bluuebunny/crossref_metadata_2025 huggingface dataset:
Heavy Oil in Ecuador: Pungarayacu Field, New Insights and Predictions for Development Strategy
Authors: Males Saverio Carlos Alfredo , Miranda Díaz Guillermo Javier , Palacios Serrano Diego Gabriel
Published: July 2020

Pungarayacu field is believed to has the largest heavy oil concentration in the Ecuadorian Oriente Basin. This study re-evaluates the Original Oil in Place (OOIP) and the potential reserves to be obtained by applying SAGD and steam flooding. The static and dynamic models were constructed considering new stratigraphic and sedimentological findings.

The proposed static model includes non-reservoir coaly facies obtained from density logs in order to generate a new petrophysical interpretation. Considering that some wells were drilled 30 to 40 years ago and the density logs were either reported in counts per second or non-existent, it was necessary to create a synthetic density log by Neural Network (NNT) for most of the wells in the northern part of Pungarayacu. A structural model was developed that represented the geological structure of the Hollin formation. Field is compartmentalized due to the presence of faults that generate several blocks with different WOCs (Water Oil Contacts). For building stratigraphic and sedimentological model, it was used stratigraphic correlations and previous depositional environments analysis of Upper Hollin sandstone (influenced by tides) and Lower Hollín sandstone (fluvial). For the petrophysical model the petrophysical properties distribution were based on probability maps and variograms. Pungarayacu oilfield has 8°API and a viscosity from 66,000 cp to 11,000,000 cp at 40°C showing severe oil biodegradation. Considering previous EOR screening analysis, the injection pilot of Cyclic Steam Stimulation developed by the last operator in the field and the quality of the sand; SAGD technique was applied in areas where the Hollin formation presents a low presence of shale and sandstone continuity; this allowed to develop a steam chamber for efficient oil drainage. In areas with shale intercalations, steam flooding was applied, because it allows lateral sweeping of the oil zone and improve the recovery factor. The new OOIP reported is approximately 21 billion barrels, from which 12.7 billion barrels can be produced by these two EOR thermal methods and the other 8.3 billion barrels are considered to be at depths shallower than 95 meters. In addition, the simulation results show that in 15 years the recovery factor will be 1.52 percent, equivalent to approximately 194 MMSTB, and in 32 years the recovery factor will be 3.15 percent equivalent to approximately 400 MMSTB.
Unexpected Low-Resistivity Pay Zone while Drilling a Horizontal Well: A Case Study from the Oriente Basin in Ecuador
Authors: Ameneiro Rosamary , Chiluiza Luis , Espinel Gavino , Guerrero Manuel Santiago , Ramirez Diana
Published: July 2020

Low-resistivity pay reservoirs have been described in many basins around the world. Technical information available explains the causes related to hydrocarbon bearing zones, represented by low resistivity values. These causes are mainly associated with mineralogy and complex pore structures. All the wells drilled and produced in the Johanna Este field in Ecuador have met the condition of pay zones with high resistivity values in relation to the well-known water formation resistivity.

A step change in the understanding of the main reservoir M1 sandstone occurred after drilling the horizontal well JE34H. The first half of the lateral section was drilled with resistivity values close to water resistivity. Vertical variations in the resistivity were confirmed in the second half of the well, with no lithologic barriers between both zones observed in the logs. The oil production obtained from this well was recognized as a field record, and the first time it was associated with low resistivity values.

After an exhaustive review of the available information including LWD electrical logs, the tool functioning, and cuttings description, it was possible to explain the low-resistivity pay within the M1 sandstone reservoir at the mineralogical level. The density-neutron cross-plots used for lithology identification show that the reservoir is mainly quartz with some mineral mixture. The target zone is mainly made up of medium-to-coarse grain with no visible matrix in the composition, showing no evidence of compaction or cement in density-neutron logs. Macroscopic anisotropy was also discarded as the reason for the decrease in the measured resistivity. In addition, structural compartments and preferential pathways for water invasion created by faults and/or fractures were discarded based on the azimuthal density image interpretation. The possible causes for the low resistivity pay were microporosity, presence of disseminated clay, and presence of conductive minerals. Special analysis (cores, magnetic resonance, capillary pressure, SEM) are required in order to understand the mineralogy and porosity distribution.

A low-resistivity pay within the M1 has opened a door for future analysis by means of conventional or special open hole and cased hole logs in order to identify reserves that could be bypassed.
Surface Facilities Development for Steam Flue Gas Injection in a Colombian Heavy Oil Reservoir
Authors: Perez Cordoba Jean Heli , Gonzalez Sanchez Edward David , Martinez Vertel Jaime Jose , Muñoz Navarro Samuel Fernando
Published: July 2020

Steam injection in heavy oil recovery often reaches the economical limit. Factors such as steam-oil ratio, generation costs, formation injectivity, reservoir pressure and heat losses are critical for the viability of these projects. This works presents a workflow to develop a scheme of surface facilities for different field conditions, that allows the capture, storage and usage of flue gas generated by steam generators and use it in a steam-flue gas injection process, which is going to mitigate the CO2 emissions, increase oil production and improve the results of steam injection alone in terms of energy efficiency.

