Stratigraphic interpretation of Well-Log data of the Athabasca Oil Sands of Alberta Canada through Pattern recognition and Artificial Intelligence

Dissertation submitted in partial fulfillment of the requirements for the Degree of Master of Science in Geospatial Technologies.Automatic Stratigraphic Interpretation of Oil Sand wells from well logs datasets typically involve recognizing the patterns of the well logs. This is done through classification of the well log response into relatively homogenous subgroups based on eletrofacies and lithofacies. The electrofacies based classification involves identifying clusters in the well log response that reflect ‘similar’ minerals and lithofacies within the logged interval. The identification of lithofacies relies on core data analysis which can be expensive and time consuming as against the electrofacies which are straight forward and inexpensive. To date, challenges of interpreting as well as correlating well log data has been on the increase especially when it involves numerous wellbore that manual analysis is almost impossible. This thesis investigates the possibilities for an automatic stratigraphic interpretation of an Oil Sand through statistical pattern recognition and rule-based (Artificial Intelligence) method. The idea involves seeking high density clusters in the multivariate space log data, in order to define classes of similar log responses. A hierarchical clustering algorithm was implemented in each of the wellbores and these clusters and classifies the wells in four classes that represent the lithologic information of the wells. These classes known as electrofacies are calibrated using a developed decision rules which identify four lithology -Sand, Sand-shale, Shale-sand and Shale in the gamma ray log data. These form the basis of correlation to generate a subsurface model

Evaluating the potential of carbonate sub-facies classification using NMR longitudinal over transverse relaxation time ratio

   While the well log-based lithology classification has been extensively utilized in reservoir characterization, the classification of carbonate sub-facies remains challenging due to the subtle nuances in conventional well-logs. The nuclear magnetic resonance (NMR) log provides extra information of pore size and pore geometry features, improving differentiating carbonate sub-facies. Here we explore the feasibility of using the ratio between NMR longitudinal relaxation time and transverse relaxation time as a potential lithology indicator to determine carbonate sub-facies. We analyzed a series of logging data and corresponding core samples of Arbuckle Group carbonate containing mudstone, packstone, grainstone, incipient breccia, and breccia in northern Kansas for the characteristics of longitudinal relaxation times, transverse relaxation times, and longitudinal over transverse relaxation time ratios. The results show that mudstone, packstone, and grainstone exhibit high, intermediate, and low longitudinal over transverse relaxation time ratios, respectively, while incipient breccia and breccia have a wide range of longitudinal over transverse relaxation time ratios. Furthermore, we evaluated the potential of using longitudinal over transverse relaxation time ratios to classify carbonate sub-facies using multivariate analysis. By adding longitudinal over transverse relaxation time ratios to neutron porosity, total gamma-ray, and conductivity logs as inputs of automated facies classification, the prediction error decreased, especially for incipient breccia. On the contrary, when photoelectric log and computed gamma-ray are also available, adding longitudinal over transverse relaxation time ratios does not improve the accuracy of sub-facies classification. Our results suggest that longitudinal over transverse relaxation time ratio is an independent lithology indicator. However, it cannot replace other logs like gamma-ray and photoelectric logs in classifying carbonate sub-facies. Our study provided valuable evidence and credible elucidation of the importance and physicochemical mechanism of longitudinal over transverse relaxation time ratios, which is essential for deciphering NMR logging data in carbonate reservoirs.Cited as: Zhang, F., Zhang, C. Evaluating the potential of carbonate sub-facies classification using NMR longitudinal over transverse relaxation time ratio.  Advances in Geo-Energy Research, 2021, 5(1):  87-103, doi: 10.46690/ager.2021.01.0

Sequence-Stratigraphic Analysis of the Rollins and the Cozzette Sandstone Members, the Upper Cretaceous Mount Garfield Formation of the Piceance Basin, Colorado.

Sequence-stratigraphic study of the Cozzette and the Rollins Sandstone members, of the Mt. Garfield Formation of the Mesaverde Group, in the southern part of the Piceance basin (western Colorado), utilizes mainly well-log data along with limited outcrop data. Outcrop description of the Rollins Sandstone Member indicates a depositional succession that changes from complex marginal marine deposits at the base to marine wave-dominated shoreface successions at the top. The lower marginal-marine deposits are interpreted to occur within multiple incised-valley fills that nest and form a main stratigraphic element landward, particularly within the uppermost part of the Cozzette Sandstone Member. Incised-valley fills thin basinward. Sequence-stratigraphic interpretation of the subsurface data provides a stratigraphic history similar to that interpreted from the outcrop exposures across a regional realm. The subsurface analysis of the study interval distinguishes 5 depositional sequences that change in thickness throughout the study area and are listed as follows: CZ1, CZ2, CZ3, R1 and R2. The depositional sequence R2 is the youngest incomplete sequence within the study interval. Each depositional sequence is composed of incised-valley fills at the base and highstand deposits with marine shoreface at the top. The incomplete depositional sequence R2 is represented by incised-valley fills alone. The vertical chronostratigraphic architecture of the sequence set (CZ1, CZ2, CZ3, R1) show a regional change in stacking pattern from retrogradational (CZ1, CZ2, and CZ3) to progradational (R1). The turnaround from retrogradational to progradational stacking is probably the stratigraphic limit between the Cozzette and the Rollins Sandstone members; its stratigraphic expression is probably gradational and complex in a landward direction. Incised valleys are superimposed landward, probably along axes between raised mires, and exhibit highly variable log patterns that reflect complex marginal-marine deposits

