bluuebunny/crossref_metadata_2025 huggingface dataset:
Iron Sulfide and Removal in Scale Formation Sour Gas Wells
Authors: Wang Qiwei , Leal Jairo , Syafii Irfan , Mukhles Amro E. , Chen Tao , Chang Frank , Espinosa Mauricio
Published: April 2016

Scale formation has been a persistent challenge in many sour gas wells producing from one of the world's largest gas reservoir in Saudi Arabia. Accumulation of scale deposits on downhole tubular and in wellhead manifold interferes field operation, limits well accessibility and decreases well productivity. Extensive efforts have been devoted to understand the scale formation process and to develop cost-effective mitigation strategy. This paper discusses the up-to-date knowledge on the scale formation in these prolific gas wells and presents the descaling technologies deployed and currently considered.

Scale composition analyses have been performed for a large number of deposits collected during well workovers and interventions. Wide range of mineral phases were identified and their distribution showed significant variations with samples. Scale often consisted of several different mineral phases. Iron sulfides were usually the dominant components, these included pyrrhotite, troilite, mackinawite, pyrite, marcasite and greigite. Ferric iron scales, such as hematite, magnetite, akaganeite, goethite and lepidocrocite, were also common in the scale mixtures. Common mineral scales, especially calcite, were often found. In addition, iron carbonate and other ferrous iron compounds were also identified. The relative abundance of these minerals showed wide-ranging variations from well to wells. Those variations also changed and with depth and time in the given wells. A more interesting phenomenon was the layered structure in the scale deposits, with two distinct layers having very different compositions. These results provided critical information for the understanding of scaling formation process.

Scale removal with chemical method had limited success in past. Scale dissolvers, based on HCl acid, caused severe tubular corrosion and formation damage. Different mechanical techniques have been tested and implemented over the years. These field experiences are reviewed in the paper. Also, challenges and requirements for scale dissolvers are discussed.
The Impact of Vapour-Liquid Equilibria VLE Calculations on Scale Prediction Modelling
Authors: Ribeiro Ayrton S. , Silva Duarte , Mackay Eric J. , Sorbie Ken S.
Published: April 2016

Vapour-Liquid Equilibria (VLE) calculations, particularly involving the phase behaviour of CO2 and H2S, are used in scale prediction modelling. In this work, the impact of VLE calculations for CO2 and H2S-rich gas phases and for acid and sour gas mixtures on scale prediction calculations is evaluated.

Three Equations of State (EOS), viz. Soave-Redlich-Kwong (SRK), Peng-Robinson (PR) and Valderrama-Patel-Teja (VPT), are implemented in the Heriot-Watt model and used in VLE calculations. The solubility of single-component CO2 and H2S in water and the solubility of a gas mixture in water were compared with experimental data in terms of the Absolute Relative Deviation (ARD). The solubility data were then used in PHREEQC to calculate the impact of using different EOS on carbonate and sulphide scales, particularly on CaCO3 and FeS.

Average ARDs of 6.04%, 4.10% and 3.77% between experimental and calculated values for CO2 solubility in water were obtained for SRK, PR and VPT EOS, respectively. Similarly for H2S solubility in water, average ARDs of 6.49%, 6.66% and 6.48% were obtained. For the solubility of sour and acid gas mixtures in water, average ARDs of 13.92%, 13.25% and 10.78% were obtained. It has thus been concluded that VPT EOS performs better than SRK and PR in VLE calculations for the analysed data.

The errors introduced in VLE calculations have been found to impact the calculation of the amount of CaCO3 precipitated with consequences for scale inhibitor selection. Higher deviations were found in the amount of CaCO3 precipitation for gas mixtures when compared to single component CO2 rich phase. Furthermore, the large errors occurring in VLE calculations for H2S solubility have not been found to impact the calculation of the amount of FeS precipitated when H2S is in excess with respect to Fe2+.

Scale prediction calculations carried out using PHREEQC demonstrate that VLE calculations can have a high impact on mineral precipitation. Thus, it is recommended that the best VLE model available should always be used for scale prediction modelling, particularly when mixtures of gases are present.
The Solubility and Dissolution of PPCA_Ca Complex in Precipitation Squeeze Processes
Authors: Farooqui Nazia M. , Sorbie K. S. , Boak L. S.
Published: April 2016

Phosphino poly carboxylic acid (PPCA) is one of the most commonly used polymeric scale inhibitors (SI) for application in precipitation squeeze treatments. Precipitation processes with PPCA generally occur by forming the sparingly soluble SI_Ca complex. The SI return curve in this process is then governed by the solubility (Cs) of this complex and the kinetics of the dissolution. As in all squeeze treatments, the objective is to control the precipitation in a way that leads to optimum squeeze lifetime without causing any significant formation damage.

In this paper, the fundamental mechanism of the precipitation and dissolution of the PPCA_Ca complex is studied in order to help us to design more efficient precipitation squeeze treatments using PPCA and other polymeric scale inhibitors. At high temperature, the precipitated complex separates out and this precipitate is enriched in (less soluble) higher molecular weight (MW) species. The precipitate is then successively exposed to fresh brine samples in a "successive extraction" process in which we observe that the lower MW components are more available for dissolution. We refer to this as a "stripping" dissolution mechanism.

