bluuebunny/crossref_metadata_2025 huggingface dataset:
Deepest Deployment Of Riserless Dual Gradient Mud Recovery System In Drilling Operation In The North Sea
Authors: Claudey Eric , Maubach Caroline , Ferrari Sandy
Published: March 2016

Riserless Dual Gradient Drilling (DGD) using a specialized subsea pump placed on the seafloor during top hole drilling has been widely used on offshore subsea wells prior to installing the blow out preventer (BOP). Riserless DGD systems, kown as riserless mud recovery (RMR), have been developed to allow riserless sections to be drilled with weighted mud while taking returns back to surface. This allows the operator to set surface casing strings deeper, thereby reducing the total number of liners/casing strings in the well.

This paper addresses the deepest RMR operation on the Norwegian Continental Shelf to date. The water depth was 854m and the 26″ hole section was successfully drilled to 1972mMD (1913mTVD). The riserless mud recovery system enabled the 20″ shoe to be set at a sufficient depth to allow elimination of the 16″ liner, thereby reducing casing strings, cost, well complexity and most importantly setting up the 13-5/8″ string cementation for success. This was mission critical from a well integrity perspective in the context of a big bore 9-5/8″ upper completion. Following the successful drilling of the 26″, the 20″ casing was installed and cemented. Foam cement was pumped using the riserless mud recovery system in cuttings transfer mode to prevent accumulation of returned cement at the well head. The 20″ casing was successfully tested after installing the BOP and marine riser.

The paper describes the riserless mud recovery equipment and the planning of the well, plus the engineering of a multi-stage subsea pump and the subsequent seabed deployment in order to drill the longest and deepest 26″ section on the field. A 26″ directional BHA with a 1.30sg surface mud weight (1.18sg downhole mud weight) KCL glycol mud at flow rates of up to 4800 lpm was used to drill to TD. At TD the well was circulated at a lower rate to 1.38sg surface mud weight at 3200lpm to provide trip margin over the effective mud density required for wellbore stability.
Perched Water Static Model
Authors: Rolfsvåg Trond A. , Danielsen Thomas M.
Published: March 2016

Perched water occurs when oil invades a reservoir and eventually traps pools of water at the bottom of the reservoir. The pools of perched water are separated laterally. When the reservoir is unsegmented and in equilibrium, with both water and oil being continuous phases, the saturation curves have to be identical in the upper part of the reservoir. However, the water pressure is increased inside the trap due to the push of the invading oil. As long as the reservoir rock is water-wet, water will try to escape the trap through the continuous water film on the rock surface. The escaping water will have to overcome the capillary pressure building up from the new shallow free water level inside the perched water pool. The perched water pool will become stable at an elevated pressure compared to the water in the main body of the reservoir.
Observing 2nd Mode of Torsional Vibration of the Drill String Using a High Resolution Downhole Data Recorder
Authors: Corrie G. , Jeffrey C. , Keshiyev S.
Published: March 2016

A rarely recorded drilling harmonic is noted to have occurred in two North Sea applications. Torsional vibration at the second harmonic frequency of the drill string has been recorded and validated with the aid of Finite Elemenet Analysis (FEA). Heavy wear to the drill pipe hardbanding was observed in one well which is believed to be related to the second harmonic torsional vibration.

Although Stick-Slip during drilling is fairly common, little is done to understand the frequency of the Stick-Slip cycle. The typical model assumes string RPM to be constant at surface with greatest variation at the bit (first harmonic frequency). However analysis of downhole data has shown this is not always the case. Torsional vibration or Stick-Slip is typically relatable to the first harmonic frequency of the drill string, i.e. maximum RPM variance occurs at one point only (the bit). For the system to enter the second harmonic frequency (two points of maximum RPM variance) there should be an additional excitation factor. In the two wells analysed there are notably high contact forces in the casing around the upper anti-node of the drill string. It is understood that the high force of the string acting against the wellbore can create a reactive torque large enough to excite the system into the second torsional harmonic. The high contact forces can be attributed to areas of high dog leg severity (DLS) at this point in the well. Although the DLS may not be exceptionally high, its position higher up in the well is of critical importance. This is due to the magnitude of tension in the pipe at this depth created by the weight of the string below. The combination of high tension in the pipe and deviation in the well path will provide contact forces high enough to create the shift from first to second torsional mode.
Increasing Quality in QHSE Work Processes by Introdusing a Common Platform for the Industry
Authors: Holst Jens Christian , Snøtun Håkon , Mathisen Petter
Published: March 2016

Objective

Safety first has been a slogan for many operators and services companies for a long time, but how is the industry making sure that this leads to actual improvement? Many accident investigations at different levels have revealed that there is a lack of common taxonomy, standardized work processes within and across companies and openness for external audits. We want to point out the areas where we believe that the Oil and Gas industry could learn from other industries, such as car manufacturing as well as the IT industry.

Our work has initially been focused on literature studies and interviews with companies and organizations on the NCS. We have looked at license owners, operators and service companies as well as the authorities, and how they all have been practicing QHSE measurements, improvement, including communication between all involved parties. In the process our aim was to find what system would ideally help a company, independent of size and business area to both capture, follow up and learn from incidents without being dependant on constraints such as the human error factor or large bureaucratic systems.

