bluuebunny/crossref_metadata_2025 huggingface dataset:
Soil Loss and Sediment Export from Land Use of the George Town Conurbation Catchment
Authors: Rahaman Zullyadini A. , Omar Mohamad Adam , Samat Narimah , Mahamud and Mohd Amirul
Published: August 2020

The information on the land use and soil conservation practice based on year 2006, 2010 and 2014, hence offering an opportunity to model the impacts of land use change on erosion, deposition and surface water runoff. Limitation in the use of hydrological models had been their inability to handle the large amount of input data that describe the heterogeneity of the natural system. In this study, a procedure that takes into account soil conservation practice based on the land use change, the response of soil erosion and sediment export from the George Town Conurbation catchment area, and average annual sediment yields were estimated for each grid cell of the watershed to identify the critical erosion areas of rural and urban planning proposes. Average annual sediment yield and data on a grid basis estimated using Universal Soil Loss Equation (USLE) and an emerging technology represented by Geographic Information System (GIS) used as a tool to produce a map for erosion rate. The changing of the land use from forest to agriculture and then to an urban area is a challenging task to research on land use demand for population, and environmental impact assessment is important for the planning of natural resources management, allowing research the modification of land use properly and implement more sustainable for long term management strategies. The challenge is to formulate strategies that would promote an integrated approach to the land use planning at an appropriate level as to address the issues that arose. Modelling for creating urban growth boundary for the George Town Conurbation must have to be controlled surface runoff and soil loss and sediment export from land use of the George Town Conurbation catchment.
Ablation-Dominated Arcs in CO2 Atmosphere - Part I: Temperature Determination near Current Zero
Authors: Methling Ralf , Khakpour Alireza , Götte Nicolas , Uhrlandt Dirk
Published: August 2020

Wall–stabilized arcs dominated by nozzle–ablation are key elements of self–blast circuit breakers. In the present study, high–current arcs were investigated using a model circuit breaker (MCB) in CO2 as gas alternative to SF6 and in addition a long polytetrafluoroethylene nozzle under ambient conditions for stronger ablation. The assets of different methods for optical investigation were demonstrated, e.g. high-speed imaging with channel filters and optical emission spectroscopy. Particularly the phase near current zero (CZ) crossing was studied in two steps. In the first step using high-speed cameras, radial temperature profiles have been determined until 0.4 ms before CZ in the nozzle. Broad temperature profiles with a maximum of 9400 K have been obtained from analysis of fluorine lines. In the second step, the spectroscopic sensitivity was increased using an intensified CCD camera, allowing single-shot measurements until few microseconds before CZ in the MCB. Ionic carbon and atomic oxygen emission were analyzed using absolute intensities and normal maximum. The arc was constricted and the maximum temperature decreased from >18000 K at 0.3 ms to about 11000 K at 0.010 ms before CZ. The arc plasma needs about 0.5-1.0 ms after both the ignition phase and the current zero crossing to be completely dominated by the ablated wall material.
Suspected Serious Adverse Drug Reactions in Hospitalized COVID-19 Patients
Authors: Ramírez Elena , Urroz Mikel , Rodríguez Mariblanca Amelia , Martín-Vega Alberto , Villán Yuri , Seco Enrique , Monserrat Jaime , Frías Jesús , Carcas Antonio J. , Borobia Alberto M.
Published: August 2020

BACKGROUND: From March to April 2020, Spain was the center of the SARS-CoV-2 pandemic, particularly Madrid with approximately 30% of the cases in Spain. The aim of this study is to report the suspected serious adverse drug reactions (SADRs) in COVID-19 patients versus non-COVID-19 patients detected by the prospective pharmacovigilance program based on automatic laboratory signals (ALSs) in the hospital (PPLSH) during that period. We also compared the results with the suspected SADRs detected during the same period for 2019. METHODS: All ALSs that reflected potential SADRs (including neutropenia, pancytopenia, thrombocytopenia, anemia, eosinophilia, leukocytes in cerebrospinal fluid, hepatitis, pancreatitis, acute kidney injury, rhabdomyolysis and hyponatremia were prospectively monitored in hospitalized patients during the study periods. We analyzed the incidence and the distribution of causative drugs for the COVID-19 patients. RESULTS: The incidence rate of SADRs detected in the COVID-19 patients was 760.63 (95% CI 707.89–816.01) per 10,000 patients, 4.75-fold higher than the SADR rate for non-COVID-19 patients (160.15 per 10,000 patients,95% CI 137.09–186.80), and 5.84-fold higher than the SADR rate detected for the same period in 2019 (130.19 per 10,000 patients, 95% CI 109.53–154.36). The most frequently related drugs were tocilizumab (59.84%), dexketoprofen (13.93%), azithromycin (8.43%), lopinavir-ritonavir (7.35%), dexamethasone (7.62%), and chloroquine/hydroxychloroquine (6.91%). CONCLUSIONS: The incidence rate of SADRs detected by the PPSLH in patients with COVID-19 was 4.75-fold higher than that of the non-COVID-19 patients. Caution is recommended when using medications for COVID-19 patients, especially drugs that are hepatotoxic, myotoxic, and those that induce thromboembolic events.
Elevated CO2 and Water Stress in Combination in Plants: Vanguards for Adaptation to Changing Climate
Authors: Shanker Arun
Published: August 2020

