bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spread Dynamics of Perennial Pepperweed (Lepidium latifolium) in Two Seasonal Wetland Areas
Authors: Renz Mark J. , Steinmaus Scott J. , Gilmer David S. , DiTomaso Joseph M. 
Published: March 2012

AbstractPerennial pepperweed is an invasive plant that is expanding rapidly in several plant communities in the western United States. In California, perennial pepperweed has aggressively invaded seasonal wetlands, resulting in degradation of habitat quality. We evaluated the rate and dynamics of population spread, assessed the effect of disturbance on spread, and determined the biotic and abiotic factors influencing the likelihood of invasion. The study was conducted at eight sites within two wetland regions of California. Results indicate that in undisturbed sites, spread was almost exclusively through vegetative expansion, and the average rate of spread was 0.85 m yr−1 from the leading edge. Spread in sites that were disked was more than three times greater than in undisturbed sites. While smaller infestations increased at a faster rate compared with larger populations, larger infestations accumulated more newly infested areas than smaller infestations from year to year. Stem density was consistently higher in the center of the infestations, with about 2.4 times more stems per square meter compared with the leading edge at the perimeter of the population. The invasion by perennial pepperweed was positively correlated with increased water availability but was negatively correlated with the cover of perennial and annual species. Thus, high cover of resident vegetation can have a suppressive effect on the rate of invasion, even in wetland ecosystems. On the basis of these results, we recommend that resident plant cover not be disturbed, especially in wet areas adjacent to areas currently infested with perennial pepperweed. For infested areas, management efforts should be prioritized to focus on controlling satellite populations as well as the leading edge of larger infestations first. This strategy could reduce the need for costly active restoration efforts by maximizing the probability of successful re-establishment of resident vegetation from the adjacent seedbank.
Integrated Management of Scotch Broom (Cytisus scoparius) Using Biological Control
Authors: Herrera-Reddy Angelica M. , Carruthers Raymond I. , Mills Nicholas J. 
Published: March 2012

AbstractIntegrated weed management strategies (IWM) are being advocated and employed to control invasive plants species. In this study, we compared three management strategies (biological control alone [BC], BC with fire [BC + F], and BC with mowing [BC + M]) to determine if physical controls reduce seed production by Scotch broom and interfere with the action of the biological control agent—the Scotch broom seed weevil. We measured seed production and seed predation by the weevil at both pod and plant scale, and seed bank density over two field seasons. We found no difference in the number of seeds per pod among management strategies. However, combining management strategies (BC + M and BC + F) resulted in significant reductions in pods per plant, mature seeds per plant, and seed bank density relative to biological control alone. We did not find differences among management strategies in number of weevils per pod or proportion of seeds predated by the weevil at either pod or whole-plant scale. However, combining management strategies (BC + M and BC + F) resulted in a significant reduction in healthy mature seeds per plant relative to biological control alone. Although both integrated strategies outperformed biological control alone in reducing seed production and the seed bank, with no statistical difference between them, we propose that short-rotation prescribed fire could prove to be a more effective strategy for long-term management of Scotch broom due to its potential for slightly greater depletion of the seed bank.
Plant‐mediated and nonadditive effects of two global change drivers on an insect herbivore community
Authors: de Sassi Claudio , Lewis Owen T. , Tylianakis Jason M. 
Published: March 2012

Warmer temperatures can alter the phenology and distribution of individual species. However, differences across species may blur community‐level phenological responses to climate or cause biotic homogenization by consistently favoring certain taxa. Additionally, the response of insect communities to climate will be subject to plant‐mediated effects, which may or may not overshadow the direct effect of rising temperatures on insects. Finally, recent evidence for the importance of interaction effects between global change drivers suggests that phenological responses of communities to climate may be altered by other drivers. We used a natural temperature gradient (generated by elevation and topology), combined with experimental nitrogen fertilization, to investigate the effects of elevated temperature and globally increasing anthropogenic nitrogen deposition on the structure and phenology of a seminatural grassland herbivore assemblage (lepidopteran insects).We found that both drivers, alone and in combination, severely altered how the relative abundance and composition of species changed through time. Importantly, warmer temperatures were associated with biotic homogenization, such that herbivore assemblages in the warmest plots had more similar species composition than those in intermediate or cool plots. Changes in herbivore composition and abundance were largely mediated by changes in the plant community, with increased nonnative grass cover under high treatment levels being the strongest determinant of herbivore abundance. In addition to compositional changes, total herbivore biomass more than doubled under elevated nitrogen and increased more than fourfold with temperature, bearing important functional implications for herbivores as consumers and as a prey resource. The crucial role of nonnative plant dominance in mediating responses of herbivores to change, combined with the frequent nonadditive (positive and negative) effects of the two drivers, and the differential responses of species, highlight that understanding complex ecosystem responses will benefit from multifactor, multitrophic experiments at community scales or larger.
Experiences in Eliminating Steam Breakthrough & Providing Zonal Isolation in SAGD Wells
Authors: Brooks Robert T. , Tavakol Habib 
Published: March 2012

