Sensitivity analysis of the backprojection imaging method for seismic event location

Accuracy of earthquake location methods is dependent upon the quality of input data. In the real world, several sources of uncertainty, such as incorrect velocity models, low Signal to Noise Ratio (SNR), and poor coverage, affect the solution. Furthermore, some complex seismic signals exist without distinguishable phases for which conventional location methods are not applicable. In this work, we conducted a sensitivity analysis of Back-Projection Imaging (BPI), which is a technique suitable for location of conventional seismicity, induced seismicity, and tremor-like signals. We performed a study where synthetic data is modelled as fixed spectrum explosive sources. The purpose of using such simplified signals is to fully understand the mechanics of the location method in controlled scenarios, where each parameter can be freely perturbed to ensure that their individual effects are shown separately on the outcome. The results suggest the need for data conditioning such as noise removal to improve image resolution and minimize artifacts. Processing lower frequency signal increases stability, while higher frequencies improve accuracy. In addition, a good azimuthal coverage reduces the spatial location error of seismic events, where, according to our findings, depth is the most sensitive spatial coordinate to velocity and geometry changes.

Suitability assessment for electricity generation through renewable sources: towards sustainable energy production

Power generation through renewable sources is an effective alternative to mitigate climate change as its environmental impact is lower compared to fossil fuels. However, socio-economic problems are constant in sites where power plants are installed, especially in developing countries. In this paper, an innovative methodology was developed to assess the suitability of electricity generation through solar, wind, and biomass energy. Unlike most studies found in scientific literature, this work considers social, environmental, and economic aspects as key to determine the suitability of energy projects. First, we carried out a comprehensive analysis on social acceptance and resilience towards renewable energy and the conditions for communities to benefit from these projects; then, we analyzed the availability and capacity of renewable energy sources in Mexico, as a case study. Next, a set of indicators related to the three pillars of sustainability was developed to assess the conditions of each place with the best renewable resources in the country. The life cycle and capacity factor of each technology were also considered. Lastly, a mathematical model was developed to determine the most suitable locations and technologies for power generation. The results show a trend towards the states of northern Mexico, especially those bordering the United States, as the most viable for electricity generation. The most appropriate technology is wind energy. Finally, Oaxaca, the state with the best wind resources and current leader in wind power generation in Mexico is, by contrast, the least viable state for wind generation, as has been later confirmed by scientific evidence, as wind facilities are associated with severe socio-cultural and economic damage in host communities in this state.

Comparative analysis of matching pursuit algorithms for Kirchhoff migration on compressed data

Currently, the amount of recorded data in a seismic survey is in the order of hundreds of Terabytes. The processing of such amount of data implies significant computational challenges. One of them is the I/O bottleneck between the main memory and the node memory. This bottleneck results from the fact that the disk memory access speed is thousands-fold slower than the processing speed of the co-processors (eg. GPUs). We propose a special Kirchhoff migration that develops the migration process over compressed data. The seismic data is compressed by using three well-known Matching Pursuit algorithms. Our approach seeks to reduce the number of memory accesses to the disk required by the Kirchhoff operator and to add more mathematical operations to the traditional Kirchhoff migration. Thus, we change slow operations (memory access) for fast operations (math operations). Experimental results show that the proposed method preserves, to a large extent, the seismic attributes of the image for a compression ratio up to 20:1.

Bulk rheology characterization of biopolymer solutions and discussions of their potential for enhanced oil recovery applications

Enhanced oil recovery (EOR) techniques are essential to improve oil production, and polymer flooding has become one of the promising technologies for the Brazilian Pre-Salt scenario. Biopolymers offer a range of advantages considering the Pre-Salt conditions compared to synthetic polymers, such as resistance to high salinity, high temperature, and mechanical degradation. In that sense, bulk rheology is the first step in a workflow for performance analysis. This paper presents a rheological analysis of four biopolymers (Schizophyllan, Scleroglucan, Guar Gum, and Xanthan Gum) in concentrations from 10 to 2,300 ppm, generally suitable for EOR applications, in temperature levels of 25, 40, 50, 60 and 70°C and two brines of 30,100 ppm and 69,100 ppm total dissolved solids, which aim to model seawater and the mixture between injected seawater and reservoir water typical in Pre-Salt conditions. The pseudoplastic behavior, the overlap concentration, and the activation energy were determined for each polymer solution. The structural differences in the polymers resulted in different rheological behaviors. Schizophyllan is the most promising, as its viscosifying power is higher than synthetic polymers comparable to Xanthan Gum. Its resistance at high temperatures is higher than that of synthetic polymers. Scleroglucan behaved similarly to Xanthan Gum, with the added advantage of being nonionic. Guar Gum had the lowest viscosities, highest overlap concentrations, and most pronounced viscosity decay among the tested polymers. To the author’s knowledge, rheological studies of the biopolymers presented here, considering the viscosities and the overlap concentration and activation energy, in the Pre-salt conditions, are not available in the literature and this will benefit future works that depend on this information

