The mud-to-cement conversion or 'slag-mix' technology displays several advantages when compared to conventional well cementing operations. This alternative method means to combine drilling fluids, accelerators, and finely granulated slag as the hydraulic material. Steam injection is commonly used to improve crude oil production in the Lagunillas field (state of Zulia, NW Venezuela). This work compares the use of two slag-mix systems containing two polymer-based drilling muds during cementing of injection wells: an aqueous drilling fluid and an oil-in-water emulsion mud. After comparing the use of the two study drilling mud systems with a typical lignosulfonate slag-mix system, it can be stated that both systems may be suitable to be used in the application of the mentioned-above technology in steam stimulated wells. The aqueous formulations under study and a typical slag-mud slurry containing lignosulfonate show relatively similar values for most physic-mechanical properties. In contrast, the slag-mix emulsion system under consideration shows distinctive rheological and filtration behaviours compared to the other study polymer-based slag-mud slurry, but similar mechanical properties. [Received: April 26, 2019; Accepted: August 1, 2019]

Sr-87/Sr-86 ratios, delta C-13, and delta O-18 determinations performed on 30 bulk carbonate rocks are presented to constrain the isotope characteristics regarding Oceanic Anoxic Event 3 in the La Luna Formation, Maracaibo Basin. The samples were collected along a 22 m profile in San Miguel region (Merida State, Venezuela). The exhibited Sr-87/Sr-86 ratios are between 0.707659, at the base, and 0.707733 at the top of studied section, corresponding estimated younger numerical ages than the inferred ages dated as Santonian (85.8-83.5 Ma) based on occurrence of Dicarinella asymetrica. The obtained Sr-87/Sr-86 ratios are certainly higher than expected for Santonian sea Sr and they are attributed to regular riverine strontium fluxes in the restricted (gulf-like) Maracaibo Basin. The values of delta O-18 data between -3.76 parts per thousand and -11.76 parts per thousand are distributed in two distinct clusters in a same way and coherent as for 8.13C data which are in a range between -1.75 parts per thousand and -13.87 parts per thousand. One of the clusters delta C-13 = -2.5 +/- 1.0 parts per thousand and delta O-18 = -10.0 +/- 1.5 parts per thousand), illustrate the homogeneous marine deposition under tropical conditions, while the other, more variable, probably could reflect the cyclicity of temporally changes in Pacific versus Atlantic Ocean circulation with cooling water or cooling trend climate. These delta C-13 values around -2.5 +/- 1.0 parts per thousand do not fit with the significant carbon isotope excursion as expected for the oceanic anoxic event (OAE) and support the work hypothesis that Coniacian Santonian anoxic event (denominate as OAE3) is not a global one. (C) 2016 Elsevier Ltd. All rights reserved.

Here we undertook an inorganic geochemical study of Cenomanian-Campanian bedded cherts (the Táchira Ftanita Member of the La Luna Formation) in the western region of the Táchira State, Venezuela. The aim of this study was to determine the paleo-oceanographic and paleo-environmental conditions that governed the deposition of chert beds and put forward a sedimentation model for the Táchira Ftanita Member in the study area. Seventy-two chert samples were collected and trace/rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Rb, Cs, Th, U, Y, Co, and Sc) and major/trace elements (SiO2, TiO2, Al2O3, Fe2O3, MgO, CaO, Na2O, K2O, P2O5, Mn, Ba, Sr, Cr, Ni, and V) were determined by ICP-MS and ICP-OES, respectively. On the basis of the stratigraphic abundance and distribution of relatively immobile elements, as well as the distribution of rare earth elements, we established that the detrital sediments associated with the sequences studied have matching characteristics with distinct continental materials, with an intermediate composition, thus pointing to the Guayana Massif as the main source of sediments. In addition, we also determined the influence of hydrothermal input on the chemical composition of some cherts from La Molina Mine. On the basis of geochemistry, we found a biological influence regarding the uptake of dissolved silica for forming chert beds. The application of parameters for relatively immobile elements allowed us to establish a still proximal continental-margin (hemipelagic) for most samples from the Zorca River and a continental-margin for almost all the cherts from the Delicias-Villa Páez section and the remaining samples from La Molina Mine. Finally, we propose that the rhythmicity that accompanies the sequence of bedded cherts is related to changes in the intensity of upwelling patterns of water and/or to variability in the supply of silica dissolved in the Táchira sub-basin.

This paper focuses on the sedimentary environment and sedimentary geochemistry of El Paraiso Formation in Purureche section, Falcon state. This outcrop was studied and sampled every 50 cm for foraminifers analyses, petrography of sandstones, determination of major, minor and trace elements (Al, Ba, Ca, Ce, Cr, Cu, Fe, La, Mg, Mn, Ni, Pb, Sc, Si, Sr, Ti, V, Y, Zn, Zr), S and TOC. This unit is characterized by claystones, siltstones and sandstones and four coarseningupward intervals were identified represented by thin-interbedded claystones and siltstones that ended with a sandstone of one to two meters thick (I and IV interval), or by claystones, thin-interbedding of claystones and sandstones ending with a sandstone of two or three meters thick (II and III interval). Sedimentological and geochemical results suggest a front delta - upper prodelta environment for the studied unit in this locality. Sediments provenance is associated with a recycled orogen that collided with the northwestern edge of South America; source rock was composed of metamorphic, sedimentary and felsic igneous rocks.

