bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced Exudation of DIMBOA and MBOA by Wheat Seedlings Alone and in Proximity to Wild Oat (Avena fatua) and Flixweed (Descurainia sophia)
Authors: Lu C. H. , Liu X. G. , Xu J. , Dong F. S. , Zhang C. P. , Tian Y. Y. , Zheng Y. Q.
Published: August 2012

The allelochemicals 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) and 6-methoxy-benzoxazolin-2-one (MBOA) in wheat are considered to have a role in plant defense against weeds. This study explored the effect of proximity to two weeds, wild oat and flixweed, on DIMBOA/MBOA production in wheat seedlings under hydroponic culture to identify whether the breeding of modern wheat varieties with higher concentrations of these compounds could ensure plant-mediated weed control. MBOA was detected and was noted to exert a significant response; its exudation by some wheat seedlings was significantly increased irrespective of whether the roots were in contact with or separate from those of the weeds. The weeds were a source of biotic stress to wheat when grown in proximity to it, and the stress resulted in production of higher levels of MBOA in wheat seedlings, although the concentration varied with the wheat cultivar. Therefore, the synthesis and exudation of DIMBOA/MBOA in wheat seedlings appears to be an active metabolic process influenced by the environment, particularly the presence of weeds.
Pollen-Mediated Dispersal of Glyphosate-Resistance in Palmer Amaranth under Field Conditions
Authors: Sosnoskie Lynn M. , Webster Theodore M. , Kichler Jeremy M. , MacRae Andrew W. , Grey Timothy L. , Culpepper A. Stanley
Published: August 2012

In addition to being a strong competitor with cotton and other row crops, Palmer amaranth has developed resistance to numerous important agricultural herbicides, including glyphosate. The objective of this study was to determine if the glyphosate-resistance trait can be transferred via pollen movement from a glyphosate-resistant Palmer amaranth source to a glyphosate-susceptible sink. In 2006 and 2007 glyphosate-resistant Palmer amaranth plants were transplanted in the center of a 30-ha cotton field. Susceptible Palmer amaranth plants were transplanted into plots located at distances up to 300 m from the edge of the resistant pollen source in each of the four cardinal and ordinal directions. Except for the study plots, the interior of the field and surrounding acreage were kept free of Palmer amaranth by chemical and physical means. Seed was harvested from 249 and 292 mature females in October 2006 and 2007, respectively. Offspring, 14,037 in 2006 and 13,685 in 2007, from glyphosate-susceptible mother plants were treated with glyphosate when the plants were 5 to 7 cm tall. The proportion of glyphosate-resistant progeny decreased with increased distance from the pollen source; approximately 50 to 60% of the offspring at the 1- and 5-m distances were resistant to glyphosate, whereas 20 to 40% of the offspring were resistant at the furthest distances. The development of resistance was not affected by direction; winds were variable with respect to both speed and direction during the peak pollination hours throughout the growing season. Results from this study indicate that the glyphosate-resistance trait can be transferred via pollen movement in Palmer amaranth.
Phenotypic Plasticity of Spiny Amaranth (Amaranthus spinosus) and Longfruited Primrose-Willow (Ludwigia octovalvis) in Response to Rice Interference
Authors: Chauhan Bhagirath Singh , Abugho Seth Bernard
Published: August 2012

The growth of spiny amaranth and longfruited primrose-willow was studied by growing them alone and in competition with 4 and 12 rice (cv. RC222) plants. Interference with 12 rice plants reduced the height of spiny amaranth beyond 6 wk after planting. The height of longfruited primrose-willow was significantly reduced by the crop interference starting from 4 wk after planting. Both weed species showed the ability to reduce the effects of rice interference by increasing leaf area, leaf and stem biomass in the upper half of the plant, and specific stem length. At 9 wk after planting, for example, longfruited primrose-willow had 89 and 99% leaf biomass in the upper half of the plant when grown with 4 and 12 rice plants compared with only 34% when grown alone. These values for spiny amaranth were 15, 29, and 72% when grown alone, with 4 rice plants, and 12 rice plants, respectively. Despite such plasticity, spiny amaranth's aboveground biomass at final harvest was reduced by 34 and 70% when grown with 4 and 12 rice plants, respectively, compared with its biomass without crop interference. The corresponding values for longfruited primrose-willow were 92 and 98%, respectively. These results suggest that uniform and high crop density could be an important tool to reduce competition from these weeds in direct-seeded rice.
Control of Silk Tree (Albizia julibrissin) with Aminocyclopyrachlor and Other Herbicides
Authors: Koepke-Hill Rebecca M. , Armel Gregory R. , Brosnan James T. , Breeden Gregory K. , Vargas Jose J. , Mueller Thomas C.
Published: August 2012

