Llanos Foreland Basin Research Articles

Implications of groundwater flow on preservation of heavy and extra-heavy oil accumulations in Southern Llanos Basin, Colombia

The southern sector of the Llanos Basin in Colombia is a heavy and extra-heavy crude oil province where it has been hypothesized that hydrodynamic flow has influenced the potential of hydrocarbon storage and production. In this area, the hydrodynamic flow and the geochemical nature of the fluids are thought to decrease the potential for hydrocarbon retention. This work provides a comprehensive view on the impact of the regional hydrodynamic flow on the retention of the heavy oil accumulations present in the reservoirs that are part of the most important regional flow unit identified in the Southern Llanos Basin. The Basal Flow Unit (BFU) constitutes a basin-scale flow unit that hydraulically and laterally connects rocks from the Cretaceous (west) to the Oligocene (east) and extends from the basin's southwestern margin up to hundreds of kilometers within the Llanos foreland basin, and whose main water recharge zone has been identified towards the eastern flank of the Serranía de la Macarena. To understand the impact of the physicochemical properties of the fluids on hydrocarbon retention, we analyze the relationship between hydraulic data and the main characteristics of the fluids present in the BFU as well as their spatial distribution. This analysis integrated information from hydraulic heads, SARA analysis (Saturates, Aromatics, Resins, and Asphaltenes), Whole Oil Gas Chromatography analysis, API-gravity, and oil densities. In addition, hydrochemical analyses of the primary ions were performed in groundwater samples from the BFU, which was integrated with deep resistivity data measured in producing and exploratory oil wells in the area. The results allowed identifying the southwestern corner of the southern Llanos Basin as the area with the highest hydrodynamic flow impact, and therefore, the area with the least potential for hydrocarbon retention. We attribute the main causes to: 1) the proximity to recharge areas, and 2) the low contrast of fluids densities (freshwaters and highly biodegraded heavy crude oils), implying high Tilt Amplification Factor (TAF) values (10–100). In addition, the highest values of hydraulic heads (200–400 m), groundwater with the lowest ion concentrations (up to < 5 ppm Cl−), highly biodegraded crude oils, and the presence of poorly developed geological structures with low dip angles occur in this area, which allows us to interpret that the water washing process has decreased the hydrocarbon retention potential for this sector of the Llanos basin. Furthermore, gradual changes in resistivities (decreasing eastward) and ions concentration (increasing eastward) in groundwaters suggest the eastern flank of the Serranía de la Macarena as the main recharge zone of meteoric waters into the BFU. Finally, numerical simulation techniques were used to analyze the behavior of hydrocarbon drainage under hydrodynamic conditions, obtaining a first approximation to the average linear groundwater flow velocities between 10−3 and 10−4 ft/day.

Integrated seismic and well-log analysis for the exploration of stratigraphic traps in the Carbonera Formation, Llanos foreland basin of Colombia

The Llanos foreland basin of Colombia is the country's most prolific oil producer, with the most known oil fields found in normal fault traps created during flexure of the foreland basin. The objective of the study is to evaluate the potential of stratigraphic traps in the Late Eocene-Early Miocene Carbonera Formation, a 400-1800 m-thick reservoir unit with numerous traps related to unfaulted, sand-prone fluvial deposits. We integrated 700 km2 of 3D seismic data with eight wells near the ~8600 bcd Cubiro field in the central area of the Llanos foreland. Interpretations of well logs and stratal slices through multi-attribute and iso-frequency amplitude cubes show that the Carbonera Formation contains tectonically-controlled, sinuous channel belts seen on seismic lines as strong, high-amplitude, concave reflections with variable width-to-depth ratio. Well logs through the Carbonera Formation record two regressive-transgressive cycles with greater preservation of non-reservoir, shaly transgressive deposits within the intermediate Carbonera members 5 and 3, and sandy, lowstand deposits in the lower and uppermost Carbonera members 7 and 1, respectively. Seismic and gamma-ray facies analyses allowed the distinction of prospective, sand-rich point bars, scrolls, and basal lag deposits from non-prospective, mud-rich abandoned channels. Stratal slices within the Carbonera Formation show changes from Late Eocene-Early Oligocene, northeast-flowing channel belts of a main axial fluvial system -proposed to be the proto-Meta River-, to a Late Oligocene southeast-flowing tributary channels interpreted as a result of eastward flexural migration, enhanced accommodation from loading of the Eastern Cordillera and a shift from an underfilled to overfilled foreland basin.