The changing dynamics in climate is the primary and important determinant of agriculture productivity. The effects of this changing climate on overall productivity in agriculture can be understood when we study the effects of individual components contributing to the changing climate on plants and crops. Elevated CO2 and drought due to low variability in rainfall is one of the important manifestations of the changing climate. There is considerable amount literature that addresses these aspects in terms of effects on plants systems from molecules to ecosystems. Of particular interest is the effect of increased CO2 on plants in relation to drought and water stress. As it is known that one of the consistent effects of increased CO2 in the atmosphere is increased photosynthesis, especially in C3 plants, it will be interesting to know the effect of drought in relation to elevated CO2. The possible mechanisms by which this occurs will be discussed in this minireview. Interpreting the effects of short term and long term exposure of plants to elevated CO2 in context of ameliorating the negative impacts of drought will show us the possible ways by which there can be effective adaption to crops in the changing climate scenario.
Advanced Oxidation Process Based Water Disinfection- the Microbiology Beyond Bacterial Inactivation
Authors: A.P Habeeb Rahman , Mishra Amrita , Lundborg Cecilia Stålsby , Tripathy Suraj Kumar
Published: August 2020

Different water treatment regiments are revealed to have potential in enriching antibiotic resistant bacteria (ARB). Advanced oxidation processes (AOPs) based disinfection techniques have been studied widely in the recent times due to their advantages over conventional treatment methods. However, bacterial response and adaptations against the hostile environments of AOPs is not clearly understood yet. Based on the existing knowledge on the ways in which bacteria surpass the antibiotic treatment, here we propose few important aspects of bacterial adaptation which could be true for AOPs as well since both antibiotics and AOPs generate reactive oxygen species (ROS) during their modes of action. We discuss the plausible role of ROS in the selection of ARB and bacterial heterogeneity as a strategy to bypass the lethal action of AOPs. Understanding bacterial adaptation during disinfection plays a vital role in devising strategies to outclass the bacterial survival. Hence, more importance should be given to such studies in the near future for the successful implementation of AOPs.
A Review of Agricultural Extension and Advisory Services in sub-Saharan African Countries: Progress with Private Sector Involvement
Authors: Nwafor Christopher , Nwafor Ifeoma
Published: August 2020

Agricultural extension and advisory services in Africa have significant impact on food security as well as economic and social development. Recent moves towards a pluralistic delivery system, including the emergence of private-sector led initiatives in many countries are subject of policy and academic discourse. Our study used an adapted, fit-for-purpose market systems development framework to review available research in extension and advisory services in selected sub-Sahara Africa countries. Using a literature survey methodology, we report evidence of multiple actors in extension delivery, findings that point towards evolution towards mixed delivery as well as objectives. While there are significant uptake of cost-recovery approaches among commercially-oriented farmers, many smallholder farmers still depended on donor-funded services. Our review adds to existing knowledge through incorporating a market systems development framework, which extends the often-used willingness to pay approach, and highlights the need for merger of the public and private-sector objectives to achieve developmental outcomes.
Forecasting Intense Cut-Off Lows in South Africa Using the 4.4 Km Unified Model
Authors: Muofhe Tshimbiluni Percy , Chikoore Hector , Bopape Mary-Jane , Nethengwe Nthaduleni S , Ndarana Thando , Rambuwani Gift Tshifhiwa
Published: August 2020

Mid-tropospheric cut-off low (COL) pressure systems are linked to severe weather, heavy rainfall and extreme cold conditions over South Africa. They often result in floods and snowfalls in winter disrupting economic activities. This paper examines the evolution and circulation patterns associated with severe COLs over South Africa. We evaluate the performance of the 4.4 km Unified Model (UM) which is currently used operationally by the South African Weather Service to simulate daily rainfall. Circulation variables and precipitation simulated by the UM were compared against ECMWF’s ERA Interim reanalyses and GPM precipitation at 24-hour timesteps. We present five recent (2016-2019) severe COLs that had high impact and found higher model skill when simulating heavy precipitation during the initial stages than the dissipating stages of the systems. A key finding was that the UM underestimated precipitation mainly due to inaccurate placing of COL centers and areas of heavy rainfall by up to 5° of latitude away from the actual location, due to the poor formulating of cumulus and microphysics schemes in the model. Understanding the performance and limitations of the UM model in simulating COL characteristics can benefit severe weather forecasting and contribute to disaster risk reduction in South Africa.
Geochemical Modeling of Wormhole Propagation During Carbonate Acidizing with Consideration of Fractures
Authors: Wei Wan , Yu Wei , Chen Youguang , Sepehrnoori Kamy
Published: August 2020

