bluuebunny/crossref_metadata_2025 huggingface dataset:
Macroalgas em nascentes e arredores de riachos na região noroeste do estado de São Paulo
Authors: Pereira Jeferson Luizi , Branco Luis Henrique Zanini
Published: March 2013

Macroalgas são organismos tipicamente bentônicos, constituídos por um talo maduro, discreto e reconhecível a olho nu, cuja identificação microscópica é necessária. Diversos estudos foram realizados visando o conhecimento taxonômico em riachos brasileiros, no entanto, são raros os trabalhos que abordam as algas que se desenvolvem nas nascentes destes riachos. De fevereiro a setembro/2007 coletas mensais foram realizadas em nascentes e em suas imediações (solos úmidos dos afloramentos d'água) de quatro riachos na região noroeste do estado de São Paulo. O levantamento taxonômico resultou na identificação de 13 espécies, sendo 54% dos táxons pertencentes a Cyanophyta e 46% a Chlorophyta. Cylindrospermum gorakhpurense, Mougeotia gotlandica, Spirogyra gallica e S. taftiana são registradas pela primeira vez para o Brasil. A flora aquática encontrada diferiu da regional devido à presença de organismos da família Zygnemataceae (Chlorophyta) em estágio reprodutivo. Este tipo de hábitat mostrou-se especialmente favorável à reprodução das Zygnemataceae.
Contribuição ao conhecimento de Cosmarium Corda ex Ralfs (Desmidiaceae, Zygnematophyceae) para a Bahia e o Brasil
Authors: Oliveira Ivania Batista de , Bicudo Carlos Eduardo de Mattos , Moura Carlos Wallace do Nascimento
Published: March 2013

Este estudo teve como objetivo identificar os táxons do gênero Cosmarium presentes em duas Áreas de Proteção Ambiental da planície litorânea do norte da Bahia e contribuir para o conhecimento da biodiversidade do estado, bem como ampliar o conhecimento da distribuição dos táxons identificados na Bahia e no Brasil. O levantamento taxonômico foi baseado em coletas realizadas no verão (janeiro a março de 2007) e no inverno (junho a agosto de 2007). As amostras foram obtidas através de rede de plâncton com 20µm de abertura de malha e imediatamente fixadas em solução de Transeau. As análises qualitativas e ilustrações foram obtidas utilizando microscópio óptico binocular e máquina fotográfica digital acoplada. Foram registrados 43; táxons, destes, três espécies e duas variedades são ocorrências novas para o Brasil, e 28 espécies e três variedades são novos registros para o estado da Bahia.
Circumscribing Vellozia hirsuta and V. tubiflora (Velloziaceae)
Authors: Mello-Silva Renato de
Published: March 2013

Vellozia hirsuta and V. tubiflora belonged to Vellozia sect. Radia, a poliphyletic taxon. Due to different choices of characters for delimiting the species, from 21 species formelly included in the section, only three are now recognised. The hypanthial tube longer than ovary, and deciduous in fruit, distinguishes V. hirsuta and V. tubiflora from all other Velloziaceae. Although consistently delimited, they exhibit wide intraspecific variation. Thus, V. hirsuta encompasses four taxonomic synonyms, and V. tubiflora, 19. On the other hand, the many different populations of both species lead to the recognition of 14 morphological patterns within V. hirsuta and eight within V. tubiflora, although those patterns cannot receive taxonomic status.
Polypores from Morro Santana, Rio Grande do Sul, Brazil
Authors: Westphalen Mauro Carpes , Reck Mateus Arduvino , Silveira Rosa Mara Borges da
Published: March 2013

In the survey of polypores from Morro Santana, Porto Alegre, Rio Grande do Sul, accomplished from March 2007 to March 2009, 44 species were identified. Identification keys and remarks about all the species are given. Full descriptions and illustrations of Datronia caperata, Junghuhnia polycystidifera, Oxyporus obducens, Phellinus umbrinellus, Phylloporia frutica and Tinctoporellus epimiltinus are presented. Tinctoporellus epimiltinus is a new records from Rio Grande do Sul.
Building bridges from the Foyle to Ojague
Authors: Donald Philip T. A.
Published: March 2013

In 1984 the Foyle Bridge in Northern Ireland was completed and opened to traffic. During construction by the RDL–Graham joint venture the seven prestressed concrete approach spans were supported by temporary works which included considerable quantities of Bailey bridging equipment. In 2005 Graham donated this Bailey bridging material to a charity, Friends in Action, which knew of villages in Guinea, West Africa that were isolated for five months every year during the rainy season. The author of the present paper was asked to act as consulting engineer to the project. The Bailey equipment was used to build two bridges, in 2006 and 2007, in Guinea. This paper outlines the environment, the background, the preparations, the design, together with details of the construction methods, the plant and materials used, the problems encountered, their solution and the outcome. Conclusions are derived, and recommendations given to help ensure the success of similar low-tech bridge projects in developing countries.
Improving the mechanical response of kaolinite and bentonite through exposure to organic and metallorganic compounds
Authors: GAJO A. , MADASCHI A. , GIRARDI F. , DI MAGGIO R.
Published: March 2013