Monitoring runoff coefficients and groundwater levels using data from GRACE, GLDAS, and hydrometeorological stations: analysis of a Colombian foreland basin

The determination of space–time variation in groundwater accumulation in Colombia’s Eastern Llanos foreland basin from 2003 to 2014 was done using terrestrial water storage (TWS) anomalies identified in two versions of the Gravity Recovery and Climate Experiment (GRACE) data—from the Global Data Center for Space Research (CSR) at the University of Texas at Austin (USA) and from the Institute of Geodesy at the Graz University of Technology (ITSG, Austria)—and also soil moisture storage (SMS) data from the Global Land Data Assimilation System (GLDAS). These data were compared to changes in groundwater storage obtained using the water-budget equation, calculated based on recorded data from hydrometeorological stations. This study confirmed the viability of using satellite information to understand and monitor temporal variation in groundwater recharge in the study area. Temporal variations in TWS, SMS, and groundwater level were shown to correspond to regional rain and drought periods, which are sensitive to climate phenomena such as El Nino and La Nina. Comparing changes in TWS and groundwater level to changes in infiltration and recharge revealed correlation coefficients of 0.56 and 0.98 with CSR data and 0.71 and 0.86 with ITSG data, respectively.

Hyperspectral imaging for the determination of bitumen content in Athabasca oil sands core samples

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.

Application of seismic attributes and spectral decomposition for reservoir characterization of a complex fluvial system: Case study of the Carbonera Formation, Llanos foreland basin, Colombia

Hydrocarbon exploration in the Llanos foreland basin of eastern Colombia has traditionally focused on structural traps. However, in the past decade, the country’s oil demand has generated an increased interest in exploration for stratigraphic traps. We integrated [Formula: see text] of 3D seismic data volumes with eight wells in the Central Llanos area to assess the reservoir potential of the fluvial channel deposits of the Late Eocene–Oligocene Carbonera Formation in the Casanare Province. Distinguishing nonproductive, mud-filled channels from productive sand-filled channels is of economic importance for hydrocarbon exploration because both channel types can exhibit a similar seismic character. Our interpretation of the fluvial sandstone and the reservoir identification was based on 3D seismic attributes, including coherence, curvature, and spectral decomposition, and the analysis of fluvial geomorphology. Analysis of stratal slices through coherence, isofrequency amplitude cubes, and curvature cubes revealed (1) a northeast-trending meandering fluvial system with changes in the rivers’ paleoflow direction from southwest to northeast during the period of the Late Eocene to the Early Miocene, (2) development of prospective sandy point bars, scrolls, and sand bar deposits, and (3) channel ridges and bases accentuated by differential compaction dependent on the channel’s filling material. Based on our attribute analysis, we were able to characterize nonprospective mud-filled channels versus prospective sand-filled channels.

Evaluating the mechanical compaction of quartzarenites: The importance of sorting (Llanos foreland basin, Colombia)

Mechanical compaction is the main porosity-reducing process in sandstones, including high-reservoir-quality rigid-grain sandstones. For such sandstones, the extrapolation of theoretical or experimental compaction algorithms needs calibration with rocks having well constrained burial histories. Evaluating the compaction of these rocks is achieved by comparing current intergranular volume (IGV) with depositional IGV, which is strongly dependent on sorting. However, because sandstone sorting is difficult to measure accurately, its impact on depositional porosity and compaction state is largely underestimated. We use the quartzarenites of the Oligocene Carbonera Formation in the subsurface of the hydrostatically-pressured Llanos basin to illustrate the importance of sorting when evaluating the compaction of rigid-grain sandstones. IGV and sorting were measured in core samples using a combination of transmitted-light and cathodoluminescence images, resulting in improved accuracy over standard procedures. The compaction state of clean quartzarenites at given depths is best described using IGV-versus-sorting plots, which are used to derive compaction curves for specified sorting values. The IGV-versus-sorting trends are displaced to lower IGV values with increasing burial depth. The differences in IGV caused by differences in sorting exceed the differences in IGV resulting from 1000 m of burial, illustrating the high impact of sorting when evaluating compaction. Contrasting with published experimental results, the compaction of the Llanos basin ductile-grain-poor quartzarenites is independent of grain size, and grain rearrangement is the main compaction mechanism during the first ∼1.6 km of burial. Based on the Llanos data, we have generated IGV-versus-depth curves for clean pure quartzarenites of specific sorting, which can be used to predict their maximum primary porosity up to moderate burial depths. Differences with other published burial curves are probably related to unaccounted variations in sorting, ductile-grain content and framework-strengthening cements. However, the Llanos basin quartzarenites contain virtually no cements, explaining their high degree of compaction relative to other rigid-grain sandstones, and making them ideal to isolate the effects of compaction on the IGV of quartzarenites. The Llanos basin data suggest that, below ∼2.5 km of depth, clean well- to moderately well sorted quartzarenites continue reducing their IGV by mechanical compaction below the 26% limit, which should apply only to extremely well sorted, rigid grain, uncemented sandstones.