The bulk results from the successive extraction experiments on the PPCA_Ca complex are then compared with dynamic sand pack results. The objective of these floods was to investigate the dynamic precipitation /dissolution characteristics of the precipitate at various flow rates for the PPCA system. These floods can be shown to range from equilibrium to non-equilibrium dissolution conditions. Non-equilibrium experiments were conducted to analyse the effect of multiple flow rates on the precipitated SI effluent concentrations. The cation concentrations were also analysed to investigate their involvement in the retention mechanism.

This study establishes a hypothesis about the dissolution of SI_Ca complex which we believe can be generalised to any polymeric SI which is applied in a precipitation squeeze. These results clearly point to a "stripping" model of the polymer/Ca complex dissolution where the lower MW species are preferentially dissolved into supernatant brine until some equilibrium is reached. This model of dissolution is very different from a normal "solubility product" model as would apply to a sparingly soluble salt of a phosphonate, for example. This should now be taken into account in the modeling of polymeric SI precipitation squeeze processes.
Citrate Assisted Metal Phosphonate Colloidal Scale Inhibitors For Long-Term Squeeze Treatments
Authors: Ruan Gedeng , Kan Amy T. , Yan Fei , Zhang Fangfu , Bhandari Narayan , Alsaiari Hamad A. , Dai Zhaoyi , Liu Ya , Zhang Zhang , Tomson Mason B.
Published: April 2016

To overcome the drawbacks of conventional squeeze treatment, such as short lifetime and high initial concentration spike, a new metal phosphonate solid inhibitor has been synthesized and its long-term squeeze performance in different formations has been demonstrated. A combination of cations (Ca, Mg, Zr) and anions (citrate, DTPMP) are used to synthesize the metal phosphonate colloidal inhibitors with high product yield. Compared with amorphous metal phosphonate synthesized by direct precipitation, the solubility of this new metal phosphonate colloidal inhibitor is at least one order of magnitude lower. The proposed mechanism is that due to the formation of metal citrate complex, the initial free cation concentration is low so that the low solubility crystalline metal phosphonate product is formed. This colloidal inhibitor shows good permeability through sand packed columns. Laboratoy squeeze simulation shows low initial inhibitor return percentage and long lifetime of squeeze treatment in different rock formations. The colloidal inhibitor formula can be tailored to different minimum inhibitor concentrations (MIC) to protect the oil wells of different scaling risks. This new colloidal inhibitor will have significant implications in long-term squeeze treatment to lower the cost of overall downhole scale treatment.
The Importance of Scale Inhibitor Analysis in Scale Management - A State of the Art Overview to Provide Cost Effective Scale Control from Simple to Complex Production Scenarios
Authors: Heath Stephen , Ross Gill , Graham Gordon , MacKinnon Kirsty
Published: April 2016

The accurate and precise analysis of scale inhibitors can play an important role in conjunction with other field data like ion analysis, total suspended solids and productivity index in making key decisions on the efficiency of scale squeeze and continuous chemical injection treatments. It is essential to have reliable data on scale inhibitor residuals in produced fluids to prevent wells from scaling and to enable maximum lifetime for scale squeeze treatments especially in complex operating environments.

A variety of techniques exist for scale inhibitor analysis including the more simple methods like hyamine, fluorescence and Inductively Coupled Plasma Optical Emission Spectroscopy (ICPOES) to more complex techniques like high pressure liquid chromatography (HPLC) and mass spectroscopy (MS). All of these techniques, including combinations thereof, are currently in use and the advantages and disadvantages of each technique will be compared and contrasted for the different types of scale inhibitor.

The impact of phosphorus speciation in phosphorus tagged polymers and for thermal degradation of phosphonates and phosphate esters will also be considered. Examples will be provided of how the analysis results can be misinterpreted if the wrong analysis techniques are used. In addition, specific scenarios in North Sea fields for treating conventional and co-mingled sub-sea wells will be discussed to highlight the use of scale inhibitor analysis techniques to aid chemical selection based upon chemical retention, minimum inhibitor concentration (MIC), detection limits and well production conditions.

This paper will present a state of the art review of scale inhibitor analysis techniques and describe how these techniques can be used to provide cost effective scale management in simple to complex production scenarios.
New Robust Analytical Development for Sulphonated Polymers in Oilfield Brines
Authors: MacKinnon Kirsty , Ewing Sarah J. , Graham Gordon M.
Published: April 2016

Residual scale inhibitor analysis in produced waters, particularly for the sulphonated co-polymers is recognised as an ongoing challenge for many operators and chemical suppliers. Early benchtop methods have been well used and documented (e.g. dialysis / Hyamine based techniques etc.) however are considered time-consuming and laborious. This is one of the key problems faced when assaying residual sulphonated polymers to ppm and sub ppm levels as separation of the inhibitor from the brine is often a difficult operation. This has led to the development of improved solid phase extraction techniques using anion exchange cartridges for sulphonated species in our labs as detailed in our previous works in SPE 131100. [1] In addition, chromatographic techniques including Gel Permeation Chromatography (GPC) [2] and various other methodologies (described in the literature as 2nd and 3rd generation approaches [3, 4]) have been developed. These have all focused on improving accuracy, speciation (assay of specific polymers in solutions containing residual levels of different polymers) and automation, thereby reducing the labour intensive nature and reducing the potential for human error.

