ALBERT

Description: In Colombia, palynology has been widely used as a biostratigraphic tool in oil exploration over the last two decades and, as a result of these efforts, an understanding of the chronostratigraphic range of thousands of palynomorph species is now available. Furthermore, because of their relative resistance to physical and chemical degradation, palynomorphs can often survive several tectonic-erosive cycles, allowing them to be used as unique tracers of long-term sedimentological changes. In this work, we use the palynological record from wells and outcrops in the Llanos foothills and the Llanos basin of Colombia to establish the intensity of Cenozoic reworking and its relationship to the tectonic evolution of the Colombian Andes. Using this approach, we were able to discern several tectonic episodes associated with the uplift of the Eastern Cordillera. We documented three periods of either faster erosion in the hinterland or more widespread areas being eroded in the catchment areas (late Paleocene–early Eocene, early to mid Miocene and Pliocene) and two periods of tectonic quiescence (mid-Eocene and mid–late Miocene). These periods correlate well with the deposition of different elements of the petroleum systems in the Llanos basin of Colombia (seals and reservoirs).

Description: FETKIN is a C++ program for forward modeling thermochronological ages on a two-dimensional geological cross section. Modeled ages for various thermochronometers are computed from time-temperature histories that result from coupling the modeled kinematics of deformation obtained from commercial software for balanced reconstructions (2DMove) and a Finite Element (FEM) computation of temperatures. Additional capabilities include the ability to accommodate: a) A smooth change of topological relief; b) The influence of variation in rock physical properties; and c) Multi-kinetic modeling of fission-track ages and length distributions, as well as apatite and zircon (U-Th)/He, and muscovite 40Ar/39Ar systems. A joint first order analysis of the impact of erosion parameters and material properties improves age predictions and allows for a more complete analysis of observed cooling ages based on their modeled thermal histories.Thus, this paper presents a new software tool that has been developed as a basic support for the methodological approach used to build the kinematic restorations shown in this volume, which are the basic input for petroleum systems modelling and prediction in the Colombian Eastern Cordillera and Llanos foothills basin.