Matrix acidizing is a widely-used stimulation treatment performed below the fracture pressure of the formation. The purpose of acidizing is to improve or restore the formation permeability through rock dissolution. Natural fractures exist in approximately 50% of carbonate reservoirs worldwide (Jo Garland et al. 2018). In this paper, a two-scale continuum model is implemented in UTCOMP (a 3D compositional reservoir simulator) with consideration of fractures using EDFM (Embedded Discrete Fracture Model). The model is also coupled with IPhreeqc (an open- source geochemical program) to calculate reactions occurring among minerals and geochemical species in the aqueous phase. In the coupled model, the two-scale continuum model describes convection and dispersion while IPhreeqc is responsible for the dissolution calculation both in the matrix and on the fracture surface. We validated the simulation model by comparing with the analytical solution. We used two methods for reaction calculation; in the first method we assumed a simple first-order reaction between acid and mineral; in the second method the UTCOMP-IPhreeqc coupled model is used to calculate complex reactions among geochemical species and different mineral compositions. Consistent results were obtained between the simple-reaction model and the UTCOMP- IPhreeqc coupled model by tuning the reaction calculation in the IPhreeqc database. On this basis, we investigated the effects of fractures on acidizing efficiency and wormhole propagation. It is found that for homogeneous matrix with existence of fractures, wormhole in the matrix is generated along the fracture. For heterogeneous matrix, the initiation of the wormhole is dependent on the permeability distribution in the matrix, but wormhole propagation after the initiation is dependent on the position of the nearest fracture tip and the fracture orientation. As a high- conductivity flow path, fracture retards wormhole propagation in the matrix by attracting most acid. As acid dissolves the minerals on the fracture surface, the fracture conductivity is increased and the fluid leak-off into the matrix is reduced. For a vertical fracture with a smaller height compared with the matrix thickness, wormhole propagation is slowed down for the entire matrix. For the first time, it is possible to simulate formations with hydraulic fractures or natural fractures during acidizing, with consideration of geochemical reactions among aqueous phase and different rock compositions. The presented model improves our understanding in acidizing optimization.
In-Situ Generation and Propagation of a Nanocellulose Reinforced CO2 Foam in Tight Formation Fractures for Conformance Control
Authors: Wei Bing , Chen Shengen , Tian Qingtao , Xu Xingguang , Li Xinyuan , Lu Jun
Published: August 2020

EOR projects implemented in Bakken and Changqing tight formations demonstrated that the fractures could cause early breakthrough of the injected CO2 and finally led to undesirable oil recovery. Therefore, conformance control technologies should be developed for the outstanding EOR performance in fractured tight formations. Given this, a nanocellulose (NCF) reinforced CO2 foam was rationally designed in the present work and the flow behaviors in tight formation fractures including generation, propagation and permeability reduction were investigated. The bulk properties of NCF-CO2 foam in gas and supercritical states including foam stability and texture were thoroughly evaluated in a high-pressure-high-temperature (HP-HT) windowed cell. A series of model fractures with certain apertures in tight rocks were designed and assembled for coreflooding experiments. The differential pressure (ΔP) across the core sample during foam flow was continuously monitored. At the end of the experiments, the produced ΔP as a function of gas and water injection rate was mapped. The results showed that the addition of NCF into CO2 foam considerably retarded foam film drainage and bubble coalescence thereby improving the stability of the induced foam. The NCF-CO2 foam had finer bubbles and more robust lamella film than conventional CO2 foam. As a consequence, the half-life of NCF-scCO2 (supercritical state) foam was found to be two times longer than the counterpart conventional scCO2 foam. It was also observed that NCF-CO2 foam could rapidly generate in-situ in fractures and propagate throughout the models. Small fractured aperture led to high ΔP under identical experimental conditions. In addition, NCF-scCO2 foam exhibited noticeably higher ΔP compared to conventional scCO2 and NCF-CO2 foams, validating the effectiveness of the conformance control strategy. Furthermore, the flow of NCF-CO2 foam in fractures significantly decrease the fracture permeability and the most noticeable reduction occurred at fg=0.67 (foam quality). This work, for the first time, demonstrates that the nanocellulose can be applied to effectively boost the scCO2 foam stability. In addition, the flow characteristics of this foam in fractures are investigated, which provides insights into conformance control for tight formations.
Sizing Gelant Treatment for Conformance Control in Hydraulically-Fractured Horizontal Wells
Authors: Liang Bin , Jiang Hanqiao , Li Junjian , Li Min , Lan Yuzheng , Seright Randall
Published: August 2020

Horizontal wells are subject to water breakthrough problems caused by natural or hydraulic fracture connections. Treatment with gelant normally is an effective choice. However, at present, no methods can provide quantitative guidance for designing gelant treatment in fractured horizontal wells. In this paper, we proposed a fracture-conductivity-based analytical model to guide sizing gelant treatment in hydraulically fractured horizontal wells. It includes the evaluation of fracture number intersected with the horizontal well, calculation of gelant leakoff distance according to the desired water productivity reduction, and the method to determine optimal gelant volume. The principle for controlling gelant injection and the method for forecasting water shutoff performance are also included. The successful application is based on two requirements: (1) gelant can penetrate a short distance from fracture surface into adjacent matrices; and (2) gelant or gel can reduce permeability to water more than to hydrocarbon. Finally, we summarize a 9-step procedure for sizing gelant treatment in fractured horizontal wells. This work provides quantitative guidance for water shutoff treatment using cross-linked polymer gels that create disproportionate permeability reduction.
Insights into Field Application of EOR Techniques from Modeling of Tight Reservoirs with Complex High-Density Fracture Network
Authors: Niu Geng , Schechter David
Published: August 2020

Pilot tests of surfactant additives in completion fluid and gas huff n' puff in depleted wells have proven the possibility of production enhancement in unconventional liquid reservoirs (ULR). However, numerical simulation studies regarding EOR techniques neglect two important features of the ULR: extensive fracture discontinuity and high fracture density. This work explores how these two features effect depletion forecasts and EOR evaluation in ULR by applying discrete fracture network (DFN) modeling and optimized unstructured gridding.

