Maracaibo, Venezuela


Maracaibo, Venezuela
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Marquez G.,University of Huelva | Escobar M.,CARBOZULIA | Escobar M.,University of Zulia | Esquinas N.,University of Huelva | And 3 more authors.
Marine and Petroleum Geology | Year: 2017

Here we characterized asphaltic oil occurrences in the Misoa C2 and C3 reservoirs within Area 2 South of the Ceuta Field (Lake Maracaibo Basin, NW Venezuela). To perform the geochemical and petrological characterization of the C2 and C3 sub-units, which cover an interval in which tar-like material was detected, we analyzed core (18) and cutting (123) samples using the Rock-Eval 6 technique in reservoir mode. Samples were studied under fluorescence light and scanning electron microscopy (SEM), showing the presence of two charges of oils and the relationships within silica cements and clay minerals. To evaluate vertical inter-reservoir communication and lateral intra-reservoir continuity, we also studied 12 oil samples from wells in Area 2 South. Biomarkers and isotopic signatures were examined using gas chromatography-mass spectrometry (GC-MS) and isotope ratio mass spectrometry (IRMS). The results suggest that oil and core extracts belongs to a single family derived from two pulses of hydrocarbon generation from the La Luna source rock, which was deposited in a marine reducing environment. The oil samples are a mixture of a paleobiodegraded oil charge and a later fresh, more mature oil recharge. The geochemical analyses also evidence that the formation of heavy oil tar zones can be related to biodegradation and in-reservoir oil mixing, though other formation mechanisms for the tar are also feasible. Finally, the GC fingerprints of the oils are indicative of lateral reservoir continuities across the F-1 and F-2 faults and vertical communication between the Misoa C2 and C3 sub-units in Area 2 South, suggesting that tar occurrences do not act as permeability barriers within the two reservoirs studied. © 2017 Elsevier Ltd

Quintero K.,Central University of Venezuela | Martinez M.,Central University of Venezuela | Hackley P.,U.S. Geological Survey | Marquez G.,University of Huelva | And 3 more authors.
Energy Sources, Part A: Recovery, Utilization and Environmental Effects | Year: 2011

The aim of this work was to carry out a geochemical study of channel samples collected from six coal beds in the Marcelina Formation (Zulia State, western Venezuela) and to determine experimentally the gas content of the coals from the Paso Diablo mine. Organic geochemical analyses by gas chromatography-mass spectrometry and isotopic analyses on-line in coalbed gas samples were performed. The results suggest that the Guasare coals were deposited in a continental environment under highly dysoxic and low salinity conditions. The non-detection of 18α(H)-oleanane does not preclude that the organic facies that gave rise to the coals were dominated by angiosperms. In addition, the presence of the sesquiterpenoid cadalene may indicate the subordinate contribution of gymnosperms (conifers) in the Paleocene Guasare mire. The average coalbed gas content obtained was 0.6 cm 3/g. δ 13C and D values indicate that thermogenic gas is prevalent in the studied coals. Copyright © Taylor & Francis Group, LLC.

Marquez G.,University of Huelva | Escobar M.,CARBOZULIA | Escobar M.,University of Zulia | Lorenzo E.,University of Huelva | And 3 more authors.
Fuel | Year: 2016

Here we analyzed oil samples from 35 wells in the Ceuta Southeast Area (Lake Maracaibo Basin, northwestern Venezuela) in order to evaluate lateral intra-reservoir continuity in the Misoa B4 unit. Biomarkers, isotopic signature, and also V and Ni were examined using gas chromatography-mass spectrometry (GC-MS), isotope ratio mass spectrometry (IRMS), and inductively-coupled plasma atomic emission spectroscopy (ICP-AES). Multivariate statistical analysis was also applied to obtain useful information from geochemical data. On the basis of the characterization of these samples, we conclude that they all fall into various oil families derived from two pulses of hydrocarbon generation, migration and accumulation from the calcareous La Luna source rock, deposited in an anoxic marine environment under reducing conditions. Thus, these oils are a mixture of an earlier biodegraded, less mature oil charge and a later fresh non-biodegraded oil recharge. In addition, we applied asphaltene pyrolysis to one (LG-62) of the three "anomalous" oils. The LG-62 sample was confirmed as an almost "pure" paleobiodegraded end-member, whereas the VLF-3020 oil was tentatively classified as the unaltered end-member oil-type. Finally, the GC fingerprints and Fourier Transform Infra Red (FTIR) spectroscopic indices of the oils were used to detect minor variations in composition that are indicative of reservoir compartmentalization. © 2015 Elsevier Ltd. All rights reserved.