Throughout our work it has become evident that there are several ways to capture and share experience and incidents between the different companies and systems. We have found that even on a company level there are internal variations in the way this information is gathered. As information is not gathered in a uniform way, analyzing and reporting the data will be a challenge. As we have found that there is no common taxonomy, no standard reporting or standards related to follow-up actions, we anticipate that there will be a large variation in the quality of this. As several organizations are working together on different projects, their different systems are united and expected to communicate. We believe that the high difference in systems and processes makes this impossible and that the solution to is to generate a common tool to address these issues.

How can we based on our findings say that as an industry, we are prioritizing"Safety first"? Why is each and every company developing separate systems and processes, and why is the focus not on quality and simplicatrion. For the petroleum industry to further develop on the NCS, we believe that it needs to learn from other industries work on a common platform where the aim must be to improve, not just to make reports and statistics.
Cuttings Transport Modeling - Part 1: Specification of Benchmark Parameters with a Norwegian Continental Shelf Perspective
Authors: Busch A. , Islam A. , Martins D. , Iversen F. P. , Khatibi M. , Johansen S. T. , Time R. W. , Meese E. A.
Published: March 2016

In oil and gas drilling, cuttings transport related problems are a major contributor to well downtime and costs. As a result, solutions to these problems have been extensively researched over the years, both experimentally and through simulation. Numerous review articles exist, summarizing not only the research history but also the qualitative effect of individual case parameters such as e.g. pump flow rate, pipe rotation, rate of penetration on cuttings transport. However, comparing different studies is challenging, as there is no common reference basis defined in the form of typical and representative set of case parameters.

In order to develop relevant and accurate cutting transport models, it is critical that both experiments and models are targeting flow cases, which are relevant for respective drilling operations. By developing a clear understanding of the industrial parameter space, as well as establishing critical benchmarks, the development of models and corresponding laboratory experiments will become much easier.

Other industries have established such benchmarks (e.g. the "NREL offshore 5-MW baseline wind turbine" in wind power research), providing a standardized set of case parameters and profiles, readily available for use to researchers worldwide and resulting in straightforward benchmark and validation as well as faster project set-up and definition.

For application to modeling of cuttings transport phenomena, we propose a methodology how to derive a well-defined and standardized set of geometrical, operational, and environmental case parameters describing various working points of actual drilling operations and procedures as well as simplified problems. The relevance and application of standard parameters is briefly discussed in the light of modeling, both experimentally and through simulations.
Expandable Liner Hanger Technology Provides Metal-to-Metal Sealing and Improved Anchoring Solution for ERD Wells: Case History in North Sea
Authors: Stautzenberger Arthur , Baird Stuart , Lundgård Geir
Published: March 2016

Extended reach drilling (ERD) wells provide challenges in achieving successful liner hanger installations and liner cement jobs. This paper reviews successful expandable liner hanger (ELH) installations in challenging ERD wells in offshore North Sea and discusses how the metal-to-metal sealing ELH provides a solution to these challenges.

The paper discusses the advantages of the new ELH design, which adds metal-to-metal sealing technology to the existing proven elastomer-sealing technology. In addition, the new design offers improved ELH anchor capability. The paper also describes how the new features of this ELH design provide consistent results to meet the challenges of ERD wells. The paper also examines case histories of four metal-to-metal sealing ELHs set successfully in ERD wells in the North Sea since May 2015.

The metal-to-metal sealing technology of the new ELH design (Fig. 1) provides gas-tight sealing at high and low temperatures, and the existing elastomer seals provide field-proven, gas-tight sealing capability in a wide range of applications. The improved ELH anchor design increases the anchoring capability of the hanger allowing operators to run extremely long liners and meet the demands of ERD wells. Another critical advantage of the ELH is the ability to reciprocate and rotate while running in hole and during the entire cement job preventing bridging and packoffs and providing a quality cement job. These case histories provide evidence the sealing and anchoring technologies combined with the reciprocation capabilities of ELH are critical to successful cemented liner hanger jobs in ERD wells.

This paper presents technical information to increase industry awareness of an additional ELH technology. Because ERD wells are becoming more prevalent, solutions are needed that provide improved reliability, increased operational capabilities, and the ability to provide a quality cement job in a challenging application. The metal-to-metal ELH provides the industry with additional technologies to meet these requirements to successfully drill extended-reach wells.
An Ensemble 4D Seismic History Matching Framework with Sparse Representation Based on Wavelet Multiresolution Analysis
Authors: Luo Xiaodong , Bhakta Tuhin , Jakobsen Morten , Nædal Geir
Published: March 2016

In this work we propose an ensemble 4D seismic history matching framework for reservoir characterization. Compared to similar existing frameworks in reservoir engineering community, the proposed one consists of some relatively new ingredients, in terms of the type of seismic data in choice, wavelet multiresolution analysis for the chosen seismic data and related data noise estimation, and the use of recently developed iterative ensemble history matching algorithms.