El objetivo de este trabajo fue estudiar el ambiente sedimentario y la geoquimica sedimentaria de la Formacion El Paraiso que aflora en la quebrada Purureche, estado Falcon. Para ello, se procedio con la descripcion de campo de esta seccion y se tomaron muestras a intervalos de 50 cm, a las cuales se les realizaron: lavado de arcillitas para la separacion de microfosiles, analisis petrograficos de areniscas, determinacion de los elementos mayoritarios, minoritarios y trazas (Al, Ba, Ca, Ce, Cr, Cu, Fe, La, Mg, Mn, Ni, Pb, Sc, Si, Sr, Ti, V, Y, Zn, Zr), S y COT. La Formacion Paraiso esta caracterizada por la presencia de arcillitas, limolitas y areniscas; se identificaron cuatro intervalos granocrecientes representados por intercalaciones de delgadas capas de arcillitas y limolitas que culminan con una arenisca de uno a dos metros de espesor (intervalos I y IV), o representados por arcillitas, intercalaciones de delgadas capas de arcillitas y areniscas que culminan con una arenisca de dos a tres metros de espesor (intervalos II y III). Las caracteristicas sedimentologicas y el comportamiento de los elementos quimicos permiten proponer un ambiente de sedimentacion de frente deltaico – parte superior del prodelta para esta unidad en esta localidad. La fuente de sedimentos se asocia a un orogeno reciclado que colisiono con el extremo noroccidental de la placa Suramericana, la misma estaba conformada por rocas metamorficas, sedimentarias e igneas felsicas. ABSTRACT This paper focuses on the sedimentary environment and sedimentary geochemistry of El Paraiso Formation in Purureche section, Falcon state. This outcrop was studied and sampled every 50 cm for foraminifers analyses, petrography of sandstones, determination of major, minor and trace elements (Al, Ba, Ca, Ce, Cr, Cu, Fe, La, Mg, Mn, Ni, Pb, Sc, Si, Sr, Ti, V, Y, Zn, Zr), S and TOC. This unit is characterized by claystones, siltstones and sandstones and four coarsening-upward intervals were identified represented by thin-interbedded claystones and siltstones that ended with a sandstone of one to two meters thick (I and IV interval), or by claystones, thin-interbedding of claystones and sandstones ending with a sandstone of two or three meters thick (II and III interval). Sedimentological and geochemical results suggest a front delta - upper prodelta environment for the studied unit in this locality. Sediments provenance is associated with a recycled orogen that collided with the northwestern edge of South America; source rock was composed of metamorphic, sedimentary and felsic igneous rocks.Keywords: Oligocene, Recycled orogen, Mouth bars, Prodelta, Geochemical associations.

The La Luna Formation was deposited under anoxic/dysoxic conditions in a tropical epicontinental sea on the northwest South America margin. Sedimentological, micropaleontological and geochemical evidence provides insights into factors that influenced the sedimentation and controlled the accumulation of organic-rich deposits at decimeter and meter scales during the youngest of the Cretaceous oceanic anoxic events (OAE).The La Luna Formation consists of an alternation of black marlstones interbedded with black limestones and black marly limestones. The benthic foraminifera assemblages indicate sedimentation in the upper neritic to upper bathyal environment. These rocks contain large amounts of organic matter. It is interpreted that a combination of warm global and rainy climate and the presence of bathymetric barriers caused poor circulation and low rates of water column ventilation during a high sea level in the early Santonian leading to the preservation of carbon-rich deposits in this region. During the late Santonian, a cooling-trend in global climate increased wind strength and upwelling; this change probably reduced runoff causing a weakening of the pycnocline and destabilized the stratification in the water column providing a progressive increase in oxygen in the water column and on the sea floor and a decrease in total organic carbon preservation in a shallower basin. These changes and the establishment of full mid- and deep-water exchange in response to the deepening and widening of the Equatorial Atlantic Gateway could have been important mechanisms for ending the epeiric sea anoxia. Changes through time in the vanadium-nickel fraction, planktonic and benthic foraminifera assemblages, productivity proxy elements, and lithological characteristics support this model.Superimposed on the general trend, variations in calcium carbonate and total organic carbon percentages at the scale of tens of centimeters reveal high frequency cyclic variations, which apparently correspond to the main frequencies of orbital forcing. This cyclicity is interpreted as a primary depositional signal and is the result of orbital-controlled fluctuations in terrigenous dilution and variations in oxygen concentration at the base of the water column. Variations in the intensity of upwelling can be observed, but they did not control the cyclicity. (C) 2004 Elsevier B.V. All rights reserved.