This paper describes significant progression for the analysis of sulphonated co-polymers. The new methodology, based on ion pair (IP) chromatography, is more robust and utilises conventional C18 reverse phase columns which were previously disregarded as being completely ineffective for separation of the anionic sulphonated co-polymers. This marks a step change in our ability to isolate and detect sulphonated polymers utilising standard robust (and long wearing) C18 columns together with an ion-pair reagent.

This breakthrough followed an extensive search for alternative columns (including a variety of anion exchange columns) all of which proved fruitless for separation and repeatable, reliable assay of sulphonated polymers. This paper describes the development and effectiveness of this new technique and summarises the various alternative columns and HPLC approaches trialed prior to our successful development. Results from validation exercises and further developments have also been described.
Prediction of Sulphide Scales - Improvement of Our Understanding of Heavy Metal Sulphide Solubility
Authors: Saidoun M. , Mateen K. , Baraka-Lokmane S. , Hurtevent C.
Published: April 2016

An accurate scale prediction is crucial for the design of field production systems and treatment strategy. Existing models do not predict accurately ZnS and PbS scaling risks.

In this paper, we share the findings of using ScaleSoftPitzer (SSP2014) model, developed by Rice University, for this purpose. SSP has been extensively evaluated against both the relevant density and solubility data related to the carbonates, sulfates, and halide scales. However, it has not been closely evaluated against the sulphidic scales, due to lack of high quality experimental observations.

The evaluation of solubility as a function of multiple parameters is presented. Simulations results are compared to literature and field data. The method used to generate comparison is based on the total metal concentration at equilibrium. Temperature, pH, and composition are found to be strongly interplaying effects since aqueous phase metal complexes control the solubility of sulphide minerals. Chloride complexes are believed to be mainly responsible for metals aqueous speciation transport in oil and gas systems, however, hydrosulfide/sulfide complexes may play a role when pH increases or when brine salinity is low. The equilibrium measurements and extrapolated calculations are in reasonable agreement with field observations assuming sulphide minerals are in equilibrium with the produced brine at reservoir conditions. Research showed that colloidal dispersion phenomena and other specific interactions might play a significant role in metal sulphide systems; calcium seems to impact speciation. Two approaches are proposed to improve the model: (i) a short term solution using existing literature data to implement the principal complexes (ii) a more rigorous approach involving additional laboratory study acquisition of metal complexes.
A Systematic Investigation of Factors Affecting the Formation of Zinc Sulfide ZnS
Authors: Graham A. J. , Singleton M. A. , Sorbie K. S. , Collins Ian R
Published: April 2016

Work was undertaken to systematically investigate the factors that affect the formation of zinc sulfide in an aqueous system. Experiments were performed at a series of temperatures from room temperature up to 90 °C, at a range of initial pH values and in two brines systems. The effect of pH was further examined by changing the salt from Na2S.9H2O to NaSH.xH2O, therefore changing the initial sulfide source from S2- to HS-, as part of an ongoing method development strategy.

A variation of the standard barium sulfate static bottle test was used, in which the two bottles to be mixed contained aqueous "H2S" and zinc, respectively. Having pH adjusted the zinc brine to values calculated by the FAST sulfide model, the brines were pre-heated to the required temperature and mixed. Aliquots were removed at 2, 4 and 24 hours to perform elemental analysis by ICP and pH measurements were performed on all samples once they had returned to room temperature. In addition, particle size analysis and ESEM examination of the resulting precipitate were also performed for a subset of the samples prepared.

The reaction between zinc and aqueous "H2S" was quantitative at all temperatures up to 90 °C and in both brines. The final pH values of the supernatant were independent of the zinc brine pH and instead were dependent on the molar ratio of zinc and sulfide ions. A high pH, sulfide dominated, and a low pH, zinc dominated, plateau region were seen with a sharp inflection between the two. As a consequence, reaching field representative pH values was seen to be extremely difficult while retaining the ability to alter the relative concentrations of the reacting ions. Altering the sulfide source yielded the same trend, albeit with different absolute values. These observations have been rationalised with reference to the thermodynamic constants governing the reaction through scale prediction modelling.

The work presented here provides a greater understanding of the factors governing the formation of zinc sulfide scale and the considerations required for more industrially relevant formation and inhibition experiments in the future.
Analysis of Mineral Reactions Occurring in the Gyda Field Under Seawater Injection with the Help of Geochemical Non-Isothermal Model and Produced Water Data
Authors: Hu Yisheng , Mackay Eric
Published: April 2016

The evidence from the produced brine chemistry suggests that the Gyda field has experienced a variety of geochemical reactions due to the high temperature and initial calcium concentration, and so it is worth reviewing the produced water dataset and studying what in situ geochemical reactions may be taking place.