In this study, grid generation algorithms for Perpendicular Bisection (PEBI) gridding are improved to handle reservoirs with complex fracture geometry and high fracture intensity. The depletion behavior of the dual-porosity methods and the DFN method are compared based on the "sugar-cube" conceptual model. Data including outcrop maps and FMI log are used to characterize fracture network geometry and build DFN models to represent realistic stimulated tight reservoirs. Dynamic fluid flow models are calibrated through history matching of depletion. To properly model EOR processes at the field scale, results from publications of lab experiments regarding surfactant imbibition and CO2 huff n' puff are used to generate simulation parameters. A series of surfactant spontaneous imbibition and gas huff n' puff simulations are performed on those calibrated DFN models to study the impact of fracture geometry on EOR performance.

Simulation results indicate that dual-porosity methods are not correct if the transient period of fracture-matrix flow lasts for extaned periods or the continuity of fractures is poor, both of which are very common in ULR. By tuning parameters within a reasonable range, DFN dynamic fluid flow models match the production data and can represent the realistic stimulated ULR. Surfactant assisted spontaneous imbibition (SASI) in the matrix domain results in a marginal production increase compared to water imbibition. It is found that wettability alteration incurred in the fracture system may play a more important role in production enhancement. Simulation results of gas huff n' puff indicate the main recovery mechanisms are re-pressurization and viscosity reduction characteristic of multicontact miscibility. And for reservoirs below the bubble-point, another recovery mechanism is the increase of heavy components' flux. However, either increasing the soak period or increasing the portion of the production period in each cycle has a minor effect on recovery enhancement.

This study reveals the significance of using DFN with the unstructured grid to study the EOR processes in ULR. This approach can capture the rapid and extreme change in phase saturation and component fraction within the stimulated reservoir volume (SRV). Our results demonstrate the important factors that affect the field-scale EOR performance in ULR.
Wettability Altering Surfactants for High Temperature Tight Carbonate Reservoirs
Authors: Alammari Faisal G. , Miller Chammi S. , Mohanty Kishore K.
Published: August 2020

Most tight carbonate reservoirs have low oil recovery factors after the primary and secondary recovery stages. High-temperature carbonate reservoirs tend to be oil-wet/mixed-wet due to positively charged minerals and negatively charged oil molecules, hence reducing oil relative permeability. This study aims to enhance oil recovery from tight carbonates by virtue of wettability alteration using surfactants. Twenty different surfactants of different classes and different functional groups are systematically evaluated by first testing their aqueous stability at reservoir conditions. The aqueous stable surfactants were tested for contact angles on the mineral surface. Seven surfactant candidates were selected for spontaneous imbibition experiments, where oil recovery was monitored as a function of time. Wettability-altering surfactants increase the oil recovery by spontaneous imbibition. Up to 190% increase in oil recovery from outcrop core plugs was observed compared to the control sample with sea water.
Visualization the Surfactant Imbibition at Pore Scale by Using of Fractured Micromodels
Authors: Yu Fuwei , Jiang Hanqiao , Ma Mengqi , Xu Fei , Su Hang , Jia Junjian
Published: August 2020

Recovery in low permeability oil reservoirs is challenging because they are often high fractured and oil-wet. Microemulsion-forming surfactant solutions, which can replace oil from tight matrix by imbibition, have been verified as effective enhanced oil recovery fluids for tight reservoirs. To better understand the mechanisms of oil recovery from oil-wet, fractured rocks using microemulsion-forming surfactants, microfluidic experiments including single channel micromodel tests and fractured micromodel imbibition tests which could visualize the in-situ phase changes were conducted in this work. Through on our study, the priority of wettability alteration and phase change with a function salinity was clarified. Besides, the imbibition dynamics of microemulsion-forming surfactants at different salinities were provided, and further understanding about the equilibrium process of microemulsion during imbibition was obtained. Based our studies, we suggest a moderate salinity for microemulsion-forming surfactants enhanced imbibition recovery.
Offshore Polymer EOR Injection Philosophies, Constrains and Solutions
Authors: Flavien Gathier , Christophe Rivas , Lionel Lauber , Antoine Thomas
Published: August 2020

In the past decade, the number of polymer injection projects has greatly increased worldwide, with more and more full field implementations. More recently, the focus has shifted toward the deployment of such technologies offshore which presents very specific constraints in terms of facilities, logistics and produced water treatment.

One restraint is related to the surface facilities and the footprint available to install the required equipment. This can have a great impact on the choice of the chemical form; two forms are usually considered (powder or emulsion) which dictate the type of equipment necessary and the complexity of the injection process.

