Presentaciones a Congresos

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Polymer viscosity: understanding of changes through time in the reservoir and a way to predict them
(2019-09) Katz Marquez, Román E.
Polymer rheological behavior in an Enhanced Oil Recovery (EOR) project is one of the critical factors to determine whether the polymer injection would be effective to increase the oil production in a field. Due to complications on the measurement of this parameter and its variation within the reservoir, the challenge of understanding viscosity behavior relies on lab and field tests that become key factors to solve this issue. This study was conducted during an injectivity test for an EOR project in Los Perales field (Santa Cruz, Argentina) in three wells with different operational and subsurface conditions, and tests were performed twice a day for 30 days each in order to obtain sufficient time span of data. From lab rheology tests performed at reservoir conditions, where the main objective was to analyze viscosity changes through time, two different tendencies were observed: one that affects in early times and another that becomes preeminent at late times. With these results, a describing equation was developed to predict viscosity evolution over time. The equation consists of three terms including thermal variation, chemical degradation and the final viscosity towards which the polymer tends. Although the equation properly describes both lab and field polymer solution, there is a considerable difference, especially when the effects mentioned become preponderant. This difference is attributed to both the water used for the mixture and the possible impurities that may be incorporated during the maturation or transfer of the polymer. Since most of the data used was obtained from field tests, this emphasizes the appliance of the equation on the field. Impurities turn out to be crucial, specially oxygen (O2) and hydrogen sulfide (H2S) combined. Their presence highly impacts the asymptotic viscosity, so a correlation between H2S content and final viscosity was also developed. Finally, an analysis of the temperature influence on the viscosity was conducted. A correlation between the final viscosity and temperature was found and used to incorporate temperature variations in the predictions and therefore to relate measurements performed at different conditions. The primary advantage of this study is that the equation and correlations enable the prediction of the polymer solution viscosity at any time. This allows the estimation of actual polymer viscosity in the reservoir from a routine measurement at any temperature and impurities content. The versatility of this equation is what makes it novel and useful in an industry going towards EOR projects.
Simulation of viscosity enhanced CO2 nanofluid alternating gas in light oil reservoirs
(2017-05) Gallo Jiménez, Gonzalo Augusto; Erdmann, Eleonora
"Thickened CO2 nanofluids are a mean to improve volumetric sweep efficiency and gas production in CO2 EOR projects in contrast CO2 flooding. Alternating injection of plain CO2 with thickened CO2 nanofluid is proposed as an economical alternative using the findings of CO2 viscosity enhancement through nanoparticles in current studies. This was achieved by using CMG GEM simulator and contrasting findings with other WAG and CO2 flooding simulations. The simulation was done on a light oil (40 °API) from a Neuquén Basin reservoir. A sensitivity analysis was done to contrast different type of injection schemes. As CO2 nanofluids can be tailor made in order to adjust their viscosity (and other properties like asphaltene deposition control) diverse results were observed. Nanofluids improve the volumetric sweet efficiency, and even low viscosity increment increase the overall gas utilization and conformance compared to CO2 flooding. Since there is no face change, the use of CO2 based nanofluids can be a mean to control CO2 EOR projects avoiding injectivity loss problems. It was observed that injection of mere nanofluid (without alternating CO2) is not technically nor economically convenient as it decreases production rates and has an overall lower economic performance than both WAG and CO2 flooding. Nevertheless, alternating nanofluid with plain CO2 enables higher sweep efficiency while lowering the operational costs due to lower volumes of nanofluid utilized. Adding nanofluid to a WAG scheme also shows improvements in EOR performance."
Depositional controls over the lacustrine source rocks of the cuyana basin: an approach to model a mechanical cyclicity through an integrated analysis of sequence stratigraphy, petrophysics and rock properties
(2017-05) Barredo, Silvia; Sosa Massaro, Agustín; Fuenmayor, Evanna; Abalos, Roxana; Stinco, Luis; Abarzúa, Fernando
"Integrating field and laboratory data is possible if there are strong geologic criteria to relate them. This challenge demands understanding rocks from the fabric and mineralogy up to the architectural elements of rock bodies at a basinal scale. The geological properties of rocks, being them clastic, chemical or biochemical, influence reservoir quality and hydrocarbon producibility, but continental mudrocks/siltstones (shales) are by far more complex because of their depositional nature and ighly variable vertical and lateral sedimentary characteristics. Grain size variability and sedimentary structures are common in these rocks. From outcrops, well logs and the source rocks of the Cuyana Basin (Argentina) could be characterized as deposited in lacustrine environments under a strong tectonic and climatic influence. Silty sandstones, limestones, massive and laminated bituminous shales developed in underfilled and balanced to overfilled lakes. They display arallel/inclined/rippled laminations, coarsening/fining upwards patterns, nodules, scour surfaces and pedogenic features. Total organic content may reach 14 % and corresponds to macro and micro floral remains, reshwater invertebrates and kerogen types I and II. These lithofacies are vertically stacked in patterns that can be related to cycles with different mechanical properties. In outcrops and with the help of seismic lines third order depositional sequences representing basin variations in accommodation space were recognized as low accommodation (LAS) to high accommodation (HAS) sequences developed in each of the three rifting stages. Using detailed information about mineralogy and fossil content climate was characterized and fourth order parasequences could be characterized. Fifth order (bedset-rhythms) cycles were interpreted on the basis of outcrops and well logs. Inorganic (especially clays) and organic content, pedogenic fabric, burrows and microfracturing represent weakness planes and as they vary according to these cycles, it was possible to model a mechanical cyclicity along the whole lacustrine column and to analyze their depositional controls. This integrated study has provided relevant data for the understanding of the geological and mechanical properties that will contribute to the optimization of fracture programs."
