Abstract not available

Gerenciar riscos é fundamental para que investimentos estejam protegidos de quaisquer fatores que possam modificar um cenário idealizado. Imprevistos não podem ser controlados, mas seus impactos podem ser minimizados se forem tomadas medidas de planejamento considerando diversos cenários da realidade. A indústria mineral se encaixa neste paradigma, pois diversas de suas áreas são estocásticas, desde flutuações econômicas e políticas até fenômenos relativos ao clima e à geologia. Uma destas características de difícil previsão é o volume das mineralizações em um depósito. Um cenário ideal é aquele em que é conhecido o valor esperado da variável de interesse, bem como sua dispersão, com mínimo e máximo definidos. Isto pode ser obtido a partir da combinação dos resultados de estimativa, que resultam em um valor esperado, aliados ao resultado das simulações, em que pode ser obtida a variância entre todos os cenários equiprováveis. Este trabalho propõe uma técnica para quantificar a incerteza dos volumes na modelagem geológica de domínios mineralizados em dois modelos geológicos, interpolado e interpretado, através da transferência da variância obtida nos resultados da simulação, e desta forma criar uma ferramenta de gerenciamento de risco e planejamento a partir dos resultados de incerteza. Para isto foram utilizados os dados de descrição geológica de 168 testemunhos de sondagem de um depósito de cobre, localizado no norte da Bahia. Os resultados mostraram a possibilidade em se utilizar os dados de variância da simulação para quantificar a incerteza em cada domínio do depósito. A partir do volume esperado em determinado modelo, e com os valores da variância da simulação, foi possível identificar uma gama de possibilidades volumétricas. Adicionalmente, a probabilidade de que cada bloco faça parte de um domínio foi calculada, e os volumes dos domínios foram parametrizados para auxiliar na avaliação da incerteza. / Managing risks is essential for investments being safe from any factors that may modify an idealized scenario. Unpredictabilities cannot be controlled, but their impacts can be minimized if planning measures are taken considering various scenarios of reality. The mining industry fits this paradigm, since several of its fields are stochastic, from economic and political fluctuations to phenomena related to climate and geology. One of these characteristics, which are difficult to predict, is the volume of mineralization at the deposit. An ideal scenario is the one in which both the expected value and its dispersion are known, with defined minimum and maximum. This can be achieved with the combination of results from estimates and simulations, the first providing the expected value and the last providing the variance of the variable. This research proposes a technique to quantify the volumetric uncertainty in geological modeling of mineralized domains on two geological models, interpreted and interpolated, by transferring the variance obtained in the simulation results, thus creating a risk and planning management tool from the uncertainty results. For that, we used a geological logging from a database set with 168 drillholes of a copper deposit located north of Bahia state, Brazil. The results showed that it is possible to use the variance from simulation to quantify the uncertainty in each deposit domain. Using the expected volume value in a specific model with the variance values of the simulations, it were able to identify a range of possibilities for the volumetric content of each domain. In addition, the probability of each block being a domain was calculated, resulting in a volume parametrization by probability that can assist in the uncertainty analysis.

Reservoir economic performance is based upon future cash flows which can be generated from a reservoir. Future cash flows are a function of hydrocarbon volumetric flow rates which a reservoir can produce, and the market conditions. Both of these functions of future cash flows are associated with uncertainties. There is uncertainty associated in estimates of future hydrocarbon flow rates due to uncertainty in geological model, limited availability and type of data, and the complexities involved in the reservoir modeling process. The second source of uncertainty associated with future cash flows come from changing oil prices, rate of return etc., which are all functions of market dynamics. Robust integration of these two sources of uncertainty, i.e. future hydrocarbon flow rates and market dynamics, in a model to predict cash flows from a reservoir is an essential part of risk assessment, but a difficult task. Current practices to assess a reservoir’s economic performance by using Deterministic Cash Flow (DCF) methods have been unsuccessful in their predictions because of lack in parametric capability to robustly and completely incorporate these both types of uncertainties. This thesis presents a procedure which accounts for uncertainty in hydrocarbon production forecasts due to incomplete geologic information, and a novel real options methodology to assess the project economics for upstream petroleum industry. The modeling approach entails determining future hydrocarbon production rates due to incomplete geologic information with and without secondary information. The price of hydrocarbons is modeled separately, and the costs to produce them are determined based on market dynamics. A real options methodology is used to assess the effective cash flows from the reservoir, and hence, to determine the project economics. This methodology associates realistic probabilities, which are quantified using the method’s parameters, with benefits and costs. The results from this methodology are compared against the results from DCF methodology to examine if the real options methodology can identify some hidden potential of a reservoir’s performance which DCF might not be able to uncover. This methodology is then applied to various case studies and strategies for planning and decision making. / text