The mechanical response of soft clays can be modified through change of the adsorbed ions or by adding lime or cement using deep mixing tools. This work focuses on analysing the effects induced by a new class of chemical agents, which can be driven through soft clays and lead to cementing bonds, without being associated with any deformation. The resulting technique could be of benefit for improving in situ soil properties, for instance beneath existing foundations. Both kaolinite and sodium- and potassium-bentonites are subjected to different chemical compounds, considering the effects on the liquid limit, residual friction angle and apparent preconsolidation pressure.
Briefing: Young Coastal Scientists and Engineers Conference 2012
Authors: Green J. A. Mattias , Davies Alan G. , Bowers David G. , Zhu Fangfang , Ward Sophie L. , Porter Kate
Published: March 2013

The 24 papers and posters presented at the eighth Young Coastal Scientists and Engineers Conference held at Bangor University in April 2012 were of a high standard, typical of that expected at a leading international conference. They gave a good indication of the breadth of basic and applied research currently being pursued in UK universities and consultancies. Papers covered a wide range of topics, including coastal management, shelf sea turbulence, renewable energy, cliff erosion, sediment transport, morphological modelling, nutrient and pollution transport, and scour protection, to mention but a few. This briefing reproduces the abstracts of the two Keynote lectures and of three presentations judged by the organising committee to be of particular merit. The next UK Young Coastal Scientists and Engineers Conference will be organised by Marine Scotland in Aberdeen in spring 2013.
Briefing: Between paradigms – a place for landscape
Authors: Kirby Val
Published: March 2013

This briefing explores the relevance of Kuhn's analysis of paradigm change in the physical sciences to paradigm change in the wider world. It looks at progress from a world view dominated by a commitment to short-term economic growth, to one that favours longer-term, environmentally and socially sustainable public decision-making. The specific focus is the author's interest in a landscape-led approach to planning for resource use and land management. Here, landscape is defined in the inclusive way taken by the European Landscape Convention. The briefing concludes that society is currently between paradigms, and that this situation will take some time to resolve; however, there are already places where a landscape-led approach is helping to build bridges between the old and the emerging paradigms.
A Review of Total Job Times for Repair and Maintenance Jobs for Well Servicing Activities in the Permian Basin
Authors: Conine Lynn W. , Burke Phil
Published: March 2013

The well servicing function is one of the last frontiers in the exploration and production industry to utilize modern instrumentation coupled with continuous improvement techniques to improve the safety, quality and efficiency of this particular industry segment. In 1999 Newman, et al, described a device for recording critical rig parameters while operating a well service unit. In a later paper (2002) he described several examples of how to utilize the data to gain insight into the operation of the service unit. This current paper analyzes job time data for 4,532 Repair and Maintenance jobs in the Permian Basin performed during 2009-2012. All jobs utilized in the analysis include rod and tubing activities but do not include traditional workover activities such as cementing, logging, perforating, swabbing or acidizing. The data encompasses twenty one counties in the heart of the Permian Basin from a variety of operators, although no individual operators are named. Several standard metrics such as total job time and job time versus depth will be included. The job times will also be subdivided into various groups of activities (categories) such as mobilization, tripping activities, BOP/TAC/PKR activities, transition activities, well control activities, crew break time, safety time, wait time and miscellaneous activities. In addition, ranges of expected performance times will be shown for both total job times and activity groups (categories) based on Statistical Process Control calculations. It is anticipated that by establishing quantitative benchmarks for service rig activities, producers will be able to identify areas for operational improvement, thereby resulting in an increase in the well service rig productivity. The basic data for this study has been obtained from the Key Energy Services Database. The authors are not aware of any previous papers which have presented this type of detailed well servicing time based information.
Enhanced Plunger Lift Performance Utilizing Reservoir Modeling
Authors: Parsa E. , Ozkan E. , Lowery B. , Cathcart D. , Lohmann M.
Published: March 2013

Liquid loading is an important determinant for the performance of tight, unconventional gas wells. Although plunger lift is one of the best solutions when applicable, marginal economics of unconventional gas production does not tolerate un-optimized plunger lift performance. In this paper a reservoir-performance based algorithm proposed by Ozkan et al. (2003) is applied to optimize the gas production and shut-in periods of plunger lift operation. The objective of the optimization is to maximize gas production with the condition that the liquid loaded during production can be lifted to the surface by the pressure that builds up during the following shut-in period. Unlike the current plunger lifts that work in time mode (like timer clock), this algorithm is based on pressure (pressure mode). The optimization algorithm combines the conventional plunger-lift theory with an analytical description of the reservoir performance. The conventional plunger lift theory provides the pressure required for lifting the plunger with a liquid column on top of it, and the analytical reservoir model is used to optimize the sequence of production and shut-in times. The optimization algorithm presented in this paper improves the economics of unconventional gas production not only by increasing gas production but also automating the process by which optimization is achieved. Another advantage of the proposed method is the ability to automatically adjust to changes in the line pressure. A case study is presented to demonstrate that the proposed automated model can achieve the same optimization performance as that implemented by expert technicians.
The Flow Behavior of Friction Reducer in Microchannels during Slickwater Fracturing
Authors: Sun Yongpeng , Wu Qihua , Bai Baojun , Ma Yinfa
Published: March 2013