Other factors come into play when choosing the product form, including weather conditions, available storage, logistics and the existing infrastructure. Many projects are being constrained by the presence of subsea chokes, which can degrade the polymer solution and compromise the economics if not dealt with adequately.

In this paper we will review the existing projects and discuss the offshore deployment philosophies for polymer injection. Then, the focus will be on brown fields and the differences between polymer emulsion and powder forms and how both can be processed in the field. Specific highlights will be on polymer design and selection, equipment and logistics for a real field case.

Recent developments will be presented in relation to viscosity preservation during injection even in the presence of subsea chokes. Different approaches will be proposed including the deployment of non-degrading chokes or the use of Delayed Viscosity Polymer.
Use of In-Situ CO2 Generation in Liquid-Rich Shale
Authors: Ogbonnaya Onyekachi , Wang Shuoshi , Shiau Benjamin , Harwell Jeffrey
Published: August 2020

Modified in situ CO2 generation was explored as an improved tool to deliver CO2 indirectly to the target liquid rich shale formations. Once injected, the special CO2- generating compound, urea, decomposes deep in fractures at the elevated temperature conditions, and releases significant amounts of CO2. For field implementation, the minimum surface facility is required other than simple water injection equipment. Injection of urea solution may be easier and cheaper than most gas injection approaches.

In this effort, in situ CO2 treatment and designs were carried out on a group of Woodford shale core samples. The oil saturated shale cores were soaked in different urea solutions kept in pressurized (1500 and 4000 psi) and heated extraction vessels at temperature of 250 °F. The adopted treatment step closely simulates the huff-and-puff technique. A series of experiments were run with various ingredients, including brine only, brine plus surfactant, brine plus urea and ternary mixture of brine/surfactant/urea. In addition, the extraction experiments were tested at below and above MMP conditions to decipher the principal recovery mechanism.

Based on our preliminary observations, the sample cores did not lose their stability after an extended period of oil extraction with in situ CO2 treatment. The urea only case could recover up to 24% of the OOIP compared to about 6% for the brine only case and 21% for the surfactant only case. Also adding a pre-selected surfactant to the urea slug did not have any benefit. There was no significant difference in oil recovery when the test pressure was below or above MMP. The main recovery mechanisms were oil swelling, viscosity reduction, low interfacial tension and wettability alteration in this effort.

Multiple researchers reported successful lab scale CO2 gas extraction EOR experiments for liquid rich shale like upper, middle and lower Bakken reservoir. The best scenario could recover 90% of the OOIP from the shale core samples. The evidences of this effort offer a strong proof of concept of in situ CO2 generation potential for liquid rich shale reservoirs.
Practical Chemical Formulation Design – Time to Break Away from Micellar Polymer Floods, Again
Authors: Dean Elio , Pitts Malcolm , Wyatt Kon , James Dean , Mills Kathryn , Al-Murayri Mohammed , Al-Kharji Anfal
Published: August 2020

With a resurgence of chemical EOR opportunities throughout the world, high concentration surfactant design has re-emerged its uneconomic face. High concentration surfactant formulation is the micellar polymer design from the past that produced high oil recoveries in the lab but were uneconomic in the field. Formulation designs must consider factors beyond simply oil recovery for economic success and to minimize production issues in the field.

Analysis and comparison of micellar polymer design projects from the 1970-1980s to current SP/ASP formulation designs are discussed. A simple formulation cost calculator is showcased, costs of all formulations are presented, and price per incremental barrel produced (chemical cost only) are shown assuming a 0.1 PV of incremental recovery.

Analysis concludes the following:

Micellar polymer floods were phased out because they were uneconomic. Key reasons are high cost of surfactant and emulsion problems faced when produced surfactant concentration exceed a certain threshold resulting in either greater production cost or disposal of produced oil in the form an unbreakable emulsion. Alkali can improve economics as a low-cost commodity product that can be used to reduce surfactant concentration required to attain high oil recoveries. Alkali is an order of magnitude lower cost per pound than the typical surfactant and can be used as an enhancing agent to improve the performance of other injected chemicals. Alkali is not a "silver bullet" that will save economics, and adds challenges and cost for water softening, which can be economically detrimental to field projects. Many high concentration surfactant formulation floods are being re-introduced to the industry. Not only are these designs un-economic but include multiple chemicals that add complexity and cost to the facilities and difficulty for facility personnel. A formulation that requires more than $20 of chemical per barrel of incremental oil is unlikely to be economic with $50/bbl oil. Key differences between laboratory results and field implementation results are discussed. Geologic uncertainty is addressed since it is the greatest challenge to field economic success.