A neuro fuzzy approach to recognize rock magnetic and lithological patterns in a stratigraphic well from the Llanos Foreland Basin (Colombia)

The Neuro Fuzzy System (NFS) is a hybrid algorithm that combines fuzzy logic with neural networks. Since it can be used as a pattern recognition technique, we explore its potential to characterize the major lithological units encompassed by the first 512 m of the Colombian stratigraphic well Saltarin 1A (Guayabo and Leon Formations). Thus, we employ the NFS to infer the magnetic remanence S-ratio using bulk magnetic susceptibility (κ), κ-normalized saturation isothermal magnetization (SIRM κ) and/or volume of shale (Vsh) obtained from a gamma-ray log. The best results in terms of their corresponding Root Mean-Square Error (RMSE) values, throughout most of the upper Guayabo Formation, where magnetite seems to be an important magnetic phase, are attained with logκ and SIRM κ as input variables. Beyond 350 m downcore, the quality of the inference decreases over the Leon Formation, characterized by a significant presence of pyrrhotite. However, the extra input variable Vsh adjusts the inferred S-ratio to their experimental counterparts throughout this formation suggesting that the early diagenesis process that led to the formation of dispersed clay in these samples was also responsible for the formation of pyrrhotite. Hence the inclusion of manifold input data increases the ability of the net to predict S-ratio in complex geological settings with a sequence of changing lithologies, varying amounts and types of magnetic minerals, and different distributions of mineral grain sizes. In case these variables do not properly infer the actual S-ratio data, the extent of the different lithostratigraphic units would be still identifiable in some cases by the uneven quality of the correlation observed between inferred and experimental values.

Thick-skin orogen–foreland interactions and their controlling factors, Northern Andes of Colombia

Abstract The study draws from reflection seismic, in-situ stress and low-temperature geochronology data on the Eastern Cordillera–Llanos foreland basin system of Colombia, which is an example of the retro-wedge of the orogen with an advancing subduction zone. The system was obliquely converging during deposition of the Lower Oligocene–Lower Miocene Carbonera to recent Guayabo formations, recording it by the northeastward depocentre shift in the proximal Llanos Basin. While the southern portion of the foreland did not flex and undergo flexural normal faulting after Carbonera deposition, the northern portion did. The earthquake data indicate that the northern Eastern Cordillera undergoes strengthening by internal deformation, while the southern segment is already strong enough to undergo significant displacements dominantly along its bounding fault systems. Furthermore, the southern segment initiated detachment of the first thick-skin blocks from the proximal Llanos Basin. Such co-existence of different convergence maturity stages along the orogen strike allows unravelling of its development starting with internal deformation and foreland flexure, followed by mountain building and large-scale boundary fault displacements, to the large-scale foreland deformation. The onset of new foreland accretion seems to be controlled by the resistance of the foreland plate to flexing, given that the orogenic engine continues to drive convergence. Supplementary material: Discussion of evidences for dextral transpression in the Eastern Cordillera, data on exhumation history of the Eastern Cordillera and colour versions of Figures 4–6 are available at http://www.geolsoc.org.uk/SUP18629

Deformation partitioning in the Llanos foreland basin during the Cenozoic and its correlation with mountain building in the hinterland