Produced brine chemistry data from 16 wells in the Gyda field are plotted and analysed in combination with general geological information and the reservoir description. A one dimensional reactive transport model is developed to identify the possible geochemical reactions occurring within the reservoir triggered by seawater injection, then extended with the inclusion of thermal modelling and also to be a two dimensional vertical cross section model.

Three possible classes of formation water compositions in different regions of the Gyda field have been identified by analysis of the produced water dataset. Anhydrite and barite precipitation are the two dominant mineral reactions taking place deep within the reservoir. Magnesium stripping may be a result of multi-component ion exchange, dolomite precipitation or a combination of both. Reservoir temperature is lowered during cold water injection. The solubility of anhydrite increases at lower temperature, and anhydrite will gradually dissolve in response to the movement of the temperature front, which is much slower than the formation/injection water mixing front. The extent of mineral precipitation within the reservoir can be reduced by the heterogeneity; the modelling shows that the extent of ion stripping caused by mineral reactions in the reservoir is greatest when simulating a single uniform layer. Brine mixing and the occurrence of geochemical reactions due to vertical mixing are not observable, even when assigning a high vertical permeability in a heterogeneous model.

Thermal modelling is included to evaluate the effect of non-isothermal processes and heat transport on the geochemical reactions, especially the anhydrite mineral reaction. We have investigated how the difference in horizontal permeability in the two layers affects brine mixing of formation and injection water and geochemical reactions.
Iron Carbonate Scaling on Hot Surfaces in Monoethylene Glycol MEG Solutions
Authors: Seiersten Marion , Beck Ralf
Published: April 2016

Monoethylene glycol (MEG) used as hydrate inhibitor in pipelines picks up corrosion products from carbon steel walls. This comes in addition to salts from produced fluids. Iron carbonate (siderite) scale can form on heat exchanger tubes when the MEG is heated and becomes supersaturated with respect to the solubility product of iron and carbonate. In this work a tube heat exchanger loop has been used to measure the scale growth rate of FeCO3 on hot surfaces simulating conditions typical for such heat exchangers. The scale growth rate was measured as function of skin temperature and FeCO3 supersaturation.

The temperature distribution in a tube heat exchanger is complex. The skin temperature is a function of the flow rate, temperature and heat capacities of the heating medium and the process fluids. In this work a tube heat exchanger model was used to calculate the skin temperature based on these parameters. The heat transfer to the test liquid depended on the MEG concentration in the liquid. The skin temperature in pure water was significantly lower than in MEG solutions at the same flow rate. This is mainly attributed to different viscosity. In the experiments, the flow rate on the MEG solution side was adjusted to achieve approximately the same Reynolds number for the various fluids to obtain comparable skin temperatures and flow patterns when the MEG concentration varied.

The FeCO3 supersaturation was adjusted to yield scaling only in the heated test section and avoid bulk nucleation and growth as well as scaling on other parts of the loop. MEG clearly decreases the scaling rate and the scale growth rate (Gscale) as a function of the supersaturation followed the equation: Gscale=kg⋅(Sskin−1)1.5 where kg is a MEG-dependent scale growth rate constant and Sskin is the supersaturation at the scale surface. The supersaturation is a function of the skin temperature, but the intrinsic effect of the skin temperature on the scaling rate was so small that it could be justified to ignore it in the expression.

The paper presents new knowledge on scale growth on hot surfaces in general and growth of iron carbonate in particular.
The Impact of Petrophysical and Completion Parameters on Production in the Denver-Julesburg Basin
Authors: Miller Fred , Payne Jon , Melcher Howard , Reagan Jim , Weijers Leen
Published: April 2016

The Denver-Julesburg (DJ) Basin has seen oil and gas production for more than a century. It is going through a new cycle of development with horizontal drilling and high-intensity hydraulic fracturing. Since the first horizontal wells in 2008 nearly 4,000 Niobrara and Codell horizontals have been drilled. While completion practices have remained fairly standard across the basin, production results vary wildly.

We utilized a high-quality digital log dataset to accurately characterize reservoir quality in the Niobrara and Codell formations in the DJ Basin. The final dataset included 562 digital logs spread across the current extent of horizontal drilling in the DJ Basin. A petrophysical workflow was developed and detailed mapping of the reservoir attributes was completed. The log derived parameters, along with an aeromagnetic and vitrinite reflectance dataset, provided excellent insight into which geologic parameters could be best tied to well production response.

Through bivariate and multivariate analyses using reservoir and completion data, and an economic evaluation to determine the "best bang for your buck", we have identified several completion changes for the basin that result in a significant reduction in the cost per bbl of oil produced. While geological parameters have been found to matter greatly for the production success of DJ horizontals, completions matter as well.