Assessment of reducing sugars production from agro-industrial wastes by batch and semicontinuous subcritical water hydrolysis

Reducing sugars produced from agro-industrial wastes by means of hydrolysis represent a promising alternative of chemicals and energy. Yet, large scale production still struggles with several factors involving process complexity, sugars degradation, corrosion, enzyme recyclability, and economic feasibility. More recently, sub and supercritical water hydrolysis has been reported for the production of reducing sugars as a readily available alternative to acid and enzymatic biomass hydrolysis. Accordingly, in this work, the results of batch and semicontinuous lab scale subcritical water hydrolysis experiments of agro-industrial wastes of pea pot and corn stover are discussed. Experiments were carried in the temperature range 250 to 300 °C, pressures up to 3650 psi, residence times up to 30 minutes in batch mode operation, or water flowrates up to 12 mL/min in semicontinuous mode operation. Produced sugars were assessed in the effluent of each experimental run by means of dinitrosalicilic acid method (DNS). A maximum total reducing sugar (TRS) yield of 21.8% was measured for batch pea pot subcritical water hydrolysis experiments at 300°C, 15 minutes, 3650 psi, and 1:6 biomass to water mass ratio. Semicontinuous subcritical water hydrolysis of corn stover showed a maximum TRS accumulated yield of 19% at 290 °C, 1500 psi, and water flowrate of 9 mL/min. The results showed the feasibility of producing reducing sugars from agro-industrial wastes currently discarded through subcritical hydrolysis.

Critical factors for unconventional hydrocarbon resources development

Countries all over the world struggle to exploit their Unconventional Hydrocarbon Resources (UHR) to secure energy supply, but only a few of them have succeeded. Regulators and decision-makers should understand the critical factors required for companies to attract capital, technology, and good practices to promote innovation and generate the virtuous cycle that translates into sustainable production. This study seeks to identify the most relevant factors for UHR commercial development. We assessed the UHR exploiting state in 60 countries and identified the critical common development factors for the 22 that are most active. The proposed Unconventional Hydrocarbon Development Index (UDI) allows to model, rank, benchmark, and forecast UHR development activity for any given country. We focused on the case of Colombia to illustrate the validity of this Index. Evidence suggests countries where National Oil Companies (NOCs) address the challenge of exploiting UHR on their own, may lack the required expertise, despite having governmental support and capital availability. It is easier for them to emulate resilient North American firms exploiting UHR by partnering with them to effectively incorporate best practices Governments can facilitate the process through UHR support, surface and subsurface risk reduction, a proper tax regime, and ESG practice promotion.

Ultraviolet Radiation to control Bacteria in oil well injection water

Biocorrosion is a phenomenon that strongly affects the integrity of the materials used in the oil and gas industry. Different types of biocides are currently used to control bacteria in industrial water; however, they have disadvantages such as microbial resistance to these chemical compounds and possible impact on biodiversity due to eventual contamination of natural water. There are several alternatives for the elimination or control of bacteria, among which one is the use of type C ultraviolet (UV-C) radiation. Nevertheless, the use of these micro-organism removal systems could be affected by water quality and its efficiency can be improved by using LED diodes of lower energy consumption and greater versatility in exposure to high temperatures. This work was aimed to evaluate the use of such radiation as a strategy for the control and/or elimination of sulfate reducing bacteria (SRB), and acid producing bacteria (APB) present in both corrosion and souring processes. For this purpose, injection water from oil and gas industry and a dynamic system which flow variation enabled the evaluation of different water exposure times to UV-C light (1-20 minutes) were used. Efficiencies ranging between 99-100% were achieved in the elimination of SRB and APB from produced water measured by two different techniques, selective culture media for these microbial populations, and qPCR detecting a specific gene from the SRB population.