Abstract Previous studies have argued that deformation in foreland basins is either controlled by inherited structures, is a direct response to the advancing orogenic load or is a combination of these two factors. To provide insights into the relative importance of these processes in foreland basin development, we generated an inventory of syn-kinematic relationships for the Llanos foreland of Colombia using an extensive (∼5000 km) network of 2D seismic lines. The results of this work indicate that most of the Miocene extensional deformation in the central Llanos trends parallel to the orogen and follows the propagation of orogenesis to the east. Thus, the dominant control on deformation of the Llanos foreland basin is related to flexure during episodes of enhanced orogenic load. This observation is fundamental to understand the nature of deformation in continental interiors and cratonic areas in front of active orogens.

Rock magnetic characterization of early and late diagenesis in a stratigraphic well from the Llanos foreland basin (Eastern Colombia)

Abstract We have carried out rock magnetic characterizations of different lithofacies along the stratigraphic well Saltarín 1A, in order to learn about the various diagenetic events that could have affected the Miocene sequence of the Llanos foreland basin (Colombia). Thermomagnetic and low-temperature susceptibility measurements performed on some selected samples were complemented with analyses of Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) and isothermal remanent magnetization (IRM) acquisition curves. The identification of the magnetic mineral assemblages at each depth level analysed, as well as their relative concentrations, were determined from a direct signal analysis (DSA) of the IRM curves. Samples from the top of the Guayabo formation reveal the presence of hydrocarbons-related microscopic framboids of pyrite with partial replacement of magnetite. The bottom of the Guayabo formation shows hematite and goethite and appears to record a thoroughly documented Middle Miocene global regression. In samples from the León formation, pyrrhotite could have resulted from an early diagenesis that took place in a lacustrine environment via sulphate reduction. Traces of crude oil in samples from the Carbonera formation, and the additional occurrence of hematite and magnetite, suggest that a hydrocarbons-mediated late diagenesis could also have affected the lowermost levels of Saltarín 1A.

Clastic deposition, provenance, and sequence of Andean thrusting in the frontal Eastern Cordillera and Llanos foreland basin of Colombia

Sedimentological, provenance, and detrital thermochronological results for basin fill at the modern deformation front of the northern Andes (6°N latitude) provide a long-term, Eocene to Pliocene record of foreland-basin sedimentation along the Eastern Cordillera–Llanos basin boundary in Colombia. Lithofacies assemblages and paleocurrent orientations in the upward-coarsening, ~5-km-thick succession of the Nunchia syncline reveal a systematic shift from craton-derived, shallow-marine distal foreland (back-bulge) accumulation in the Mirador Formation, to orogen-sourced, deltaic, and coastal-influenced sedimentation of the distal to medial foreland (foredeep) in the Carbonera and Leon Formations, to anastomosing fluvial and distributive braided fluvial megafan systems of the proximal foreland (foredeep to wedge-top) basin in the lower and upper Guayabo Formation. These changes in depositional processes and sediment dispersal are supported by up-section variations in detrital zircon U-Pb and (U-Th)/He ages that record exhumation of evolving, compartmentalized sediment source areas in the Eastern Cordillera. The data are interpreted in terms of a progressive eastward advance in fold-and-thrust deformation, with late Eocene–Oligocene deformation in the axial zone of the Eastern Cordillera along the western edge of Floresta basin (Soapaga thrust), early Miocene reactivation (inversion) of the eastern margin of the Mesozoic rift system (Pajarito and Guaicaramo thrusts), and middle–late Miocene propagation of a footwall shortcut fault (Yopal thrust) that created the Nunchia syncline in a wedge-top (piggyback) setting of the eastern foothills along the transition from the Eastern Cordillera to Llanos foreland basin. Collectively, the data presented here for the frontal Eastern Cordillera define a general in-sequence pattern of eastward-advancing fold-and-thrust deformation during Cenozoic east-west shortening in the Colombian Andes.

