Deep-water Clastic Reservoirs Research Articles

Impact of sediment provenance and depositional setting on chlorite content in Cretaceous turbiditic sandstones, Norway

AbstractChlorite minerals, mainly in the form of clay coats, play a critical role in determining the reservoir quality of siliciclastic rocks. They can positively influence reservoir quality by preserving porosity during deep burial, but they can also play a negative role by reducing permeability through pore filling. The main aim of this research is to determine the optimal conditions for chlorite growth in sedimentary basins. This study investigates the Lower Cretaceous turbidite sandstone of the Agat Formation in the North Sea. We used a source‐to‐sink approach to investigate the impact of sediment source composition, chemical weathering and depositional environment on chlorite formation. Understanding the interplay between these processes can help refine exploration and exploitation strategies, optimise hydrocarbon recovery, and reduce exploration risks. Representative samples from two hydrocarbon fields (the Duva and Agat fields) were investigated using petrography, geochemistry, heavy mineral identification and quantification, and U–Pb geochronology of detrital zircons. Our results show a strong heterogeneity in the sediment provenance between the two turbidite systems. In the Duva field, the sandstone is derived from a mixture of mafic and felsic sources, producing Fe‐rich sediments. Intense chemical weathering generates fine fraction materials rich in kaolinite, vermiculite, and hydroxy‐interlayered clays, which are transported into shallow marine settings. Subsequent interaction with seawater results in the formation of glauconitic materials, Fe‐illite, and phosphatic concretions. These Fe‐rich materials are remobilised into deep marine settings, providing precursors for the development of authigenic Fe‐clays such as berthierine and chlorite. Conversely, in the Agat field, the sandstone is predominantly sourced from felsic rocks that underwent low chemical weathering, producing sediment rich in quartz and feldspar with a low amount of clays. With few Fe‐rich materials transported into the basin, the development of chlorite in the Agat field was less pervasive. Basin configuration and depositional environment exerted additional control on chlorite distribution. In the confined turbidite system (e.g. Duva field), chlorite is typically found as coating, whereas in less confined turbidite systems (e.g. Agat field) chlorite shows complex distribution related to depositional environment and dewatering processes. Our findings demonstrate the importance of considering the entire sediment routing system, from source to sink, when predicting chlorite occurrence and its impact on reservoir quality in deep marine settings. This integrated approach can guide exploration and development efforts in deepwater clastic reservoirs.

Hybrid event beds in the proximal to distal extensive lobe domain of the coarse-grained and sand-rich Bordighera turbidite system (NW Italy)

The Upper Cretaceous Bordighera Sandstone of NW Italy is a coarse-grained, sand-rich elongated turbidite system (ca. 15 × 45 km in outcrop) up to 250 m thick, interpreted to have been deposited in a trench setting. The siliciclastic succession interfingers with muddy calcareous turbidites, which become more abundant toward the lateral and distal domains. Bed type associations allow the distinction of a proximal channelized domain which transitions to a more distal lobe domain, characterized by abundant mudclast-rich sandstones and by bipartite and tripartite beds with a mud-rich middle or upper division (hybrid event beds). The transition between the proximal and distal domains occurs over a relatively limited spatial extent (ca. 5 km). The presence of lenticular bed-sets made up of coarse grained and mud-poor sandstones throughout the distal domain suggests that distributary channels were present, indicating sediment bypass further down-dip toward the most distal and not preserved parts of the system. Hybrid event beds - commonly associated with distal and marginal fan environments such as fan fringes - are present throughout the lobe domain and extend for up to ca. 30 km in down-dip distance. They are more abundant in the proximal and axial depositional lobe domain and their appearance occurs within a short basin-ward distance from the inferred channel-lobe transition zone. Flow expansion at the termination of the channelized domain and the enhanced availability of cohesive substrate due to the presence of intra-basinal muddy calcareous beds are interpreted as the key controls on the widespread occurrence of mudclast-rich and argillaceous sandstone beds. The abrupt appearance and the persistent occurrence of such beds across an extensive domain have implications for characterizing bed-scale (sub-seismic) heterogeneity of deep-water clastic hydrocarbon reservoirs.

From qualitative to quantitative interpretation: An interpreter’s guide to fluid prediction in Pliocene to Turonian deepwater turbidites from West Africa to Asia Pacific