The proposed workflow has 4 phases: 1) material balance to estimate the composition of flue gas generated based in generator parameters as gas feed, energy capacity and air excess; 2) numerical simulation of the involved processes as combustion, compression and heat exchange to study thermodynamic properties of the flue gas generated; 3) integrity analysis for equipment selection; and 4) determination of the most adequate scheme for flue gas managing according to field requirements.

Different case studies for surface facilities development are presented. High initial flue gas temperatures (400°F) and corrosion rates mainly by the presence of CO2 and O2 were identified as critical operation parameters. Since above 140°F corrosion rate gets higher compromising the integrity of the equipment, optimal relation between the gas feed used and an excess of air (15%) might allow a full combustion process decreasing the CO and hydrocarbons fraction in flue gas stream. Cooler units are required after the gas is compressed since the temperature raises, H2O separation has to be done after the first cooling process in order to mitigate the possible formation of carbonic acid on the stream; facilities dimensions are related to the capacity of steam generators and availability of flue gas volumes. The development of an adequate scheme of surface facilities requires an analysis of the conditions described before. Considering that each field has its own characteristics, the current workflow allows to develop optimal facilities for different projects using numerical simulation of multiple processes.

The methodology presented allows to determine the adequate facilities for different field conditions, in order to implement a steam flue gas enhanced oil recovery project that increases production and mitigates environmental impacts.
A Methodology to Identify the Root-Cause and Conditions of Sand Production, by Integrating Production, Reservoir and Completion Variables. Applied to a Colombian Field
Authors: Charry Torrado Anggie Paola , Vargas Silva Diego Armando , Mantilla Hernandez Hernan Darío , Quintero Peña Yair Andres
Published: July 2020

Sanding during hydrocarbon production is a critical problem in many fields around the world, in Colombia it is common in fields of the Magdalena Middle Valley, which entails high costs for operating companies due to continue cleaning and damaged equipment interventions, as well as, decrease in production. That is why predicting conditions under which sanding is being generated is an important component of field management. In this work a methodology has been applied that integrates into a diagnostic diagram: production information, sand production interventions, fluids, completion and formations, correlating the most critical sanding zones with the behavior of rock destabilizing variables such as: rates and fluid type (drag forces), liquid levels (drawdown impact) and rock competence.

From this analysis, it is possible to recognize the areas that are most sensitive to producing sand and the operating conditions that sharpen the scenario. For the field under study, Formation A was identified as the most prone to sanding due to the low resistance and degree of consolidation of its rocks, as well as the high water cuts and pressure depletion of the reservoir. Similarly, it was possible to identify drawdown management as a sanding-prevention measure, and the installation of Gravelpack as an exclusion method.

As a result of the state of the art carried out in support of this research, it was found that existing methodologies focus on estimating the stresses under which the rock fails and therefore produces sanding but they do not focus on analyzing the root cause and conditions that can cause sand production in the first place, which is important to understand the behavior of the rock under different stresses.
Quantification of Uncertainty in Model Based Type Well Construction
Authors: Ravikumar Arjun , Lee John
Published: July 2020

Production forecasting in unconventional reservoir systems is an important problem for the industry. While "averaging" observed production profiles is often used to construct type wells, model-based methods have significant advantages, including observance of basic fluid-flow principles. Model-based approaches for type well construction involve using analytical and numerical models for a representative well in a group of wells. Scaling factors are used to apply the model to the rest of the wells in the group. However, there is uncertainty in the estimates of these scaling factors that is not accounted for when we use point estimates. In this work, we calculate the uncertainty in the scaling factors in a group of analog wells. We then account for this uncertainty in the estimation of the P10, P50 and P90 type wells within the group of analog wells, using a Bayesian hierarchical model.

We select a group of analog wells and fit a model to a representative well in the group. We then calculate the scaling factor for each well in the group as a probability distribution. We pool these distributions to estimate the variation in scaling factors between different wells. This represents the uncertainty in the scaling factors across the group. We translate this into uncertainty in the production rate profile across the group. Finally, we generate P10, P50 and P90 production profiles from the distribution. These represent type wells for the group of analog wells.

We show that our technique is superior to point estimates of scaling factors traditionally used in the industry, due to pooling of distributions. Point estimates ignore possible variation in the scaling factor due to noise and presence of outliers. We show that this could accumulate and have a significant impact on the estimated type well. This propagates to the calculation of estimated ultimate recovery. We validate our method with simulated data, with and without added noise.