Research was conducted to determine the efficacy of aminocyclopyrachlor in comparison to glyphosate, clopyralid, fluroxypyr, and triclopyr for silk tree (commonly known as mimosa) control. In the greenhouse, aminocyclopyrachlor was applied at 8.75, 17.5, 35, and 70 g ha−1with and without methylated seed oil (MSO) at 0.5% v/v. Efficacy of these treatments was compared to glyphosate and triclopyr at 1,350 g ha−1, fluroxypyr at 103 g ha−1, and clopyralid at 100 g ha−1. Few differences in silk tree control were detected by 28 d after treatment (DAT), as aminocyclopyrachlor with MSO controlled silk tree 87 to 100% compared to 53 to 100% for aminocyclopyrachlor without MSO. Aminocyclopyrachlor at 35 g ha−1provided silk tree control similar to glyphosate, triclopyr, clopyralid, and fluroxypyr regardless of adjuvant. Inclusion of MSO enhanced initial activity of aminocyclopyrachlor after application. At 7 DAT, 8.75 g ha−1of aminocyclopyrachlor plus MSO controlled silk tree similar to aminocyclopyrachlor alone at 70 g ha−1. In laboratory studies, absorption of14C-aminocyclopyrachlor 2 h after treatment (HAT) with MSO measured 93% compared to only 62% for14C-aminocyclopyrachlor without MSO. By 24 HAT, absorption of14C-aminocyclopyrachlor measured 99 and 71% for applications with and without MSO, respectively. Increased foliar absorption with MSO may explain enhanced activity observed 7 DAT in greenhouse studies, as no effects in14C-aminocyclopyrachlor translocation due to adjuvant were observed. Responses suggest MSO increased the speed of silk tree control with aminocyclopyrachlor and may also improve rainfastness of aminocyclopyrachlor applications for control of silk tree and other woody species.
Imazamox Absorption, Translocation, and Metabolism in Red Lentil and Dry Bean
Authors: Bukun Bekir , Nissen Scott J. , Shaner Dale L. , Vassios Joseph D.
Published: August 2012

Imazamox is an imidazolinone herbicide used to control many grasses and broadleaf weeds in leguminous crops such as soybean, alfalfa, and dry bean; however, imazamox cannot be used on red lentil due to unacceptable injury. Studies were conducted to compare imazamox absorption, translocation, and metabolism in red lentil and dry bean to determine if any or all of these factors contributed to differential crop sensitivity. Radiolabeled imazamox was applied to three young red lentil leaves and the youngest, fully expanded dry bean trifoliolate leaf. Absorption, translocation, and metabolism were followed over a 96-h time course. Red lentil had more rapid absorption compared to dry beans with 64 and 54% of the applied dose absorbed 12 h after treatment (HAT), respectively. Maximum absorption was also greater in red lentil than dry bean, 79 and 61%, respectively. Translocation out of the treated leaf was significantly higher in red lentil compared with dry bean, 16 and 0.5%, respectively, at 96 HAT. Translocation was greater to red lentil roots compared to shoots, 9 and 7%, respectively, at 96 HAT. In dry bean only 14% of applied14C-imazamox remained intact 24 HAT, while 79% of the radioactivity was imazamox in red lentil 24 HAT. Both species metabolized the herbicide to more polar metabolites. The inherent sensitivity of aceolactate synthase (ALS) from dry bean and red lentil was also evaluated. ALS from both species had similar I50values for imazamox, 7.2 and 8.2 µM, respectively. The combined effects of increased imazamox absorption and reduced imazamox metabolism are the major contributors to differential selectivity between dry bean and red lentil. Rapid imazamox metabolism in dry bean significantly limited herbicide translocation out of the treated leaf.
Local Conditions, Not Regional Gradients, Drive Demographic Variation of Giant Ragweed (Ambrosia trifida) and Common Sunflower (Helianthus annuus) Across Northern U.S. Maize Belt
Authors: Wortman Sam E. , Davis Adam S. , Schutte Brian J. , Lindquist John L. , Cardina John , Felix Joel , Sprague Christy L. , Dille J. Anita , Ramirez Analiza H. M. , Reicks Graig , Clay Sharon A.
Published: August 2012

Knowledge of environmental factors influencing demography of weed species will improve understanding of current and future weed invasions. The objective of this study was to quantify regional-scale variation in vital rates of giant ragweed and common sunflower. To accomplish this objective, a common field experiment was conducted across seven sites between 2006 and 2008 throughout the north central U.S. maize belt. Demographic parameters of both weed species were measured in intra- and interspecific competitive environments, and environmental data were collected within site-years. Site was the strongest predictor of belowground vital rates (summer and winter seed survival and seedling recruitment), indicating sensitivity to local abiotic conditions. However, biotic factors influenced aboveground vital rates (seedling survival and fecundity). Partial least squares regression (PLSR) indicated that demography of both species was most strongly influenced by thermal time and precipitation. The first PLSR components, both characterized by thermal time, explained 63.2% and 77.0% of variation in the demography of giant ragweed and common sunflower, respectively; the second PLSR components, both characterized by precipitation, explained 18.3% and 8.5% of variation, respectively. The influence of temperature and precipitation is important in understanding the population dynamics and potential distribution of these species in response to climate change.
Pollen Biology and Dispersal Dynamics in Waterhemp (Amaranthustuberculatus)
Authors: Liu Jianyang , Davis Adam S. , Tranel Patrick J.
Published: August 2012