To mitigate exploration risk in deepwater settings, subsurface analysis increasingly has to rely on integration of qualitative with quantitative techniques. To predict pay in turbidite sandstones, proven statistical and analytical methods can routinely be run on well and seismic inversion data. However, quantitative interpretation (QI) should begin with a responsible audit of available well logs and seismic data, succeeded by data conditioning, proceeding with quality control, and placing elastic attribute responses within their geologic context. To address these issues, we evaluate geologic controls on porosity change as manifested by overpressure and compaction on calibration and analysis of elastic attributes. Following calibration of seismic inversion data, we provide tutorial-style interpretations of deepwater clastic reservoirs from the Gulf of Guinea, West Africa, to the Sabah trough, Borneo. Case study examples offer interpreters the potential to use workflows surrounding data mining in exploration or during field development. In our first example, a comparison of univariate statistics run on compressional- and shear-wave impedances and Poisson’s ratio is introduced to potentially data mine 3D seismic over turbidite fairways. Joint interpretation of P-wave and S-wave impedances is combined with innovative uses of bivariate statistical analysis for anomaly detection. Additionally, the geologic rationale of interpreting elastic relationships of calibrated attributes, such as Lambda Rho and Mu Rho, is discussed on the seismic scale of a single reservoir layer using a combination of statistical methods and rock physics. Here, qualitative interpretation, via application of principles from seismic stratigraphy and seismic geomorphology, ultimately unlocks ambiguity in rock-physics-driven, quantitative lithology determination, guiding application of QI routines toward correctly predicting the prevailing fluid type. Elastic calibration permits seismic lithofacies classification of Cretaceous turbidite sandstones deposited as middle to lower slope channels canyon-fill and basin-floor channel complexes.

Rapid earth modelling for appraisal and development studies of deep-water clastic reservoirs and the concept of ‘procycling’

Creating earth models for deep-water appraisal and development studies is perhaps the most challenging task confronting the petroleum geologist today. Data are limited (few wells, limited core, untested seismic quality), time is limited and drilling, testing and facilities costs are very high. Uncertainty in geological characterization of the reservoir can have the greatest potential impact on project value. How can a thorough characterization of reservoir uncertainty be made based on limited data and in a timely fashion? A workflow for creation of suites of models for appraisal and development studies of deep-water reservoirs is described. The goal of the workflow is to rapidly construct suites of earth models based on limited data that capture the full range of uncertainty in reservoir characteristics and properties. After characterizing possible distributions for individual parameters, suites of earth models are built in a single step using an experimental design framework, aided by a powerful workflow manager which automates earth model construction. Earth models created using the experimental design framework are seamlessly linked to flow simulation software. Plackett–Burman, folded Plackett–Burman and Full Factorial experimental designs were used in different appraisal and development cases. Multiple experimental designs were produced by adding and modifying uncertainty parameters as additional data arrived, and ideas about the possible character of the reservoir evolved. In the appraisal case described here, 6 experimental designs were made, 388 earth models were created and studied, and 79 of those models were dynamically simulated. The process of quickly building and re-building suites of earth models using experimental designs to address changing perceptions and concerns about uncertainty in reservoir character is termed here ‘procycling’. Procycling is complementary to experimental design studies, in that multiple experimental designs are employed over time: procycling focuses on changes in predictions made by individual experimental design studies. The results of procycling are not necessarily to change the perception of uncertainty (for example the range of possible outcomes), but to anchor what the limits of uncertainty are and what the most important uncertainties are with the given data.

Deep-water clastic reservoirs: a leading global play in terms of reserve replacement and technological challenges

Experience from the exploration for, and development of, deep-water clastic reservoirs offshore NW Europe has provided an important testing ground for new technology and has subsequently been applied globally. In NW Europe, Upper Jurassic, Lower Cretaceous and Paleogene intervals have proven play fairways, all of which retain exploration potential. Ancient, particularly Tertiary, passive margins are identified as the main areas of current global deep-water exploration interest; a review of play characteristics is given. Innovative geophysical data and data analysis play an important role in deep-water clastic reservoir geology. The roles of AVO and seismic inversion are emphasized in the context of direct hydrocarbon indication and reservoir delineation. In areas of modern deep water, when drilling for ancient deep-water clastic targets, the importance of acquiring the right data at the right time is critical to creating robust predictive models.

About this title

This publication reflects a growing appreciation of yhe extent to which turbidite depositional system development is fundamentally affected by basin-floor topography. In the many turbidite and turbidite hydrocarbon reservoirs, depositional patterns have been moderately to strongly confined by pre-existing slopes; thus 'submarine fans' may be far from fan-shaped where constrained by significant bathymetric features. This volume examines aspects of sediment dispersal and accumulation in deep-water systems where sea-floor topography has exerted a decisive control on deposition, and explores the associated controls on hydrocarbon reservoir architecture and heterogeneity. The papers presented here offer a global perspective, which is wide-ranging in terms of approach as well as location, including contrasting reviews and case studies of outcrop, subsurface, modern and experimental systems. This book will be of use both to academic geologists and to geoscience professionals in industry dealing with characterization and modelling of deep-water clastic reservoirs.