Forecasting production for producing wells and estimating production on proved undeveloped reserves are problems of engineering and economic importance. Existing methods using empirical averaging of production profiles or point estimates for scaling factors fail to use information on the uncertainty of the scaling factors. By discarding this information, we discard uncertainty that could influence reserves estimates. We present a method that incorporates this uncertainty into the analysis transparently. Our method can also be used to pool uncertainty across various well groups.
New Integrated Capillary Pressure and Initial Water Saturation Modeling
Authors: Liao Yizhu
Published: July 2020

This paper presents a new capillary pressure model, integrated and consistent capillary pressure modeling, and initial fluid saturation along wells and in reservoirs.

The new capillary pressure model is obtained by fitting Pc curves, end Pc values at end saturations, and threshold entrance Pc values satisfactorily. Analytical Pc derivative is then obtained. A consistent Pc derivative value can be used to obtain irreducible water saturation and corresponding maximum capillary pressure. After Pc curve fitting for multiple cores, correlations can be developed for the parameters in the new Pc model with different reservoir rock types and reservoir properties.

The new capillary pressure model is then used with free water level and reservoir fluid gravity to obtain the initial water saturation at any place in the reservoir. The initial water saturation vs. depth obtained dynamically from the new Pc model is integrated with that obtained statically from logs to achieve the integrated, reconciled, and consistent initial water saturation vs. depth.

Real examples are presented to show the step by step workflow procedure to obtain the new capillary pressure model and the integrated initial water saturation vs. depth. These examples include SCAL Pc curve data from cores and log Swi data vs. depth from wells in two offshore reservoirs.

This paper has three significant technical contributions. The new capillary pressure model is more versatile than those published and can handle Pc data while other existing Pc models cannot. The analytical Pc derivative from the new capillary pressure model can provide a consistent criterion for obtaining irreducible water saturation and maximum capillary pressure values for different rocks. The new capillary pressure model, when integrated with initial water saturation vs. depth from logs, can provide a consistent initial fluid saturation distribution in integrated static and dynamic reservoir modeling.
Connecting Wells in Environmentally Sensitive Areas Using Magnetic Ranging-While-Drilling Technology for Enhanced Hydrocarbon Recovery
Authors: Lips Jean Paul , Rassadkin Georgy , Dorey Jamie
Published: July 2020

When emergency situations in environmentally sensitive areas occur, drilling a relief well to intercept and kill the blowout well often requires various types of magnetic ranging technologies to navigate into the problematic well. Outside this scenario, we do not commonly hear about magnetic ranging.

The main objective of this paper is to raise awareness among operators about magnetic ranging-while-drilling technology as wellbore placement service to make planned wellbore intersections to boost production.

Reactivation of mature fields is often an economically viable option when demand for energy pushes oil prices upwards. In order to boost production from an existing mature field, an operator provided a service company with an interesting challenge: utilize proven directional drilling expertise in conjunction with alternative wellbore positioning techniques to drill two high-angle deviated wells from opposing directions and intercept a common vertical producer well for a gravity drainage concept. During the pre-planning phase, one of the major challenges was MWD survey accuracy for the horizontal wells. The 2-sigma major-axis uncertainty of the MWD surveys after applied corrections at the point of planned contact with the vertical producer was over 106 ft while the size of the target to intercept was only 1 ft in the lateral dimension.

Implementation of magnetic ranging while drilling technology combined with north-seeking gyroscopic sensor allowed optimal positioning of all three wells relative to each other. Bottom hole assembly equipped with a smart mud motor, MWD, and magnetic bit-sub avoided collisions and steered successfully between other producing wells in the mature field. This challenging project from two opposite surface locations took several weeks of directional drilling and resulted in precise positioning both horizontal drainage sections within close proximity of vertical producer. Hydraulic communication with the vertical producer was successfully established from both horizontal wells after completion of the drilling operations.
Assessment of the Potential for Gas Production from Marine Methane Hydrate Reservoirs by Numerical Simulation
Authors: Tomasini Juan , Stephen Karl
Published: July 2020

In this work the potential for gas production from two selected methane hydrate deposits which are situated offshore from Uruguay is assessed along with the validity of numerical simulations as a tool for analysis in this environment. Gas hydrates are crystalline solids formed by gas and water, in which gas molecules are accommodated within a solid water lattice in a cage-like structure. They form in thermobaric conditions of relatively high pressure and low temperature which in nature occur in permafrost and deep water sediment environments. Marine methane hydrates represent a huge potential as an unconventional gas resource and production tests have already been perfomed offshore Japan and China confirming the validity of depressuration as a method of production.

Available 3D seismic data was utilized for the identification of interesting areas for gas hydrate studies focused on resource exploitation allowing the acquisition of the corresponding architectural parameters. Due to the lack of well data at the selected locations, geological models and reservoir properties were defined based on published data from studies on analogue situations including data from the first production test performed offshore of Japan. Reservoir simulations were carried out to assess the response of selected prospects to depressurization induced dissociation.