Abstract
For the last two decades major oil companies in Canada have been paying much attention to heavy oil which is an alternative unconventional reservoir (Canada and Venezuela have some of the largest bitumen deposits in the world). Main reasons for development could be the high price of oil, and improved technology to extract heavy oil, with a high recovery factor (up to 60% of the oil in place). Injecting steam is the most distinctive technique of heating up the formation rock and assisting in oil flow. Controlling steam injection and its distribution, and achieving economical recovery in an effective manner, has been a continuous mind-boggling issue for the heavy oil producers, and has been a great challenge.
High-temperature water and oil swellable packers have been developed to aid, and optimize, cyclic steam stimulation and Steam Assisted Gravity Drainage (SAGD) applications in heavy oil reservoirs. Simplicity is one of the great advantages of the swellable packers, which provide an ease of operation. The packer allows uniform or selective placement of steam along the entire length of horizontal section, and is designed to handle high temperature 575°F (302°C), and more than adequate differential pressures, associated with steam injection. Screens or slotted liners are run in hole to allow steam to be pumped in between the well pairs. Steam breakthrough, or diversion, has been experienced in numerous wells due to sand erosion and/or plugging of the slotted liners, which creates problems for continuous production. Swellable packers can be installed in conjunction with screens or slotted liner in order to distribute steam and provide zonal isolation. In the event of steam breakthrough, swellable packers can be deployed to isolate the affected zone(s). This intervention technique will assist in efficient continued production, elimination of sand production and steam breakthrough.
The technique of steam injection has been improving over the years, but still has room for refining of the processes. Some older wells have encountered with issues of steam channeling through the cemented casing &amp; breaking out at the surface; which has been seen to create a threat to the environment. A horizontal well completed with slotted liner, or recently with specially designed type of screens, provides a far better method than perforated casing for injecting steam into the formation.
This paper presents solutions for SAGD wells with a unique technique for resolving wasted steam injection at the toe section of the well, and repair of steam breakthrough in production legs. Every operator is coming across new learning experience almost every day, although most of this information is proprietary, we are proposing a different solution path to overcome some of these issues.
Successful Techniques for Competently Abandoning Wells with Severe Casing Restrictions
Authors: Renting Deanne , Aparicio Tarcisio 
Published: March 2012

Abstract
Chevron has developed a number of new techniques for abandoning wells with severe parted casing, which have been successfully applied in an unconventional Californian reservoir. A number of wells have developed severe doglegs or parted casing. Such restrictions have prevented traditional workover techniques from reaching the reservoir to ensure a standard abandonment, referred to as ‘complex damage’. The first key learning is to maintain access to the reservoir as long as possible, by not pulling the equipment (tubing and packer) out of the wellbore when parted casing is suspected. In cases where it may not be possible to abandon the well after equipment is pulled from the well-bore, solidly cementing the equipment in the well may be a more robust abandonment technique than pulling the equipment and risking not being able to re-access the reservoir. When complex damage has developed, milling and explosive tools have been successfully applied to re-access the reservoir, run on tubing, wireline and coiled tubing. To evaluate the restrictions, diagnostics such as down-hole cameras are critical to develop and execute a successful abandonment plan. Using these techniques, Chevron abandoned several wells with complex damage in 2011.
Evaluation of CO2-EOR and Sequestration in Alaska West Sak Reservoir Using Four-Phase Simulation Model
Authors: Nourpour Aghbash Vahid , Ahmadi Mohabbat 
Published: March 2012