Tight formations with extremely low matrix permeabilities, such as gas shale, can produce at economical rates is due to inborn fissures and fractures introduced during hydraulic stimulation. Hydraulic fracturing in gas shale can connect/generate these microfractures, causing them to become much more complex fracture networks. During a fracturing treatment, a pair of main fractures firstly is generated perpendicular to the wellbore direction. As the fluids continue to pump, more micro-sized fractures are generated near the main fractures. These microfractures have much more contact area with the matrix and therefore hold the majority of the productivity potential of gas shale. Slickwater fracturing has been proved to be an effective method by which to increase the recovery of shale gas reservoirs.

Friction reducer is the primary component of this fluid. It can decrease the flowing friction in macro tubing. Lab tests and field applications have addressed this issue thoroughly. However, the flow characteristics of this solution in microfractures are not clear.

The present study attempts to represent how this solution flows in microfractures by considering how it flows in microchannels. A commercial friction reducer was prepared with deionized water. The size of the particles in the FR first was analyzed from the macro to the nano scale. Then, the FR solution fluxed the microchannels with various velocities. Different solution concentrations, microchannel size effects and Reynolds number (Re) were investigated in detail. The Microchannels wettabilities, fluid shear rates and residual resistance factors also were studied. Finally, the experimental results were compared with field data, and its impact on the gas shale matrix was analyzed.
Pipe Diameter Effect on Liquid Loading in Vertical Gas Wells
Authors: Skopich A. , Pereyra E. , Sarica C. , Kelkar M.
Published: March 2013

The effect of pipe diameter on liquid loading initiation has been experimentally investigated using 2-in and 4-in pipe diameters. Two-phase flow parameters such as pressure gradient and liquid holdup were measured. Flow characteristics were determined by visual observation using a high speed video camera. Critical gas flow rate for liquid loading initiation has been identified and comparison between the two pipe diameters is presented. The critical superficial gas velocity corresponding to the minimum pressure gradient is larger for the smallest diameter. When the comparison is carried out in terms of mass flow rates, critical flow rate for liquid loading in 2-in pipe is smaller than that in 4-in. pipe. This supports the use of velocity strings to extend the production life of the gas well. Additionally, comparison of the data with available mechanistic models prediction shows significant discrepancies. Possible reasons for these discrepancies are presented.
Solutions for Difficult Reservoirs Direct NMR Fluid Type and Permeability
Authors: Smith Charles H. , Ramakrishna Sandeep , Hamilton Layne
Published: March 2013

Conventional reservoir calculations using resistivity and density/neutron porosity have been the industry standard for defining reservoir characteristics. The calculation of water saturation from these measurements is used in every reservoir situation. Many reservoirs are not easily analyzed; therefore, various and complicated analysis techniques have been developed.

In some cases, years were spent in characterization before these log measurements could be applied with confidence. This time and expenditure of resources drained capital from exploration to research processes and produced many inefficient completion attempts in reservoirs that were incorrectly characterized as productive.

The great hope with the introduction of NMR tools to the industry was that reservoir parameters could be established and applied in an uncomplicated manner. Advances in technology of NMR responses have produced the ability to capture polarization time and relaxation time in a single pass through the reservoir. Nuclear magnetic polarization time has been demonstrated to have a relationship to the fluid type in the reservoir. The relaxation time (T2) has been used to characterize permeability with an excellent relationship to production. The Bray-Smith permeability equation was developed from this observation. This equation incorporates relaxation time and calculates permeability. No alterations to the equation for rock type or texture changes were needed.

This paper presents examples of logs in three different and difficult-to-evaluate reservoirs. A reservoir with lenticular sand, another with a thinly-bedded sand and shale sequence, and a conglomerate/mudstone reservoir are each evaluated for fluid type and permeability. Effective porosity, fluid type, and permeability are all resolved accurately by the NMR. Comparisons to production results are presented.
Reactions of Simple Organic Acids and Chelating Agents with Dolomite
Authors: Adenuga Olusegun Olatunbosun , Nasr-El-Din Hisham A. , Sayed Mohammed Ali Ibrahim
Published: March 2013

Abstract

Regular HCl has been used as the main acidizing fluid. At high temperatures, rapid spending of the acid with carbonates prevents deeper penetration of the acid into the formations. Alternatives such as acetic and formic acid have lent themselves to retarded reaction rates, low corrosivity and reduced tendency to form acid/oil sludge in asphaltene-rich crudes. The same problem of high reaction rate is still observed with organic acids at very high temperatures.