The industry is taking steps back to an uneconomic time of chemical EOR by obscuring the difference between designs meant to increase reserves (economic oil) versus those that serve an academic or research purpose. Operators are unwittingly paying the price to advance the science of chemical EOR when service companies provide formulations that are not economic. This paper is meant to remind the industry that high concentration surfactant formulations never were economic and certainly will not be economic in today's price environment.
Improving Polymerflood Performance Via Streamline-Based Rate Optimization: Mangala Field, India
Authors: Chen Hongquan , Park Jaeyoung , Datta-Gupta Akhil , Shekhar Sunit , Grover Kavish , Das Joyjit , Shankar Vivek , Suresh Kumar M. , Chitale Ashish
Published: August 2020

This paper describes a novel streamline-based rate allocation approach to maximize oil recovery from polymerfloods and its application to an ongoing polymerflood in the Mangala field, India which is one of the largest polymerfloods in the world. With over 130 injectors and producers, the field-scale optimization is challenging because of the long simulation times, operational constraints at the well, group and field level and changing field conditions.

The FM-1 unit which is the main producing zone of the Mangala field comprises of multi-layered single storied fluvial channel sands of thickness ranging 3-10m with excellent flow characteristics. The gross thickness of FM-1 is about 90m. The sand is under a five-spot pattern polymerflood with a well spacing of aproximately 200m. A finite difference simulator is used for modeling the polymerflood performance with all relevant physics (mobility control, adsorption, residual resistance factor, polymer rheology/shear thinning, inaccessible pore volume and time-dependent degradation). Streamlines are generated from the flux field extracted from the finite difference simulation and are used to calculate pair-wise efficiency for each injector-producer streamline bundle. The pair-wise efficiency quantifies how much oil is recovered given a barrel of water injection. The streamline-based optimizer iteratively reallocates the fluids to injectors and producers by diverting the injected fluid to high efficiency pairs located in unswept oil regions. After optimization, injection efficiency plots as well as streamline/time of flight plots are used to examine and visualize the flow pattern changes leading to the improved flood performance.

The reservoir model is first calibrated with 10 years of waterflood history. The polymer injection concentration and tapering schemes are determined based on extensive laboratory experiments. The optimization focuses on reallocating the well rates while maintaining the well, group and field level constraints. Two optimization scenarios were studied to examine the potential benefits of rate allocation: (1) optimization of rate allocation for both injectors and producers, (2) optimization of rate allocation for injectors only. Both the scenarios yield improved oil recovery (~5 MMSTB), accelerated production and reduced polymer usage (utility factor). The streamline and injection efficiency plots clearly reveal regions of improved sweep efficiencies, providing an intuitive explanation of the enhanced performance.
A 1D Analytical Solution to Determine Residual Oil Saturations from Single-well Chemical Tracer Test
Authors: Doorwar Shashvat , Tagavifar Mohsen , Dwarakanath Varadarajan
Published: August 2020

Single well chemical tracer tests (SWCTT) have been extensively used in the field to estimate residual oil saturation in a reservoir for more than 50 years. They are often used as characterization methods to gauge EOR potential/performance. Therefore, an accurate estimation of Sor from SWCTT's is critical. Current approaches for SWCTT interpretation use a combination of history matching with numerical modeling tools or use of an approximate analytical technique developed for partitioning interwell tracers. History matching is more accurate, requires multiple assumptions and can be potentially time consuming. The basic analytical solution for partitioning inter-well tracer neglects tracer hydrolysis and provides approximate estimations of Sor. We solve for the exact solution of the 1-D convection-reaction solution using the modified method of moments. No additional simplifying assumptions such as slow reaction rate, fast flowback etc. were made while solving the flow equation. We tested the resulting exact solution against synthetic numerical simulations and 50+ published field cases and compared actual versus calculated oil saturations. The synthetic tracer data was generated for different heterogeneities, tracer reaction rate, partition coefficients and tracer soak time. Analysis of the synthetic SWCTT result shows that our analytical approach correctly estimates oil saturation. The calculated residual oil from our analytical model was consistently within ±0.02 saturation units while the original analytical model consistently underpredicts oil saturation.

Novelty of this model is in its simplicity in calculating residual oil saturation from SWCTT's. The model requires only tracer concentration histories as an input to be able to calculate the near-wellbore residual oil saturation. The developed method can be solved directly in Microsoft excel without requiring any advanced computation/simulation tools.
Designing a Robust ASP Formulation for The Kuparuk Field
Authors: Torres Lopez David Enrique , Burns Bobby J , Solairaj Sriram , Jensen Trond B , Needham Riley
Published: August 2020

This paper discusses surfactant, co-solvent, alkali and polymer (ASP) formulations developed for the Kuparuk Field in Alaska. This field is a mature conventional reservoir that exhibits favorable characteristics for surfactant flooding.

The formulations have been tested in the laboratory and in the field with good results. In core floods with live oil and reservoir core, oil saturation has been driven below 5% (Sorc) recovering more than 90% of the waterflood residual oil (Sorw). An ASP treatment, via a single well chemical tracer test, has yielded an Sorc of 1% recovering 96% of the Sorw in the field. However, the process of developing ASP formulations that effectively recover residual oil and represents a commercially viable ASP flood has been challenging. Driving the surfactant retention to low values has required the use of enhanced alkoxylated surfactants and co-solvents that provide low interfacial tension (IFT) micro-emulsions with low viscosity under broad salinity ranges. Kuparuk's rock mineralogy has also played an important role due its heterogeneity and high clay content. Clays with iron bearing minerals and significant ionic exchange have required a systematic study to better understand the effect of reservoir rock on the surfactant treatment. The impact of calcium and magnesium released by the reservoir rock was of primary concern.