Abstract
Injection of CO2 into West Sak reservoir of Alaska was studied. The study was conducted with the objective to store CO2 and enhance the oil recovery. Due to low reservoir temperature, mixing of possible injected mixtures, including pure CO2 and HC-enriched CO2, and the in-place hydrocarbon will result in development of three hydrocarbon phases, gas, oil-rich and CO2-rich phases, at certain pressures encountered in reservoir. Commercially available simulators are incapable of appropriate identification of this new phase and using them will result in unrealistic results and wrong predictions.
A compositional EOS simulator, capable of handling up to four phases, including two HC liquid phases, was used. A three dimensional simplified model of the reservoir was built, based on reservoir core data, to study the oil displacement by various injected fluids including pure CO2. Sensitivity of the results to the relative permeability parameters of the second liquid phase was studied. Effect of using WAG with different water to gas ratios on the oil recovery and CO2 sequestration was also investigated. Various simulations runs resulting from combining different water-CO2 injection plans, well completion schemes, well spacing and production constraint were conducted to propose an injection-production strategy that can optimize the oil recovery and CO2 storage.
Results show that the second liquid phase significantly affects both breakthrough time and total oil recovery. The sensitivity analysis of relative permeability parameters shows its profound effect on the results, emphasizes the need to use accurately measured relative permeability data to produce accurate results.WAG scheme improves the sweep efficiency but decreases the amount of stored CO2.Within the range investigated, 880 -1240 ft, we found higher recovery rate for smaller well spacing but negligible change in ultimate recovery.
West Sak contains 7 to 9 billion barrels of original oil in place. Its high viscosity makes the primary recovery scheme inefficient. Although waterflooding was successful to a certain degree but CO2 injection can be a successful option to increase recovery and store considerable mass of CO2 that might be produced from coal-bed gasification in Alaska. Although CO2 cannot develop full miscibility with West Sak oil; however, it causes the oil to swell, oil viscosity to decrease, and recovery to increase.
Applying Method of Characteristics to Model the Flow of Compressible CO2 in Aquifers
Authors: Ghanbarnezhad Moghanloo Rouzbeh 
Published: March 2012

Abstract
This paper presents the first semi-analytic solution of two-phase two-component compressible flow in permeable media using method of characteristics (MOC). Analytical solutions are important as numerical simulations do not yield explicit expressions in terms of the model parameters. However, the previously developed MOC solutions rely on the incompressible fluid and rock assumptions that are rarely met in practice Furthermore, numerical simulations that provide the most comprehensive solutions to multiphase flow problems are computationally intensive. In this study, the method of characteristics (MOC) solution of the overall mass conservation equation of CO2 in two-phase two-component flow through permeable media is derived with no restriction on the compressibility of fluids and the rock.
A simulation approach is used to verify the derived analytical solutions. The simulation models consist of a vertical injection well and a producer located at the ends of a one-dimensional (1D) grid. The pace at which specific gas saturations propagate along the permeable medium are compared with the gas saturation profiles obtained when no compressibility is involved.
The results suggest that the velocity of a wave, which is associated with the transport of a certain mass of CO2 along the permeable medium, is a function of the gas saturation, compressibility of the rock and fluids, and the pressure gradient. The results reveal that the wave velocity will only be a function of the gas saturation and pressure gradient if the compressibility of the rock is negligible compared to that of CO2. Hence, the waves’ velocity will only depend on saturation, as is for an incompressible flow system, when changes in pressure gradient are minimal.
Thus, this paper explains how fast a compressible CO2 plume will travel along the aquifers length. In practice, the fate of the injected CO2 plume is essential to determine the storage capacity of aquifers and to evaluate the risk associated with the CO2 sequestration projects.
Evaluation of Electromagnetic Heating for Heavy Oil Recovery from Alaskan Reservoirs
Authors: Peraser V. , Patil S. L. , Khataniar S. , Dandekar A. Y. , Sonwalkar V. S. 
Published: March 2012

Abstract
Traditional thermal methods for heavy oil recovery involve use of steam to heat the wellbore and the reservoir. While the steam-based methods are widely in use and are generally successful, they also have high energy requirements, are not very efficient, and have environmental concerns. In addition, these methods are not readily applicable in Alaska, which is estimated to contain 18 to 27 billion barrels of heavy oil. Steam injection into the Alaskan heavy oil reservoirs is logistically complex, and is not practical due to the presence of a thick layer of permafrost. Hence, alternative methods to heat these reservoirs have to be considered.
The use of high frequency electromagnetic (EM) heating has been studied for a couple of decades now and is one of the approaches that has shown potential as a non-steam based thermal method for heavy oil recovery. Electromagnetic heating has several advantages over steam injection. The efficiency of steam injection is often limited by low formation permeability. Because EM energy is also absorbed by the formation, permeability of the formation is not as critical. Also, EM heating can be confined to the areas of interest and is easily controllable. This method seems to be ideally suited for the Alaskan heavy oil reservoirs as it does not entail steam injection through the permafrost.
In this study, use of EM heating for heavy oil recovery was examined mathematically by using engineering and physics-based computational modules. Using the fluid flow and heat transfer applications on a radial well model, the effects of EM power levels and frequency on heat penetration into the reservoir, temperature, and oil production were evaluated. The results showed that EM heating can increase heavy oil production rates by more than 200% using only moderate power levels, and continuous oil production could be sustained without any need to shut the well for heat dissipation or “soaking”. The use of EM heating appears to be a realistic approach towards developing Alaskan heavy oil reserves.
Using San Joaquin Valley Oil Fields as a Technology Test Bed To Mature Steamflood Technology
Authors: Stevenson J. K. , Behrens R. E. , Foote J. T. , Cassidy S. D. 
Published: March 2012