The high GOR areas of Inner Core Wattenberg benefit most from jobs with more proppant, whereas areas with poorer reservoir quality generally benefit from higher stage intensity and jobs with larger fluid volumes. All suggested completion changes have a major impact on lowering $/boe over the long term and result in lowering incremental cost per incremental boe within a period of only 365 producing days in the current low oil price environment.
Marcellus Wells' Ultimate Production Accurately Predicted from Initial Production
Authors: Male Frank , Marder Michael P. , Browning John , Ikonnikova Svetlana , Patzek Tad
Published: April 2016

The advent of horizontal drilling technology and hydraulic fracture completions has fundamentally altered the geometry of flow in shale gas systems, requiring new decline curves to forecast production. In this work we perform automatic decline analysis on Marcellus gas shale wells, and predict ultimate recovery for each well. We use a minimal model that captures the basic physics and geometry of the extraction process.

This model allows us to scale all individual wells' gas productions to fit upon a single, universal curve. This scaling curve predicts the production rate will decline as 1 divided by the square root of time early in the life of the well, and eventually rate declines exponentially. We fit cumulative production to the results of this model to determine time to boundary-dominated flow and ultimate recovery. For wells that have not entered boundary dominated flow, we use a new technique to estimate ultimate recovery, relying on early production.

We find 404 wells that are experiencing boundary-dominated flow. One would expect the time to boundary dominated flow varies due to well completion and reservoir properties. Instead, we find ultimate recovery in wells that have experienced boundary dominated flow is largely predicted by initial production, and time to exponential decline varies surprisingly little. Utilizing this information, we forecast gas production for 5,275 horizontal wells in Pennsylvania and West Virginia for a period of 25 years. We find that the median 25-year EUR is 3.6 Bcf with a standard deviation of 3.6 Bcf. The median time to interference is 3.9 years. From these results, we propose a new method for estimating time to boundary dominated flow for young wells. Our key discovery is that wells can have their EURs estimated early in life with surprising accuracy.
Slimhole Refracturing Case Studies and Experience Utilizing Mechanical Isolation for Effective Refracture Treatments
Authors: Hlidek B. , MacDonald D. , Gee C. , Makowecki B.
Published: April 2016

Refracturing or restimulation of existing producing wells is an economical option for increasing production when compared to new drills. However, stage isolation during restimulation of horizontal laterals can be a challenge, especially in wells with extended laterals and many perforated zones. This paper presents six case studies utilizing mechanical isolation technology for restimulation.

In some cases, existing wells may not have been effectively stimulated. Slimhole reentry systems have been successfully utilized to achieve mechanical isolation in horizontal laterals. This paper describes slimhole tool systems, the process of their installation, and the limitations. In order to evaluate refracturing success, initial post-fracture production of each well in the study is compared to post-refracture production data. The six case studies covered are from five different producing formations, covering locations in Alberta, British Columbia, Colorado and Texas.

This paper shows that slimhole refracturing technology is an effective method for restimulation. Stage isolation in existing producing wells can be reliably achieved using mechanical packer systems. In one of the Canadian examples, a producing well in the Montney formation in British Columbia was restimulated after more than three years on production. The resulting production increased from about 175 Mscf/D to a stabilized production rate of 700 Mscf/D more than 20 months after the restimulation. In San Juan County, Colorado monthly BOE increased 79 times after five months and in Limestone County, Texas monthly BOE increased 2.5 times after five months. In the Alberta Glauconite formation, production one year following restimulation resulted in over 435 MMscf of additional gas recovered.

Mechanical isolation packers are a viable and effective alternative to temporary isolation techniques for extended horizontal wellbores. Multiple formations, both oil and gas in United States and Canada are used as examples. Long term production is now available to validate refracturing benefits using slimhole systems that provide mechanical isolation.
Numerical Study of Proppant Transport in Complex Fracture Geometry
Authors: Han Jiahang , Yuan Peng , Huang Xu , Zhang Hao , Sookprasong Andy , Li Chunlou , Dai Yi
Published: April 2016

The key in unlocking unconventional reserves is to create massive fracture surface area. During the fracturing treatment, a huge volume of fracturing fluid is pumped to generate fractures and then followed with a large amount of proppant to provide enough conductivity for reservoir fluid to flow to the wellbore. The ultimate proppant distribution in the fracture system directly impacts well productivity and production decline rate. However, it is very challenging to predict how far proppants can go and where they will settle because of the complexity of the fracture system. Therefore, accurate modeling of proppant transport inside the fracture system is critical to enable stimulation optimization. Previous modeling and experimental studies were usually based on simple proppant settling velocity models and limited only to planar fracture cases. To accurately evaluate propped complex fracture systems, which are more common in unconventional reservoirs, advanced proppant transport models are required.

In this paper, proppant transport in various fracture geometries is investigated using computational fluid dynamics (CFD) models, in which the interaction between proppant particles and the carrying fluid phase is fully coupled to track proppant movement in the fractures. The planar fracture case is first investigated using a CFD model and benchmarked with results from commercial software. The CFD models are then used to simulate the proppant transport in T-junction and crossing-junction scenarios, which are often seen in unconventional reservoir fracture systems. Parametrical studies are also conducted to better understand how proppant transport is affected by fracture fluid viscosity, proppant density, and fluid injection rates.