Typical seismic data used for history matching, such as acoustic impedance, are inverted quantities, whereas extra uncertainties may arise during the inversion processes. In the proposed framework we avoid such intermediate inversion processes. In addition, we also adopt wavelet-based sparse representation to reduce data size. Concretely, we use intercept and gradient attributes derived from amplitude versus angle (AVA) data, apply multilevel discrete wavelet transforms (DWT) to attribute data, and estimate noise level of resulting wavelet coefficients. We then select the wavelet coefficients above a certain threshold value, and history-match these leading wavelet coefficients using an iterative ensemble smoother.

As a proof-of-concept study, we apply the proposed framework to a 2D synthetic case originated from a 3D Norne field model. The reservoir model variables to be estimated are permeability (PERMX) and porosity (PORO) at each active gridblock. A rock physics model is used to calculate seismic parameters (velocity and density) from reservoir properties (porosity, fluid saturation and pressure), then reflection coefficients are generated using a linearized AVA equation that involves velocity and density. AVA data are obtained by computing the convolution between reflection coefficients and a Ricker wavelet function. The multiresolution analysis applied to the AVA attributes helps to obtain a good estimation of noise level and substantially reduce the data size. We compare history matching performance in three scenarios: (S1) with production data only, (S2) with seismic data only, and (S3) with both production and seismic data. In either scenario S2 or S3, we also inspect two sets of experiments, one using the original seismic data (full-data experiment) and the other adopting sparse representations (sparse-data experiment). Our numerical results suggest that, in this particular case study, using production data largely improves the estimation of permeability, but has little effect on the estimation of porosity. Using seismic data only improves the estimation of porosity, but not that of permeability. In contrast, using both production and 4D seismic data improves the estimation accuracies of both porosity and permeability. Moreover, in either scenario S2 or S3, provided that a certain stopping criterion is equipped in the iterative ensemble smoother, adopting sparse representations results in better history matching performance than using the original data set.
Enhanced Oil Recovery On Troll Field By Implementing Autonomous Inflow Control Device
Authors: Halvorsen Martin , Madsen Martin , Vikøren Mo Mathias , Isma Mohd Ismail , Green Annabel
Published: March 2016

The implementation of autonomous inflow control device (AICD) has been a success at the Troll field with the objective to limit gas production for long horizontal wells in a thin oil column reservoir. First installed in 2008, recently the AICD was adopted as part of the standard lower completion solution at Troll. To date more than 30 wells have been completed with AICD, demonstrating significant increase in cumulative oil production.

Troll is a large subsea development offshore Norway which started oil production in 1995. Troll multilateral horizontal wells are drilled with total reservoir length typically 3 to 5 km within the thin oil column. Production has been aided by inflow control devices to ensure contribution from all reservoir sections and limit gas production by postponing gas breakthrough and choking gas production after breakthrough.

The Autonomous Inflow Control Device (AICD) provides the same functionality as a passive ICD in that it helps to create a more even inflow along the horizontal section prior to gas breakthrough, but also has a self-regulating adjustable design to provide greater production choking where gas breakthrough occurs. This chokes production from compartments producing large amounts of gas leading to greater oil recovery and lower gas production.

To evaluate the performance of the AICD a comprehensive multi-phase flow model of the autonomous performance has been developed and workflow created for simulation of performance within the reservoir.

This paper will describe the advances in the technology since the first field installation in 2008, and the development and challenges of performance prediction and assessment.
Innovation of Annular Sealants During the Past Decades and Their Direct Relationship with On/Offshore Wellbore Economics
Authors: Jimenez Walmy Cuello , Urdaneta Javier A. , Pang Xueyu , Garzon Juan R. , Nucci Gino , Arias Henry
Published: March 2016

Annular sealants are used as static barriers to avoid fluid communication in-between zones and provide proper isolation of the different formations as well as support and protection to the casing. Therefore, the sealant can have a direct relationship to wellbore integrity. Data suggest more than 4 million hydrocarbon wells have been drilled globally; interestingly, some datasets indicate well integrity failure is highly variable (1.9 to 75%).

Historically, sealants have been characterized for short-term placement properties up to the point at which the sealant is pressure tested and a log is performed to establish if the annulus is properly sealed. However, as hydrocarbon resources are becoming gradually depleted in easy-to-recover environments, harsher conditions are more common. Additionally, stimulation and enhanced oil recovery (EOR) techniques involving high-pressure and high-temperature (HP/HT) cycles during the entire well life pose significant challenges to the sealant's integrity.

Sealant integrity issues can result in very high remediation costs, reduction of hydrocarbon production, and in some cases, loss of the well. All of these can lead to an increased cost per barrel of oil equivalent (BOE). During the last few decades, in view of the drastic changes in drilling conditions toward more challenging environments, the industry has opted for a sealant design approach, which considers all of the events that occur throughout the entire life of the well and their effects on integrity of the sealant and wellbore. This approach can be successful by employing analytical tools, which allow for synchronizing all of the different events and/or operations occurring during wellbore construction (from drilling to abandonment) with the different elements that encompass the wellbore architecture (geometry, formations, casing, and sealant). The use of these tools' forecasting capabilities can result in data-led decisions that allow operators to construct wellbores more efficiently and with more confidence, which should ultimately help reduce production costs.