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: This study investigates the crustal structure, and assesses the qualitative and quantitative impacts of crust-mantle dynamics on subsidence pattern, past and present-day thermal field and petroleum system evolution at the southern South African continental margin through the application of a multi-disciplinary and multi-scale geo-modelling procedure involving both conceptual and numerical approaches. The modelling procedure becomes particularly important as this margin documents a complex interaction of extension and strike-slip tectonics during its Mesozoic continental rifting processes. Located on the southern shelf of South Africa, the Western Bredasdorp Basin (WBB) constitutes the focus of this study and represents the western section of the larger Bredasdorp sub-basin, which is the westernmost of the southern offshore sub-basins. To understand the margin with respect to its present-day structure, isostatic state and thermal field, a combined approach of isostatic, 3D gravity and 3D thermal modelling was performed by integrating potential field, seismic and well data. Complimenting the resulting configuration and thermal field of the latter by measured present-day temperature, vitrinite reflectance and source potential data, basin-scale burial and thermal history and timing of source rock maturation, petroleum generation, expulsion, migration and accumulation were forwardly simulated using a 3D basin modelling technique. This hierarchical modelling workflow enables geologic assumptions and their associated uncertainties to be well constrained and better quantified, particularly in three dimensions. At present-day, the deep crust of the WBB is characterised by a tripartite density structure (i.e. prerift metasediments underlain by upper and lower crustal domains) depicting a strong thinning that is restricted to a narrow E-W striking zone. The configuration of the radiogenic crystalline crust as well as the conductivity contrasts between the deep crust and the shallow sedimentary cover significantly control the present-day thermal field of the study area. In all respects, this present-day configuration reflects typical characteristics of basin evolution in a strike-slip setting. For instance, the orientations of the deep crust and fault-controlled basin-fill are spatially inconsistent, thereby indicating different extension kinematics typical of transtensional pull-apart mechanisms. As such, syn-rift subsidence is quite rapid and short-lived, and isostatic equilibrium is not achieved, particularly at the Moho level. Accompanied syn-rift rapid subsidence and a heat flow peak led to petroleum preservation in the basin since the Early Cretaceous. Two additional post-rift thermal anomalies related to the Late Cretaceous hotspot mechanism and Miocene margin uplift in Southern Africa succeeded the syn-rift control on maturation. This thermal maturity of the five mature source rocks culminated in four main generation and three main accumulation phases which characterise the total petroleum systems of the WBB. The Campanian, Eocene and Miocene uplift scenarios episodically halted source maturation and caused tertiary migration of previously trapped petroleum. Petroleum loss related to the spill point of each trap configuration additionally occurs during the Late Cretaceous-Paleocene and Oligocene-Early Miocene. The timing and extent of migration dynamics are most sensitive to the geological scenario that combined faulting, intrusive seal bypass system and facies heterogeneity. In fact, for models that do not incorporate facies heterogeneity, predicted past and present-day seafloor leakage of petroleum is largely underestimated. This complex interplay of generation and migration mechanisms has significant implications for charging of petroleum accumulations by multiple source rocks. Due to early maturation and late stage tertiary migration, the syn-rift source rocks particularly Mid Hauterivian and Late Hauterivian source intervals significantly control the extent of petroleum accumulation and loss in the basin. Lastly, the modelled 3D crustal configuration and Mezosoic to Cenozoic thermal regime of the WBB dispute classic uniform lithospheric stretching for the southern South African continental margin. Rather, this PhD thesis confirms that differential thinning of the lithosphere related to a transtensional pull-apart mechanism is the most appropriate for accurately predicting the evolution of basin and petroleum systems of the margin. Also, the presented 3D models currently represent the most advanced insights, and