Description: Previously unreleased fission-track results and regional structural relationships are used to interpret the migration of deformation during Cenozoic orogenesis in the Eastern Cordillera (Cordillera Oriental) of the Colombian Andes. Low-temperature thermochronological results are based on apatite and zircon fission-track analyses of 41 samples collected along vertical and horizontal transects across the Eastern Cordillera at 4–7°N latitude. Inverse modeling of fission-track results helps delimit the most probable cooling histories caused by exhumation linked to upper-crustal deformation. These inverse models are constrained by known structural geometries, chronostratigraphy, biostratigraphy, and vitrinite reflectance data. Fission-track data and modeling results indicate a close correspondence in the timing and style of deformation along the western and eastern flanks of the Eastern Cordillera. East-directed fold-thrust deformation along the eastern boundary with the Llanos foreland basin was underway by the late Oligocene and early Miocene. Similarly, west-directed fold-thrust structures along the western boundary with the intermontane middle Magdalena Valley Basin became active at approximately the same time. Less well known is the time of initial shortening within the axial segment of the Eastern Cordillera; although fission-track results suggest active exhumation by the early Miocene, shortening may have commenced much earlier during the late Eocene. Timing relationships for the Eastern Cordillera have important implications for the generation, migration, and accumulation of petroleum in the middle Magdalena Valley intermontane basin and the Llanos foreland basin. Our study provides a regional context to assess the timing of structural trap development and improve exploration and development of new and existing reservoirs in Colombia and analogous fold-thrust systems elsewhere. Andrés Mora is a senior researcher and leader of the Cronologia de la deformaciòn en las Cuencas Subandinas research project at Ecopetrol-Instituto Colombiano del Petróleo. He received his B.Sc. degree in geology from the Universidad Nacional de Colombia in 1999 and his Ph.D. from the Institut für Geowissenschaften, Universität Potsdam (summa cum laude) in 2007. His research interests include structural geology, thermochronology, and basin analysis. Brian Horton is an associate professor at the Department of Geological Sciences and Institute for Geophysics in the Jackson School of Geosciences at the University of Texas at Austin. He received his B.S. degree in geology from the University of New Mexico (1992), his M.S. degree in earth sciences from Montana State University (1994), and his Ph.D. in geosciences from the University of Arizona (1998). His research interests include basin analysis, tectonics, and clastic sedimentology. Andrés Mesa is an exploration geologist who worked in Hocol S.A. from 2005 to 2009 and was in charge of an exploration and production contract in the Eastern Cordillera Basin. He received his B.Sc. degree in geology from the National University at Bogotá (Colombia) in 2005 and is currently doing an M.Sc. degree at Royal Holloway-University of London. His principal interest is basin analysis. Jorge Rubiano is a senior geologist at Ecopetrol-Instituto Colombiano del Petróleo. He obtained a B.Sc. degree from the National University at Bogotá (Colombia) and an M.Sc. degree in basin analysis from the University of South Carolina. Over the past years, he has worked for Ecopetrol on research projects addressing the stratigraphy, structure, basin evolution, and hydrocarbon systems of sedimentary basins in the northern Andes. Richard Ketcham is an associate professor of geological sciences at the University of Texas at Austin. He received his B.A. degree in geology and computer science from Williams College in 1987 and his Ph.D. in geological sciences from the University of Texas at Austin in 1995. His active research interests include thermochronology and geological applications of high-resolution x-ray computed tomography. Mauricio Parra graduated in geology from the National University of Colombia at Bogota in 2000 and received a Ph.D. in geosciences from Potsdam University (Germany) in 2009. He has worked in the tectonic evolution of the Colombian Andes and the associated foreland basin system using low-temperature thermochronometry and basin analysis. He is now a postdoctoral researcher at the Jackson School of Geosciences, University of Texas at Austin. Vladimir Blanco is the current leader of the organic geochemistry lab at Ecopetrol-Instituto Colombiano del Petróleo. He received his B.Sc. degree in geology from the Universidad Industrial de Santander at Bucaramanga (Colombia). He has worked on multiple projects from Ecopetrol since 2006 by giving technical support in basin modeling and characterization of source rocks and crude oils. Diego Garcia joined Ecopetrol-Instituto Colombiano del Petróleo (ICP) in 1998. He holds a diploma in geology from the National University at Bogotá (Colombia), an M.Sc. degree from the Institut Français du Pétrole School (France) on basin analysis, and a Ph.D. from the Federal University of Rio de Janeiro on petroleum and gas exploration. Currently, he is the technical leader of the geological research program of ICP. His research interests include the prediction of petroleum composition, thermal modeling, and the geological controls on petroleum migrations. Daniel Stockli is an associate professor in tectonics and thermochronometry at the University of Kansas and has been the director of the KU (U-Th)/He thermochronometry laboratory since 2001. He received his diploma in geology from the Eidgenössische Technische Hochschule Zürich in 1995 and his Ph.D. from Stanford University in 1999. His interests include continental tectonics, geo- and thermochronology, structural geology, and isotope geochemistry.

Description: Analysis of fracture systems in subsurface structures is limited by the amount and uncertainty of available data. With the aim of analyzing the distribution of fracture systems, we studied surface structures as analogs for oil fields in the fractured reservoirs of the Llanos foothills of Colombia. Here, we document the presence of four widespread fracture systems whose distribution is related to fold geometry and folding mechanism. At surface, in the Tierranegra and Silbadero anticlines, the principal fracture systems are symmetrical with respect to northeast- and northwest-trending fold axes, showing higher fracture intensities in the forelimbs of the structures. In the Guavio anticline, higher fracture intensities are located in the backlimb, with principal east–west and northwest–southeast directions. In contrast, we document northeast–southwest fractures near the hinge zones in the adjacent synclines. This distribution suggests that in the Guavio anticline, fractures respond to movement of the hanging-wall above a ramp, consistent with a fault-bend-fold model. Whereas, in the Tierranegra and Silbadero anticlines, fractures respond to limb rotation and hinge migration consistent with detachment fold models. Comparing these with subsurface structures, we identified that El Morro anticline has fracture distributions like those in the Tierranegra and Silbadero anticlines, but have higher fracture intensities. In the case of the Cusiana Structure, fracture intensities are higher in the crest but not in the limbs, and intensities differ from the ones found in the Guavio anticline, showing that these structures are not appropriate analogs. The results show how fracture distribution depends on structural position and fold evolution, and is controlled in part by folding mechanism. This suggests that models based on Holocene fold geometry cannot accurately predict the observed fracture distributions and should not be used to construct discrete fracture network models. Instead, the patterns we describe can be used as a guide for similar structures. Our work illustrates the possibility of having different fracture patterns and fracture abundances in adjacent folds in the same fold-thrust belt.