This study focuses on illustrating an analytical tool for predicting the sealant's performance in both onshore and offshore cases throughout the life of the well and determining how this affects wellbore economics in the long term. Moreover, this paper discusses how sealants have evolved from conventional Portland cements to elastic-, foamed-, glass-bead-extended cements, and epoxy-resins based on wellbore integrity predictions performed by analytical tools. The impact of nanomaterials in converting cement/sealant systems into multifunctional and/or smart materials capable of self-sensing specific stimuli (i.e. stress, strain, etc.) is also shown.
Economical Slot Recovery Using Open Hole Cement Plug Kick Offs, a Proven Success in North Sea
Authors: Hussain Sajjad , Dhaher Karam Sulaiman , Bjoerneli Hans Magnus , Noekland Magnar , Blackburn Jason , Monsen Gisle Otto , Haaland Sigurd , Hongdul Thanong
Published: March 2016

In recent years, slot recovery to drill more wells in brownfields has posed different challenges due to extensive and time consuming Plug and abandonment (P&A) and casing cut and pull operations [SPE 173954].

In 2013, For the first time on Statfjord Field, a ruggedized point the bit rotary steerable system (RSS) and Gyro while drilling (GWD) were used to sidetrack off cement plug in 17 ½-in hole section through a narrow window (80m) between 20-in casing shoe and 13 3/8-in casing stump. This reduced risk and saved time by sidetracking and drilling the section in one run. In similar scenarios on previous wells, mud motors had been used to kickoff and sidetrack from a cement plug between the casing shoe and casing stump. Two runs were always required to complete the sections; first run with a dedicated sidetracking assembly (motor BHA) and a second run with a drilling assembly (RSS BHA). After this success another attempt was made in 2014 where 17 ½-in section was sidetracked and drilled to TD through 40m narrow window between 20-in casing shoe and 13 3/8-in casing stump in high well collision risk environment. Significant time and cost saving was achieved on this project. In 2015 a challenging well was planned where kick off had to be done through 37m window and close to six producers. Due to high risk of collision and no possible option of whipstock exit, new Point the bit RSS technology was employed to kick off in high magnetic interference environment and drill the section in one run.

With the ruggedized point the bit RSS and GWD service, it was possible to constantly monitor direction and inclination in real time and thereby tracking the trajectory progress in the loose formations at shallow depth. This allowed to guard against dropping back to the mother bore and hitting the 13 3/8-in casing stump. Sidetracking in open hole from cement plug also increased formation strength at 20-in casing shoe and saved time/cost compared to whipstock exit.

During execution all three wells were sidetracked successfully from motherbores in the first attempt and drilled to section TD in one run saving significant rig time and cost.

This paper discusses the planning and execution phases of these three successful reentry wells drilled on Statfjord Field, one of the largest field on North Sea Continental Shelf (NCS).
Mathematical Approach of MSE in Thermo-Poro-Elastic Conditions Improves Decision Making to Use RWD
Authors: Roohi Abbas , Elmgerbi Asad , Nascimento Andreas , Prohaska Michael , Thonhauser Gerhard
Published: March 2016

Historically Reaming While Drilling (RWD) operations have been restricted to softer formations. The objective in this study is to create a thermoporoelastic model of Mechanical Specific Energy (MSE) for RWD in order to shed important new light on the decision process how to use RWD for a specific formation as well as a recommendation for reamer-pilot size ratio.

The analytical approach developed in this paper calculates thermoporoelastic coupled time-dependent stress, pore pressure and temperature variations for an inclined borehole that is drilled through permeable or impermeable formation and which is subjected to far field three dimensional in-situ stresses. Apparent rock strength of the rock in Depth of Cut (DOC) zone beneath the reamer can be determined by using Mohr-Coulomb theory. By using Apparent Rock Strength (ARS) the analytical Mechanical Specific Energy (MSE) can be estimated afterwards. This parameter can be used as a key decision to determine whether a specific formation is a good candidate for RWD or not.

A proper combination of pilot and reamer is absolutely critical to optimize bottom hole assembly (BHA) performance and durability. For many years, a trial-and-error technique has been employed by the drilling industry to determine advantages or drawbacks of reamer in the BHA and the optimum reamer-to-pilot-size ratio and bit characteristic for drilling, which requires a significant investment of time and money.

The comparison of reamer's MSE, to destroy rock around the wellbore, with bit's MSE, to destroy rock at the bottom of the hole, shows how efficiently reamer can drill rock around the wellbore in certain formation, and in some other formations the drawbacks are outweigh of its advantages. This in turn makes it possible to determine proper formation characteristics to employ reamer in the BHA and also the maximum reamer/bit size ratio for certain rock characteristics in order to support efficient drilling operations.

