The El Niño - Southern Oscillation (ENSO) has global effects on the hydrological cycle, agriculture, ecosystems, health, and society. We present a novel non-homogeneous Hidden Markov model (NHMM) for studying the underlying dynamics of sea surface temperature anomalies (SSTA) over the region, 150E -80W, 15N-15S from Jan-1856 to Dec-2019, using the monthly SSTA data from the Kaplan Extended SST v2 product. This non-parametric Machine Learning scheme dynamically simulates and predicts the spatiotemporal evolution of ENSO patterns, including their asymmetry, long-term trends, persistence, and seasonal evolution. The model identifies five hidden states whose spatial SSTA patterns are similar to the so-called “ENSO Flavors” in the literature. From the fitted NHMM, the model shows that there are systematic trends in the frequency and persistence of the regimes over the last 160 years that may be related to changes in the mean state of basin temperature and/or global warming. We evaluated the ability of NHMM to make out of sample probabilistic predictions of the spatial structure of temperature anomalies for the period 1995-2016 using a training period from Jan-1856 to Dec-1994. The results show that NHMMs can simulate the behavior of the Niño 3.4 and Niño 1.2 regions quite well. The NHMM results over this period are comparable or superior to the commonly available ENSO prediction models, with the additional advantage of directly providing insights as to the space patterns, seasonal and longer-term trends of the SSTA in the equatorial Pacific region.

In this study we describe an innovative method to determine potential sites for optical and infrared astronomical observations in the Andes region of northern South America. The method computes the Clear sky fraction (CSF) from Geostationary Observational Environmental Satellite (GOES) data for the years 2008-12 through a comparison with temperatures obtained from long-term records of weather stations and atmospheric temperature profiles from radiosonde. Criteria for sky clearance were established for two infrared GOES channels in order to determine potential sites in the Andes region of northern South-America. The method was validated using the reported observed hours at Observatorio Nacional de Llano del Hato in Venezuela. Separate CSF percentages were computed for dry and rainy seasons for both, photometric and spectroscopic night qualities.Twelve sites with five year averages of CSF for spectroscopic nights larger than 30% during the dry seasons were found to be suitable for astronomical observations. The best site with (220±42) spectroscopic clear nights per year is located in the Andes of Venezuela (70 • 28'48"W, 9 • 5'60"N) at an altitude of 3480 meters.Lower quality regions were found in Sierra Nevada de Santamarta and Serranía del Perijá with (126±34) and (111±27) clear nights per year, respectively. Sites over the Andes are identified in Norte de Santander with (107±23) and in the north-east part of Boyacá with a mean of (94±13) clear nights per year. Two sites at low latitude located in Ecuador with more than 100 clear nights per year and with similar seasonal CSF percentages were also identified. Five year evolution suggest a possible correlation between the lowest percentages observed during the rainy seasons of 2010 and 2011 with positive values of the Southern Oscillation Index. Subject headings: Astronomical Instrumentation. Recently, Marín et al. (2015) computed the CSF at high altitude sites by using a new clearance algorithm based on global meteorological models. CSF values were then used for precipitable water vapour estimations at two astronomical sites in the north of Chile. Even though most of the methods are based on the comparison of radiances, fluxes or temperatures at each pixel of the satellite image with threshold values previously defined there is no standard methodology for CSF computations. Cavazzani & Zitelli (2013) used -5monthly thresholds defined as the maximum radiance at clear nights along the month.Thresholds may also be defined by using an atmospheric model (9). In this study, we introduce a novel methodology involving the use of monthly thresholds of temperature at different altitudes from the surface up to the upper troposphere. Our thresholds definitions were based on the altitude of the terrain, long-term records of weather stations and radiosonde data archives.The thresholds definitions are based on monthly mean records of both, air temperature at the site and vertical temperature profile between 8 and 10 km of altitude which make more precise the predictions for clear...