Waterhemp is a major weed of field crops in the Midwestern United States. Its prevalence is at least partly due to its rapid evolution of resistance to many groups of herbicides over the last two decades. In light of its dioecy and anemophily, pollen movement in waterhemp is considered to be an important factor in the spread of herbicide resistance genes. Thus, the biology and dispersal profile of waterhemp pollen are critical determinants for understanding and predicting the spatial population dynamics of herbicide resistance in this species. In this study, pollen longevity was investigated with greenhouse experiments, and pollen dispersal and the effect of pollen competition were investigated in field plots. Pollen dispersal was determined by measuring the frequency of seeds produced on receptor plants positioned at various distances from a pollen source, which flowered in synchrony with the receptor plants. Results indicated that waterhemp pollen can remain viable up to 120 h, implying a low limitation of pollen dispersal by its longevity. Effective pollen dispersal declined exponentially with distance, with most pollen fertilizing recipient plants within 50 m of the pollen source. However, long distance pollen dispersal (800 m) was also observed. We also saw evidence for pollen swamping in this species. Under conditions of pollen competition among distinct genotypes, pollination success was inversely related to distance between pollen donors and receptors. However, relative pollen density may also play an important role in determining the rate of long distance gene flow. This study confirmed the potential of waterhemp pollen to effect long distance gene flow and provides supporting data for quantitative spatial modeling of waterhemp resistance dynamics.
Seed Dormancy and Seedling Recruitment in Smooth Barley (Hordeum murinum ssp. glaucum) Populations in Southern Australia
Authors: Fleet Benjamin , Gill Gurjeet
Published: August 2012

Weedy barley species have emerged as important weeds in southern Australia, where they can be particularly difficult to control in cereal crops. Knowledge of seed dormancy mechanisms, germination ecology, and recruitment behavior in the field would facilitate development of effective weed-control programs for these weed species. Based on somatic chromosome number, smooth barley was identified as the species infesting all the sites sampled in South Australia. Smooth barley populations from cropping fields and noncrop habitats showed large differences in their pattern of dormancy loss. Noncrop populations (EP2, EP3, and MN2) rapidly lost dormancy during dry after-ripening and showed 70 to 95% germination at 3 mo after maturity. Five populations collected from cropping fields (EP1, EP4, EP5, MN1, and MN3), on the other hand, showed < 30% germination, even at 8 mo after maturity, when germination was assessed at 20/12 C day/night temperatures. These dormant, smooth barley populations from cropping fields were found to be highly responsive to cold stratification, with germination increasing in response to the duration of the treatment. Germination of dormant, smooth barley populations increased with the addition of gibberellic acid (0.001 M GA3), but only when lemma and palea had been removed. Recruitment behavior of smooth barley in the field was influenced by the population and the tillage system. A nondormant population, collected from a long-term pasture (MN2), showed high seedling emergence (> 90%) during autumn, which was well before planting of the winter crop (lentil). In contrast, the other three populations sampled from cropping fields showed very little seedling establishment (< 10%) before crop planting, which would make them difficult to control in cereals because there are no selective herbicides available for the control of weedy barley species. There was a significant seeding system by emergence time interaction (P < 0.001), which was reflected in greater in-crop, smooth barley plant densities under zero-till than under conventional tillage and no-till systems.
Influence of Time of Emergence on the Growth and Development of Wild Oat (Avena fatua)
Authors: Dai Jing , Wiersma Jochum J. , Martinson Krishona L. , Durgan Beverly R.
Published: August 2012

Successful control of wild oat in cereal crops requires an accurate prediction of the developmental stages of wild oat plants that emerged during the growing season. The main objective of this research was to evaluate wild oat growth and to predict the phyllochron of wild oat plants that emerge at various times in the Red River Valley region of Minnesota and North Dakota. Field experiments were conducted in 2002 and 2003 in Crookston, MN, and Fargo, ND. Four emergence cohorts were established in 4 successive wk. Research plots were arranged in randomized complete blocks with six replications. From the naturally emerged wild oat population, 10 randomly selected plants per plot were evaluated for plant height, leaves on main stem, tillers per plant, total leaves per plant, days to flag leaf emergence and to heading, biomass per plant, and seeds per plant. Haun's numerical cereal development scale was regressed on days after emergence (DAE), day length (DL), growing degree days (GDD), or photothermal units (PTU). Wild oats that emerged first required more time for flag leaf emergence and heading, were taller, and had more biomass, leaves, tillers, and seed production than wild oat plants that emerged later. Wild oat phyllochron intervals were 5.3 d, 94 GDD, or 1,468 PTU, regardless of emergence timing. These data suggest that wild oat phyllochron is primarily driven by air temperature and is relatively stable during the extended emergence period. Later-emerging wild oat plants, although not as competitive as earlier emerging ones, still have the potential to contribute to the seed bank if left uncontrolled.
Simulated Acid Rain Accelerates Litter Decomposition and Enhances the Allelopathic Potential of the Invasive PlantWedelia trilobata(Creeping Daisy)
Authors: Wang Rui Long , Staehelin Christian , Dayan Franck E. , Song Yuan Yuan , Su Yi Juan , Zeng Ren Sen
Published: August 2012

