Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p> A well-recognized characteristic of the World Stress Map (WSM) database is the continued presence of large spatial gaps in the distribution of the data records despite the more than 40 years development history of the database. The current release has more than 30,000 high-quality (A-C) data records (often referred to as “stress indicators”), but while some continental areas (such as Australia) have seen a significant increase in spatial converge with the latest release other continental regions (Africa, central Asia, most of South America) remain markedly sparse. In this contribution we 1) review the current state of the spatial distribution of stress indicators in the continental regions (above sea level); 2) quantify the clustering of the stress indicators in the latest WSM release using the Hopkins statistic as a way to explore the current spatial distribution of the indicators and assess future WSM releases; and 3) present three approaches (joint inversion, seismic anisotropy, and InSAR) that provide a way to fill in the gaps (both in the SHmax orientation and principal stress magnitudes) in regions which lack active seismicity and where borehole drilling is cost prohibitive. These three approaches have the potential to guide procedures for improving <jats:italic>apriori</jats:italic> estimates of the ambient stress field in the Earth's crust and reduce the uncertainty in predicting both the magnitude and orientation of the principal tectonic stresses. </jats:p>

<jats:title>Abstract</jats:title> <jats:p> Stress barriers play a key role in the propagation of hydraulic fractures. They are local maxima in the stress field that constrain vertical fracture propagation. The development of stress barriers is influenced by rock mechanical properties, pore pressure, and tectonic stresses. However, stress prediction models are highly sensitive to available geophysical measurements and assumptions made on rock constitutive models. We compare stress estimations performed with elastic isotropic, anisotropic and viscoplastic models using Thomsen's notation ( <jats:italic>ε</jats:italic> , <jats:italic>δ</jats:italic> , <jats:italic>γ</jats:italic> ) to quantify anisotropy and its effects on hydraulic fracture geometry. Using a single depth for principal stress calibration, we compare stress distributions and simulate hydraulic fractures geometries along simple vertical and horizontal well sections. Prediction errors stemming from isotropic models along anisotropic intervals increase when tectonic stresses increase. Errors generated by either over or underestimation of <jats:italic>δ</jats:italic> increase for tectonically passive environments, while errors generated by either over or underestimation of <jats:italic>ε</jats:italic> increase for tectonically active environments. Additional corrections but also uncertainties can be introduced by considering viscoelastic rock behavior. Because of stress shadowing and fracture interaction, the risk of stress barrier underestimation is higher when estimating hydraulic-fracture geometries along the various stages of horizontal wells. </jats:p>

<jats:title>Abstract</jats:title> <jats:p>Stress variations in the Earth's crust need to be understood in both the spatial and temporal domains to address a number of pressing societal issues. In this paper, precise three dimensional records of fault kinematic behaviour obtained by mechanical extensometers are used to investigate changes in stress states along major faults in the Eastern Alps. The monitored faults are fractures with evident Upper Quaternary displacement and are directly attributed to their master tectonic structures. The results demonstrate that activity at the submillimetric scale is highly episodic; periods of repose are punctuated by conspicuous reactivation events affecting one or more of the displacement components. An original approach named the SMB2018 method is used to define the stress state associated with each fault reactivation event. The outputs evidence significant short term changes in the local stress regime. The directions of the principal normal stresses calculated from these reactivation events present generally similar patterns for both compressional and extensional stress states. Consequently, submillimetric fault activity cannot be controlled by a rotating stress field; such shifts can only be caused by a change in the magnitude of the individual principal normal stresses so that the maximum compression changes to the minimum and vice versa.</jats:p>

<jats:title>Abstract</jats:title> <jats:p> Knowledge of subsurface stresses is critical to management and prediction of fluid behaviour in the Earth's crust. However, uncertainties associated with the estimation of vertical stress magnitudes are rarely explored. In settings where the principal stresses are close, small changes of only a few MPa can have drastic effects on, stress regime prediction, fault reactivation and expected fracture behaviour. Using petroleum data sets from the Moomba Gas Field in the Cooper Basin, Australia, we assess the effects of interpolation between gaps in density wireline logs that have been filtered to remove sections of poor density tool contact in coal-bearing sequences. In addition, we compare the sonic velocity-density Nafe-Drake and Gardner transforms by comparing estimates of density from sonic velocity against density from wireline logs. Results indicate vertical stress could be underestimated by ≈ 3 MPa at ≈ 3 km in well Moomba 61, using traditional methods. The Gardner transform shows a stronger correlation between sonic and density values for rocks in the Cooper Basin. However, once calibrated to the regional sonic velocity-density trend, the Nafe-Drake transform better matches the density logging tool in Moomba 61. This study delivers a more robust workflow for estimating S <jats:sub>v</jats:sub> in basins with deep coal-bearing strata. </jats:p>