Complex thermodynamics equilibrium and reaction kinetics have been cited as issues apparent in selecting suitable organic acid as a stimulation fluid for specific acidizing treatment. Chelating agents, with the added advantage of complexing with carbonate to form a water-soluble product, have been introduced as stimulation fluids. Glutamic acid diacetic acid (GLDA), is a polycarboxylic acid with this property.

To predict the spending of GLDA relative to the organic acids, the kinetics of dolomite dissolution in organic acids and GLDA solution was investigated. The rotating disk apparatus was used to compare the reactivity of these solutions by varying the disk rotational speed from 100 to 1500 rpm and for 0.886N solutions at 120°C. Samples of the reacted acids, from the reactor, were collected and analyzed with Inductively Coupled Plasma.

Experimental results indicated that dolomite dissolution rates increased in all the acid solutions as the disk rotational speed increased at 120°C. At disk rotational speed of 1000 rpm and higher; the dissolution rate of dolomite in formic acid remained the same. Hence, the prevailing reaction regime in the acid solutions were mass transfer limited processes until the process shifted to reaction kinetics controlled at 1000 rpm in formic acid. Compared to the organic acids, GLDA demonstrated the lowest reactivity with dolomite at the same acid molarity and reaction conditions.
Analytical Determination of Interwell Connectivity Based on Flow Rate Fluctuations in Waterflood Reservoirs
Authors: Dinh Anh V. , Tiab Djebbar
Published: March 2013

Interwell connectivity, an important element in reservoir characterization, especially for secondary recovery such as waterflooding, is essential when making decisions on well patterns, infill wells, and injection rates for oil recovery optimization. An existing technique uses multivariate linear regression analysis of flow rates in a waterflood to infer interwell connectivity. Advantages of this technique include a simplified one-step calculation and the availability of production data. A capacitance model was introduced as an extension of the technique to account for shut-in periods and changes in bottomhole pressures in the producers; however, this approach is based on trial and error and requires subjective judgment.

This paper presents an alternative analytical approach based on analytic concepts, providing an in-depth understanding of the technique and relationships between interwell connectivity coefficients and other reservoir parameters. The analytical approach uses a mathematical model for bottomhole pressure responses of injectors and producers in a waterflood system. The model is based on a solution for fully penetrating vertical wells in a closed rectangular reservoir with an assumption of steady-state flow. This model is then used to calculate relative interwell permeabilities, which represent the connectivity levels of signal response well pairs.

Different synthetic reservoir models were analyzed, including homogeneous, anisotropic reservoirs, and reservoirs with high-permeability channels and transmissibility barriers. Comparisons with results obtained from previous studies of production data and bottomhole pressure data are presented.

The main findings of this study are: (a) the mathematical model performs well with interwell connectivity coefficients calculated from flow rate data to quantify reservoir parameters; (b) the proposed approach provides a better understanding of interwell connectivity determination from flow rate data;and (c) the results for relative interwell permeability from flow rate data are similar to those obtained from previous studies of bottomhole pressure data.
Inferring Interwell Connectivity in a Reservoir from Bottomhole Pressure Fluctuations in Hydraulically Fractured Vertical Wells, Horizontal Wells, and Mixed Wellbore Conditions
Authors: Dinh Anh V , Tiab Djebbar
Published: March 2013

A technique using interwell connectivity is proposed to characterize complex reservoir systems and provide highly detailed information about permeability trends, channels, and barriers in a reservoir. The technique, which uses constrained multivariate linear regression analysis and pseudosteady-state solutions of pressure distribution in a closed system, requires a system of signal wells and response wells.

Signal wells and response wells can be either producers or injectors. The response well can also be either flowing or shut in. In this study, for consistency, waterflood systems are used in which the signal wells are injectors and the response wells are producers. Different borehole conditions, such as hydraulically fractured vertical wells, horizontal wells, and mixed borehole conditions, are considered.

Multivariate linear regression analysis was used to determine interwell connectivity coeffients from bottomhole pressure data. Pseudosteady-state solutions for a vertical well, a well with fully penetrating vertical fractures, and a horizontal well in a closed rectangular reservoir were used to calculate the relative interwell permeability. The results were then used to obtain information on reservoir anisotropy, high-permeability channels, and transmissibility barriers.

The following are some conclusions drawn from this study: (a) the interwell connectivity determination technique using bottomhole pressure fluctuations can be applied to waterflooded reservoirs that are being depleted by a combination of wells (e.g., hydraulically fractured vertical wells and horizontal wells); (b) wellbore conditions at the observation wells do not affect interwell connectivity results; (c) the complex pressure distribution caused by a horizontal well or a hydraulically fractured vertical well can be diagnosed using the pseudosteady-state solution and, thus, its connectivity with other wells can be interpreted.