Invasive species and acid rain cause global environmental problems. Creeping daisy, an invasive exotic allelopathic weed, has caused great damage in southern China, where acid rain is prevalent. The impact of the acidity of simulated acid rain (SAR) on soil nutrients, the decomposition of creeping daisy litter, and on the allelopathic potential of the surrounding soils was investigated. Litter was treated with SAR at different acidity (pH 2.5, 4.0, 5.6) or with water (pH 7.0) as a control. After 70 d, the remaining amount of creeping daisy litter, nutrient contents, and allelopathic potentials in the surrounding soil were determined. The litter decomposition was commensurate to the increase in the acidity of the SAR. Total C and N contents, NO3−-N and available P increased, levels of NH4+-N, the ratio of C/N and soil pH values decreased, water contents increased and then decreased, whereas available K did not significantly change in the soil surrounding the litters in response to the increase in the acidity of the SAR. Bioassays showed that SAR promoted the allelopathic activity in the soil surrounding the litter, as measured by seedling growth of turnip and radish. In conclusion, our results indicated that SAR influenced soil nutrient status, accelerated creeping daisy litter decomposition, and enhanced the allelopathic potential of its litter in the surrounding soil, suggesting that acid rain may enhance the invasiveness of creeping daisy plants.
Flexural fatigue analysis of self-compacting concrete beams
Authors: Goel Sanjay , Singh Surinder P. , Singh Partap
Published: August 2012

Results of an investigation of the probability distributions and flexural fatigue performance of self-compacting concrete beams are presented. The fatigue tests were carried out with a 100 kN capacity closed-loop servo-controlled actuator on 100 × 100 × 500 mm size beam specimens under four-point flexural loading. The static flexural strength of the self-compacting concrete was determined before the fatigue tests. The test data have been used to examine the distribution of fatigue life of self-compacting concrete at different stress levels. It has been shown that the statistical distribution of fatigue life of self-compacting concrete at a given stress level can be modelled by the two-parameter Weibull distribution with its distribution parameters estimated by different methods of analysis. The results indicate that there was lower variability in the distribution of fatigue life of self-compacting concrete compared to that of normally vibrated concrete. The fatigue life data have also been presented in the form of an S–N diagram and the two-million-cycles fatigue strength of self-compacting concrete has been found to be marginally higher than that of normally vibrated concrete. The fatigue life data of normally vibrated concrete used for comparison were obtained from the literature.
Spectral analysis of minimum structure platforms
Authors: Grewal Gage S. , Lee Marcus M. K.
Published: August 2012

This paper discusses the physical characteristics and frequency content of ship collision loads that are imparted to three minimum structures and a jacket platform, namely the shape and duration of the pulse load, and how they can be described by a half-sine pulse load. This was achieved by carrying out spectral analyses on the time histories of ship collision pulse loads and comparing those from a half-sine and a rectangular pulse load. The spectral analyses produced the frequency bandwidths within which most of the excitation energy was located and showed whether they coincided with the natural frequencies of the platform. Spectral analyses were also carried out on the dynamic response at the topside and the impact nodes, to identify those mode shapes that contributed prominently to the dynamic response of the platform. There is a discussion on how this information can be used in collaboration with the acceleration spectrum technique used in a previous paper by the authors, in order to assist the engineer in designing topside equipment to survive excessive vibrations resulting from a ship collision.
Absorption and discharge capacity tests on natural prefabricated vertical drains
Authors: Asha B.S. , Mandal J.N.
Published: August 2012

ABSTRACT: This paper reports absorption and discharge capacity tests conducted in the laboratory on four types of newly developed and fabricated band-shaped prefabricated vertical drain (PVD) made from natural geotextiles and commercially available polymer-based prefabricated vertical drains (PPVDs). The natural PVDs are made from single-layer woven or nonwoven geotextile jute sheath wrapped around a core of coir ropes or coir mats, designated as natural prefabricated vertical drains (NPVDs 1, 2, 3 and 4). Short-term, rubber-membrane-confined discharge capacity tests were conducted at different compressive stresses and hydraulic gradients. The tests were carried out for a better understanding of the influence of NPVD configuration, compressive stress and hydraulic gradient on discharge capacity. The test results for the NPVDs are compared and discussed, together with the results from PPVDs. NPVD 4, which is made of woven jute sheath and corrugated coir mat core, has a greater discharge capacity than the other NPVDs at all the normal stresses and hydraulic gradients studied. The core configuration of NPVD 4 supports the jute sheath better, to prevent it from collapsing into the core as the compressive stress is increased. Although nonwoven jute sheath is a better water-absorbing geotextile than woven jute sheath, the lowest discharge capacity is observed in NPVD 2, which is made from nonwoven jute wrapped around coir ropes. Flow conditions through all the NPVDs are linear at all hydraulic gradients, satisfying the theoretical requirement of PVDs.
Stability analyses of reinforced walls subjected to simulated toe scouring
Authors: Huang C.-C. , Chen Y.-S.
Published: August 2012