Two prospects, interpreted as turbidite type deposits and located at 1850 m and 788 m of water depth, were selected for the modelling studies. The simulation of short term production tests of 60 days indicates average gas release rate values from 34 100 std m3/d to 6700 std m3/d for the deeper and shallower prospect respectively. The simulations were greatly affected by geometrical non-geological parameters like the proximity of model boundaries as well as type and level of discretization. We found that for finer discretization cases, the use of logarithmically distributed radial grid cells led to the existence of artifacts at early time on the gas release rate curves while the use of uniformly distributed radial cells results in more stable behaviour of the gas release rate. Several realizations of the geological models were used and sensitivity analysis was carried out regarding permeability and hydrate saturation. A longer term production regime (10 years) for a heterogeneous layered case was also simulated for the deeper prospect resulting in very useful average gas release rates of approximately 70 000 std m3/d, essential to satisfy gas requirements of Uruguay. We predict that only a few wells would be needed.

For the first time, reservoir simulation was applied for prospects in Uruguay and the gas release potential for marine methane hydrate deposits in the Southern Atlantic margin was assessed. Simulation results are encouraging. Additionally the results of this work at the identified prospects may be useful for site selection for any future campaign for gas hydrate exploration offshore Uruguay.
New Alternative to Optimize Cyclic Steam Injection: Field Pilot
Authors: Bustos Acevedo Carlos Alberto , Yatte Garzon Fabian Camilo , Lozano Guarnizo Eduardo , Higuera Daniel
Published: July 2020

This paper presents a technical evaluation of the results obtained in a field pilot to optimize the cyclic steam stimulation (CSS) by evaluating the performance of the indicator of oil steam ratio (OSR). The pilot was based on numerical simulation, where several alternatives or strategies were identified to improve the current technique applied for wells with more of 15 cycles as a method of improved or enhanced recovery in a madure heavy oil field. In a heat transfer process, in this case used by cycle steam injection, once it has maximum use, the next step in most of the termal process is to apply or move to steam flooding tecnic, but the implementation of it requires high investments that currently are not viable. However, it is necessary to provide solutions that contribute to improve the CSS efficiency of the field.

The following workflow was developed: (1) research of literarature and field experiences of different alternatives to increase the actual CSS efficiency by only changing the steam injection strategy, without including additional costs related to additives or technologies. (2) selection of the pilot area based on the current petrophysical, production, steam injection conditions and supported by a numerical reservoir simulation model with different sensitivities to define the base case to be developed in the field and (3), the optimal case was implemented in the field during one year. Results are discussed in this paper. An area of the field under study was selected, considering the following conditions: low pressure, high water cut, number of CSS per well greater than 15, inefficient CSS response. (4) alternatives for the optimization of the CSS were identified; these were evaluated by numerical simulation and it was found the optimal development strategy the intermittent injection.

With these results, a field pilot was implemented which consisted of 3 injection wells in 3 different patterns, for a period of 12 months of evaluation. During this period, it was possible to reduce the strong decline in oil production presented in the area from 23% to increase to −25% A.e., saving 20,000 mmbtu/ of steam in a year, generating an increase in the OSR of 0.12 BBl / MMBTU; and a decreasing the number of well services jobs from 51 to 27. This result was achieved because areas with oil saturation that had not been previously stimulated in the conventional process of CSS were contacted under this new scheme. The current conditions of the field, low pressure and high saturation of unconnected remaining oil during the conventional cyclic steam injection until now applied in the field, led to propose new cyclic stimulation alternatives such as the one presented in this paper; highlighting the technical results of the pilot developed without additional cost, just changing the injection strategy to optimize the current state of the field.
A Gas Lift Innovative Completion Design for Extended Perforated-Interval Gas Wells. A 5 Year and 25 Wells Successful Experience in a Mature Gas Field, Agua Del Cajón Field, Neuquén Basin, Argentina
Authors: Bodini Santiago Alejandro , Gonzalez Montero Gustavo Daniel , Telleria Nicolas
Published: July 2020

Agua del Cajón Field produces from conventional and unconventional formations since 1970. As a mature gas field, the average gas rate per well is 7.000 m3/d with a GLR of 10.000. Reservoir pressure is 25% of its original and 70% of the wells produce from several formations, with perforated intervals longer than 500 meters.

As flow rate decreases, gas doesn't have enough turbulence to remove liquid, leading to an increase in dynamic bottomhole pressure due to liquid loading. This effect deepens the decline resulting in gas resources unproduced.

There are different solutions for these kind of problems: reducing wellhead pressure using compression, capillary strings for foamer injection, velocity string or gas lift.

Gas lift is an attractive solution to reach gas speeds higher than critical by injecting a supplementary gas flow. This technique has achieved good results during several years in Agua del Cajon field. Despite working properly in the tubing (being efficient to remove liquid from injection mandrels to surface), it didn't solve liquid accumulation in the perforated interval.