<jats:title>Abstract</jats:title> <jats:p> Inversions of earthquake focal mechanisms are among the most accessible and reliable methods for determining crustal stress. However, the use of this method varies widely, and assumptions that underpin it are often violated, potentially compromising stress estimates. We investigate the consequences of violating the little-studied assumption that the focal mechanisms have diverse orientations. Our approach is to employ data-informed synthetic mechanisms, with nodal plane orientations defined by recent earthquake lineaments in the Midland Basin, western Texas, and rakes consistent with slip in the mapped stress field. Using both the traditional stress inversion method that assumes constant shear stress magnitudes on the causative faults as well as a recently published variable shear stress method, we show that low fault plane diversity can cause maximum horizontal stress ( <jats:italic>S</jats:italic> <jats:sub>Hmax</jats:sub> ) orientation and relative principal stress magnitude (faulting regime) estimates to differ markedly from the true values. This problem is compounded for catalogs with even modest amounts of noise (≤15°) or few (e.g., 20) mechanisms. Significantly, traditional approaches for quantifying uncertainty such as the bootstrap can severely underestimate the true uncertainty under these circumstances. To remedy this, we provide simple tools to quantify nodal plane orientation diversity and stress inversion reliability. </jats:p> <jats:p content-type="supplementary-material"> Supplementary material at <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" specific-use="dataset is-supplemented-by" xlink:href="https://doi.org/10.6084/m9.figshare.c.6935953">https://doi.org/10.6084/m9.figshare.c.6935953</jats:ext-link> </jats:p>

<jats:p> Geomechanics has a marked impact on safe and sustainable use of the subsurface. This Special Publication contains contributions detailing the latest efforts in present-day <jats:italic>in-situ</jats:italic> stress characterization, prediction and modelling on a borehole to plate-tectonic scale. A particular emphasis is on the uncertainties that are often associated with geomechanics. </jats:p>

<jats:title>Abstract</jats:title> <jats:p>The thermal evolution of continental rifted margins is key to understanding margin subsidence and hydrocarbon prospectivity. Observed heat-flow values however, do not always comply with classic rifting models. Here, we use 2D numerical models to investigate the relationship between rifting, sedimentation and thermal history of margins. We find that during the synrift, the basement heat flow and temperature are not only controlled by extension factor, but also by synrift sediment thickness and the evolution of deformation. As this progressively focuses oceanward, the proximal sectors thermally relax, while the distal sectors experience peak temperatures. In the postrift, the lithosphere under the hyperextended margins does not return to its original state, at least for ∼100 Myrs after breakup. Instead, it mimics that of the adjacent oceanic plate, which is thinner than the original continental plate. This results in heat flow increasing oceanward at postrift stages, when classic rifting theory predicts complete thermal relaxation. Our models also predict slightly increased heat flows in the adjacent oceanic crust, potentially extending hydrocarbon plays into distal margins and oceanic crust, previously discarded as immature. Finally, our models indicate that commonly used temperature approximations to calculate heat-flow during rifting, may strongly differ from those occurring in nature.</jats:p> <jats:p content-type="supplementary-material"> Supplementary material at <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" specific-use="dataset is-supplemented-by" xlink:href="https://doi.org/10.6084/m9.figshare.c.6986110">https://doi.org/10.6084/m9.figshare.c.6986110</jats:ext-link> </jats:p>