Shale gas prospectivity studies in the Perth Basin, Western Australia

The Early Permian Carynginia Formation and the Late Triassic Kockatea Shale are prospective shale gas resources in the Perth Basin. Various geological studies such as visual core description and petrography were conducted to understand about the lithofacies and depositional environments in the target formations. Key geochemical parameters such as TOC, thermal maturity and RHP were identified through rock-eval pyrolysis. Petrophysical studies were applied in detecting organic richness and fracability of the under-study shale plays

Identification of technical barriers and preferred practices for oil production in the Appalachian Basin

The Appalachian Basin is characterized by great number of stripper wells and marginally producing oilfields that face a number of production problems. The purpose of this study was to identify the main problematic issues and preferred solutions for oil production in the Appalachian Basin. Investigation and identification of oil production problems and preferred solutions began with searches in the Society of Petroleum Engineer (SPE) library, and Petroleum Technology Transfer Council (PTTC) website. In addition, journals, workshop, conference were used to find additional information. Formal interviews were arranged with oil producers to gain more insight into problems in the Appalachian Basin. Accordingly, the following production problems were identified and ranked in order of decreasing importance: water production, poor understanding of reservoir heterogeneity, limited availability of compatible water for water injection, lack of sufficient reservoir data such as permeability, porosity, and primary production data for reservoir characterization, and paraffin and asphaltene causing operational issues. The technologies that are investigated included: water controls treatment, water-handling methods, and reservoir characterization using Artificial Neural Networks, paraffin and asphaltene control. In addition, corrosion problems and electrical cost reduction are discussed

Subsurface Relationships between the Sebree Trough and Carbonate-Siliciclastic Mixing in the Upper Ordovician Lexington-Trenton and Point Pleasant-Utica Intervals in Ohio, USA, using Multivariate Statistical Well Log Analysis

The Upper Ordovician (lower Katian; upper Chatfieldian-lower Edenian) Lexington-Trenton limestone and Point Pleasant-Utica shale intervals are important subsurface stratigraphic units across Ohio as they are the sources of significant conventional and unconventional hydrocarbon resources. However, both units exhibit anomalous distributions across the state and heterogeneous relationships, especially in areas where they intertongue. The limestone units show a peculiar SW-NE thinning trend across Ohio, whereas the overlying shale units show an anomalous thickening along the same trend—a trend associated with the poorly understood Sebree Trough, a supposed Late Ordovician paleobathymetric low related to the coeval Taconic Orogeny. To explore relationships amon Lexington-Trenton carbonates, Point Pleasant-Utica shales, and the presumed Sebree Trough, multivariate statistical analysis was used to compare geophysical well logs across the state with well logs referenced to the mineral content of 4 Lexington-Trenton-Point Pleasant-Utica cores. Comparing well-log responses with the mineral content of the reference cores allowed the discernment of 10 electrofacies, keyed to lithofacies in the cores. Software analysis of many other well logs across the state then made electrofacies assignments by comparing well-log responses from the other wells with well-log responses from the reference cores preset into the software. Electrofacies responses were color-coded, mapped in wells at 0.6 m (2 ft) resolution, and used to make section lines and isopach maps of similar electrofacies. Isopach maps and cross sections confirm the presence of the Sebree Trough across Ohio, with trends that parallel existing and projected basement structures. This suggests that the Sebree Trough in Ohio was a bathymetric low, which was, at least in part, controlled by reactivation of basement structures due to far-field Taconic stresses

Integração de caracterização de reservatórios com ajuste de histórico baseado em poços piloto : aplicação ao campo Norne