Different synthetic reservoir simulation models are analyzed, including homogeneous reservoirs, anisotropic reservoirs, and reservoirs with a high-permeability channel, or a partially sealing barrier, or a sealing barrier.
Comparative Study Between Guar and Carboxymethylcellulose Used as Gelling Systems in Hydraulic Fracturing Application
Authors: Trabelsi Siwar , Kakadjian Sarkis
Published: March 2013

Guar gum and its derivatives are the most frequently used thickening agents in hydraulic fracturing. They account for possibly 90% of all gelled fracturing fluids. Carboxymethylcellulose (CMC) has little use today in hydraulic-fracturing applications. Due to uncertainity in guar availability, CMC is being recommended as an effective polymer alternative in hydraulic-fracturing applications. In order to evaluate this option, a comparative study was conducted between guar and CMC performance as gelling agents in hydraulic fracturing.

CMC can be an effective alternative to guar and as this study illustrates can minimize formation and proppant pack damage. Furthermore, the critical overlap concentration, C* was determined as an indicator of crosslinkability at low polymers concentration for both guar and CMC.

This study was also conducted in order to evaluate the effect of several breakers (ammonium persulfate, sodium persulfate and enzymes) on linear polymer and crosslinked gel systems degradation. Viscosity, particle size distribution and regain conductivity were measured as a function of breaker type and concentration. Design schedules of hybrid fracturing jobs performed with CMC and guar in similar completion conditions in the Permian Basin were reported.
Matrix Stimulation: An Effective One-Step Sandstone Acid System
Authors: Gomaa Ahmed M. , Cutler Jennifer , Qu Qi , Boles Joel , Wang Xiaolan
Published: March 2013

Sandstone acid systems, which are composed of HCl and HF, are commonly used to remove the formation damage in sandstone reservoirs. However, to perform any treatment using these acid systems, a preflush and/or a postflush of HCl plain acid must be injected to eliminate CaF2 precipitation and secondary precipitation. In this study, a new sandstone acid formulation was developed that can be used as a one-step sandstone acid system (OSSA). This system eliminates the requirement of preflush and postflush HCl acid stages, reduces the treatment complexity, reduces the HCl requirements, and reduces the overall treatment/rig time.

A coreflood study was conducted using different sandstone cores at 180°F. In additional to quartz, the tested cores had varying amounts of clay mineral, feldspar, and carbonate. Consequently, they can be used to judge the performance of the new OSSA system.

Based on the experimental results, regular sandstone acid must be used with a preflush stage of HCl acid to maximize its performance and eliminate CaF2/MgF2 precipitation. The needs of the postflush stage must be confirmed as it can cause damage for sandstone that has HCl sensitive clay mineral. All selected one-step sandstone acid formulations (Acids A, B, C, and D) were able to successfully treat Bandera sandstone cores. For Bandera sandstone cores, increasing HCl/HF ratio increased the permeability enhancement and reduced the injected acid volume. Using the same acid volume and composition, a higher permeability enhancement was observed for the core that had less clay and carbonate content. Based on HCl:HF ratio and sandstone composition, a minimum acid volume is required to achieve a permeability enhancement. For the Bandera sandstone formation, only 8 PV of the OSSA system was required to achieve 26% permeability enhancement. However, for a Berea sandstone core that had less clay mineral, 4PV of OSSA system increased the permeability by 86%. The feldspar amount in the composition of sandstone can significantly impact the permeability enhancement of Acid C, while kaolinite amount has nearly no effect. A corrosion test was conducted at 180°F for 6 hr using a two pipe grades (Cr-13 and N-80). Two types of corrosion inhibitor were evaluated at different concentrations. All tested formulas had a very low corrosion rate (less than 0.03 lb/ft2). For both corrosion inhibitor types, corrosion rate was increased by reducing the HCl/HF ratio and/or inhibitor concentration.
An Offshore Field Development Plan to Optimize the Production System from the Reservoir to the Tank
Authors: Karimi Vajargah A. , Usman M. , Brito R. , Karami Mirazizi H. , Ettehadi Osgouei R.
Published: March 2013

To perform a successful optimization of large and complex production facility, there should be a good communication between engineers at different departments (Reservoir, Production, Geological, etc). However, as a common practice, their decision making process is separate from each other. This may result in under-designing such as flow bottlenecks or over designing, which imposes unnecessary expenditures. This lack of communication can be alleviated by coupling the reservoir flow model to the facility network by means of enhancements in software development that can perform networking analysis in an effective manner.

This paper presents a work methodology and recommendations through a case study to develop an offshore field that contains both heavy and medium oil. First, commercial software is utilized to build the model according to the input data. Subsequently, a development plan has been suggested for this field and number of wells to be drilled in the reservoir has been determined. Then sensitivity analysis is performed to find out the best possible scenario to produce from the field. Economical analysis is performed for each case to assure profitability.