The results from the proposed CFD models indicate that proppant transport within complex fracture geometries is significantly affected by fracture fluid dynamics and proppant properties. At fracture junctions, turbulent flow regime will develop, which helps proppant propagate to natural fractures. According to the parametrical studies, higher injection rate and light-weight proppant are beneficial in transporting proppant through fracture junctions to reach further in both hydraulic fractures and natural fractures.

Proppant transport models developed in this work fully incorporate the interaction between proppant particles and carrying fluid dynamics. This study extends the current understanding of proppant movement in complex fracture geometries and helps optimize hydraulic fracturing design to improve unconventional well production performance.
Mineralogy Derived Brittleness from the Qemscan: Niobrara Case Study
Authors: Katz David , Jung Marshall , Canter Lyn , Sonnenfeld Mark , Odegard Mark , Daniels John , Byrnes Alan , Guisinger Mary , Jones Kim , Forster John
Published: April 2016

The brittleness of sedimentary rocks is a critical aspect of their potential to form hydraulically stimulated fractures, resist embedment after stimulation, and thereby produce hydrocarbons over economically significant periods more efficiently. As such it is important to understand how brittle versus non-brittle rocks are organized within a play to improve the recovery of petroleum reserves by identifying higher potential stimulation intervals. The goal of this study is to document the link between the sequence stratigraphic hierarchy and its control on the evolution of mineralogy by FEI's QEMSCAN system, unconfined compressive rock strength, and dipole sonic derived brittleness for the Niobrara Formation. The Niobrara ultimately consists of a combination of sharply to diffusely bedded rocks composed of chalks to claystones with variable organic matter. It is mainly calcium carbonate rich with changing concentrations of detrital quartz, clay, and organic matter that function as the main variables of the mineral brittleness index. The detrital and organic components are relatively dominant in the transgressive systems tract (TST) in the form of laminated and sharply laminated-gradational millimeter to centimeter to decimeter intervals of organic rich chalky claystones-to-marly chalks; high resolution scanning electron photomicrographs also document that this fine scale bedding continues at the nanometer to micrometer scale. Discretely interbedded chalks and marly chalks are interbedded with marls at the cm to decimeter scale during the highstand systems tract (HST); by HST time the shorelines have been pushed landward the furthest and detrital terrestrial contribution to the marine environment has been reduced. This environment is ultimately more favorable to chalk deposition and an overall more brittle mineral assemblage. Mineral derived brittleness logs of the Niobrara ultimately covary with dipole sonic derived rock mechanics (Young's Modulus and Poisson's Ratio), unconfined compressive rock strength measurements from the Equotip-Piccolo, and gamma ray values from downhole tools which in turn may be tuned to identify hydraulic stimulation targets away from cored wells.
Pressure Dependent Permeability of Tight Rocks
Authors: Akai T. , Takakuwa Y. , Sato K. , Wood J. M.
Published: April 2016

According to Terzaghi's principle, the effective stress σ' is related to the total stress σ and the pore pressure Pp by the relationship σ' = σ - Pp. In a typical reservoir depletion scenario, the pore pressure decreases under constant total stress, and as a result, the effective stress increases. The increase of the effective stress has a negative impact on permeability due to rock compaction, while the decrease in pore pressure enhances the apparent permeability because of the gas slippage effect. In tight gas reservoirs, since the slippage effect is no longer negligible, the pressure dependency of the permeability is very complicated.

In this paper, we used three samples from the Montney tight gas siltstone reservoir in western Canada, whose absolute permeabilities range from in the order of 10-4 mD to 10-3 mD. Permeability measurements under different pressure conditions using both the unsteady state pressure decay and the pressure pulse decay methods were carried out.

Based on the measured data, permeability was modeled as a function of reservoir pressure. Using this function, we carried out reservoir simulations and examined the impact of pressure dependence of permeability on the gas recovery process from a tight gas reservoir.
Study of the Rock/Fluid Interactions of Sodium and Calcium Brines with Ultra-Tight Rock Surfaces and their Impact on Improving Oil Recovery by Spontaneous Imbibition
Authors: Valluri M. K. , Alvarez J. O. , Schechter D. S.
Published: April 2016

This work is a novel attempt to analyze rock/brine and oil/brine interactions in heterogeneous unconventional liquid reservoir rocks and the effect of these interactions on oil recovery. There is very limited literature on the impact of brine salinity on shale wettability alteration and spontaneous imbibition experiments. This study includes a comprehensive approach that analyzes rock-fluid interactions through contact angle and zeta potential measurements followed by imbibition studies monitored by CT scan technology to understand the effect of salinity on CT penetration profiles and the resultant oil recovery.

The rock samples were obtained from sidewall coring of an ultra-tight liquid rich shale in South Texas composed predominantly of carbonate while sodium chloride and calcium chloride brines of varying concentrations were used as testing fluids. Contact angle and IFT experiments were conducted on unaltered samples aged in oil obtained from the same well the sidewall samples were retrieved. The captive bubble method was used to measure the contact angles of oil droplets on the rock while IFT was measured using the pendant drop technique. Zeta potentials were measured to assess the stability of thin brine films on the powdered rock samples and oil droplets. Finally, spontaneous imbibition was carried out at optimum salt concentration that resulted in maximum water wetness to measure oil recovery while Computed Tomography (CT) based imaging was used to analyze imbibition profiles and quantify penetration of fluids into the rock.