The physical description of the atmosphere’s general circulation over Northern South America and Meso-America deserves a more comprehensive explanation. This work presents the Pacific coast of Colombia as the rainiest place on Earth, with annual rainfall averaging 5000 to 13,000 mm, and record values as high as 13,159 mm for the location of Puerto López (77∘14′ W, 2∘50′ N). Using information from the ECMWF ERA-40 Atlas and ERA-Interim Reanalysis, we describe the existence of a concentrated diabatic heating source due to condensation and the main features of its related circulation over Northern South America and Meso-America. For simplicity, we used the analytical solution of the Phlips-Gill Model to diagnose the main flow patterns. Results show that the diabatic source over western Colombia generates equatorial trapped Rossby-Kelvin waves, which dominate the low-level circulation. A Kelvin wave explains the low-level easterly flows over the Tropical Atlantic Ocean, the Caribbean Sea, the Venezuelan-Colombian Llanos, and the Northern Amazon Basin. This circulation is analogous to a Walker cell. To the west, two cyclonic flows and strong westerly winds are present in Meso-America and the far eastern Pacific because planetary waves propagate there. A slight asymmetry in the equator’s diabatic heating location is responsible for the intense low-level pressure over Panama. The vertical velocity over the source area induces vortex tube stretching, and zonal mean flow excites a mixed wave and a northward flow.

Managed Pressure Drilling (MPD) is an existing technology that is emerging in Deepwater drilling operations. This paper provides a case study from the Operator’s view, of preparing and deploying an MPD Surface Back Pressure (SBP) system for use in a shallow horizontal well with narrow drilling margins in 8,000ft water depth in the Gulf of Mexico. This paper will describe the engineering, preparations and operational challenges of deploying a Below Tension Ring (BTR) MPD system. The paper will also include information on the hazard assessments, Mud Gas Separator (MGS) considerations, training plan, deployment plan and results, and engagement with the regulator. The paper will present a case for the requirement of MPD for use in the narrow margin shallow horizontal wells, including an analysis of the required mud weights and surface back pressure to drill through narrow margins. It will also include a summary of best practices and lessons learned.

Naturally fractured sandstone reservoirs are susceptible to drilling mud damage both at the fracture and matrix level. This problem becomes especially severe as reservoir pressure depletes due to: (i) the loss of backpressure preventing static and dynamic mud losses and; (ii) loss of energy for well clean up. Although several completion practices are covered by the experimental techniques described, of special interest in this study is cemented and perforated liners which can have some particular constraints if not properly designed and executed when drilling and completing mature naturally fractured sandstone reservoirs.While drilling, the overbalance pressure exerted by the drilling mud on producing formations is a means for avoiding wellbore stability problems. When the reservoir pressure is close to its initial value, the near-wellbore region affected by mud losses and invasion is normally restricted to a few inches. Additionally, the reservoir often has enough energy to overcome filtrate damage within the rock matrix and inside natural fractures. This condition changes as reservoir becomes depleted, as a higher drilling overbalance occurs for the same mud weight, and reservoir energy for subsequent well clean-up is reduced.The following study presents an experimental evaluation of synthetic oil-based mud (SOBM) drilling damage on naturally fractured reservoir cores. Two conditions were simulated: first, a condition in which mud invasion takes place into open natural fractures, followed by simulated under-balanced perforating and post draw-down stimulation. A second scenario is then considered in which simulates mud invasion into open fractures, but which is then followed by on-balance perforating and stimulation, and only after this is a draw-down imposed on the sample.Results from the study indicate that very high levels of formation damage are caused when natural fractures get plugged and/or closed-over by mud filter-cake and lost circulation material (LNM) solids. Fluid pressure drawdown in the nearwellbore region and induced fracture closure pressures can, in the field, essentially create a compacted "new rock", with very low permeability and very high tensile stress. In this particular case study, this last condition is evident in the very low injectivity of the stimulation fluid and the very low value of regained permeability. When natural fractures are stimulated before imposing a drawdown, very good return permeability is achieved with an even higher value after closing fractures and re-stimulating.