Considering that so fare in the market there is no evidence of a specific model to predict rock strength bellow the reamers, this research and study show its degree of novelty since it propose a model to fill this gap, which can in the future and after tuning be used as a reference application in the petroleum industry for decision making and project cost analysis. Validation in different environments is still to be concluded as a next step in this research.
Nanoscale Morphology of Brine-Oil-Mineral Contacts in Connected Pores of Carbonate Reservoirs: Insights on Wettability from Cryo-BIB-SEM
Authors: Schmatz Joyce , Klaver Jop , Jiang Mingze , Urai Janos L.
Published: March 2016

We used Broad Ion Beam slope-cutting in combination with Scanning Electron Microscopy undertaken under cryogenic conditions (Cryo-BIB-SEM) to study mineral-oil-brine contacts in reservoir carbonates. This direct imaging method allows pore scale investigation of in-situ fluids and their distributions down to the nanometer scale.

In this study we compare two types of carbonate reservoirs: a fine-grained Lixhe limestone (Belgium) and a coarse grained limestone from the Maastricht area (Netherlands). In both samples we first quantify the porosity using BIB-SEM and derive the spatially resolved pore connectivity of the rock from BIB-SEM on Wood's Metal (WM) injected sub-samples. In the second step sub-samples were saturated with the oil analogue n-hexadecane and NaCl-brine.

Cryo-BIB-SEM in combination with high resolution EDS imaging and automated image analysis on the saturated samples allowed for a quantification of the oil droplet size, the lengths of oil-carbonate contacts and the 2D contact angle of carbonate with brine and oil. Our results show that these features (e.g., contact line length, contact angles, effect of surface roughness) are present on the scale of a few tens of nanometers to a few micrometers, which is in agreement with numerous theoretical and experimental studies. Hence, this technique permits the testing of predictions on the morphology and dynamics of contact lines in relation the mineral properties, which is not possible with other imaging methods, such as X-Ray Micro Computed Tomography (µ-CT), due to limits in resolution. Our results call for improvements in models of multiphase pore-scale flow in digital rocks.
Determining Optimum Aging Time Using Novel Core Flooding Equipment
Authors: Ahkami Mehrdad , Chakravarty Krishna Hara , Xiarchos Ioannis , Thomsen Kaj , Fosbøl Philip Loldrup
Published: March 2016

New methods for enhanced oil recovery are typically developed using core flooding techniques. Establishing reservoir conditions is essential before the experimental campaign commences. The realistic oil-rock wettability can be obtained through optimum aging of the core. Aging time is affected by temperature, crude oil, formation brine, and coreplug lithology. Minimum time can significantly reduce the experimental cost while insufficient aging time can result in false conclusions.

Real-time online resistivity measurements of coreplugs are presented and a novel method is introduced for determining the optimum aging time regardless of variations in crude oil, rock, and brine properties. State of the art core flooding equipment has been developed that can be used for consistently determining the resistivity of the coreplug during aging and waterflooding using advanced data acquisition software. In the proposed equipment, independent axial and sleeve pressure can be applied to mimic stresses at reservoir conditions. 10 coreplugs (four sandstones and six chalk samples) from the North Sea have been aged for more than 408 days in total and more than 29000 resistivity data points have been measured to consistently investigate the change of wettability during aging.

At 60°C and 100 bars a homogeneous sandstone coreplug attained optimized wettability after 5 days, a heterogeneous coreplug required 30 days of aging. Chalk coreplugs needed 45 days of aging. This shows that coreplugs originating from the same field, when aged at equivalent conditions can have significantly different aging times because of minor variations in the coreplug properties. No fixed aging time can be recommended on the other hand a method is recommended which can determine the extent of aging. Coreplug aging patterns were studied for variation in pressure (20 to 130 bar) and temperature (60 to 130°C). Based on these experiments an algorithm has been developed which distinguishes the effect of wettability alteration, pressure, and temperature on coreplug resistivity.

This study highlights the use of hydraulic oil to avoid release of fluids in the effluent pipes during the aging process. Furthermore, the described multiple monitoring devices are useful in detecting any experimental error that may have occurred during mounting of the coreplug in the core holder. Thus imperfect waterflooding which can otherwise produce misleading data can be avoided.

The presented equipment can instantly and continuously calculate the mineral wettability throughout the aging process at any pressure, temperature condition and for any combination of rock and crude oil. Thus, using the stated core flooding equipment can not only decrease the cost and time of doing aging and waterflooding studies but can also significantly increase the accuracy in conducting core flooding experiments.
Solutions to the Curve Fitting Problem of Mathematical Correlation and SCAL Data
Authors: Arief I. H. , Xue Lili , Lomeland F.
Published: March 2016

Mathematical correlation has been widely used in oil and gas industry to model relative permeability and capillary pressure from water saturation. The application of mathematical correlation is essential especially in the absence of laboratory data. Additionally, the correlation is also applied to generate a refined relative permeability and capillary pressure table as the input to reservoir simulation.

There are several correlations being used in the industry such as Corey, Skjæveland and LET correlation. The focus in this paper is the LET correlation. The correlation offers more flexibility as well as accuracy in matching the responses from laboratory experiments.