Orientador: Denis José SchiozerTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica e Instituto de GeociênciasResumo: As incertezas inerentes à simulação numérica de reservatórios podem originar modelos com diferenças significativas relativamente aos dados dinâmicos observados. A redução destas diferenças, processo conhecido por ajuste de histórico, é muitas vezes acompanhada por certa negligência da consistência geológica dos modelos, comprometendo a confiabilidade no processo e nas previsões de produção. Para manter a consistência geológica dos modelos, é fundamental integrar iterativamente o processo de ajuste de histórico com a modelagem geoestatística do reservatório. Apesar das diversas abordagens apresentadas nas últimas décadas, este processo de integração continua a ser altamente desafiante. Este trabalho propõe um fluxograma de modelagem geológica integrado com um fluxograma de ajuste de histórico, baseado no conceito do ponto piloto. O método do ponto piloto é uma técnica de parametrização geoestatística aplicada a modelos de reservatório, gerados a partir de um conjunto de dados medidos e de dados sintéticos definidos em outros pontos do reservatório, designados por pontos piloto. Neste trabalho os dados sintéticos correspondem a poços sintéticos e, por isso, designados por poços piloto. A metodologia é aplicada a um reservatório real, o reservatório arenítico de Norne, testando, desta forma, os diferentes procedimentos num cenário de elevada complexidade. Numa primeira etapa, é efetuada uma caracterização das heterogeneidades geológicas através da classificação de electrofacies juntamente com um refinamento do malha de simulação, por forma a obter volumes de fácies e propriedades petrofísicas com elevada resolução. Esta etapa apresenta diversas vantagens: (1) permite-nos mapear as heterogeneidades de pequena escala materializadas por camadas muito finas de folhelho e carbonatos cimentados que poderão atuar como barreiras estratigráficas verticais à dispersão dos diferentes fluídos; (2) permite a definição de novos atributos a serem usados durante a fase de ajuste como permeabilidade e transmissibilidade verticais, diferentes curvas de permeabilidade relativa associadas a diferentes tipos de rocha e, sobretudo, a definição das propriedades a serem incluídas nos poços piloto; (3) aumenta o controle geológico do processo de ajuste de histórico. Após a classificação de electrofacies, os modelos de alta resolução são integrados num processo iterativo entre a modelagem geológica e um processo de ajuste de histórico probabilístico e multiobjectivo guiado por poços piloto. Um dos maiores desafios do método dos poços piloto reside na configuração a adotar (número, localização e propriedades a modificar), sendo a flexibilidade do método uma das suas maiores vantagens. A configuração tem em conta os dados de produção, linhas de fluxo e enquadramento geológico-estrutural. A flexibilidade do método é demonstrada por meio de dois estudos de caso: a geração de figuras sedimentares, como é exemplo, o canal construído no segmento-G; a capacidade para procurar a melhor localização das camadas carbonatadas, altamente restritiva ao deslocamento dos fluídos no segmento C. Em última análise, o processo iterativo de modelagem geológica e ajuste de histórico guiado por poços piloto permitiu obter modelos geologicamente mais fiáveis que honrassem ao mesmo tempo o dado observadoAbstract: The inherent uncertainties in numerical reservoir simulation can lead to models with significant differences to observed dynamic data. History matching reduces these differences but often neglects the geological consistency of the models, compromising forecasting reliability. To maintain the geological consistency of the models, the history-matching process must be integrated with geostatistical modeling. Despite many suggested approaches in recent decades, this integration process remains a challenge. This work proposes a geological modeling workflow integrated within a general history-matching workflow, utilizing the pilot point¿s concept (in this study assuming the form of pilot wells). The pilot point method is a geostatistical parameterization technique that calibrates a pre-correlated field, generated from measured values and a set of additional synthetic data at unmeasured locations in the reservoir, referred to as pilot points. In this study, the synthetic data corresponds to synthetic wells, henceforth referred to as pilot wells. The methodology is applied to a real, complex, sandstone reservoir, the Norne field. The geological heterogeneities are characterized, in detail, through electrofacies analysis and combined with a refined simulation grid, to create high-resolution facies and petrophysical 3D models. This stage has several advantages: (1) allows the mapping of fine-scale heterogeneities generally comprising decimeter shales and calcareous-cemented layers that may act as stratigraphic barriers to vertical fluid displacement; (2) allows the addition of new attributes used during the history-matching stage, such as properties used in the pilot wells, vertical permeability and transmissibility models, and different kr curves assigned to different rock types; and (3) increases geological control over the history-matching process. After analyzing electrofacies, the high-resolution datasets are integrated into an iterative loop between geostatistical modeling and a probabilistic, multi-objective history-matching process, guided by pilot wells. A key challenge using the pilot wells method is to optimize the pilot well configuration (number, location and properties to disturb), and the flexibility of the pilot well method is a principal advantage. The configuration includes production data, the preferred fluid flow paths (revealed during a streamline analysis) and the geological framework. The flexibility of the method is demonstrated in the two case studies presented here: generating specific sedimentary features (e.g. channels in the G-segment) and finding the best location for the cemented stringers responsible for the fluid behavior observed in C-segment. This work shows that the iterative process combining geological modeling and geostatistical-based history matching, guided by pilot wells, created geologically consistent models that honor observed dataDoutoradoReservatórios e GestãoDoutor em Ciências e Engenharia de Petróle