thus have clear implications for assessing associated risks in basin and prospect evaluation of the margin as well as other similar continental margins around the world. / AFRIKAANSE OPSOMMING: Hierdie studie ondersoek die korsstruktuur en evalueer die kwalitatiewe en kwantitatiewe impakte van kors-mantel-dinamika op insinkingspatroon, die termiese veld en petroleumstels evolusie aan die suidelike Suid-Afrikaanse kontinentale grens, in die hede en die verlede, deur die toepassing van ’n multidissiplinêre en multiskaal-geomodelleringsprosedure wat beide konseptuele en numeriese benaderings behels. Die modelleringsprosedure veral is belangrik aangesien hierdie kontinentale grens ’n komplekse interaksie van uitbreidings- en strekkingsparallelle tektoniek gedurende die Mesosoïese vastelandskeurprosesse daarvan dokumenteer. Omdat dit op die suidelike platvorm van Suid-Afrika geleë is, maak die Westelike Bredasdorp Kom (WBK) die fokus van hierdie studie uit, en verteenwoordig dit die westelike deel van die groter Bredasdrop-subkom, wat die verste wes is van die suidelike aflandige subkomme. Om die grens met betrekking tot sy huidige struktuur, isostatiese staat en termiese veld te verstaan, is ’n kombinasie benadering bestaande uit isostatiese, 3D-gravitasie- en 3D- termiese modellering gebruik deur potensiëleveld-, seismiese en boorgatdata te integreer Ondersteunend totot die gevolglike konfigurasie en termiese veld van die laasgenoemde deur middel van hedendaagse temperatuur, soos gemeet, vitriniet-refleksiekoëffisiënt en bronpotensiaal data, komskaal-begrawing en termiese geskiedenis en tydsberekening van brongesteentematurasie, is petroleumgenerasie, -uitwerping, -migrasie en -akkumulasie in die toekoms gesimuleer deur gebruik te maak van ’n 3D-kommodelleringstegniek. Hierdie hierargiese modelleringswerkvloei maak dit moontlik om geologiese aannames en hulle geassosieerde onsekerhede goed aan bande te lê en beter te kwantifiseer, veral in drie dimensies. In die hede word die diep kors van die WBK gekarakteriseer deur ’n drieledige digtheidstruktuur (met ander woorde voorrift-metasedimente onderlê deur bo- en benedekors domeine) wat dui op ’n baie wesenlike verdunning, beperk tot ’n dun O-W-strekkingsone. Die konfigurasie van die radiogeniese kristallyne kors, sowel as die konduktiwiteitskontraste tussen die diep kors en die vlak sedimentêre dekking, beheer grotendeels die hedendaagse termiese veld van die studiearea. Hierdie hedendaagse konfigurasie weerspieël in alle opsigte tipiese eienskappe van kom-evolusie in ’n skuifskeur omgewing. Byvoorbeeld, Die oriëntasies van die diep kors en verskuiwingbeheerde komsedimentasie byvoorbeeld is ruimtelik inkonsekwent en dui daardeur op verskillende ekstensiekinematika, tipies van transtensionale tensiemeganisme. As sulks, is sin-rift-versakking taamlik vinnig en kortstondig, en word isostatiese ekwilibrium nie by die Moho-vlak, in die besonder, bereik nie. Samehangende sin-rift vinnige versakking en hittevloeihoogtepunt het gelei tot petroleum behoud in die kom sedert die vroeë Kryt. Twee bykomende post-rift termiese anomalieë wat verband hou met die laat Kryt-“hotspot” meganisme en die Mioseense kontinentale grensopheffing in Suidelike Afrika het die sin-rift-beheer met maturasie opgevolg. Hierdie termiese maturiteit van die vyf gematureerde brongesteentes het in vier hoofgenerasie- en drie hoofakkumulasie fases, wat die totaliteit van die petroleumstelsels van die WBK karakteriseer, gekulmineer. Die Campaniese, Eoseense en Mioseense opheffings senarios het episodies bronmaturasie gestop en tersiêre migrasie van petroleum wat vroeër opgevang was veroorsaak. Addisioneel vind petroleumverlies gekoppel aan die spilpunt van elke opvanggebiedkonfigurasie tydens die laat Kryt-Paleoseen en Oligoseenvroeë Mioseen plaas. Die tydstelling en omvang van migrasiedinamika is die sensitiefste vir die geologiese scenario wat verskuiwing, seëlomseilingstelsel en fasiesheterogeniteit kombineer. Trouens, vir modelle wat nie fasiesheterogeniteit inkorporeer nie, is voorspellings van vroeëre en huidige seebodemlekkasie van petroleum grotendeels onderskattings. Hierdie komplekse wisselwerking van generasie- en migrasiemeganismes het beduidende implikasies vir die laai van petroleumakkumulasies deur veelvoudige brongesteentes. Vanweë vroeë maturasie en laatstadiumtersiêre migrasie, oefen die sin-rift-brongesteentes, veral middel Hauterivium- en laat Hauteriviumbronintervalle, beduidende beheer oor die omvang van petroleumakkumulasie en -verlies in die kom uit. Laastens weerspreek die gemodelleerde 3D-korskonfigurasie en Mesosoïese-tot-Senosoïesetermiese regime van die WBK ’n klassieke uniforme litosferiese rekking vir die suidelike Suid- Afrikaanse kontinentale grens. Inteendeel, hierdie PhD-proefskrif bevestig dat ’n differensiële verdunning van die litosfeer, gekoppel aan ’n transtensiemeganisme, die beste geskik is om ’n akkurate voorspelling oor die evolusie van kom- en petroleumstelsels van die kontinentale grens mee te maak. Verder, verteenwoordig die 3D-modelle, wat hier aangebied word, tans die mees gevorderde insigte, en het hierdie modelle dus duidelike implikasies vir die assessering van verwante risiko’s in kom- en petroleum teikene valuering van die kontinentale grens, so wel as van ander soortgelyke kontinentale grense regoor die wêreld.