Abstract
Many heavy oil resources are giant, legacy-type assets that may take a century or longer to fully exploit. A key opportunity is to apply new technology and techniques to maximize recovery and economic performance. By selecting the right technology projects and managing them efficiently and effectively, we can reduce the cycle time to unlock this resource potential. Technology projects by their nature have large degrees of uncertainty that quite often cannot be resolved until tested in the field. Chevron has been using Kern River and other San Joaquin Valley oil fields as a technology development test bed for more than 50 years to unlock the resource potential of heavy oil.
The San Joaquin Valley is an ideal environment with a number of desirable attributes which facilitate Chevron’s field tests and pilots including:
• Location – accessible, onshore location with existing operations and major infrastructure
• Local Industry Capability – full spectrum of oil and gas service providers as well as highly capable personnel with extensive thermal recovery experience
• Resource Type and Size – large number of similar heavy oil assets which provides an economy of scale for applying new technology
• Risk – relatively low financial and Health, Environment & Safety (HES) exposure
• Heavy Oil Center of Excellence (HO CoE) - co-location of a corporate technology company unit and operating unit
• Ownership Structure – mostly 100% company owned and operated fields
The paper describes these factors and includes a number of technology examples that highlight considerations related to field testing and piloting in order to mature R&D projects.
Ensuring Better Well Stimulation in Unconventional Oil and Gas Formations by Optimizing Surfactant Additives
Authors: Xu Liang , Fu Qiang 
Published: March 2012

Abstract
Proper application of surfactant is critical to the completion process. It not only enhances initial production (IP), but helps sustain long-term production. Conventional wisdom suggests that the use of a nonemulsifying surfactant will work appropriately across most low-permeability reservoirs. Laboratory and field results, however, suggest that a weakly emulsifying surfactant is, in fact, far more efficient in solubilizing and mobilizing oil globules.
In this paper, an experimental toolbox and key strategies are presented for properly selecting surfactants for specific reservoir conditions. Dynamic surface tension, emulsion tendency, oil recovery, wettability and adsorption tests were all considered to select the proper surfactant for the case study. On the basis of these results, the field performance of both the nonemulsifying and weakly emulsifying surfactants are evaluated using production data from the Eagle Ford. The production-enhancement data appears to correspond well to lab results and strongly suggests that weakly emulsifying surfactants are superior at enhancing production.
Associative Data Modeling and Ant Colony Optimization Approach for Waterflood Analysis
Authors: Popa Andrei S. , Sivakumar Kailash , Cassidy Steve 
Published: March 2012

Abstract
Waterflooding is one of the oldest and most used techniques for increasing recovery in oil reservoirs. While successfully applied in sandstone formations, it presents certain challenges in tight, heterogeneous or unconventional reservoirs. Several strategies for pattern sizing, injection volumes and injection rates have been tested and implemented over the years by different operators in an attempt to optimize production and increase recovery. However, for unconventional reservoirs such as Diatomite formations, little information was documented on the success or failure of waterflood development scenarios. Using only high-level production and injection data, the objective of the study is to investigate the influence of pattern size on waterflood response and compare the various injection strategies executed in the field.
The paper presents two complementary approaches in an attempt to identify waterflood development best practices and optimization opportunities for the field. The first describes a relatively new clustering technology, Ants Colony Optimization (ACO), to find a sensible organization of “objects” into distinct groups, thus recognizing any patterns in the data. In our case, the “objects” are uniform grid blocks with distinct cumulative production and injection data. The algorithm utilizes a system of software ants, which mimics the actual way in which ants find the shortest path between their nest and food sources. The second approach involves an Associative Modeling technique, which works with entities that have a discrete independent existence, and their relationships are modeled as associations. Knowledge is inferred using an unconventional approach by comparing the normalized response of a random section area overlapped on different pattern sizes active in the field. Entities are expressed in terms of cumulative production and injection, and number of producers/injectors were then compared for these sections. The modeling contrasts different strategies, injection volumes and rates, used in different development areas.
This study introduces an innovative, fast, concise and simple approach for large data analysis and knowledge-extraction while demonstrating two intelligent approaches: ACO clustering and associative modeling. This approach can be easily adapted and applied to similar fields as a powerful method for comparing production/injection strategies on a large scale.