Geological reservoir modelling for Whicher Range Field tight gas sand

A poor understanding of the reservoir properties within the Whicher Range area has led to unsuccessful exploration and appraisal strategies. A key driver for this research is to develop a geological reservoir model on the tight gas sand Permian section in the southern Perth Basin that contribute to the development and production of the field by integrating core, well logs and analogue data within a sequence stratigraphic framework and generating a plausible depositional model that constrained the reservoir architecture and facies distribution over the field

Facies and sequence stratigraphic implications of the Statfjord formation (upper triassic-lower Jurassic), northern north sea, UK

Detailed sedimentological logging of core, and interpretation of wireline logs from the Brent Oil Field, northern North Sea, have allowed for the identification of sedimentary facies and environments of the Upper Triassic-Lower Jurassic Statfjord Formation. The Statfjord Formation is interpreted to have been deposited within a diversity of sedimentary environments. These include delta plain, meandering rivers, braided rivers, tidally influenced fluvial systems and a shallow, high energy transgressive marine environment. Within the fluvially-dominated part, which is by far the most important volumetrically, two distinct facies associations were recognized: channel and overbank. The channel facies association is in turn divided into three discrete end members: low sinuosity, high sinuosity and minor/crevasse channel facies. Similarly, the overbank facies association comprises a variety of sedimentary facies including levee, crevasse splay, swamp, flood plain and rare lacustrine and lacustrine deltas. Low sinuosity channel facies are divided on the basis of their architectural style, into three different types. Type 1 low sinuosity channel facies dominates the northern part of the study area and resembles the sandy Platte River model of Miall (1977). Type 2 low sinuosity channel facies dominates the southern part of the study area and is characterized by numerous internal scour surfaces. This channel type is interpreted to have been deposited within a relatively proximal braided river system. Type 3 low sinuosity charmel facies is a transitional facies between the proceeding two low sinuosity channel types and is similar in character to the South Saskatchewan and the Battery Point River models of Cant and Walker (1978). Documented point bar sediments within the high sinuosity channel facies association indicate that channel bankfull depths may have reached as much as 4.5 m. The lack of evidence of exposure of the in-channel sediments in addition to the thick, consistent bedforms suggest that the rivers were probably of a perennial nature. Palaeoflow indicators obtained form HDT log analysis reveal that the Statfjord Formation m the Brent Field has been deposited by a north to northwest flowing drainage systems. Thorium/potassium cross-plots from NGS logs indicate an upward reduction in sandstone mineralogical maturity which may imply an upward reduction in the degree of reworking of sediments and a least sediment transport. The overall spatial and temporal consistency of the palaeocurrent indicators coupled with the upward decrease of sandstone maturity further indicate that no flow reversal occurred throughout the geological evolution of the Statfjord Formation. Sequence stratigraphic concepts applied in conjunction with detailed facies analysis indicate that sedimentary facies of the Statfjord Formation are arranged within two successive depositional sequences. Although the sequences are incomplete they possess all the attributes of the depositional sequences described by Posamentier and Vail (1988) and Van Wagoner et al. (1990). The lower sequence comprises sediments deposited within a highstand systems tract. The lowermost part is characterised by low net/gross ratio and is interpreted to have been deposited within early highstand systems tract most likely in an upper delta plain setting. As the rate of additional subaerial accommodation space approaches zero during a stillstand and eventually reverses, high sinuosity rivers are thought to have migrated laterally during a late highstand combing the previously deposited fine-grained sediments. The upper sequence overlies a regional sequence boundary unconformity and comprises an early lowstand wedge systems tract which is characterised by braided river sediments deposited during a slightiy rising base level. As the rate of additional subaerial accommodation space increases isolated high sinuosity river sediments are interpreted to have been deposited during a late lowstand wedge systems tract. Cyclic rhythmites reflecting neap-spring-neap tidal cyclicity of a diurnal palaeotidal regime represent the first 'local' major marine flooding. These are probably equivalent to a condensed section in the coeval marine realm and mark the onset of a transgressive systems tract: Continued rnarine transgression is documented by the deposition of the overlying high-energy, transgressive marine sandstone which is probably separated from the underlying tidally influenced strata by the occurrence of a ravinement surface indicating a progressively landward migrating shore line. In. considering the relative tectonic quiescence of the area during the deposition of the formation which occurred during a post-rift thermal subsidence phase, the close link between variations m the stacking patterns of facies tracts and the eustatic curve reveal that the stratigraphy and deposition of the Statfjord Formation were largely controlled by processes of sea level fluctuations in a near-shore setting