<jats:title>Abstract</jats:title> <jats:p>Oil seeps related to igneous rocks in the Neuquén Basin have been known since pre-Hispanic times (16th century) and have been explored in the southern Mendoza province since the late 19th century. In the 1980s YPF began the exploration of igneous rocks as hydrocarbon reservoirs in the Río Grande Valley area. The possible productivity of these ‘unconventional’ reservoirs was recognized by studying outcrops and well data of sills and dikes emplaced in different formations of the fold and thrust belt of the northern Neuquén Basin. Mudlogging control, as well as the evaluations with drill stem tests (DST), were decisive to define these reservoirs as prospective. From petrographic reports on samples from outcrops and cores, six lithological types could be distinguished in the igneous units for this region. Recent works confirm that this volcanism belongs to two predominant cycles from the late Oligocene to the Miocene (“Molle”) and middle to upper Miocene (“Huincán”). Although in igneous reservoirs it is difficult to forecast the estimated ultimate recovery (EUR), sills that crosscut the source rocks of the Vaca Muerta and Agrio formations demonstrate surprisingly high production rates, although the number of wells for the complete development is always difficult to establish.</jats:p>

<jats:title>Abstract</jats:title> <jats:p> Lava flows form important fluid reservoirs and have been extensively exploited for water aquifers, geothermal energy, hydrocarbon production, and more recently for carbon storage. Effusive subaerial mafic to intermediate lava flows account for vast rock volumes globally, and form reservoirs with properties dictated by well-known lava flow facies ranging from pāhoehoe through several transitional forms to ‘a’ā lava. These variations in flow type lead to critical differences in the pore structure, distribution, connectivity, strength, and fracturing of individual lava flows, which, alongside lava flow package architectures, determine primary reservoir potential. Lava flow margins with vesicular, fracture, and often autobreccia hosted pore structures can have porosities commonly exceeding 40% and matrix permeabilities over 1 E-11 m <jats:sup>2</jats:sup> (&gt; 10 darcy) separated by much lower porosity and permeability flow interiors. Secondary post-emplacement physicochemical changes related to fracturing, meteoric, diagenetic, and hydrothermal alteration can significantly modify reservoir potential through a complex interplay of mineral transformation, pore clogging secondary minerals, and dissolution which must be carefully characterized and assessed during exploration and appraisal. Within this contribution, a review of selected global lava flow hosted reservoir occurrences is presented followed by a discussion on the factors that influence lava flow reservoir potential. </jats:p>

<jats:title>Abstract</jats:title> <jats:p>Volcanic plumbing systems emplaced in sedimentary basins may exert significant mechanical and thermal effects on petroleum systems. The last decade of research has evidenced that igneous intrusions may enhance thermal maturation of organic matter in source rocks and lead to both small- and large-scale structures that can deeply impact fluid migration or trapping. This contribution describes how the emplacement of a whole intrusive complex generated a dome structure of the overburden, which is the main trapping structure of a large producing oil field. Our case study is the lower Miocene Cerro Bayo de la Sierra Negra intrusive complex, Neuquén Basin, Argentina, associated with the El Trapial oil field where the main trapping structure is a large domal antiform centered on the Cerro Bayo de la Sierra Negra complex. This study integrates the large subsurface data set produced during the development of the El Trapial oil field. More than 1,200 vertical wells (producers and injectors) have been drilled in the flanks of Cerro Bayo de la Sierra Negra complex. Additionally, five 3D seismic cubes have been acquired over the years, which have been merged and re-processed in a single volume. Such data set allows a detailed characterization of both the structure affecting the Mesozoic strata, and geometry of the intrusive complex. Igneous rocks have been recognized along the entire stratigraphical section. Sill intrusions appear to concentrate in the shale units and the stacking of them has a direct impact on the doming structure generation. Our study allowed us to establish a direct correlation between the distribution of the intrusions and the extent, amplitude, and style of doming, showing that the dome structure results from the emplacement of the intrusive complex. We also show that part of doming is related to intrusions emplaced in the Mesozoic formations of the Neuquén Basin, whereas the other part of the doming is related to deeper structures not imaged on the geophysical data. We estimate the amplitude of the doming to reach up to ∼500 m. The voluminous subsurface data, combined with exposed outcrops, makes Cerro Bayo de la Sierra Negra a world-class case study for showing how the shallow plumbing system of a volcanic complex may control the growth of large-scale trapping structures for various fluids, such as drinkable water, geothermal fluids and hydrocarbons.</jats:p>