Capex developed a customized bottom-hole equipment that optimizes well performance, by injecting gas lift below the packer.

A cross-over packer with a concentric pipe design is used, allowing injected gas to be conducted through the annular space between them and to extract liquid and gas from the bottom of the well by the central tube of reduced diameter. The production gas can be produced with the liquid at the end of the pipe, or rise through the annular space (casing-outer tubing) and join the liquid production and injected gas through a crossover located below the packer. The advantage of this system is that it ensures the removal of liquids from the lower part of the well with an optimized flow of injection gas.

In the last 5 years, 25 devices were installed with operative success in all cases. Gas flow rate increased an average of 80% after the intervention. Liquid production increment is also observed in most cases. Reserves were gained as it was able to reduce the abandonment gas flow rate.
Combining Data Analysis and Simulation to Design the Largest Polymer Injection Pilot in Argentina
Authors: Perez Diego Gaston , Cocco Mauro Daniel , Pedersen Guillermo Alejandro , Volzone Dario , Fuzul Eduardo , Ursule Jean Philippe , Massaferro Jose Luis
Published: July 2020

Field tests, advanced logging and data acquisition are combined here with a multi scale reservoir model to select the sweet spot for a polymer injection commercial pilot with 19 injector wells.

We present as case study an on-going polymer injection project in a brown oil field in Golfo San Jorge Basin western flank, Argentina. Productive interval comprises a 1000 m column low net-to-gross fluvial succession in Bajo Barreal Formation. Field production is ∼100 cp oil with 94% watercut and low recovery after a 25-year waterflood.

From advanced logging we interpret waterflood response and mineralogy. We also acquire rock and fluid samples for lab analysis and execute several single well injectivity tests. Here we show the impact of this information when designing the pilot. Particularly, we ran production logs in three wells in a selected pilot area. These tests results proved their worth reducing greatly the uncertainty on production allocation and supporting our thesis relating connectivity and productivity.

Using this data, we build several dynamic models in different scales (from 10 km to 100 m) to capture depositional trends and to model stratigraphic and sedimentary heterogeneity. We use dynamic models on scales from field to plug combined with economic evaluation to improve the selection and to support decision-making.

Identification of the most sensitive parameters such as reservoir connectivity, current oil saturation, production allocation and polymer retention, validate expenditure on data acquisition on the most sensitive variables for the economic indicators.
Carbon Intensity of Unconventional and Latin American Oil Plays
Authors: Meehan Nathan , Jenvey Nigel , Datta Aparajita , Uppati Sai Pranav
Published: July 2020

Carbon intensity (CI) of oil and gas production varies widely across global oil plays. Life cycle extraction in the Latin American Region (LAR) has some of the highest and lowest values of CI and holds many opportunities to reduce carbon emissions and improve national wealth. Flaring and venting of associated or non-associated natural gas dramatically increases CI.

This paper applies peer-reviewed processes across broad averages of oil and gas activity in major fields around the world and compares them with both Latin American and North American oil plays. Ways to lower the carbon intensity for high CI fields in the region are discussed. Unique opportunities exist to minimize carbon intensity in both areas.

We perform well-to-refinery calculations of CI for major unconventional oil plays in all major Latin American fields, the largest North American unconventional plays and other major producing countries. This approach accounts for emissions from exploration, drilling & completions, production, processing, and transportation. The analysis tool is an open-source engineering-based model called Oil Production Greenhouse Gas Emissions Estimator (OPGEE). OPGEE makes estimates of emissions accounting using up to 50 parameters for each modeled field. This model was developed at Stanford University. Data sources include government sources, technical papers, satellite observations, and commercial databases.

Applied globally, OPGEE estimates show the highest values in areas with extensive flaring of natural gas and very heavy crude oils. Heavy oils require large energy inputs (e.g. steam flooding) and/or the use of light hydrocarbon diluents for transportation offset. OPGEE can be used to evaluate the CI impacts of public policy actions.

While both NA unconventional and LAR crudes will remain vital to regional and global supplies, unconventional production, especially from light tight oil is the most significant new source of fossil fuels in the last decade. Under a wide variety of carbon constraints, oil usage will continue for many decades and increase in the near term. Operators, governments and regulators need to be able to avoid "locking in" development of suboptimal resources and providing incentives for shale operators to manage resources sustainably. Oil producers must prepare by refraining from developing marginal projects, eliminating flaring, optimizing hydraulic fracture treatments, using improved recovery methods (e.g. enhanced oil recovery using anthropogenic CO2), reducing energy use, and eliminating unnecessary gas waste.
A Methodology to Use of RCX Straddle Packer Microfrac for the Determination of Minimum Horizontal Stress in Vaca Muerta Formation
Authors: Ferlaza Carlos , Merchán Vladimir , Teran Claudia , Paris Martin , Rabe Claudio , Baratcabal Julio
Published: July 2020

This paper describes the test protocols and procedures of RCX Straddle Packer Microfrac for the estimation of formation Breakdown, fracture propagation and fracture closure pressure at different levels in Vaca Muerta formation. As a result, the horizontal stress field can be estimated, which in turns allows to infer if the fracture scheme and productivity agree well with initial prognosis.