Having a representative correlation is the basic, but the curve-fitting to the experimental data is also indispensable. In a problem which involves a non-linear correlation, the attempt to find a solution which fits the experimental data becomes more complex. To overcome this problem, it is fundamental to have a search method which can fit the experiment data with the lowest possible residual errors.

In this paper, different search methods of curve-fitting are investigated. In the last part of the paper we will compare the performance of each method. The main evaluation parameters are the residual error and the computational time. The methods studied in this paper are the Levenberg – Marquardt method, particle swarm optimization and mesh pattern search.
Pore-Scale Mechanisms During Low Salinity Waterflooding: Water Diffusion and Osmosis for Oil Mobilization
Authors: Fredriksen Sunniva B. , Rognmo Arthur Uno , Fernø Martin A.
Published: March 2016

This work study pore-level oil mobilization by water diffusion and osmosis during low salinity waterflooding using microscopic visualization in sandstone silicon-wafer micromodels. The twodimensional water-wet micromodels apply a high accuracy pore network with sharp edges and surface roughness to observe displacement processes during low salinity water injection. Residual and capillary trapped oil was mobilized when a salinity gradient between high-saline connate water in matrix and low salinity water flowing in an adjacent fracture was established. Transport of water by diffusion occurred through film-flow resulting in film-expansion and droplet growth along the water-wet grains. Water transport was also driven by osmosis due to the difference in chemical potential between the high and low-saline phases. The oil-phase acted as a semi-permeable membrane in presence of an osmotic gradient to transport low salinity water into high-saline water-in-oil emulsions. The identified pore-scale displacement mechanisms, observed using a controlled state-of-the-art experimental approach, contribute to the fundamental understanding of improved oil recovery during low salinity waterflooding.
Transport Properties of Functionalised Silica Nanoparticles in Porous Media
Authors: Najafiazar Bahador , Yang Juan , Simon Christian Rone , Karimov Fuad , Torsæter Ole , Holt Torleif
Published: March 2016

Silica nanoparticles modified with a variety of chemical surface functionalities are interesting additives, which can bring enhanced properties such as increased sustainability, ductility and flexibility to polymer materials. These functional nanoparticles have already shown promising applications in paints, lacquers and coatings. By elaborating an appropriate surface functionalisation, silica nanoparticles can be adapted to the conditions in oil reservoirs, modify polymer transport, adjust their gelation behaviour and thus show a great potential for oil recovery processes.

The objectives of the present work are to investigate transport properties of functionalised silica nanoparticles and polymer in porous media by characterizing their stability, retention and other physical properties.

Transport properties of functionalised hybrid silica nanoparticles and polymer have been investigated through flooding experiments in two types of sandstones, high permeability Bentheimer and lower permeability Berea. The experiments were conducted at room temperature by use of 500 - 2000 ppm solutions of polymer and nanoparticles. Each experiment consisted of four stages; the active materials were injected at stages 1 and 3 whereas only brine was injected in stages 2 and 4. The polymer and the nanoparticles were quantified at the core outlet by inline viscosity measurements and by use of inline measurements of UV absorption or refractive index. The history of effluent concentrations was compared with un-retained flow by use of a conductivity contrast as tracer.

Mechanical entrapment, adsorption and inaccessible pore volume were estimated through analyses of component profiles and mass balance calculations. These quantities were generally found to be higher in Berea compared to Bentheimer, both for polymer and nanoparticles. Unlike polymer, nanoparticles appear to be transported through the entire pore space with low and partly reversible retention.
Early risk factors for posterior crossbite and anterior open bite in the primary dentition
Authors: Germa Alice , Clément Céline , Weissenbach Michel , Heude Barbara , Forhan Anne , Martin-Marchand Laetitia , Bonet Mercedes , Vital Sibylle , Kaminski Monique , Nabet Cathy
Published: March 2016

Objective: 

To investigate risk factors specific to posterior crossbite and anterior open bite at the age of 3 years.

Materials and Methods: 

The study included 422 children of the French EDEN mother-child cohort. The main outcomes were the presence of posterior crossbite and anterior open bite assessed by dentists at 3 years. Social characteristics (collected during pregnancy), neonatal characteristics (collected at birth), duration of breast-feeding (collected prospectively), sucking habits at 3 years, and open lips (as a proxy for mouth breathing) were studied and two logistic regressions conducted.

Results: 

Preterm birth appears to be a risk factor specific for posterior crossbite (OR: 3.13; 95% CI: 1.13–8.68), whereas small for gestational age seems to be associated with a lower risk of posterior crossbite (OR: 0.32; 95% CI: 0.12–0.87). Ongoing pacifier or thumb sucking at 3 years is a risk factor for both posterior crossbite and anterior open bite.