Significant results from the Kuparuk ASP formulation study are summarized. The performance of formulation components and their overall effect on surfactant retention, as well as rock mineralogy, are analyzed in detail. Experimental methodologies, analytical studies, and adequate core flood practices used to overcome challenges are also discussed. The lessons learned from this study have the potential to be used in other Alaskan fields, unlocking vast and valuable resources from mature reservoirs as well as new discoveries.
Applications of Rate and Pressure Transient Analysis in Huff-n-Puff Gas EOR for Unconventional Reservoirs
Authors: Haghshenas Behjat , Qanbari Farhad
Published: August 2020

Gas injection huff and puff (HnP) has been successfully applied in parts of Eagle Ford over the past few years. The success is attributed to gas and oil miscibility achieved by injection of gas at high pressure and rate in a contained hydraulic fracture system with a considerable of stimulated volume. Two key preliminary steps in gas HnP modeling include characterization of reservoir fluid (and its interaction with injected gas) and evaluation of hydraulic fracture system. This study focuses on simplified analytical tools for estimation of stimulated reservoir size from production data.

Rate-transient analysis (RTA) is a tool for identification of flow regimes and estimation of key performance metrics for multi-fractured horizontal wells. The flow regimes include enhanced fractured region (EFR), bilinear flow, transient linear flow, transitional flow, and boundary-dominated flow. In this study, the size of stimulated rock and total effective fracture area are estimated using an RTA method. Further, diagnostics fracture injection tests (DFITs) and pressure buildup tests are used to characterize the multi-fractured horizontal wells for the purpose of gas EOR evaluation. Inter-well communication test is used to quantify the conductivity of connecting fractures between communication wells.

This study helps the engineers and managers with reservoir and hydraulic fracture characterization and the screening process for gas HnP candidates. The outputs of these methods serve as first pass of SRV size for more detailed numerical modeling studies.
Effect of Biodegradation on CO2 Minimum Miscibility Pressure for the Frio Reservoir Fluids
Authors: Yuan Hua
Published: August 2020

The great Frio Salt-Dome oil fields dot the Texas coast south and southeast of Houston.  Over 2.4 billion barrels of oil have been produced since these fields were discovered in the 1920s.   Currently, oil is produced at water cuts higher than 95% from most of these fields.  With deteriorating water flood economics, over 1.7 billion barrels of remaining oil are left to be targeted by CO2 flood.   CO2 floods were successfully developed in a few Frio Fields.  The current (on 1/1/2020) combined cumulative oil production from the Oyster Bayou and the West Hastings CO2 floods is over 30 MMSTB.   Even with the high volume of remaining oil and the great success of the CO2 floods, some of the Frio fluids are a challenge for CO2 flooding due to biodegradation of the oils.  Local displacement efficiency depends on minimum miscibility pressure (MMP).  Displacement efficiency is over 90% when operating pressure is above the MMP and drops significantly when operating pressure is lower than the MMP.  In the Frio fields, however, the measured MMPs from the existing slimtube experiments were significantly deviated from what is estimated from most of the CO2 correlations.   Therefore, these correlations can’t be used in estimating MMP during the screening phase of CO2 flood in the Frio fields. In this paper, the characteristics of different Frio fluids is shown with gas chromatograms and compositional analysis.  The cause of biodegradation and its effect on CO2 MMPs in these Frio fields is discussed.  A new parameter with the ratio of xC7+xC2−4 is identified to be an indicator of the level of biodegradation for the Frio oils. This parameter along with molecular weight (MW) of C5+ or C7+ and reservoir temperature is recommended as the new parameters for generating an improved CO2 MMP correlation for a general oil, while a simple CO2 MMP correlation is also presented for the Frio oil fields.  Furthermore, guidance on screening fields from reservoir fluid aspects in the Frio Zone for CO2 flood is provided.
Proxy Based Assisted History Matching and Well Spacing Optimization in Shale Gas Development of a Real Field Case
Authors: Liu Chuxi , Yu Wei , Chang Cheng , Li Qiwei , Sepehrnoori Kamy
Published: August 2020