ABSTRACT: Limit-equilibrium-based internal and external stability analyses were performed for two carefully designed and monitored reinforced model walls reported in a companion paper. Failure mechanisms and associated safety factor changes against toe scouring were investigated. Safety factors against various failure modes – reinforcement over-stressing, reinforcement pullout, lateral sliding, overturning and bearing capacity – were derived, based on well-known material properties and theories. It was shown that the ultimate collapse state of the wall with a low reinforcement–facing connection strength was controlled by the pullout of the reinforcement from the facing. A low reinforcement–facing connection impeded the full mobilisation of reinforcement force in the lowermost layer of the reinforcement, which in turn reduced the ductility of the structure and accelerated the failure process. For the wall with high connection strength, the ultimate collapse of the wall was controlled by the bearing capacity failure near the slope toe. The analytical bearing capacity failure state was supported by the experimental observation of the failure wedge below the facing and the reinforced zone. Experimental results also suggested that a transitional wall displacement of Dh max/Ht = 0.2–1.0%, signalling rapid wall displacement for further inclined toe cutting (or further toe scouring), is associated with higher internal and external stability safety factors than those suggested in current design guidelines that do not take into account the effects of toe scouring.
The Numerical Approach for Predicting Productivity from Mutiple-fractured Horizontal Wells under Non-Darcy Conditions
Authors: Feng Yang , Ning Zhengfu , Liao Xinwei , Liu Huiqing
Published: August 2012

Horizontal wells with multiple fractures are becoming more prevalent in tight gas reservoir. However, it is uneasy to obtain the applicable deliverability formula of multiple-fractured horizontal wells using analytical method in consideration of multiple factors, such as the non-Darcy effect, interference between fractures, the coupling effect with reservoir, and formation heterogeneity.

This project investigates the deliverability formula of multiple hydraulically fractured horizontal wells in tight gas reservoir using a special numerical method with a focus on the existence of non-Darcy effect and formation heterogeneity. Numerical model expected from daily production data, including wellhead pressure history and production history, is obtained using the numerical well test method, which has an advantage in considering reservoir heterogeneity and complex boundary. The effect of non-Darcy in gas well is discussed using rate dependent skin when constructing the numerical model. The parameters of the numerical model on multiple fractured horizontal well are validated compared with analysis of real pressure build-up well test data. Productivity well test is then simulated based on the previous numerical model, and binomial deliverability equation is obtained from simulated productivity well test curve. The error of absolutely flow rate which derives from the simulation results and modified isochronal test from the field is less than 6%. This paper provides a fast and reliable numerical tool to multifractured horizontal well performance prediction in tight gas reservoir, especially considering non-Darcy effect and reservoir heterogeneous.
Casing ERD Wells to Target the New Improved Casing Flotation - A New Solution
Authors: Uzokwe F.C.
Published: August 2012

Abstract

Getting casing to total depth is one of the most important operation in extended reach drilling (ERD) as increased casing depth increases recovery efficiency hence the need to ensure as much casing as possible is deployed into the wellbore. This paper proposes a new method of casing deployment in ERD wells termed New Improved Casing Flotation (NICF). This method is based on the principle of buoyancy and utilizes multiple fluids to deploy different sections of the casing string into the wellbore. This proposed method is validated using a base case extended reach well and the maximum measured depth attained for the 95/8?? production casing compared against other casing installation techniques. From the result of the simulation, the measured depth attained using the NICF method is 29,400 ft. When compared to partial flotation (23,300 ft), full flotation (12,300 ft) and conventional method (12,300 ft), the measured depth obtained using the proposed NICF method exceed that of partial flotation by 6,100 ft, and that of conventional method and full flotation by 17,100 ft.

Introduction

The need to get hydrocarbons from ultra deep and complex wells have indeed pushed the limits of well engineering. Critical technologies have led to the advent of rotary steerable systems (RSS) and steerable motors assemblies which have enabled drilling with controlled dog legs thereby minimizing drag as the BHA proceeds through its complex trajectory (Thomas et al 2008).

The development and use of low torque drill pipes, specialty equipments like NRDPP, DSTR subs, DPB subs, bi-directional rollers, lubricating beads, spot pills and hard banding of tool joints have all proved to reduce the effect of torque and drag thereby extending the limit of drilling in their different applications (Rae, Williams and Hamilton 2003).