Computational study of particle distribution development in a cold-flow laboratory scale downer reactor

The use of downer reactors (gas-solid co-current downward flow) in the Fluid Catalytic cracking (FCC) process for the upgrading of heavy crude oil into more valuable products has gradually become more common in the last decades. This kind of reactor is characterized by having homogeneous axial and radial flow structures, no back mixing, and shorter residence times as compared with the riser reactor type. Although downer reactors were introduced a long time ago, available information in literature about the multiphase hydrodynamic behavior at FCC industrial scale is scarce. Therefore, it is necessary to conduct experimental and computational studies to enhance the understanding of the hydrodynamics of two-phase co-current downward flow. The Computational Fluids Dynamics (CFD) software, Ansys Fluent, is used to study two-dimensional gas (air) and solid (catalyst particle) flow in a downer section of a cold-flow circulation fluidized bed (CFB) system at a laboratory scale. The implemented computational model is validated by comparing numerical results for solid velocity and volume fraction with measurements carried out on a CFB system using a fiber-optic probe laser velocimeter. According to numerical results obtained for different gas velocity and solid flux, flow development cannot only be estimated by considering solid axial velocity changes along the reactor; it is also necessary to take into account solid volume fraction axial variations as radial profiles can change even when velocity profiles are developed.

Evaluation of performance and early degradation of a 180.8 KWP rooftop on a grid-connected photovoltaic system in a Colombian tropical region environment

The use of renewable energy such as photovoltaic is growing. According to IRENA, these systems are one of the most dynamic generation technologies. The global photovoltaic market has grown rapidly between 2000 and 2016 at an annual average compound rate of 44%, from 0.8 GW to 291 GW. In Colombia, regions with high solar irradiation levels have been identified as emerging markets. The Government's plan is to increase the share of non-conventional energies in the energy matrix from 2% to 8% - 10%. However, the uncertainties associated with technology and sites specific degradation rates make it difficult to calculate accurate electricity generation efficiencies and predicting future performance and material degradation rates, and thus business models exhibit considerable deviations related to the real electricity generation rates. This work studies the performance and early degradation of a 180.8 kWp rooftop on grid connected photovoltaic system, installed in Barranquilla, Colombia. Two methods were used: i) estimation of solar conversion efficiency, and ii) visual inspection. The first method includes a cross analysis of climatic conditions, irradiance levels, and the generated energy downstream the inverters. The second method consists of periodical visual inspections of installed modules to check: discoloration, delamination, busbar corrosion, cracking of solar cell, glass breakage, anti-reflection coating, and solder bond.

Mass balance of Neogene sediments in the Colombia basin relationship with the evolution of the Magdalena and Cauca River basins

The Colombia basin contains large volumes of sediment accumulated during the last 17 My. The use of isochore maps, exploratory wells, micropaleontological and geochronological dates has enabled us to estimate the volumes of sediment and accumulation rates in this basin. The analysis of source of sediments and exhumation data from the Northern Andes of South America led to the definition of areas and thicknesses of material eroded during the Neogene - Quaternary, to obtain volumes or material eroded from the continent that can be correlated with sediment volumes accumulated in the Colombia Basin. The analyzed sediment volumes suggest that during the last 17 My ~72.06x1015 Tons accumulated in the Colombia Basin, while ~ 7.16x1013 Tons accumulated in the continental catchment areas. The sedimentation in the Colombian Basin has occurred at variable rates, with values ranging from 55 MTons/My to 295 MTons/My, with a peak of 803 MTons/My in the early Pleistocene (between 2.4 and 2.2 Ma). The evaluation between the total volumes of sediment accumulated in the offshore and onshore, suggests that in the continental part of the basin less than 4% of the total volume of eroded sediment is trapped and, therefore, the behavior of the accumulation rates calculated in the offshore directly reflect the relief evolution of South America’s Northern Andes. It seems, at large, that the lithospheric convergence rates and subduction angle (South America vs Nazca and Meso Atlantic opening) have controlled the regional exhumation of the Northern Andes, with the exception of the Pleistocene high sedimentation event, which seems to coincide with local events such as the collision of the Panama Arch against Western Antioquia. It may be concluded that thanks to this collision, drainage systems such as those of the Magdalena and Cauca rivers were modified, which resulted in the formation of the Magdalena Submarine Fan.