Historically, this tool had been used for the estimation of formation pressure and fluid samples for unconsolidated formations. However, a micro-fracture job, pump capacity, packer hermeticity and a well design test protocol were the key to allow get formation breakdown, fracture propagation, fracture closure through pumping flow back and fracture reopening in various cycles. Such procedure was performed at two depths with success. Selection of the test intervals involved a preliminary geomechanical model for the determination of stress conditions, mechanical properties and wellbore stability analysis to choose proper mud density to reduce the probability of well damage (breakouts mainly), which can compromise test hermeticity. Then, after drilling, well logs including wellbore image and caliper analysis enable the determination of test intervals with minimum damage.

In the test well, Microfrac tests were performed successfully on two intervals out of four selected. Interpretation allowed the estimation of closure pressure related to minimum horizontal stress. Moreover, a rough estimation of maximum horizontal stress, based on breakdown pressure and closure pressure was performed as well. Such results agree well with the initial geomechanical model. Strike slip regime was confirmed in such a way that no alarms were set for future development through horizontal wells. But it is necessary to make a deepper investigation to ensure a favorable anisotrophy stress ratio. Some areas with unfavorable vertical to horizontal stress ratio, have been show low performance productivity. The main advantages of this type of tests are: (i) the availability to acquire information through several depths in a vertical well. (ii) Tests were performed in open hole conditions. (iii) Horizontal in situ stresses can be estimated. (iv) Time efficiency in comparison with classical DFIT tests. (v) Calibration of geomechanical model for future development.

Through the application of this tool, a new methodology was set, which allows for an early diagnose of the horizontal stress field leading to the determination of stress regime. Therefore, if the worst-case scenario appears related to inverse stress regime, development plans can be reorganized, reducing potential economic losses, considering that, as had been demonstrated in Argentina, horizontal wells placed on inverse regime led to EUR lower than breakeven.
NMR Data Processing Using Gamma Functions for the Evaluation of Heavy Oil Reservoir in the Peregrino Field
Authors: Klein Katherine , Barbosa José , Salazar Jesus Pastor , Borri Javier , Arro Roberto
Published: July 2020

The use of Nuclear Magnetic Resonance (NMR) logs for petrophysical interpretation and evaluation in the oil and gas industry has increased in recent decades, especially in Brazil, where the use of this technology was increased by more than 400% from 2011 to 2018 (from 49 to 208 runs). This increased usaged occurred mainly because the porosity estimation provided by this technology is independent of lithology. Additionally, the porosity can be associated with different pore sizes. It can also be divided to quantify the fraction of porosity for the clay bound water, bound fluid by capillary forces and movable fluid by applying cutoff times in the spectrum of T2 distribution.

Nevertheless, the presence of heavy oil in the Peregrino reservoir, with oil viscosities ranging varying from 150 to 350 cP, complicates NMR interpretation because the signal from the oil decays with a time constant that is comparable with that of capillary or clay-bound water, affecting the determination of permeability and the fluid distribution.

This paper presents the results of applying innovative Gamma Inversion to process the logging-while-drilling (LWD) NMR data acquired in a well from the Peregrino Field, offshore Brazil. The Gamma Inversion process uses probabilistic functions, instead of exponential ones, to generate a T2 spectrum that is more consistent from a mathematical and geological point of view.
Applied Learnings in Reservoir Simulation of Unconventional Plays
Authors: Altman Raphael , Tineo Roberto , Viswanathan Anup , Gurmen Nihat
Published: July 2020

Reservoir simulation is a popular tool to understand unconventional reservoirs dynamics. Applications include estimating long-term production behavior, enhancing well spacing and pad modeling efficiency, optimizing completion and stimulation of horizontal wells, and understanding production drivers that cause differences in productivity between wells. The objective of this work is to revisit fundamental concepts of reservoir simulation in unconventional reservoirs and to give several real examples that form part of an archive of lessons learnt.

Our work includes several reservoir simulation models in unconventional plays worldwide. These models are a function of the specific objective (from the 4 aforementioned applications) and reservoir type. They include structured and unstructured grid models, high- and low-resolution gridding, single porosity and dual porosity, compositional and black oil PVT, variations in the definition of complex hydraulic fractures in shale reservoirs (accounting for variations in properties that occur in time and space), and different protocols for incorporating initial water in-place as a result of hydraulic fracturing fluid.