A robust and reliable workflow for well spacing optimization in shale reservoirs development incorporating various types of uncertainties and detailed economics analysis is paramount to achieve a sustainable unconventional production. In this study, we show a novel well spacing optimization workflow based on the results of assisted history matching and apply it to a real shale gas well, incorporating uncertainty parameters such as matrix permeability, matrix porosity, fracture half-length, fracture height, fracture width, fracture conductivity and fracture water saturation. The input ranges of these parameters are 10 nd to 1000 nd, 0.038 to 0.083, 200 ft to 780 ft, 25 ft to 65 ft, 0.1 ft to 4 ft, 10 md-ft to 200 md-ft, and 0.5 to 0.9 respectively and are determined from field experience and exisiting information. Results from assisted history matching are gathered with a total of 60 HM (history matching) solutions out of 325 runs that meets the criteria of BHP (bottomhole pressure) error less than 25% and WGR (water gas ratio) error less than 60%. A total of 1548 proxy solutions out of 100,000 samplings are obtained from MCMC (markov chain monte carlo) algorithm. Embedded discrete fracture model (EDFM) is used to model hydraulic fractures along with a commercial reservoir simulator. The use of greatly facilitates the modelling process of hydraulic fractures compared to the LGR (local grid refinement) method. The uncertainty parameter distributions from our workflow is matching the posterior distribution obtained from assisted history matching. It is found out that the optimal well spacing is approximately 885 ft, with an estimated net present value (NPV) of 6.67 million dollars. Economic uncertainty evaluation is performed and it is discovered that the NPV distribution obtained from the history matching solution is more concave than the results obtained from KNN (k-nearest neighbor) proxy prediction. The optimal well spacing of 885 ft obtained from this workflow is matching closely with the field experience of approximately 1000 ft. The P50 of the NPV distributions of five spacing (1550 ft, 1033 ft, 775 ft, 620 ft, and 517 ft) are 4.04, 5.91, 7.35, 6.42, and 5.44 million dollars respectively. Gas estimated ultimate recovery per well (P50) for the abovementioned spacings are 3070, 3020, 2945, 2750, and 2565 million cubic feet respectively. There is a drastic drop of gas estimated ultimate recovery per well about 6.6% going from a spacing of 775 ft to 620 ft, indicating the onset of well interference between these distances’ range. The practicality and the convenience of our workflow make it possible to be applied to any shale gas well.
Investigation of Reservoir Permeability Impairment When Drilling with Nano Treated Drill-in Mud System
Authors: Okoro Emmanuel E. , Okafor Ikechukwu S. , Sanni Samuel E. , Obomanu Tamunotonjo , Oguntade Tomiwa , Orodu Oyinkepreye D.
Published: August 2020

A reservoir non-damaging Nano treated aqueous-based drilling fluid was proposed. The study was carried out to obtain a drilling ﬂuid with rheological properties able to keep cuttings in suspension for transport to the surface, minimize ﬁltration and ﬂuid loss. These rheological properties were also predicted using Artificial Neural Network (ANN) due to limitations of existing flow models in predicting Nano-based mud systems. Diﬀerent concentrations of the Nanoparticles were added to these suspensions of water to act as filtration loss materials. A total number of 160 data were used to train the ANN which consists of both the input data and output data acquired from the experiment. The study shows good agreement between experimental data and the artificial neural network prediction of plastic viscosity (PV) and yield point (YP), for multiwall carbon nanotubes (MWCNT) formulated muds. The addition of different concentrations of MWCNT (0.5 – 3 g) as rheology modifier-additive was put to test in a field applicable aqueous mud system. The developed neural network has a Mean Absolute Deviation (MAD) of 0.61529, MSE of 0.57174, Root Mean Square Error (RMSE) of 0.75614 and Mean Absolute Percentage Error (MAPE) of 1.92331 for the predicted plastic viscosity and yield point which are all indicative of good levels of accuracy. It is important to explore the reservoir impairment mechanisms so as to improve and optimize the reservoir performance during the production of hydrocarbons. Having satisfied all the conditions, permeability was determined using Darcy's equation. A reduction in permeability within the range of 12 – 16 mD was recorded for the Nano treated water-based mud system.
The need for home care physicians in Japan – 2020 to 2060
Authors: Iwata Hiroyoshi , Matsushima Masato , Watanabe Takamasa , Sugiyama Yoshifumi , Yokobayashi Kenichi , Son Daisuke , Satoi Yoshinao , Yoshida Eriko , Satake Sumiko , Hinata Yuki , Fujinuma Yasuki
Published: August 2020

Background Due to the fact that Japan faces the most elderly society in the world, the Japanese government has launched an unprecedented health plan to reinforce home care medicine and increase the number of home care physicians, which means that an understanding of future needs for geriatric home care is vital. However, little is known about the future need for home care physicians. We attempted to estimate the basic need for home care physicians from 2020 to 2060. Methods Our estimation is based on modification of major health work force analysis methods with previously reported official data. Two models were developed to estimate the necessary number of full-time equivalent (FTE) home care physicians: one based on home care patient mortality, the other using physician-to-patient ratio, working with estimated numbers of home and nursing home deaths from 2020 to 2060. Moreover, the final process considered and adjusted for future changes in the proportion of patients dying at home. Lastly, we converted estimated FTE physicians to an estimated head count. Results Results were concordant between our two models. In every instance, there was overlap of high- and low-estimations between the mortality method and the physician-to-patient method, and the estimates show highly similar patterns.Furthermore, our estimation is supported by the current number of physicians, which was calculated using a different method. Approximately 1.7 times (1.6 by head count) the current number of FTE home care physicians will be needed in Japan in the late 2030’s, peaking at 33,500 FTE (71,500 head count). However, the need for home care physicians is anticipated to begin decreasing by 2040. Conclusion The results indicate that the importance of home care physicians will rise with the growing elderly population, and that improvements in home care could partially suppress future need for physicians. After the late 2030’s, the supply can be reduced gradually, accounting for the decreasing total number of deaths after 2040. In order to provide sufficient home care and terminal care at home, increasing the number of home care physicians is indispensable. However, the unregulated supply of home care physicians will require careful attention in the future.