Recent discoveries made in the presalt carbonates of southeast Brazil are among the most important in the past decade. This province, especially Santos Basin, contains large accumulations of oil with excellent quality and high commercial value. The latest seismic processing technologies, along with elastic inversion, have been used for reservoir characterization and in identifying carbonates with high-permeability intervals to model flow behavior of the reservoirs. One challenge encountered is identifying the occurrence of igneous bodies within the reservoir interval and their correct characterization as input into the reservoir modeling. Igneous rocks encountered in the Brazilian presalt can be of both intrusive and extrusive origin. They may present a variety of permo-porous reservoir properties ranging from being flow barriers to acting as high-permeability corridors if fracturing is high enough. The presence of igneous rocks is not common in Brazilian presalt carbonates; therefore, specific methodologies must be used, both in seismic processing and quantitative interpretation, in order to map and predict those occurrences.
A methodology to confirm the direct contact metamorphism of intrusive rocks and related hydrothermal modification on presalt limestone reservoirs, in Libra Block of Santos Basin, is presented. The approach is based on systemic study of cores, sidewall cores, traditional wireline logging, ECS and NMR of boreholes. Type and characteristics of metamorphism in contact aureoles between intrusive bodies and limestones are confirmed. NMR was used to evaluate porosity change of limestone. Thin sections and ECS were used to identify the precipitant types and to confirm the modification of hydrothermal fluids influences on surrounding limestones.
Intrusive rocks are observed in several wells of presalt layers in Libra Block and show contact metamorphic aureoles in the surrounding limestones, characterized by a significant change on the limestone mineral size, rock color, and reservoir pore after marbleization. By combining conventional logging and NMR logging, the thicknesses of contact metamorphic aureoles are determined in multiple wells. They conform to a binomial regression relation with the thicknesses intrusive bodies. The NMR data reveals that igneous contact metamorphism exerts negative influence on pores development for carbonate reservoirs. Reservoir physical properties decrease sharply after thermal baking, generally by 4 to 8 times. The study also confirms that related hydrothermal fluids pervasively develop and have multi-types of influences on limestones, mainly due to silicification, dolomitization and calcification. They mainly brought minerals precipitation in fractures and pores that made limestone reservoir tight. In Libra presalt layers, hydrothermal modification related to intrusive bodies mainly developed at the middle-upper intervals of BVE Fm.
Combined with wells correlation sections and seismic data, a state-of-the-art model of igneous contact metamorphism and hydrothermal modification on limestone reservoirs has been developed in this paper. It can help to quantitatively predict the thickness of contact metamorphism aureole around intrusive rocks. The study also clarifies the understanding of the type of hydrothermal effects on the reservoir porosity and how to map the spatial distribution of hydrothermal deposition in the reservoir.
This paper describes the CELEPAR experience using ISO/IEC 12207-Software Life Cycle Processes [1] and the Software-CMMCapability Maturity Model [2] to improve and organize the maintenance and development processes.
Resumo A origem de ironstones oolíticos, preservados no registro sedimentar, tem sido assunto de muitos debates nas últimas décadas. Tais depósitos formam importantes unidades no registro paleozoico e a determinação de seu signifi cado sedimentológico e estratigráfi co é fundamental na interpretação do contexto deposicional dessas sucessões sedimentares. Os ironstones oolíticos da Formação Ponta Grossa estão intimamente associados aos limites de sequência e subsequentes superfícies transgressivas. Essas unidades foram descritas a partir da análise de um furo de sondagem localizado no noroeste da Bacia do Paraná. Esses ooides teriam sido depositados sob baixa taxa de sedimentação em condições marinha rasas, intercalados a eventos transgressivos episódicos, os quais retrabalhariam esses sedimentos. A descrição da evolução diagenética destes ooides de ferro foi feita através de estudos petrográfi cos e análises de difratometria de raios-X e de microscopia eletrônica de varredura (MEV). Tais análises indicam que a mineralogia dos ooides foi gerada durante a eodiagênese. Os ironstones são constituídos, principalmente, por ooides e cutículas de bertierina, cimento de siderita preenchendo os poros e por calcita ferrosa tardia. O intervalo oolítico estudado apresenta-se no furo de sondagem com laminação ondulada truncada. Esse aspecto faciológico reforça a ideia de que as condições necessárias para o desenvolvimento dos depósitos de ironstones oolíticos foi o intenso retrabalhamento sedimentar, unido às baixas taxas de acumulação.Palavras-chave: ironstone, diagênese, estratigrafi a de sequências, Bacia do Paraná.
Abstract Ironstone ocurrence in the Devonian of the Parana Basin.The ooidal ironstones origin preserved in the sedimentary record has been subject of many discussions in the last decades. These deposits form prominent units in the Paleozoic record, and an assessment of their sedimentological and stratigraphic signifi cance is essential for the interpretation of sedimentary successions. The ooidal ironstones from the Ponta Grossa Formation are associated with a major sequence boundary and subsequent transgressive surface. These ooidal ironstones were described in a borehole located in the north part of Paraná Basin. They were interpreted as they had been deposited under conditions of low net sediment accumulation with episodic storm events reworking the sediments, in a shallow-marine environment. Through petrographic studies, X-ray diffraction, and scanning electron microscope (SEM) analyses made possible the depiction of the ooidal ironstones diagenetic evolution. Such analyses indicate that the ooidal ironstone mineralogy was formed during eodiagenesis. The ironstones are dominated by berthierine ooids and grain-rimming and pore-fi lling siderite, with later ferroan calcite. The ooidal interval observed in the borehole presented wave cross lamination. This faciologic aspect reinforces the idea that the conditions required for the development of the ironstones deposits were intense sediment reworking and slow n...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.