We have encountered several challenges during this work. Some of these include: simulation model non-uniqueness, accounting for variations of reservoir properties with time and space and implications of production forecasting in volatile oils or gas condensates. Our work has brought to light important aspects of modeling unconventional reservoirs, such as changes in apparent well productivity after well shut-in or choke changes, cluster spacing, grid size and complex fracture thickness effects in horizontal wells, supercharging effects resulting from hydraulic fracture treatments, and simulation grid cell size impact on reservoir simulation cases where modeling transient flow behavior between perforation clusters. In most cases, to reduce computational time we have taken advantage of modeling a portion of the lateral and scaling up the results.

The lessons learnt continue the forum for further discussions regarding shale reservoir well and production modeling in our industry. They will provide a useful reference especially for those with little experience in unconventional reservoir simulation to better understand and develop both new and existing unconventional reservoirs.
Mathematical Correlations of Olefin and Methane Mixtures to be Applied to Synthetic Drilling Fluid During Well Control Operations
Authors: Marques Daniela C. , Ribeiro Paulo R. , Santos Otto L.
Published: July 2020

Lost circulation is one of the major concerns when drilling a well because it affects downhole well integrity, leads to monetary losses and is detrimental to the reservoir. In drilling operations, it generally occurs when the drilling fluid density exceed the formation fracture pressure. Another concern during drilling is the gas-formation influx to the wellbore, which occurs when the hydrostatic pressure becomes lower than the formation pore pressure. Therefore, the knowledge of drilling fluid density is a key factor to the operational safety and efficiency.

In view of it, a number of experiments were performed at isothermal conditions in a PVT (pressure/volume/ temperature) system with full sample visibility to study the influence of pressure, temperature and mixture composition on fluid thermodynamic properties.

Based on experimental data, mathematical correlations for density, solubility ratio and formation volume factor (FVF) for methane and linear olefin mixtures have been developed and presented in this article. In addition, an empiric correlation was presented for pure linear olefin density and was compared with results published in literature.

These analytical correlations are fundamental to well control simulations. They make possible the estimation of the pit gain (increase of drilling fluid volume on the surface after a kick has been taken) and are used in computational methodology of kick simulators as constitutive equations to improve the reliability of their predictions and consequently increasing the operational safety and efficiency.

The equations for the density, solubility ratio and oil-FVF shown in this paper are in excellent agreement with the experimental data showing a maximum absolute deviation of 3.2%. However, as the experimental data ranged from 25°C (77°F) to 80°C (176°F) and pressures up to 103 MPa (14940 psi), extrapolation of the equation may lead to larger errors.

The paper also presents a well control case study showing the practical application of these correlations.
Risk literacy assessment of general practitioners and medical students using the Berlin Numeracy Test
Authors: Friederichs Hendrik , Birkenstein Roman , Becker Jan C. , Marschall Bernhard , Weissenstein Anne
Published: July 2020

Background: The responsibility for helping patients understand potential health benefits and risks, especially regarding screening tests, falls largely to general practitioners (GPs). The Berlin Numeracy Test (BNT) specifically measures risk literacy (i.e., the ability to understand different aspects of statistical numeracy associated with accurate interpretation of information about risks). This study explored the association between risk literacy levels and clinical experience in GPs vs. medical students. Additionally, the effect of GP risk literacy on evaluation of the predictive value of screening tests was examined.Methods: The participants were 84 GPs and 92 third-year medical students who completed the BNT (total score range 0–4 points). The GPs received an additional case scenario on mammography screening as a simple measure of performance in applying numeracy skills.Results: Despite having an average of 25.9 years of clinical experience, GPs scored no better than medical students on risk literacy (GPs: 2.33 points, 95% confidence interval [CI] 2.08–2.59; students: 2.34, 95% CI 2.07–2.61; P = .983). Of all GPs, 71.6% (n = 58) greatly overestimated the real predictive value.Conclusions: In this study, we found no difference in risk literacy between current students and current GPs. GPs lack risk literacy and consequently do not fully understand numeric estimates of probability in routine screening procedures.
Short-term Outcomes of Robotic- versus Laparoscopic-Assisted Total Gastrectomy for Advanced Gastric Cancer: A Propensity Score Matching Study
Authors: Yang Changdong , Shi Yan , Xie Shaohui , Chen Jun , Zhao Yongliang , Qian Feng , Hao Yingxue , Tang Bo , Yu Pei-Wu
Published: July 2020