Conclusions: 

Children born preterm seem to be more at risk for posterior crossbite than those born at term. Different mechanisms may be involved in posterior crossbite and anterior open bite.
Herpetofaunal responses to brush management with herbicide and fire
Authors: Jones B. , Fox S. F. , Leslie D. M. ,   Society for Range Management
Published: March 2016

We examined how native herpetofauna of the Cross Timbers in Oklahoma, USA, were influenced by vegetation types derived from combinations of herbicide applications and prescribed burning. Brush management treatments consisted of tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiazol-2-y-1] -N,N'-dimethylurea)-only, tebuthiuron + fire, and untreated pastures of mature hardwood forest (no herbicide or fire). A total of 292 individuals representing 30 species was captured in 1994 and 1995 using time-constrained searching and drift-fence arrays on 3 replicates of the 3 treatments. Relative total abundance and species richness of herpetofauna were similar on all 3 treatment types. However, differences were apparent by taxonomic group. In general, amphibians were most abundant in untreated and tebuthiuron-only pastures, lizards were most abundant on the untreated pastures, and snakes were most abundant on pastures treated with tebuthiuron + fire. Maintenance of a mosaic of habitats in the Cross Timbers may enhance diversity of the native herpetofauna.
Technical note: Estimating aboveground plant biomass using a photographic technique
Authors: Paruelo J. M. , Lauenroth W. K. , Roset P. A. ,   Society for Range Management
Published: March 2016

We present a non-destructive, photographic method to estimate biomass in semiarid grasslands. Though the method needs to be calibrated, it allows for a dramatic increase in the number of samples compared with the clipping method. The method is based on a relationship between the percentage or "green pixels" in a digital image and green biomass. We identified "green pixels" as those satisfying the following condition: G/B > 1 and G/R > 1, where G, B and R are the intensities of a particular pixel in the green, blue, and red bands respectively. The percentage of green pixels of the image and green grass biomass showed a correlation of 0.87 (n = 36, p < 0.001) when data were pooled from 3 sample dates. The relationship was slightly curvilinear and a log transformation of green biomass yielded a better correlation (r = 0.91, n = 36, p < 0.001). The percentage of green pixels showed a lower correlation with total green biomass than with grass biomass (r = 0.59) for the linear model and 0.73 for the log transformed model). The relationship between the percentage of green pixels and either green grass or total green biomass changed during the growing season. Both the slope and the Y-intercept of the model differed significantly among dates. Correlation coefficients for different dates ranged between 0.76 and 0.95.
Age-stem diameter relationships of big sagebrush and their management implications
Authors: Perryman B. L. , Olson R. A. ,   Society for Range Management
Published: March 2016

Decisions to control big sagebrush (Artemisia tridentata Nutt.) on North American rangelands are traditionally based on morphological characteristics (e.g., cover) rather than more ecologically based community successional criteria. Big sagebrush standage is a critical component for evaluating successional status, but has been difficult to obtain under field conditions. Assessing big sagebrush plant age based on stem diameter would provide resource managers with an efficient field tool to make management decisions based on ecological principles. For each of 3 sub-species of big sagebrush, between 75–80 stem cross-sections were collected within each of 9 stands situated at 3 regionally dispersed locations across Wyoming. Maximum basal stem diameters were measured and plant age determined from annual growth-ring assessments. Regression analysis (95% confidence interval) relating maximum basal stem diameter to plant age produced coefficients of determination (r2) of 0.70, 0.64, and 0.61 for Wyoming big sagebrush (A. tridentata ssp. wyomingensis Beetle and Young) in each of 3 regional locations; 0.53, 0.69, and 0.64 for mountain big sagebrush (A. tridentata ssp. vaseyana [Rydb.] Beetle); and 0.50, 0.62, and 0.44 for basin big sagebrush (A. tridentata ssp. tridentata). Combined regional data for each subspecies produced r2 values of 0.54 for Wyoming big sagebrush, 0.52 for mountain big sagebrush, and 0.50 for basin big sagebrush. Results indicate that maximum basal stem diameter can be used to assess the age of big sagebrush subspecies, thus, providing land managers with an ecologically based alternative method for justifying big sagebrush management decisions.
Long-term effects of fire on sage grouse habitat
Authors: Nelle P. J. , Reese K. P. , Connelly J. W. ,   Society for Range Management
Published: March 2016

This study documented the long–term (> 10 years) impact offire on sage grouse (Centrocercus urophasianus Bonaparte) nesting and brood–rearing habitats on the Upper Snake River Plainin southeastern Idaho. The habitat of the study area is primarily mountain big sagebrush (Artemisia tridentata vaseyana Rydb.)—grassland. Twenty different-aged burns were sampled from 1996 to 1997, ranging from wildfires which burned during the 1960s to prescribed fires set during the 1990s. Canopy coverage and height of vegetation, and relative abundance of invertebrates, were estimated at burned and unburned sites within burns. Fourteen years after burning, sagebrush had not returned to pre-burn conditions. No difference was detected in forb abundance between different-aged burns. Relative abundance of ants and beetles was significantly greater in the 1-year old burn category but had returned to unburned levels by 3–5 years postburn. No benefits for sage grouse occurred as a result of burning sagegrouse nesting and brood-rearing habitats. Burning created along-term negative impact on nesting habitat because sagebrush required over 20 years of postburn growth for percent canopy cover to become sufficient for nesting.
Livestock forage conditioning: Bluebunch wheatgrass, Idaho fescue, and bottlebrush squirreltail
Authors: Ganskopp Dave , Svejcar Tony , Vavra Marty ,   Society for Range Management
Published: March 2016