Formation water flow and diagenesis in the Colombian Llanos foreland basin

The Llanos Basin of Colombia, a foreland basin of the Eastern Andean Cordillera, is a petroleum-rich province in which the water/oil ratio found in the reservoirs is anomalously large, with up to 80% water and only 20% hydrocarbons. This formation water has low salinity. Within foreland basins, flow of fresh water has generally been explained by basin-scale circulation of meteoric water percolating from adjacent topographic highs. An alternative origin is tested here by 3D modelling: the low salinity water is released by smectite-illite transformation. Since 50% of the sediments within the Llanos Basin are mudrocks, the modelling results show that a significant volume of water has been added by diagenetic reactions in the northern and western parts of the basin. The peak of low salinity water generation by diagenesis occurs at a depth of about 4 km, where compaction is almost complete. Results show that neglecting the mineral dehydration reactions can lead to misinterpretation of overall mass balance and fluid transfer operating at the basin scale.

Migration of Cenozoic deformation in the Eastern Cordillera of Colombia interpreted from fission track results and structural relationships: Implications for petroleum systems

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 4–7N 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.

Possible correlation between miocene global climatic changes and magnetic proxies, using neuro fuzzy logic analysis in a stratigraphic well at the Llanos foreland basin, Colombia

In this work we have assessed the hybrid algorithm of NeuroFuzzy logic (NFL), to establish a correlation between global climatic changes (benthic foraminiferal δ18O data), experimental S-ratio (factor characterizing stability of remanent magnetization) and magnetic susceptibility (κ). Magnetic proxies have been measured in 44 samples of the Colombian stratigraphic well Saltarin 1A (distal Llanos foreland basin). κ and Sratios were linked to global δ18O data assuming a constant accumulation rate for a 305 meters thick stratigraphic interval flanked by the two palynological age constrains available. This interval encompasses, from top to base, the bottom of the Guayabo formation, the Leon, and the upper unit of the Carbonera formations (lower to middle Miocene). The best inference is accomplished applying a Takagi-Sugeno-Kan (TSK) fuzzy model with four fuzzy rules and the δ18O, S-ratios and κ data used in a linear form to train the system. These results are interpreted as the outcome of a significant influence of global climatic changes upon magnetic proxies. A stronger correlation is perhaps prevented by the likely influence of local and regional tectonic events and climatic changes that could have affected the distal segment of the Colombian Llanos foreland basin during Miocene times. We argue that late diagenesis of primary magnetic minerals and the assumption of a constant accumulation rate might have a minor influence on these results.

Linking sedimentation in the northern Andes to basement configuration, Mesozoic extension, and Cenozoic shortening: Evidence from detrital zircon U-Pb ages, Eastern Cordillera, Colombia

Laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) analyses of 29 samples from the Eastern Cordillera of Colombia reveal the origin of northern Andean basement and patterns of sedimentation during Paleozoic subsidence, Jurassic–Early Cretaceous extension, Late Cretaceous postrift subsidence, and Cenozoic shortening and foreland-basin evolution. U-Pb geochronological results indicate that presumed Precambrian basement is mainly a product of early Paleozoic magmatism (520–420 Ma) potentially linked to subduction and possible collision. Inherited zircons provide evidence for Mesoproterozoic tectonomagmatic events at 1200–1000 Ma during Grenville-age orogenesis. Detrital zircon U-Pb ages for Paleozoic strata show derivation from Andean basement, syn depositional magmatic sources (420–380 Ma), and distal sources of chiefl y Mesoproterozoic basement (1650–900 Ma) in the Amazonian craton (Guyana shield) to the east or in possible continental terranes along the western margin of South America. Sedimentation during Jurassic–Early Cretaceous rifting is expressed in detrital zircon age spectra as Andean basement sources, recycled Paleozoic contributions, and igneous sources of Carboniferous–Permian (310–250 Ma) and Late Triassic–Early Jurassic (220–180 Ma) origin. Detrital zircon provenance during continued Cretaceous extension and postrift thermal subsidence recorded the elimination of Andean basement sources and increased infl uence of craton-derived drainage systems providing mainly Paleoproterozoic and Mesoproterozoic (2050–950 Ma) grains. By Eocene time, zircons from the Guyana shield (1850–1350 Ma) dominated the detrital signal in the easternmost Eastern Cordillera. In contrast, coeval Eocene deposits in the axial Eastern Cordillera contain Late Cretaceous–Paleocene (90–55 Ma), Jurassic (190–150 Ma), and limited Permian–Triassic (280–220 Ma) zircons recording initial uplift and exhumation of principally Mesozoic magmatic-arc rocks to the west in the Central Cordillera. Oligocene–Miocene sandstones of the proximal Llanos foreland basin document uplift-induced exhumation of the Eastern Cordillera fold-thrust belt and recycling of the Paleogene cover succession rich in both arc-derived detritus (dominantly 180– 40 Ma) and shield-derived sediments (mostly 1850–950 Ma). Late Miocene–Pliocene erosion into the underlying Cretaceous section is evidenced by elimination of Mesozoic– Cenozoic zircons and increased proportions of 1650–900 Ma zircons emblematic of Cretaceous strata.