It becomes obvious that these successes in drilling have to be complimented by successful casing running to total depth (TD) to enhance optimum production from the reservoir. These have led to great advances in the subject of casing design and running techniques. The onus being to develop casing running techniques that can match up the advances of complex drilling as well as being able to withstand all design loads and operational constraints in the most cost effective way (Jaffe et al 1997).
Accurate Estimation of Equivalent Circulating Density During High Pressure High Temperature (HPHT) Drilling Operations
Authors: Ataga E. , Ogbonna Joel
Published: August 2012

Error in equivalent circulating density estimation can be disastrous because of the narrow margin between pore and fracture pressure in HPHT wells. High temperature conditions cause the fluid in the wellbore to expand, while high pressure conditions in deep wells cause fluid compression. Failure to take these two opposing effects into account can lead to errors in the estimation of bottom-hole pressure on the magnitude of hundreds of psi. This study involves the development of a simulator called HPHT-Density Simulator to simulate the wellbore(drillpipe and annulus) during circulation as well as the temperature and pressure profiles of a wellbore during circulation.

A Bingham plastic model was incorporated into a simulator called HPHT-density Simulator which was developed using Visual Basic to simulate the wellbore during circulation. The developed HPHT-density Simulator program interface is executed with a series of user forms, which will accept data pertaining to the wellbore, drilling fluid and formation parameters and return the temperature profiles in the wellbore and formation, pressure losses in the wellbore and ECD of the circulating fluid. The user can navigate between forms and input data at leisure using the "back" and "next" input bottons. Once values of all the necessary parameters have been entered into the program, the results are displayed on a "results" forms.

The successful simulation of HPHT-Density Simulator shows a significant difference in the equivalent circulating density and bottom hole pressure profile for fluid circulation parameters of a Niger Delta well when the rheological properties were assumed to be constant as compared with when temperature-pressure varied. This can be adapted to drilling operations and thereby preventing downtime arising from kicks, blow-outs, lost circulation and formation damage due to wrong estimation of equivalent circulating density while drilling within narrow margin between pore and fracture pressure in HPHT wells.
Selection of Alternatives for Oil Field Development; Nonlinear Optimization Approach
Authors: Ohia N. P , Omeke J. E. , Achumba I. G
Published: August 2012

In the petroleum Industry, the major task is to develop a strategy to maximize the hydrocarbon production within existing physical and economic constrains. The major entities involved in solving this problem are: the oil reservoir and the oil wells. Each of these entities has a number of variables and parameters. Searching for the best configuration of these parameters, for optimum return on investment, constitute an optimization problem. In other to apply the optimization approach, an objective function must be involved. In this study, Net Present Value (NPV) was selected as the profit indicator for return on investment (ROI).

Optimization is complicated when more parameters are involved and needed to be optimized simultaneously. Major success will rely on the ability to incorporate effectively, factors (physical and economic) that influence the entire production process in an economic model called the Objective function with or without constraints. A suitable optimization method is also required.

In this work, a robust NPV objective function was developed for a reservoir under production. Reservoir, production and economic uncertainties where fully captured.

A multivariate nonlinear optimization approach was employed in determining the best configuration of the decision variable and their effect on NPV. Nonlinear optimization methods based on Newton's technique locate the extrema by approximating the objective function with a nonlinear quadratic model. The quadratic model is solved for the stationary point where its gradient goes to zero. If the quadratic model is a good approximation of the objective function, then the stationary point of the quadratic model should be near a stationary point of the objective function. The stationary point of the quadratic model is taken as the new estimate of the objective function's stationary point and the process is repeated until some form of convergence criteria is satisfied.

Sensitivity plots where generated for diagnostic purposes as well as to strengthen decision processes. Field application of the NPV model was carried out and reliable results where obtain.
Pipeline Vandalism in Nigeria: Recommended Best Practice of Checking the Menace
Authors: Udofia O. O , Joel O. F
Published: August 2012

Pipeline vandalism, in the context of this paper, refers to the willful or deliberate act of damaging petroleum pipelines with the sole aim of stealing crude oil and associated petroleum products. In the Nigerian oil & gas industry, the effects of pipeline vandalism among others include huge economic losses from pipeline & plant shutdown, environmental pollution, fire outbreaks usually resulting in loss of lives. Scarcity & shortage of petroleum products as well as decrease in electricity supply with the attendant socio-economic problems can also be attributed to pipeline vandalism. In Nigeria petroleum and associated products are transported through extensive network of pipelines that run across different locations throughout the country from remote to populated areas. These pipelines are however poorly secured thereby making them targets of repetitive attacks by vandals. Various steps have been taken by government for efficient service delivery but the problems appear to be on the increase. This paper presents an overview of the existing arrangement of pipeline monitoring protocols and recommended Best Practice for prudent pipeline management in Nigeria.
A New Analytical Method for Predicting Dew Point Pressures for Gas Condensate Reservoirs
Authors: Godwin Okpo Nnadozie
Published: August 2012

This study presents a new analytical method for predicting dew point pressures for gas condensate reservoir as a function of routinely measured gas analysis and reservoir temperature. The proposed model was developed using experimentally measured and collected data of 259 gas condensate sample covering a wide range of gas properties and reservoir temperatures obtained from the literature. The proposed correlation has an average relative deviation (ARD) of 0.0488% and absolute deviation (AAD) of 0.099%.

