 25nm to 1080nm) and geomechanical properties (e.g.: strengths from 3 to 50 MPa). The samples have also been characterized in terms of microtextures by integrating both geological and sedimentpetrological data. Tight chalks encompass different lithotypes, but the main factors controlling the microtexture are: (1) the non-carbonate content, either related to sedimentological settings (e.g. argillaceous chalks) or burial diagenesis (e.g. marl-seam chalks); (2) the degree of cementation, either eogenetic (e.g. hardgrounds) or mesogenetic. Those parameters strongly modify chalk microtexture and thus its porous network, reducing pore-throat and pore body sizes hence altering poroperm properties. Beyond petrophysical properties, cementation appears to be the main parameter controlling the strength of chalks.

The Khuff Formation in the Middle East: New Insight into Regional Stratigraphy and Palaeoenvironmental Reconstruction using Bio-assemblages and Facies Analysis

A multidisciplinary synthesis of outcrop and subsurface data of the carbonates and evaporites of the Late Permian Khuff Formation was carried out in order to constrain the spatial and stratigraphic distribution of the depositional facies.