A fluid structure interaction model for hydraulic fracture simulation on Vaca Muerta Argentina shale formation
(2017) Alderete, Ignacio D.; Sosa Massaro, Agustín; D'hers, Sebastián
"Vaca Muerta Formation in Neuquén Basin, Argentina, is one of the great worldwide promises given its potential as a non-conventional reservoir. Because of the intrinsic heterogeneity and low permeability, hydraulic fracturing is a required operation to stimulate the reservoir for better production. Simulation becomes a desirable tool to make fractures more efficient and get predictable outcomes. For this purpose, a 3D finite element analysis is performed using ADINA software to model reservoir response during the hydraulic fracturing process. This iterative, fully coupled model uses fluid structure interaction (FSI), porous elastic media and stratified materials with transversely isotropic (TI) properties. The allowed fracture distribution is proposed beforehand. A cohesive model is added via non linear springs placed along the fracture proposed path. Material models are calibrated using data from well logs and microseismics taken from one well located in the field. All the information obtained from that well is then filtered for a particular region of interest in depth, determined by the mechanical properties observed. Regarding the calculation procedure, as initial condition for the stimulated reservoir volume (SRV) the stress strain state measured in the field is adopted. Then hydraulic fracture process is simulated pumping fluid through punched holes and then fracture opening is analyzed, based on nodes displacement along the proposed path, to characterize fracture's opening and extension. The resulting state of stress developed after the fracture is updated at every calculation step. Key information such as resulting pore pressure and effective stresses can be easily computed along the fracturing process. Once obtained results are compared to analytical solutions and experimental data obtained from fractures performed in similar soil conditions with good agreement. The developed model can tackle a variety of reservoir volumes, considering stratification, geomechanical properties, fracture fluid, fracture paths and the initial state of stress. Natural cracks can be added in a rather simple fashion by adding fractures to the proposed distribution with adequate fracture strengths."
Discounting rate: a matter of common sense rather than a theoretical problem
(1999) Rosbaco, Juan
“Different rates proposed by several authors to discount cashflows of given projects are discussed. The paper starts by reviewing what the objectives of an evaluation are and later presents the different discount rates suggested by the authors. After a theoretical but fundamentally logical analysis it is concluded that there is no universal discount rate that can be used in all situations; to do so would disregard both the fact that an evaluation can have different objectives and that the environment in which projects will be carried out and companies will develop is unique in each case.”
Multiple internal rates of return: when to anticipate multiple IRRs and how to take advantage of them to perform a better evaluation
(1999) Rosbaco, Juan
“There are different rules to delimit or exactly determine the number of Internal Rates of Return a project may have or has. These rules show that, when the sequence of signs of the cumulative cash flow vs time function is the normal one - negative figures at the start and then only positive ones – there is only one Internal Rate of Return. There are few projects in which there are multiple intersections of cumulative cash flow with the time axis : a number of acceleration projects, complex financing investments, and a few other serial projects. However, not all of them have multiple Internal Rates of Return. The discussion presented in this paper addresses the question of how to empirically infer the existence of multiple rates, and how to use them for the benefit of the evaluation. Moreover, it demonstrates that all multiple rates have the same physical meaning, which does not vary with respect to the traditional single rate case.”
Importance of the study of environmental aspects in the exploitation of unconventional reservoirs for risk assessment of the activity in Argentina
(2017) De La Zerda, María Agustina; Erdmann, Eleonora; Sarandón, R.
"The objective of this work is the analysis of the envoronmental aspects associated to the extraction of UH (shale and tight)... The novelty of this work is the analysis of the factors the determine the environmental risk in the extraction of UH, especially in the hydraulic fracturing process, which includes technologies, environmental conditions at the site and the legal context in the region. This allows indentify the areas of higher and lower level of environmental risk in order to proceed to the identification, implementation and development of potential mitigation measures to achieve the sustainability of the activity."

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