The accuracy of this model was tested with 14 data sets that were not used in developing the correlation, and the accuracy of the new model was compared to order existing correlations from the literature. The result shows that the newly proposed model performed better than popular, and presently being used in the oil and gas industry such as the Nemeth and Kennedy, and A.M. El-sharkawy correlations.
Well Predictive Material Balance Evaluation: A Quick Tool for Reservoir Performance Analysis
Authors: Nwaokorie Chukwuemeka , Ukauku Ikwan
Published: August 2012

Hydrocarbon reservoirs require steady evaluation in terms of performance prediction and resource volume estimation. These evaluations are planned and carried out from point of discovery till maturation and abandonment.

Full field reservoir simulation model is the conventional tool for reservoir performance analysis via planned or existing wells. Material balance models were developed to carry out simple reservoir analysis on tank basis for resource volume estimation and prediction.

Well predictive material balance model has proved to be a quick and handy tool capable of doing reservoir analysis both at reservoir and well levels. In this paper, we will be discussing the methodologies, basic workflows and technical principles of building a simple well predictive material balance model. This tool is not a replacement of more robust reservoir simulation model but a quick win in terms of time and cost.

The study shows the implementation of this tool for a resource volume estimation and well performance prediction. It covered evaluation of saturated reservoirs with concurrent oil and gas production.

The results were compared with reservoir simulation and conventional decline curve analysis results for robustness check. Important data such as relative permeability, well models (IPR and vertical lift curves), current fluid contact and PVT data are some of the essential data required to build a good predictive material balance model.

Keys steps taken in building this model are:

Data gathering and validations Model Construction History Matching/ Simulation Prediction (reservoir and well) Result analys

The Results show good comparison with other methodologies (Simulation and DCA). The wells predictions were good and compare closely with actual well production.
Comparative Performance Analysis of Petroleum Sharing Contracts in Angola, Equatorial Guinea, Gabon And Nigeria
Authors: Echendu Joseph C. , Iledare Omowumi O. , Onwuka Emmanuel I.
Published: August 2012

Petroleum Fiscal System (PFS) is a key determinant of investment decision in the exploration and production (E&P) of oil and gas. It describes the relationship between the host governments, the investors, and community stakeholders with respect to how costs are recovered and profits are shared equitably. A comparative economics of the performance of fiscal regimes becomes imperative as it affects stakeholders in making informed decisions on the oil and gas business investments worldwides.

This paper evaluates the structure, conduct and performance of PFS in Gabon, Equatorial Guinea, Angola and Nigeria in the Gulf of Guinea (GOG). These countries hold about 90% of the GOG proved reserves. Economic analysis of the same E&P phases using hypothetical field and cost data under the different PFS are presented and discussed for comparative PFS performance evaluations. Comparison of the effects of production delay, front loaded government take and taxation shows that petroleum sharing contract fiscal terms and instruments in Gabon, Equatorial Guinea, Angola and Nigeria are relatively competitive. We found that as the risk in deepwater investment increases with water depth, return on investment rises in these GOG countries. Monte Carlo simulation process incorporated to account for risk and uncertainties reveal early discounted payout for investors in these GOG countries with significant degree of ceteris paribus.
Improving Efficiency of Oil & Gas Development through Lean Concept
Authors: Mustapha Adetoun , Ageh Ebenezer , Maduekwe Emeka , Ojulari Bayo
Published: August 2012

Population and economy are two key factors considered in global energy demand projections. With rapidly growing world population, energy security is a global concern. The 2011 World Energy Outlook projected that from the 2010 levels, global oil demand will grow by 14% while gas use will rise by more than 50% as well as account for over 25% of world energy demand by 2035. With hydrocarbons no longer easily accessible, success in the future of oil and gas will require meeting various challenges, including ensuring that both discovered and new resources can be produced in economically and environmentally sound manner to offset the natural field decline. Also, shareholders, non-government organizations and local communities are seeking for more value and demonstration of social responsibilities from the industry. Additionally, governments and policymakers are imposing stricter regulations that impact reserve maturation and production.

One of the ways stakeholders' expectations can be addressed is by making the most use of resources to lower costs and improve operational efficiency. Lean is a business improvement technique with a collection of tools to eliminate ‘'waste" in an operation and reduce cycle time. Cost reduction is achieved by improving the flow of material and information through the system and continuously finding ways to reduce the amount of work by taking out unnecessary or "waste" steps in processes. Originally developed by the Japanese automobile company, Toyota and widely employed in the manufacturing industry, more industries are adopting the Lean concept.

