Victor Matheus Joaquim Salgado-Campos

The injection of CO2 into depleted oil and gas reservoirs is part of CarbonCapture, Utilization, and Storage (CCUS) techniques, including enhanced oilrecovery (EOR) and the permanent storage of CO2 in geological formations.After the injection, the interaction between host rocks and CO2 causes dissolutionand precipitation of minerals. Therefore, the complexity of the systemdepends upon the host rock. Carbonates are challenging host rocks as theyare highly reactive, and many parameters can affect the resulting mineralogy,reason why natural analogues are valuable sources to comprehend thosechanges, but they are scarce. In Brazil, the intense activity of the oil and gasindustry in carbonate reservoirs of Pre-salt represents enormous potentialstorage volume for carbon capture purposes. Based on that, this work aimsto characterize a natural analogue for CO2 injection in the Barra Velha Formation,reservoir rocks of the Santos Basin, Brazil. Cutting samples from adrilling well were used for lithological description, X-ray Fluorescence (XRF)and X-ray Diffractometry (XRD) analysis, which were interpreted alongsidewell logs data, used to separate the well into six zones. The results showed anintense dolomitization, relevant silicification, presence of dawsonite, and lackof Mg-clay minerals. Different types of dolomites were described, presentingdistinct habits, colors, and distributions along the zones, which could be relatedto the result of different minerals interacting with CO2. This can bean indicator that CO2 intensified the dissolution of the clayey matrix, withthe precipitation of new phases of dolomite and dawsonite.

Clay mineral assemblages (CMA) provide important records of paleoclimatic variability in sedimentary basins. Unlike authigenic clay minerals formed during diagenesis, detrital clays are transported from continental source areas and reflect weathering and sedimentary processes linked to climatic conditions. This study examines the Paleozoic evolution of the Parnaíba Basin (Brazil) based on clay mineral composition, with emphasis on detrital kaolinite as a proxy for precipitation. Mineralogical data from the clay fraction were integrated with estimates of mean annual air temperature (MAAT) and mean annual precipitation (MAP). Silurian units are characterized by assemblages dominated by illite and smectite, with MAAT values between 7 and 9 °C and MAP between 200 and 600 mm/yr, consistent with reduced chemical weathering under icehouse conditions. In the Devonian, kaolinite becomes more abundant, accompanied by MAP values ranging from 800 to 1200 mm/yr, suggesting intensified precipitation and enhanced continental weathering. This pattern contrasts with the Permian interval, where kaolinite contents decrease and MAP values fall to 0–400 mm/yr, reflecting progressive aridization associated with the paleogeographic configuration of western Gondwana during the assembly of Pangea. Considered together with paleogeographic reconstructions, these variations coincide with shifts in paleolatitudinal position and associated changes in precipitation distribution. The increase in kaolinite during the Devonian and its reduction in the Permian follow the same general trend observed in the climatic parameters. The distribution of detrital kaolinite records variations in precipitation and the intensity of continental chemical weathering, reinforcing its potential as a paleoclimatic proxy in intracratonic basins throughout the Paleozoic.

Raman spectroscopy is a powerful tool for assessing the thermal maturity of kerogen; however, its application to carbonate-rich source rocks is hampered by methodological challenges, particularly spectral interference from fluorescent mineral matrices and sample heterogeneity. This study systematically evaluates three preparation protocols: fresh (raw), macerated (ground), and decarbonated, on samples from the Formação Coqueiros (Campos Basin-RJ, Brazil) to identify the most reliable workflow, using Rock-Eval pyrolysis as a geochemical benchmark. Direct analysis of fresh samples proved unreliable, yielding inconsistent data in which the combined effects of heterogeneity and mineral fluorescence masked the true kerogen signal. While mechanical maceration successfully addressed physical heterogeneity, allowing for a basic qualitative distinction between maturity levels, it was insufficient, as the fundamental problem of spectral interference remained unresolved. The decarbonated protocol, however, yielded the optimal result. This two-step procedure, involving mechanical grinding followed by targeted chemical removal of carbonates, successfully mitigated both issues, producing stable, precise, and geologically coherent maturity data that correlates with the Rock-Eval temperature of maximum hydrocarbon generation (Tmax) benchmark. This work validates the targeted procedure as a robust, accessible workflow that avoids aggressive chemical treatments that risk altering the kerogen structure, offering a more efficient and potentially more accurate path for analysis in these common lithologies.

Igneous rocks play fundamental roles in the formation and evolution of petroleum systems in several basins around the world. In the Parnaíba Basin, the diabase sills and dikes, that correspond to the Mosquito and Sardinha formations, contribute as a thermal source for an unconventional hydrocarbon generation, as well as providing trap and seal for the petroleum system. To understand these intrusions, we propose a methodology to identify the igneous intrusions in well-logs, interpret their compositional variations and suggest a hypothesis to construct a crystallization model for these sills. The methodology is based on detailed descriptions of cuttings, X-ray fluorescence (XRF), X-ray diffractometry (XRD) and well logs, such as Gamma Ray (GR), Density (RHOZ) and Photoelectric Factor (PEFZ), from six exploratory wells drilled in the main gas-producing area of the Parnaíba Basin. The intrusions present in these wells were identified through the Igneability Feature and classified based on the GR curve as either “Barriguda” or “Caixote” features. The “Barriguda” intrusions shows variations in the well logs along their section, as well as variations in Aluminum, Calcium, Potassium, Zirconium, Iron, Titanium, Magnesium, Calcium, Nickel and Chromium values, evidencing a great textural and mineralogical variation, confirmed by the mineralogical results of XRD. Data interpretation suggests that the “Barriguda” intrusions are characterized in distinct electrofacies- and chemiofacies that represent an intern variation from top to base, related to magmatic differentiation that follows Bowen’s Reaction Series.