Experimental results suggest that both sodium and calcium chloride were able to alter wettability of samples from an initial intermediate-wet state to water-wet with the maximum water wetness observed for sodium chloride. Increasing salt concentration also lowered the crude oil/brine IFT marginally. Zeta potential measurements suggested sodium brine films were more stable compared to calcium brines while double layer expansion does not completely explain the wetting changes observed. Sodium and calcium brines at optimum salinities recovered more oil compared to water alone while maximum recovery was obtained with sodium chloride which also penetrated the most into the rock matrix as found by analyzing the CT scan images. This study therefore validates the potential of affordable low salinity injection brines which have the capability to alter shale rock wettability and improve oil recovery by penetrating deeper into the reservoir rock.
Temporal variations and trends in loads of commonly used pharmaceuticals to large wastewater treatment plants in Sweden, a case study (Ryaverket)
Authors: Paxéus N. , Bester K. , El-taliawy Haitham
Published: April 2016

Loads of individual commonly used analgesics (ibuprofen, diclofenac), antibiotics (sulfamethoxazole, trimethoprim), β-blockers (atenolol, metoprolol, sotalol, propranolol) and neuroleptics (carbamazepine, citalopram) to a large-scale operating wastewater treatment plant (WWTP) in Sweden (Ryaverket) were studied by monitoring concentrations and flows during a 9-year period (2006–2015). Variations in loads due to sampling and possible errors in chemical analyses were estimated to be below 40%. The variations in loads were analyzed and discussed in terms of the design of collecting wastewater system as an integrated part of the water treatment at the WWTP as well as the prescription and use of individual pharmaceuticals. Trend analysis in daily loads of individual pharmaceuticals indicated an increase for diclofenac, no significant changes for ibuprofen and metoprolol and a decrease for the other pharmaceuticals. The latter was ascribed to a decrease in their prescription and use. The increase in loads of diclofenac was ascribed to its growing topical use not requiring prescription. In view of future regulations by the EU, growing loads of diclofenac to WWTPs and its low removal rates in WWTPs may require an upgrade of WWTPs to achieve quality standards for diclofenac in receiving waters.
Influence of bunch morphology on quality of wines produced from clones of grape variety Prokupac
Authors: Zivkovic Jelena , Savikin Katarina , Zdunic Gordana , Godjevac Dejan , Markovic Nebojsa , Przic Zoran , Menkovic Nebojsa
Published: April 2016

Wine quality depends mainly on the characteristics of the grape it is made
of, and one of the attributes affecting wine composition is cluster and berry
morphology. The aim of this study was to represent variability of
morphological characteristics between clones of the autochthonous grape
variety Prokupac and performed chemical evaluation of wines obtained from
them. Total phenolic content was generally low and it ranged from 33.0 to
114.5 mg GAE/100 mL. Six main anthocyanin compounds with malvidin as the main
anthocyanidin were detected. Malvidin-3-O-glucoside was the most abundant
anthocyanin ranging from 59.8 to 101.7 ?g/mL. Clones 43/5 and 43/4 are marked
as those from which wines with the highest quality are obtained. According to
our results clonal selection makes a significant difference in Prokupac wine
quality. On the other hand, there is a poor response of wine quality
parameters to variation in morphological attributes of clusters and berries
(bunch weight, proportion of stem, berry and seed weight, skin, pulp and seed
weight per berry).
The Brain–to–Pancreatic Islet Neuronal Map Reveals Differential Glucose Regulation From Distinct Hypothalamic Regions
Authors: Rosario Wilfredo , Singh Inderroop , Wautlet Arnaud , Patterson Christa , Flak Jonathan , Becker Thomas C. , Ali Almas , Tamarina Natalia , Philipson Louis H. , Enquist Lynn W. , Myers Martin G. , Rhodes Christopher J.
Published: April 2016

The brain influences glucose homeostasis, partly by supplemental control over insulin and glucagon secretion. Without this central regulation, diabetes and its complications can ensue. Yet, the neuronal network linking to pancreatic islets has never been fully mapped. Here, we refine this map using pseudorabies virus (PRV) retrograde tracing, indicating that the pancreatic islets are innervated by efferent circuits that emanate from the hypothalamus. We found that the hypothalamic arcuate nucleus (ARC), ventromedial nucleus (VMN), and lateral hypothalamic area (LHA) significantly overlap PRV and the physiological glucose-sensing enzyme glucokinase. Then, experimentally lowering glucose sensing, specifically in the ARC, resulted in glucose intolerance due to deficient insulin secretion and no significant effect in the VMN, but in the LHA it resulted in a lowering of the glucose threshold that improved glucose tolerance and/or improved insulin sensitivity, with an exaggerated counter-regulatory response for glucagon secretion. No significant effect on insulin sensitivity or metabolic homeostasis was noted. Thus, these data reveal novel direct neuronal effects on pancreatic islets and also render a functional validation of the brain-to-islet neuronal map. They also demonstrate that distinct regions of the hypothalamus differentially control insulin and glucagon secretion, potentially in partnership to help maintain glucose homeostasis and guard against hypoglycemia.
Prolonged intermittent virus shedding during an outbreak of canine influenza A H3N2 virus infection in dogs in three Chicago area shelters: 16 cases (March to May 2015)
Authors: Newbury Sandra , Godhardt-Cooper Jennifer , Poulsen Keith P. , Cigel Francine , Balanoff Laura , Toohey-Kurth Kathy
Published: April 2016

OBJECTIVE To estimate an appropriate isolation period for dogs infected with canine influenza A H3N2 virus on the basis of the duration of virus shedding.