Research on Anderson and Scherzinger's hypothesis that spring cattle grazing can positively affect subsequent nutritional characteristics of grasses have generated mixed results. Our objectives were: 1) to evaluate fall/winter nutritional indices of bluebunch wheatgrass (Agropyron spicatum [Pursh] Scribn. Smith), Idaho fescue (Festuca idahoensis Elmer), and bottlebrush squirreltail (Sitanion hystrix (Nutt.) Smith) in ungrazed, lightly grazed (33% utilization), or heavily grazed (69% utilization) pastures stocked with cattle at the boot stage of growth; and 2) to quantify opportunity costs of applying those treatments on fall standing crop. Compared with ungrazed stands, light and heavy spring grazing decreased September standing crop by 32 and 67%, respectively. September/December crude protein (CP) among heavily grazed grasses (x̄ = 6.9%) exceeded ungrazed controls (x̄ = 3.9%) for 11 of 12 comparisons. Crude protein of lightly grazed grasses (x̄ = 5.2%) was higher than ungrazed controls for 6 of 12 comparisons. Herbage was more nutritious during the drier of the 2 years sampled. Among grazed treatments, fall/winter CP measures were highest for bottlebrush squirreltail (x̄ = 7.4%), intermediate for Idaho fescue (5.9%), and lowest for bluebunch wheatgrass (0=4.9%). In fall/winter, herbage was most digestible in heavily grazed paddocks (x̄ = 59%), intermediate in lightly grazed paddocks (x̄ = 53%), and least digestible in ungrazed areas (x̄ = 49%). Light and heavy spring cattle grazing can augment fall/winter forage quality of bluebunch wheatgrass, Idaho fescue, and bottlebrush squirreltail. Spring grazing reduces subsequent standing crop, but remaining forage will be nutritionally superior to herbage in ungrazed stands.
Writing Book Reviews for the Journal Of Range Management and Rangelands
Authors: Scarnecchia David L. ,   Society for Range Management
Published: March 2016

Effective, analytical reviews of recently published books inform readers of their essential content, and evaluate and communicate the value of their content to professional disciplines and the reading public. Such book reviews are widely read contributions to the Society for Range Management's publications, the Journal of Range Management and Rangelands, and are important elements of evaluation and communication within the Society. This paper is designed to assist writers in developing book reviews for the Journal of Range Management and Rangelands. Much of its analysis is relevant to book reviews for other publications. It begins with preliminary considerations for prospective authors. The functions of a book review are explained. Important considerations concerning reading the book are examined. The paper emphasizes the importance of finding a theme for a review. The common parts of a written review, i.e., the introduction, description of content, analysis and evaluation, and closing are considered individually. The paper then examines aspects of editing a review, and addresses some matters of style in writing. It concludes with a brief discussion of the importance of synthesis in developing an effective book review.
Effect of canopy and grazing on soil bulk density
Authors: Tate Kenneth W. , Dudley Dennis M. , McDougald Neil K. ,   Society for Range Management
Published: March 2016

This study compared soil surface bulk density between: 1) sites not grazed by cattle > 26 years; 2) sites not grazed for 6 years; 3) sites grazed for 15 years to October residual dry matter levels of > 1100 kg ha-1; 4) sites grazed for 15 years to October residual dry matter levels of 670 to 900 kg ha-1; 5) sites grazed for 15 years to October residual dry matter levels of < 450 kg ha-1; and 6) sites subject to concentrated cattle use (trails, corrals, and supplemental feed-water stations). Sites were collected from across the 1,772 ha San Joaquin Experimental Range (SJER) in Madera County, Calif. to represent canopy cover (open grassland, blue oak (Quercus douglasii Hook and Arn.), live oak (Quercus wislizenii A.DC.), foothill pine (Pinus sabiniana Douglas), wedgeleaf ceanothus (Ceanothus cuneatus (Hook) Nutt.), and ceanothus interspace) and topography (swale, uplands) typical of the rocky coarse sandy loam soils of the southern Sierra Nevada foothill oak savannah. Soil surface (0 to 7.62 cm) bulk density (g cm-3) was determined for 1489 soil cores collected across all available combinations of grazing management, canopy cover and topographic position at the SJER. Soil surface bulk density was 0.23 to 0.30 g cm-3 lower under canopy compared to open grasslands. Bulk density was not different (P > 0.05) between sites not grazed > 26 years and sites not grazed for 6 years. Grazing to residual dry matter levels of > 1100, 670 to 900, and < 450 kg ha-1 created bulk densities which were 0.08, 0.18, and 0.21 g cm-3 greater than non-grazed sites, respectively. Cattle concentration sites had bulk densities 0.37 to 0.47 g cm-3 greater than areas not grazed > 6 or 26 years. For the purpose of maintaining soil surface bulk density current residual dry matter recommendations for sites with canopy cover > 50% appear appropriate, but recommendations for open grasslands need additional review. In particular, residual dry matter level must be directly linked to soil surface infiltration capacity.