This presentation will showcase Lean application in hydrocarbon development and production. Case studies will be provided to demonstrate how Lean implementation has helped and can be used to eliminate wastes in processes and bring about a culture change. Business results are faster hydrocarbon maturation, enhanced production, sustainable cost reduction and stakeholders reaching mutual agreement faster on sustainable development/environmental issues.
Minimum Shut-In Time Prediction Model for Pressure Build-Up Survey for a Niger Delta Onshore Field
Authors: Ejere Ekeoma , Omeke James Emeka
Published: August 2012

Allowing a well to stabilise is an important part of both pressure drawdown and build-up test. If stabilization is overlooked or is impossible, standard data analysis techniques may provide erroneous information about the formation. One of the principal objectives of pressure build-up analysis is to determine the static reservoir pressure without waiting weeks for the pressure in the entire reservoir to stabilize. The fact remains that no matter how we try to avoid long shut-in period, the shut-in time must exceed the transient and well bore storage period if a reliable result is sought. The bulk of the analysis is done at the middle transient period (MTP) which, sometimes, due to the complex nature of the reservoir, may be appreciable enough to invalidate the intention of shutting-in the well for just a short time. A minimum shut in time of six hours has been a common conventional practice in our land locations. This brings us to the question - "is this shut-in period enough or too small to provide a reliable analysis?" This shut-in period remains a paradox as long as complexities and uncertainties are present in the reservoir under study. Some reservoir with varying degree of complexities has varying shut in time. For example, the presence of faults and complex barriers may prolong the time of the reservoir to reach its middle or late transient state during build-up; hence, it becomes necessary to predict the minimum time of stabilization in the presence of these complexities so as to minimize cost. This was the focus of this paper.

The general formulas used in analyzing pressure build-up data came from a solution of the diffusivity equation with homogenous, isotropic and slightly compressible single phase fluid conditions. This equation is in its simplest form and due to the assumptions made; it is obvious that the major uncertainties that may affect the shut in time is not captured; hence a need for a robust modelling.

In this paper, a semi-analytical model for the Niger Delta onshore field was developed for optimum shut in time prediction for each well in the reservoir selected for study. A correction function which encapsulates the real reservoir complexities was introduced based on the well data under study. This correction function was modelled using Gompertz, 4 parameter Sigmoidal equation1 with the correlating constant determined by the method of least square for the specific well considered. A constrained nonlinear optimisation technique was applied to the newly developed model which serves as the objective function with the aim of minimizing the shut-in time as well as attaining an effective stabilization pressure. This procedure will, in no doubt, improve our optimism of accurate shut-in time prediction, a cost effective approach.
Evaluation of Thermal Effects on Drillability in HPHT Wells in Niger Delta
Authors: Ngwu G. I. , Dosunmu A. , Osokogwu U.
Published: August 2012

Overcoming wellbore drilling instability presents one of the major challenges to drilling engineers mostly in high pressure and high temperature wells. These are wells with reservoir pressure in excess of 10,000 psi and bottom-hole temperature exceeding 300°F, the temperature gradient between the drilling mud and the formation leads to induced thermal stresses and pore pressure responses. The aim of this work is to design an optimum mud weight at different depths and investigate the effect of temperature on wellbore stresses as it affects drillability performance. Improper mud design is one of the major causes of instability problems and also increasing temperature of the mud leads to increase in wellbore stresses which enhances the likelihood of breakouts and inhibits tensile fracture formation, and on the other hand, cooling the mud inhibits breakouts and which increases the likelihood of development of tensile wall fractures. A model was developed in this work, which was used to analyze the thermal effects on wellbore stresses and the optimum mud weight at different depth as it affect drillabilty performance. Analyses reveal that at bottom hole temperature of 300°F, the tangential stress was 7,378psi at the depth of 10,000ft. when the temperature increased to 438°F, the tangential stress was 10,025psi at the depth of 16,000ft for shale formation.
A Simple Regression-Based Approach for Prediction of Aqueous Ammonia Vapor Pressure
Authors: Bahadori A.
Published: August 2012

In the process industries, hazardous materials can be released accidentally as vapor, gas or liquid and are dispersed in the atmosphere. Ammonia is one of the most extensively used industrial chemicals. It is highly soluble in water and has toxic and corrosive effects caused by its alkalinity. The evaporation of ammonia may cause extreme cooling when spilled on the skin or eyes; cold burns may result. When inhaled, ammonia dissolves in upper airways and small amounts also in the lower respiratory tract; damage to upper airways is therefore more severe. In this paper, simple predictive tool, which is easier than existing approaches, less complicated with fewer computations and suitable for environmental experts, is presented here for the estimation of aqueous ammonia vapor pressure as a function of ammonia molar fraction in aqueous phase and temperature. The proposed predictive tool works for temperatures in the range of 273 to 373 K. The proposed method is superior owing to its accuracy and clear numerical background, wherein the relevant coefficients can be retuned quickly if more data are available in the future. Estimations are found to be in excellent agreement with the reliable data in the literature with average absolute deviation being around 1.74%. The tool developed in this study can be of immense practical value for the engineers and scientists to have a quick check on the vapor pressure of aqueous ammonia solution at various conditions without opting for any experimental measurements. In particular, chemical engineers and environmental scientists would find the approach to be user-friendly with transparent calculations involving no complex expressions.