Escobar M.,CARBOZULIA | Escobar M.,University of Zulia | Marquez G.,University of Huelva | Suarez-Ruiz I.,CSIC - National Coal Institute | And 3 more authors.
International Journal of Coal Geology | Year: 2016

The aims of this work were to carry out a combined petrographic, palynofacies, and organic geochemical study of twelve drill-core samples collected from the lowest coal seams in the Paleocene Marcelina Formation (Paso Diablo mine, Guasare Basin, northwestern Venezuela), to characterize crude oil samples from three wells in the nearby Amana Field and to evaluate oil-source correlations of these crude oils with the Paso Diablo coal extracts. The coals under study were classified as high volatile bituminous A or at the B-A boundary, and showed vitrinite contents between 50.0 and 89.4 vol.%, liptinites ranging from 1.4 to 24.2 vol.%, and inertinites in the 6.2–30.8 vol.% range. Results from organic geochemical investigations indicate that the Guasare coals were generated in a limno-telmatic to telmatic zone under fluctuating oxygen conditions. A Type III kerogen with relatively high hydrogen content and a thermal maturity corresponding to the early oil window are proposed for these coals as supported by Rock-Eval and petrographic data, as well as biomarker interpretations. Oil generation potential from Marcelina Formation coals is probably due to the perhydrous nature of the vitrinite, high bitumen contents, and considerable liptinite concentrations, mainly oil-prone resinites and exsudatinites. Palynofacies observations denote a dominance of psilate pollen grains related to angiosperm plants and, as expected, Type III kerogens or humic coals in the studied seams, the parent material of which contained a significant contribution of algae. The non-detection of 18α(H)-oleanane does not preclude the fact that angiosperms are the dominant plants in the Guasare paleomire. On the other hand, the characterization of the Amana oils suggests that they all fall into a unique oil family; the presence of 25-norhopanes in them could indicate paleobiodegradation and mixing from various hydrocarbon charges in the reservoir. Thus, the crude oils from the Amana Field seem to be a mixture of one or more oil charges from the early mature marine carbonate source rocks of the La Luna Formation, deposited under anoxic reducing conditions, and a later pulse of hydrocarbon generation which originated from an unknown – so far – nonmarine source rock. In this regard, hydrocarbon liquid derived from the lowest Marcelina coal seams may be tentatively identified as the latter oil charge. Also, this work delineates some components of a currently subcommercial and hypothetical Tertiary petroleum system – identified and named as Marcelina/Misoa C5(.) – in the Lake Maracaibo region. Finally, the coalbed gas contents of sampled coals were determined. © 2016 Elsevier B.V.

Escobar M.,CARBOZULIA | Escobar M.,University of Zulia | Marquez G.,University of Huelva | Azuaje V.,Pacific Stratus Energy Colombia Ltd. | And 2 more authors.
Fuel | Year: 2012

This work is an analysis of crude oil samples from thirty wells in the Alturitas Field (Lake Maracaibo Basin, western Venezuela). Different biomarkers, ten trace elements, and porphyrins were analysed using GC-MS, ICP-OES and UV-visible techniques, respectively. The characterization of these crude oils leads us to conclude that they all fall into a single non-biodegraded oil family derived from a single pulse of hydrocarbon generation, migration and accumulation from the thermally mature calcareous La Luna source rock deposited in an anoxic marine palaeoenvironment under reducing conditions. The main objective of this work is to present a secondary oil migration model for the Marcelina reservoir of the Alturitas Field. The multivariate statistical study of trace-element concentrations, porphyrin contents, and polar compound proportions shows that these parameters can be split into two groups. The first group (Cd, Cu, Mo, Fe, P, Zn, Ca, and Mg) indicates a chalcophic association (Cd, Cu, Mo, and Zn) or colloidal complexes with naphthenic acids (Ca, Mg, and Fe). The other two trace elements (V and Ni), together with porphyrins and polar compounds, reveal that oil compositions has been affected by geochromatography, indicating a highly probable secondary migration pathway along a preferential axis orientated southeast to northwest. © 2012 Elsevier Ltd. All rights reserved.