According to the available recoverable reserves, a 13 year production plan is proposed (average of 7.46% per year). Simulation results indicate that by the proposed scenario at least 20% more of total recoverable reserves can be produced over this period. The highest oil rate is observed at the end of fourth year (98000 STB/d), when the field is mainly developed. This case study shows that complex production systems can be modeled by commercial software, which leads into better production forecasts. In addition, it can help us in selecting proper down-hole equipments and predicting the possible problems in each well (such as sand production or asphaltene deposition in this case).
Friction Reducers as Water Management Aids in Hydraulic Fracturing
Authors: Kolla Harsha , Watson Philip , Patel Aditya , Robinson Ronald , Jackson Logan , Nair Mohan
Published: March 2013

Hydraulic fracturing has transformed the American energy industry, allowing unprecedented access to shale oil and gas deposits. However, fracturing's demand for water has raised concerns across the country, particularly in water-stressed regions like Oklahoma and Texas. Additionally, costs for disposing flowback and produced water have risen and regulations have tightened. Water management is becoming a crucial part of pressure pumping.

Instead of paying to import fresh water and paying again to dispose of produced and flowback water, many operators are now seeking to blend fresh and flowback water, but this strategy has its own challenges. Flowback water can contain elevated levels of dissolved solids (particularly polyvalent cations), bacteria, and organics, which can impair conventional friction reducer performance. Additionally, chemicals used to remediate flowback water can potentially affect friction reducer performance.

In order to aid water management efforts, Kemira has developed a friction reducer platform that shows superior performance in flowback and produced water with TDS concentrations as high as 236,000 ppm. These emulsion polyacrylamides (EPAMs) have molecular weights in the range of 20 – 40 million Daltons and are compatible with other additives such as scale inhibitors and biocides.

Friction reduction measurements were performed using a laboratory-scale friction loop designed to simulate the turbulent flow conditions encountered during hydraulic fracturing. Flow rates of 30 gallons per minute were achieved in 0.5-in diameter tubing, resulting in Reynolds numbers of 150,000. The polymers provided friction reduction up to 65% in produced and flowback water, and maximum friction reduction was reached in 50 seconds or less in all cases. By comparison, conventional friction reducers dissolved in 120 seconds in high TDS waters and gave less than 20% friction reduction.
Measured Plunger Fall Velocity Used to Calibrate New Fall Velocity Model
Authors: Rowlan O.L. , McCoy J. , Lea J. , Nadkrynechny R. , Cepuch C.
Published: March 2013

Plunger fall velocities for various plungers have been measured in many different wells in the field and measured in a large scale well simulator. A new theoretical plunger fall velocity model has been developed. This model equates plunger fall velocity to be inversely proportional to a constant multiplied by the square root of the density of the gas the plunger falls through. The measured fall velocity at a specific pressure and temperature is used to calibrate the model, and then the model can be used to calculate fall velocity at other conditions for the same plunger or used to show how changing a feature like plunger weight can impact fall velocity. The model's predicted fall velocity for different types of plungers will be compared with measured fall velocities.

A large scale plunger lift well simulator was used to determine plunger fall behavior in clear PVC tubing through compressed air and through gas free water. The performance of 36 different types and metallurgies of plungers were measured. Both in the field and at the well simulator an acoustic instrument was effectively used to accurately measure plunger fall velocity.

All plungers have the same general trend of fall velocity; where the plunger fall velocity is fast at low pressure and slows at higher pressure. Construction features of plungers and well conditions impacting plunger fall velocities will be highlighted. Using published fall velocities to determine the shut-in time period for a particular plunger type but may not be accurate for a well, because well pressure significantly impacts plunger fall velocity. The knowledge of how various parameters impact plunger fall velocity allows the operator to determine if the plunger has reached the bottom of the tubing by the end of the shut-in period and then optimize the plunger lifted well using the shortest possible shut-in time to maximize liquid and gas production.
Examination of Treatment Connectivity between Granite Wash Layers Using Microseismic, Tracer, and Treatment Data
Authors: Crawford Elspeth M. , Tehan Bob , Launhardt Bob
Published: March 2013

Linn Energy employed adjacent laterals; the upper lateral targeting the Carr Granite Wash and the lower lateral targeting the Britt Granite Wash to determine if there was fracture stimulation overlap between the two intervals. It was known from geological analysis that the two zones were separated by a Clay rich interval (Caldwell section). The discussion deals with the fracturing between zones, and what type of communication remains after the stimulation treatment has been completed.

Various completion techniques were employed including Zipper Fracs, Volume adjustments, Perforation Density and phasing changes, and pump rate variations to determine if the fracture geometry would be affected by these changes. Treatment evaluations were done using the examination of Microseismic results in conjunction with pumping treatment data and pressure data from multiple offset locations.