Description: In this paper, we demonstrate a workflow for constructing kinematic restorations in complex foothill areas devoid of growth strata and other indicators for the chronology of deformation. Our initial reconstructions utilize thermochronometric data, a well-documented structural geometry, and a first-order conversion of exhumation rates into tectonic rates. We then utilize models obtained from the new in-house–developed software FetKin to build a first version of the thermokinematic restoration. The FetKin approach is geared primarily toward testing and further calibration and refinement of the kinematic restoration, based on the extent to which the model result agrees with thermochronometric data from the study area in the form of both discrete ages and inverse-modeled time–temperature envelopes. This analysis also provides rates of shortening and time–temperature paths throughout the model space that can be used to make first-order predictions of when different source rocks entered the oil window. These capabilities are demonstrated in a pilot case study along a cross section in the Colombian Eastern Cordillera. The improved confidence in the reconstruction that this technique provides allows us to show increasing shortening rates in this part of the Andes during the Neogene reaching up to 5 mm/yr (0.20 in./yr) by the Pliocene, and constrain the timing of generation from the most important oil kitchens for the Eastern Cordillera-Llanos basin petroleum system. This approach, therefore, proves to be a useful method for creating high-resolution and high-fidelity kinematic restorations.

Description: New biostratigraphic zonations, core descriptions, sandstone petrography, facies analysis, and seismic information are compared with published detrital and bedrock geo- and thermochronology to build a Cenozoic paleogeographic reconstruction of the Andean retroarc region of Colombia, encompassing the ancestral Central Cordillera, Middle Magdalena Valley, Eastern Cordillera, and Llanos basin. We identify uplifted sediment source areas, provenance domains, depositional environments, and thickness changes to propose a refined paleogeographic evolution of eastern Colombia. We conclude that Cenozoic evolution of the northernmost Andes includes (1) a period of contractional deformation focused in the Central Cordillera and Middle Magdalena Valley that may have started by the Late Cretaceous, although thermochronological data points to maximum shortening and exhumation during the late Paleocene; (2) a period of slower deformation rates or even tectonic quiescence during the middle Eocene; and (3) a renewed phase of contractional deformation from the late Eocene to the Pleistocene/Holocene expressed in provenance, bedrock thermochronology, and increased subsidence rates in the Llanos foreland. The sedimentary response in the Llanos foreland basin is controlled by source area proximity, exhumation and shortening rates, relationships between accommodation and sediment supply, as well as potential paleoclimate forcing. This new reconstruction changes the picture of Cenozoic basin evolution offered by previous reconstructions, providing an updated chronology of deformation, which is tied to a more precise understanding of basin evolution.

Description: In this study, we provide new data to understand the groundwater flow patterns in the Llanos Basin and their impact on oil biodegradation and the geothermal regimes as well as how the structural styles and anthropogenic activities impact these patterns. Previous studies suggest an active flow of groundwater and variable salinities whose spatial pattern is apparently unrelated to topographically driven groundwater flow. These observations have led to different hypotheses regarding the influence of groundwater flow on Llanos Basin geothermal gradients and oil biodegradation.In this contribution, we present data regarding the hydraulic heads, salinities, geothermal gradients, and structural styles of the Llanos Basin to propose hypotheses explaining these observations. Structural cross sections and subsurface stratigraphic correlations allow us to suggest that the pattern of flow is best explained by a correlation between groundwater flow and structural styles. A basement map of the Llanos Basin confirms that the most important factor controlling geothermal gradients is the type of basement, whereas the factor of groundwater flow appears to be of secondary importance. The evolution of the basin and the frequent absence of correlation between fresh water and the more biodegraded oils support the interpretation that biodegradation is controlled by an older flow of water that started as early as the Oligocene. Finally, mass balances suggest that the temporal scales and volumes of groundwater flow are much larger than the scales observed during the development of the oil fields.