An integrated analysis of an orogen-sedimentary basin pair: Latest Cretaceous-Cenozoic evolution of the linked Eastern Cordillera orogen and the Llanos foreland basin of Colombia

The integration of restored basin geometry and internal features of syntectonic units (e.g., stratal architecture, thickness, sandstone composition) with fl exural modeling of the lithosphere constrains the evolution of a basin and its fl exural history related to orogenic growth (spatial/temporal loading confi guration). Using this approach, we determined the Maastrichtian-Cenozoic polyphase growth of the Eastern Cordillera of Colombia, an inverted Mesozoic extensional basin. The record of this growth occurs in an Andean (post‐middle Miocene) thrust belt (the Eastern Cordillera) and in adjacent foreland basins, such as the Llanos Basin to the east. This approach permitted the identifi cation of fitectono-stratigraphic sequences in the foreland basin and fi ve phases of shortening for the Eastern Cordillera. Thermochronological and geochronological data support the spatial and temporal evolution of the orogen‐foreland basin pair. Tectono-stratigraphic sequences were identifi ed in two restored cross sections, one located at a salient and the other in a recess on the eastern fl ank of the Eastern Cordillera. The lower two sequences correspond to late Maastrichtian‐Paleocene fl exural events and record the eastward migration of both tectonic loading and depositional zero in the Llanos Basin. These sequences consist of amalgamated quartzarenites that abruptly grade upward to organic-rich fi ne-grained beds and, to the top, light-colored mudstones interbedded with litharenites in isolated channels. Amalgamated conglomeratic quartzose sandstones of the third sequence record ~15 m.y. of slow subsidence in the Llanos Basin and Llanos foothills during early to middle Eocene time, while shortening was taking place farther west in the Magdalena Valley. The fourth sequence, of late Eocene‐ middle Miocene age, records a new episode of eastward migration of tectonic loads and depositional zero in the Llanos Basin. This sequence begins with deposition of thick fi ne-grained strata to the west, whereas to the east, in the Llanos basin, amalgamated quartzarenites unconformably overlie Cretaceous and older rocks (former forebulge). Apatite fi ssion tracks in the axial zone of the Eastern Cordillera, growth strata in the

Application of 3-D Reservoir Modeling to Development Planning and Management of the Cano Limon Field, Colombia

The Cano Limon field of the Llanos foreland basin, Colombia had a STOIIP of 2 billion barrels. A three-dimensional geological reservoir model has been constructed using the computer program MONARCH on the basis of data from 24 wells. The model includes the high net/gross M1 reservoir and the overlying, as yet undeveloped, low net/gross C5 reservoir, over an area of 9 [times] 3 km. The M1 reservoir comprises a network of fluvial sandbodies, deeply incised into a marine shale unit and may thus represent an incised valley-fill complex. The C5 interval comprises single-story channel sand bodies, isolated within thick floodplain deposits, indicative of much increased accommodation space. The Cano Limon model is represented by a matrix of 1.75 million volume elements ([open quotes]voxels[close quotes]), each measuring 50 Y 50 m horizontally and 0.6 m vertically. At each voxel, the model indicates whether shale or sand is present. MONARCH differentiates between genetic sandbody types: channel, mouthbar, and crevasse splay. Correlatable sand are mapped using a deterministic approach and the lateral extent of non-correlatable sandbodies is derived using statistical distributions of width/thickness ratios. MONARCH combines structural information, as derived from seismic, with information about sand body orientation, as provided by dipmeter, oriented more » cores and seismic amplitude maps. In the case of Cano Limon, which is produced by a strong aquifer drive with a mobility ratio of 11, this level of 3-D data integration helps provide reliable guidelines for the further development and management of the field. « less