This paper reviews the methodology employed as well as the results of pressure analysis and Microseismic mapping results to determine if the Caldwell barrier could be overcome by the Fracture Stimulation or if adequate drainage of both the Britt and Carr zones would require individual laterals.
Real-Time Data and Expert System Combine to Develop Artificial Lift Predictive Diagnostics
Authors: Blanckaert Thibault , Subervie Yves M
Published: March 2013

Abstract

Electric submersible pumps (ESPs) and progressive cavity pumps (PCPs) are used as lifting methods in many oil fields to improve oil production. Downhole gauges are now installed on most of the ESPs and PCPs, providing relevant pressure and temperature measurements to assess pump performance and potential failures. The volume of high-frequency data overwhelms the capacity of most direct assessment methods based on human observation. To address this challenge, a method using a combination of signal processing tools together with an expert system has been developed to deliver a predictive diagnostic in real time.

The data acquired is fed into a signal processing module to analyze and highlight trends and patterns. This module, based on Bayesian theory, segments the signal into a series of homogenous linear models. The segmentation is then used to provide statistical information about downhole measurements. Signal processing outputs have been designed to be probabilistic to account for uncertainties. The probability that pump intake pressure and pump discharge pressure will converge toward the same value is one example of such output. The probability of a noisy signal is another illustration of a result from the processing module. This real-time process is used to analyze all the ESP or PCP measurements available on specific criteria. Those pieces of information allow the expert system to predict pump failures. A Bayesian network with its probabilistic reasoning capabilities has been chosen to reproduce the ESP or the PCP physical knowledge. This Bayesian network contains input nodes gathering artificial lift parameters features and output nodes inferring failure probabilities.

During a test in real conditions, this concept showed its capability to predict and correctly diagnose the failure. In addition, this solution confirmed its robustness with accurate failure prediction under numerous operational conditions—even when downhole parameters were missing. This concept could be used to reduce reaction time to a failure, improve the monitoring capacity of each surveillance engineer, and improve the ESP life expectancy by early remediation of failure signs.
Partially Penetrating Hydraulic Fractures: Pressure Responses and Flow Dynamics
Authors: Al Rbeawi Salam , Tiab D..
Published: March 2013

Horizontal wells with multiple hydraulic fractures have become a common occurrence in the oil and gas industry, especially in tight formations. Published models assume that hydraulic fractures are fully penetrating the formations. However, studies have shown that fractures are not always fully penetrating the formations.

This paper introduces a new technique for analyzing the pressure behavior of a horizontal well with multiple vertical and inclined partially penetrating hydraulic fractures. The hydraulic fractures in this model could be longitudinal or transverse, vertical or inclined, symmetrical or asymmetrical. The fractures are propagated in isotropic or anisotropic formations and considered having different dimensions and different spacing. This technique, based on pressure and pressure derivative concept, can be used to calculate various reservoir parameters, including directional permeability, fracture length and percentage of penetration. The study has shown that the pressure behavior of small penetration rate is similar to the horizontal wells without hydraulic fractures.

A type curve matching technique has been applied using the plots of the pressure and pressure derivative curves. A set of type curves, which will be included in the paper, have been generated for the partially penetrating hydraulic fractures associated to the horizontal wells with different penetration rates. A step-by-step procedure for analyzing pressure tests using these type curves is also included in the paper for several numerical examples.
Rigorous Simulation of Production from Commingled Multilayer Reservoirs under Various Crossflow and Boundary Conditions
Authors: Villanueva-Triana Bielenis , Civan Faruk
Published: March 2013

An improved commingled well production model is presented by coupling of hydraulics of various reservoirs zones with wellbore in multilayer reservoirs considering different wellbore and formation cross-flow and external boundary effects, including water-influx. The pressure and production of each layer is described by the leaky-tank model of Civan (2000) under prescribed cross-flow and boundary effects. The pressure and flow along the wellbore is determined by means of the Cullender-Smith (1956) model. A Newton-Raphson iterative finite-difference numerical solution is obtained for the strongly-coupled model for accurate analysis of the optimal production, injection, and shut-in conditions at the surface for reservoir systems containing more than one layer. Application of the proposed model is demonstrated by simulating and analyzing a reservoir containing three producing layers, each having different effective thickness, permeability, skin factor, and initial reservoir pressure. The robust commingled reservoir production simulator presented in this paper may be instrumental for prediction of the prevailing fluid flow and pressure profiles along the wellbore and various reservoir layers.
More Accurate Method to Estimate the Original Gas in Place and Recoverable Gas in Overpressure Gas Reservoir
Authors: Ling Kegang , Wu Xingru , Zhang He , He Jun
Published: March 2013

Overpressure gas reservoirs with close-boundary typically have downward curving in p/z plot. The overestimations of original gas in place (OGIP) caused by incorrect extrapolations of early production data are often observed in reserve evaluation. To eliminate this error, a comprehensive compressibility term that includes the rock compressibility, water compressibility, and gas solubility in water has been introduced into the p/z plot.