DESIGN Retrospective case series.

ANIMALS 16 dogs, from 3 Chicago area shelters, naturally infected with canine influenza A H3N2 virus.

PROCEDURES Medical records of 16 affected dogs were reviewed. Nasal swab specimens from each dog had been tested periodically for a minimum of 15 days following an initial positive real-time reverse transcriptase PCR (rRT-PCR) assay result for influenza A virus shedding. Amplicons were purified, quantified, and sequenced by the Sanger DNA sequencing technique. Virus isolation and sequence results of canine influenza A H3N2 virus from nasal swab specimens were obtained in conjunction with signalment, description of clinical signs, type of treatment, and outcome.

RESULTS Viruses from each dog were identified as canine influenza A H3N2 virus on the basis of DNA sequencing. The interval between first and last positive rRT-PCR assay results ranged from 13 to 24 days, whereas the time interval from first reported clinical signs to last positive assay results ranged from 15 to 26 days. Isolation of canine influenza A H3N2 virus was successful in the late shedding period from nasal swab specimens of 4 dogs at 15 and 20 days after the first positive rRT-PCR assay result and 18 to 20 days after the first clinical signs. Clinical signs resolved for all dogs that remained in the shelters during the testing period.

CONCLUSIONS AND CLINICAL RELEVANCE Dogs infected with H3N2 virus should be isolated for a period of ≥ 21 days following onset of illness. Even when resolution of clinical signs occurs sooner than 21 days, shedding of H3N2 virus may persist.
Incorporating Inter-Professional Education into a Veterinary Medical Curriculum
Authors: Estrada Amara H. , Behar-Horenstein Linda , Estrada Daniel J. , Black Erik , Kwiatkowski Alison , Bzoch Annie , Blue Amy
Published: April 2016

Inter-professional education (IPE) is identified as an important component of health profession training and is listed in the accreditation requirements for many fields, including veterinary medicine. The goals of IPE are to develop inter-professional skills and to improve patient-oriented care and community health outcomes. To meet these goals, IPE relies on enhanced teamwork, a high level of communication, mutual planning, collective decision making, and shared responsibilities. One Health initiatives have also become integral parts of core competencies for veterinary curricular development. While the overall objectives of an IPE program are similar to those of a One Health initiative, they are not identical. There are unique differences in expectations and outcomes for an IPE program. The purpose of this study was to explore veterinary medical students' perceptions of their interprofessional experiences following participation in a required IPE course that brought together beginning health profession students from the colleges of medicine, dentistry, nursing, pharmacy, nutrition, public health and health professions, and veterinary medicine. Using qualitative research methods, we found that there is powerful experiential learning that occurs for both the veterinary students and the other health profession students when they work together at the beginning of their curriculum as an inter-professional team.
Wisteria Floribunda Agglutinin-Labeled Perineuronal Nets in the Mouse Inferior Colliculus, Thalamic Reticular Nucleus and Auditory Cortex
Authors: Fader Sarah , Imaizumi Kazuo , Yanagawa Yuchio , Lee Charles
Published: April 2016

Perineuronal nets (PNNs) are specialized extracellular matrix molecules that are associated with the closing of the critical period, among other functions. In the adult brain, PNNs surround specific types of neurons, however the expression of PNNs in the auditory system of the mouse, particularly at the level of the midbrain and forebrain, has not been fully described. In addition, the association of PNNs with excitatory and inhibitory cell types in these structures remains unknown. Therefore, we sought to investigate the expression of PNNs in the inferior colliculus (IC), thalamic reticular nucleus (TRN) and primary auditory cortex (A1) of the mouse brain by labeling with wisteria floribunda agglutinin (WFA). To aid in the identification of inhibitory neurons in these structures, we employed the vesicular GABA transporter (VGAT)-Venus transgenic mouse strain, which robustly expresses an enhanced yellow-fluorescent protein (Venus) natively in nearly all gamma-amino butyric acid (GABA)-ergic inhibitory neurons, thus enabling a rapid and unambiguous assessment of inhibitory neurons throughout the nervous system. Our results demonstrate that PNNs are expressed throughout the auditory midbrain and forebrain, but vary in their local distribution. PNNs are most dense in the TRN and least dense in A1. Furthermore, PNNs are preferentially associated with inhibitory neurons in A1 and the TRN, but not in the IC of the mouse. These data suggest regionally specific roles for PNNs in auditory information processing.