Montilla L.A.,Pdvsa | Martinez M.,Central University of Venezuela | Marquez G.,University of Huelva | Escobar M.,CARBOZULIA | And 5 more authors.
Geochemical Journal | Year: 2013

A geochemical and chemostratigraphical study was undertaken on Campanian-Maastrichtian sedimentary rocks (the Colón -Mito Juan sequence and the upper La Luna Formation) in the southwestern Maracaibo Basin, Venezuela. The objectives of this work were to determine the paieoenvironmental and physico-chemical characteristics of the Colón -Mito Juan sequence and its possible subdivision into chemofacies and to study the main chemical differences between the Colón , Mito Juan, and La Luna Formations within the study region. One hundred and ninety-one rock samples were collected, and bulk inorganic geochemistry (TiO2, Al2O3, Fe2O3, MgO, CaO, Na2O, K2O, P 2O5, C, S, Rb, Cs. Ba, Sr, Th, U, Y, Hf, Mo, V, Cr, Co, Cu, Ni, Sc, La, Ce, Nd, Sm, Eu, Yb, Lu, As, Sb, Zn, and Be) was analyzed by instrumental neutron activation analysis or inductively coupled plasma-atomic emission spectroscopy; total sulfur and carbon analyses were performed by a LECO SC-432 apparatus and coulometry, respectively. Multivariate statistical techniques were applied to evaluate correlations within this group ol variables. Using cluster-constrained analysis, eight subdivisions, or chemical facies, were defined: Two chemofacies differentiating the intervals controlled by biogenic deposition and by the predominant clastic contribution; three chemofacies correlating with the lithologic units (La Luna, Colón , and Mito Juan); and another three chemofacies related to changes in the paleoredox conditions along the stratigraphic column. All of the units studied were deposited under a relatively constant climate regime, and the composition of the sediment source showed no significant changes. The prevailing physico-chemical regime was disoxic-oxic, with a trend of increasing oxygen concentrations towards the top of the column. Copyright © 2013 by The Geochemical Society of Japan.

Escobar M.,CARBOZULIA | Escobar M.,University of Zulia | Marquez G.,University of Huelva | Inciarte S.,University of Zulia | And 3 more authors.
Organic Geochemistry | Year: 2011

The organic geochemistry of samples from 11 oil seeps was studied. The samples were collected from the Cachirí area, Carboniferous Region of Tulé (Lake Maracaibo Basin, Venezuela), associated with the Tigre Fault. Biomarkers (hopanes, steranes, n-alkanes, acyclic isoprenoids, and aromatic steroids) were analyzed using gas chromatography-mass spectrometry (GC-MS). These hydrocarbon rich fluids have undergone biodegradation (2-6 on the Peters and Moldowan scale), showing both the partial loss of n-alkanes and the microbial degradation of isoprenoids and steranes. These oil seeps were generated from a mature calcareous source rock that was deposited in a marine paleoenvironment under reducing conditions. Moreover, these seeps are likely derived from the Cretaceous La Luna Formation that reached a level of maturity near the peak of oil generation in the study area. The nature of the studied oil seeps, together with the oil generation models reported for this rock unit in the study area, suggests that these oils are a mixture of an initially heavy, altered oil and a second migrated light crude oil resulting from two generation pulses from the La Luna Formation. Evidence for the presence of light oil trapped in the study area should prompt re-exploration in the northwestern coast of Lake Maracaibo in shallow reservoirs, previously discarded because they usually demonstrated a lack of light oils. © 2011 Elsevier Ltd.

Geochemical evaluation of oil from a well recently drilled in the southeast area of Maracaibo Lake (FRA-1X, Franquera oil field) and its comparison with 5 crude oils from nearby fields, led to the conclusion that these geochemically correlated marine mature oils could be the result of the mixture into the reservoir of petroleum formed by two pulses of generation of the La Luna Formation source rocks, which fed the study area in different geological periods (Eocene and Miocene-Recent).

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