Background: Few studies have been designed to evaluate the short-term outcomes between robotic-assisted total gastrectomy (RATG) and laparoscopy-assisted total gastrectomy (LATG) for advanced gastric cancer (AGC). The purpose of this study was to assess the short-term outcomes of RATG compared with LATG for AGC. Methods: We retrospectively evaluated 126 and 257 patients who underwent RATG or LATG, respectively. In addition, we performed propensity score matching (PSM) analysis between RATG and LATG for clinicopathological characteristics to reduce bias and compared short-term surgical outcomes. Results: After PSM, the RATG group had a longer mean operation time (291.14±59.18 vs. 270.34±52.22 min, p=0.003), less intraoperative bleeding (154.37±89.68 vs. 183.77±95.39 ml, p=0.004) and more N2 tier RLNs (9.07±5.34 vs. 7.56±4.50, p=0.016) than the LATG group. Additionally, the total RLNs of the RATG group were almost significantly different compared to that of the LATG group (34.90±13.05 vs. 31.91±12.46, p=0.065).Moreover, no significant differences were found between the two groups in terms of the length of incision, proximal resection margin, distal resection margin, residual disease and postoperative hospital stay. There was no significant difference in the overall complication rate between the RATG and LATG groups after PSM (23.8% vs. 28.6%, p=0.390). Grade II complications accounted for most of the complications in the two cohorts after PSM. The conversion rates were 4.55% and 8.54% in the RATG and LATG groups, respectively, with no significant difference (p=0.145), and the ratio of splenectomy were 1.59% and 0.39% (p=0.253). The mortality rates were 0.8% and 0.4% for the RATG and LATG groups, respectively (p=1.000).Conclusion: This study demonstrates that RATG is comparable to LATG in terms of short-term surgical outcomes.
Recognition of stroke among community residents and the improvement after intensive health education: A cross-sectional study.
Authors: Zhong Xuemin , Wang Jian , He Lanying , Xu Ronghua
Published: July 2020

Background: The high morbidity, mortality, and disability rates associated with stroke cause heavy burden to the society. The level of understanding regarding stroke warning symptoms and first aid systems among community residents is generally low. This study aimed to investigate stroke-related knowledge in community residents of Jinjiang district of Chengdu and to raise public awareness regarding stroke through an intensive educational program.Methods: Nine communities in Jinjiang district were sampled, and a questionnaire about stroke-related knowledge was applied before and after stroke educational activities. We analyzed the impact of such activities on stroke recognition and management.Results: We collected 1685 valid questionnaires. The awareness about stroke risk before educational activities was 11.4%. The recognition of stroke warning signs among the community residents was 29.8-59.5%. Among these community residents, the recognition rate of major signs, such as limb weakness, language disorder, and imbalance was more than 50%. When faced with five stroke warning signs, the proportion of participants who chose to make an emergency call was 41.5%. Less than 10% of the participants chose to consult a doctor, take medicine, or wait. After strengthening the publicity and educational activities regarding stroke, there was a significant improvement in the identification of stroke risk factors and warning signs, and stroke management. The percentage of participants who chose to make an emergency call increased from 53.2% to 82.7% (p<0.001).Conclusions: The knowledge about stroke among community residents in Jinjiang District of Chengdu was low. Strengthening publicity and educational activities may raise awareness about prioritizing emergency calls after the onset of stroke signs.
Registered Nurses´ Views on Telephone Nursing for Patients with Respiratory Tract Infections in Primary Healthcare – A qualitative interview Study
Authors: Kaminsky Elenor , Aurin Ingrid Edvardsson , Hedin Katarina , Andersson Lisbet , Andre Malin
Published: July 2020

Background: Telephone nursing in primary healthcare has been suggested as a solution to the increased demand for easy access to healthcare, increased number of patients with complex problems, and lack of general practitioners. Registered nurses’ assessments may also be of great importance for antibiotic prescriptions according to guidelines. The aim of this study was to describe registered nurses’ views of telephone nursing work with callers contacting primary healthcare centres regarding respiratory tract infections.Methods: A descriptive, qualitative study was performed through interviews with twelve registered nurses in Swedish primary healthcare. Results: The overarching themes for registered nurses’ views on telephone nursing were captured in two themes: professional challenges and professional support. These included three and two categories respectively: Communicate for optimal patient information; Differentiate harmless from severe problems; Cope with caller expectations; Use working tools; and Use team collaboration. Optimal communication for sufficiently grasping caller symptoms and assess whether harmful or not, without visual input, was underlined. This generated fear of missing something serious. Professional support used in work, were for example guidelines and decision support tool. Colleagues and teamwork collaboration were requested, but not always offered, support for the interviewed registered nurses.Conclusions: The study deepens the understanding of telephone nursing as an important factor for decreasing respiratory tract infection consultations with general practitioners, thus contributing to decreased antibiotic usage in Sweden. To cope with the challenges of telephone nursing in primary healthcare centres, it seems important to systematically introduce the use of the available decision support tool, and set aside time for inter- and intraprofessional discussions and feedback. The collegial support and team collaboration asked for is likely to get synergy effects such as better work environment and job satisfaction for both registered nurses and general practitioners. Future studies are needed to explore telephone nursing in primary healthcare centres in a broader sense to better understand the function and the effects in the complexity of primary healthcare.