To satisfy the above objective, it's critical to obtain the right average reservoir pressure corresponding to the drained gas reserve at the time point. But for overpressure gas reservoirs, if we completely ignore the permeability changes as the reservoir pressure declines, the reservoir performance cannot be representative. Another substantial deficiency of the conventional method is that the solution gas in connate water is also habitually neglected in estimating the OGIP. As a result, the contribution of solution gas to the total gas production is omitted in the material balance equation (MBE). These lead to the inaccurate estimation of the OGIP and gas reserve.

Considering the permeability is not constant throughout the reservoir life, but a function of pressure, rock and fluid properties, production volume, and original pore volume, a new form of MBE is presented by this study. It includes the effects of the permeability change due to pore compaction and the contribution of solution gas in connate water to the total gas production. With the proposed semi-analytical equations, the average reservoir pressure and reservoir deliverability can be estimated accurately. Therefore the evaluations of OOIP and recoverable gas are more reliable.
Tactics and Pitfalls in Production Decline Curve Analysis
Authors: Ling Kegang , Wu Xingru , Zhang He , He Jun
Published: March 2013

The decline curve analysis (DCA) is one of the most important methods in production forecast. It has been widely used among all the dynamics methods to estimate recoverable hydrocarbon. Decline curve can be divided into three categories: exponential decline, hyperbolic decline, and harmonic decline. Superficially decline curve analysis is the simplest prediction method, but as we dig into the base for DCA we find that it is not as simple as we think before. The opinion that DCA just follows the production trend can lead to tremendous errors, or even ridiculous results.

A good DCA requires a solid background in reservoir engineering, production engineering, and even drilling engineering. In-depth knowledge is necessary on studied reservoir, surface production facility, and the drive mechanism. In this study, several tactics developed from experience are applied to get practical and effective DCA and some pitfalls are pointed out to avoid the error or inappropriate forecast in DCA. With these tactics and pitfalls in mind, DCA can be a very useful and powerful tool in predicting recoverable hydrocarbon. Applying the established tactics and acknowledged pitfalls presented by this paper would lead to an accurate production forecast and reasonable reserves evaluation.
Proppant Crush Test: A New Approach
Authors: Simo Herve , Pournik Maysam , Sondergeld Carl. H.
Published: March 2013

Hydraulic fracturing is the most efficient stimulation technique used to enhance productivity in low permeability reservoirs with the productivity enhancement strongly dependent on the resulting conductivity. In order to maintain conductivity under increasing load, proppant must be able to withstand the closure stress at the concentration level that it is present in the fracture. Among the most important characteristics for proppant selection are strength and bulk density.

Current standard procedure for measurement of proppant strength is based on concentration of 4 lb/ft2 and determination of percent crushed proppant under a specified load. The procedure does not represent realistic field conditions and fails to capture the effect of increasing closure stress on proppant and fracture conductivity loss. In this paper, a new technique to determine the failure stress of proppant is proposed and a summary of the results are presented. This new approach enables us to not only determine the behavior of different proppant pack over a wide range of pressures but also to determine failure point of proppant at a given concentration.

The new proppant crush test approach was used to compare the strength of 40/70 sand, 40/70 resin coated sand, 30/50 sand, and 30/50 resin-coated sand. The failure stresses for the above proppants were determined as a function of proppant concentration. A significant increase in failure stress was observed as proppant concentration varied from 0.5 to 2 lb/ft2. Failure stress was relatively constant for proppant concentration greater than 2 lb/ft2. In addition, different pattern of proppant behabior with closure stresse was observed for resin coated sand at concentrations above 2 lb/ft2 as compared to all other proppants and other concentrations.
Evaluation of Near-Wellbore Formation Treatment by Gel Particles Using Dimensional Analysis
Authors: Al-Ibad Adnan , Civan Faruk
Published: March 2013

Analysis and interpretation of experimental data of laboratory tests of porous formation treatment by gel particles conducted at different gel particles suspension and application conditions are presented based on the dimensional analysis method. The measured permeability reduction caused by gel particles suspension injection into sand packs is correlated successfully by using the dimensionless groups developed from the relevant variables of sand packs, gel particles suspensions, and application operation conditions. The dimensionless correlations are shown to assist in quantifying the effect of the particle-diameter to pore-throat size ratio on permeability reduction, evaluating the treatment of highly permeable and weak near well-bore formations by gel particles, and extrapolating from laboratory to field conditions. The present dimensionless correlations can predict the evolving permeability reduction under the varying conditions of gel particles suspension injection processes. The proposed dimensionless correlations can assist in effective design and mitigation of treatment of high-permeability near-wellbore formations by gel particles for avoiding drilling-fluids lost circulation, remediating reservoir permeability heterogeneity, and reducing water production in waterflooded mature oil fields.