La dynamique des courants de turbidité est fortement contrôlée par la morphologie du fond marin. Les turbidites issues de ces courants constituent des réservoirs d’hydrocarbures très importants dans les bassins sédimentaires à travers le monde. L'objectif principal de ce travail est de comprendre comment le paleorelief a contrôlé la géométrie et l'architecture des réservoirs turbiditiques, en utilisant comme zone d'étude les réservoirs du Crétacé d'un champ pétrolier du bassin de Campos (offshore du Brésil), où la tectonique a été en partie dominée par l'halocinèse. La méthodologie utilisée dans cette thèse a couplé deux approches. La première a inclus à la fois la description des séquences sédimentaires, à partir de données de sismique-réflexion et de puits, et les restaurations structurales. Six horizons régionaux et quatre unités-réservoirs ont été identifiés et cartographiés afin de construire un modèle géologique multi-2D. Ces surfaces ont ensuite été aussi restaurées. Les résultats de cette étape suggèrent que les failles liées à l'halocinèse ont contraint la paléotopographie pour le dépôt des réservoirs plus anciens et que des structures tectoniques et un canyon ont formés les contraintes paléotopographiques pour la distribution des réservoirs plus jeunes. La seconde approche a été l'analyse du rôle des paramètres des écoulements en effectuant des simulations numériques du type stratigraphique (Dionisos) et des automates cellulaires (CATS). Une surface restaurée, considérée comme référence pour le dépôt des unités-réservoirs a été utilisée comme paléotopographie pour les simulations CATS. Le modèle numérique a été contraint par les données réservoirs. Cette utilisation inédite des simulations 3D avec des automates cellulaires dans une étude de cas réel concernant des dépôts marins anciens a produit des résultats réalistes par rapport aux exemples modernes connus. Elle a également fourni des résultats plus exploitables à l'échelle de réservoir que les modèles numériques de type "stratigraphique". Ce travail met en évidence l'importance des interactions tectonique-sédimentation et de la paléotopographie pour la distribution de réservoirs turbiditiques. / The dynamic of gravity-driven turbidity currents is strongly influenced by the morphology of the seafloor. The resulting turbidites constitute important hydrocarbon reservoirs in sedimentary basins throughout the world. The main objective of the present work is thus to understand the way the paleorelief controls turbidite reservoir architectures, with application in a specific study area with Cretaceous reservoirs in Campos Basin (Brazilian offshore). The tectonics in this Basin was partly controlled by halokinesis. The first approach was describing the local Cretaceous sedimentary sequence architecture, from seismic and well data, and performing structural restorations. Six regional horizons and four reservoir-scale units were identified and mapped in order to build a multi-2D geological model. Structural restorations highlighted the structural evolution and allowed the related horizon palaeotopography to be obtained. The results of this work step suggest that the halokinesis-related listric faults regulated the distribution of the basal reservoirs. Moreover, at the top of the Albian carbonates, a canyon was identified, which, in association with the tectonic structures, forms the palaeotopographic constraints for the upper reservoir geometry. The second approach was analyzing the role of flow controlling parameters by performing stratigraphic (Dionisos) and cellular automata-based (CATS) numerical simulations. The latter provided a more appropriate reservoir scale-simulation process than Dionisos. A restored surface, considered as reference for the deposition of the reservoir units, was used as the palaeotopography for CATS simulations, having as constraints the reservoir data. This pioneer use of cellular automata simulations in a real subsurface case study produced coherent results when compared with the actual reservoir distribution. This work sheds light on the importance of tectonic-sedimentation interactions and of palaeotopography for the distribution of turbidite reservoirs.