Seismic Characteristics of Large-Scale Sandstone Intrusions in the Paleogene of the South Viking Graben, UK and Norwegian North Sea

Abstract Post-depositional remobilization and injection of sand can significantly change the geometry of deepwater clastic reservoirs. Features associated with these processes are particularly well developed in the lower Paleogene of the South Viking Graben of the UK and Norwegian North Sea. Seismic scale sandstone intrusions can be grouped in two classes. Class 1 comprises low-angle (20-40 degrees) tabular sandstone intrusions emanating from steep-sided in situ sand bodies within the Balder Formation. The intrusions may be 5-30+m thick and crosscut 120-250+m of compacted stratigraphic section. They terminate at an unconformity at the top of the Frigg interval where they may have extruded onto the palaeo-seafloor. Class 2 comprises conical sandstone intrusions that emanate some 50-300+m upward from distinct apexes located 400-700+m above the nearest depositional sand body. The conical intrusions may have been sourced from underlying sand bodies by clastic blow out pipes. Both types of intrusions seem to adopt their particular geometry independently of (but occasionally exploiting) polygonal faults within the encasing mudstones. Sandstone intrusions may be highly porous and permeable and are thus important both as reservoirs and as plumbing within thick mudstone sequences.

ABSTRACT: A GIS database for deep-water clastic reservoirs: organization and applications

ABSTRACT: A GIS database for deep-water clastic reservoirs: organization and applications

Sand-Rich Fairways in Deep-Water Clastic Reservoirs: Genetic Units, Capturing Uncertainty, and a New Approach to Reservoir Modeling

Correlation in sand-rich deep-water clastic reservoirs using sedimentary characteristics is examined using well-exposed outcrop data. Individual bed thickness, or the sedimentary characteristics of single beds, and packages of beds when viewed in one dimension are found to give an inadequate basis for interwell correlation over distances greater than 100 m. Offset stacking of beds is the main control over bed thickness variations with scouring playing a minor role. Composite units are identified that can be traced over kilometer-scale distances. These units are potentially identifiable on seismic data and are valuable for interwell-scale reservoir modeling. Pinch-out of sand units is characterized in two end-member styles, onlap and infill. Onlap and infill indicate the influence of paleotopography on deposition, reflecting deposition onto low and high relief, respectively. Onlap is characterized by gradual deterioration of reservoir quality toward the pinch-out, whereas infill maintains good reservoir quality without significant deterioration close to the pinch-out. Prediction of the proximity of 1-D (one-dimensional) sections to termination of reservoir units at a pinch-out is problematic for both styles. Although 1-D sections provide invaluable data for reservoir characterization prediction of 3-D (three-dimensional) sand body geometry from borehole sections is problematic. Commonly cited channelized and lobate sandstone body geometry does not have diagnostic sedimentary features and recognition of alternative sand body geometry is needed. The difficulty in selecting key, small-scale sedimentary features that, in turn, are diagnostic of larger scale geometric features limits their value in the up-scaling of reservoir characteristics. A new approach to reservoir modeling of sand-rich deep-water clastic reservoirs is proposed that involves down-scaling from mapping of seismically detectable, interwell-scale packages of beds and the paleotopography on which they lie. Once these features are constrained smaller scale characteristics are modeled.

Abstract: Correlative Units And Reservoir Modelling In Sand-rich Deepwater Clastic Reservoirs 

Abstract: Correlative Units And Reservoir Modelling In Sand-rich Deepwater Clastic Reservoirs 

Producibility and Characteristics of Oil and Gas Fields with Deepwater Clastic Reservoirs: ABSTRACT

Producibility and Characteristics of Oil and Gas Fields with Deepwater Clastic Reservoirs: ABSTRACT

Structural/Stratigraphic Reconstruction of Frontal Choctaw"Triangle Zone Within Oklahoma Atoka Trend: Early Controls (Prethrusting) on Deposition of Deep-Water Clastic Reservoirs"

A structural and stratigraphic study in S.W. Oklahoma, encompassing approximately 30 townships in Atoka, Coal and Pittsburg counties, was completed, using several hundred wells, surface geologic maps and more than 400 miles of 1980's vintage seismic data. Tsopach maps were made of six Atokan sands, covering various areas, all within a deep water fan setting. Structural balancing was carried out on numerous geologic cross sections of six miles or less, for log correlation of the various reservoirs and structural details within the frontal "Choctaw" triangle zone. Two regional cross sections were made based on 12 and 16 miles, respectively, of recent high fold CDP seismic lines, with a minimum of one well per mile control, dipmeter data and surface geology. These cross-sections were reconstructed by line balancing, to illustrate the amount of thrusting in the section and the pre-Penn normal faulting that subtly control the Atoka sands depositional framework. The thickest and most channelized sands are found downthrown to these earlier faults, with this past relationship now obscured by post-Atokan thrusting. * Previously...Sr. Geophysicist-Arkla Exploration, Shreveport, La. ++Previously...Arkla Exploration, Shreveport, La.

Deep water clastic reservoirs in the Gulf of Mexico: A depositional model

A conceptional model has been developed relating the deposition of thick sand sequences in deep water regions of the Gulf of Mexico to episodes of high volume Mississippi River discharge. In accordance with the model, coarse sand units are deposited by turbidity currents as submarine fans on the lower slope and in the deep basin during periods of rapid glacial melting. These sands are predicted to be more extensive and cleaner than those deposited under glacial and interglacial conditions. Evidence supporting this interpretation is provided from projections of the high rates of river discharge and sediment transportation at the end of the Wisconsin glacial epoch.