bluuebunny/crossref_metadata_2025 huggingface dataset:
Complex Genetics Control Natural Variation inArabidopsis thalianaResistance toBotrytis cinerea
Authors: Rowe Heather C , Kliebenstein Daniel J
Published: October 2008

The genetic architecture of plant defense against microbial pathogens may be influenced by pathogen lifestyle. While plant interactions with biotrophic pathogens are frequently controlled by the action of large-effect resistance genes that follow classic Mendelian inheritance, our study suggests that plant defense against the necrotrophic pathogen Botrytis cinerea is primarily quantitative and genetically complex. Few studies of quantitative resistance to necrotrophic pathogens have used large plant mapping populations to dissect the genetic structure of resistance. Using a large structured mapping population of Arabidopsis thaliana, we identified quantitative trait loci influencing plant response to B. cinerea, measured as expansion of necrotic lesions on leaves and accumulation of the antimicrobial compound camalexin. Testing multiple B. cinerea isolates, we identified 23 separate QTL in this population, ranging in isolate-specificity from being identified with a single isolate to controlling resistance against all isolates tested. We identified a set of QTL controlling accumulation of camalexin in response to pathogen infection that largely colocalized with lesion QTL. The identified resistance QTL appear to function in epistatic networks involving three or more loci. Detection of multilocus connections suggests that natural variation in specific signaling or response networks may control A. thaliana–B. cinerea interaction in this population.
The Mating-Type-Related Bias of Gene Conversion inSchizosaccharomyces pombe
Authors: Parvanov Emil , Kohli Juerg , Ludin Katja
Published: October 2008

The mating-type bias (mat-bias) of gene conversion was previously described as a phenomenon in which the number of prototrophic recombinants in an ura4A heteroallelic two-factor cross relates to the mating types of the parents. We show now that the mat-bias is restricted neither to ura4A nor to recombination hotspots, but occurs at other genomic loci, too. It is specific for gene conversion and absent in azygotic meiosis. Thus, the mat-bias must originate from mating-type-specific “imprinting” events before karyogamy takes place. Structural variations of the mating-type locus, such as h+N, h+S, h−S, h+smtΔ, or h−smtΔ, showed mat-bias manifestation. Mutations in genes coding for histone acetylase (gcn5, ada2) and histone deacetylase (hos2, clr6) activities smooth or abolish the mat-bias. In addition, the mat-bias depends on the presence of Swi5. We propose a new role for Swi5 and the histone acetylation status in mat-bias establishment through directionality of repair from the intact chromatid to the broken chromatid.
Telomere Loss Provokes Multiple Pathways to Apoptosis and Produces Genomic Instability inDrosophila melanogaster
Authors: Titen Simon W A , Golic Kent G
Published: October 2008

Telomere loss was produced during development of Drosophila melanogaster by breakage of an induced dicentric chromosome. The most prominent outcome of this event is cell death through Chk2 and Chk1 controlled p53-dependent apoptotic pathways. A third p53-independent apoptotic pathway is additionally utilized when telomere loss is accompanied by the generation of significant aneuploidy. In spite of these three lines of defense against the proliferation of cells with damaged genomes a small fraction of cells that have lost a telomere escape apoptosis and divide repeatedly. Evasion of apoptosis is accompanied by the accumulation of karyotypic abnormalites that often typify cancer cells, including end-to-end chromosome fusions, anaphase bridges, aneuploidy, and polyploidy. There was clear evidence of bridge–breakage–fusion cycles, and surprisingly, chromosome segments without centromeres could persist and accumulate to high-copy number. Cells manifesting these signs of genomic instability were much more frequent when the apoptotic mechanisms were crippled. We conclude that loss of a single telomere is sufficient to generate at least two phenotypes of early cancer cells: genomic instability that involves multiple chromosomes and aneuploidy. This aneuploidy may facilitate the continued escape of such cells from the normal checkpoint mechanisms.
Sexual Back Talk With Evolutionary Implications: Stimulation of the Drosophila Sex-Determination Gene Sex-lethal by Its Target transformer
Authors: Siera Scott G , Cline Thomas W
Published: October 2008

We describe a surprising new regulatory relationship between two key genes of the Drosophila sex-determination gene hierarchy, Sex-lethal (Sxl) and transformer (tra). A positive autoregulatory feedback loop for Sxl was known to maintain somatic cell female identity by producing SXL-F protein to continually instruct the target gene transformer (tra) to make its feminizing product, TRA-F. We discovered the reciprocal regulatory effect by studying genetically sensitized females: TRA-F from either maternal or zygotic tra expression stimulates Sxl-positive autoregulation. We found female-specific tra mRNA in eggs as predicted by this tra maternal effect, but not predicted by the prevailing view that tra has no germline function. TRA-F stimulation of Sxl seems to be direct at some point, since Sxl harbors highly conserved predicted TRA-F binding sites. Nevertheless, TRA-F stimulation of Sxl autoregulation in the gonadal soma also appears to have a cell-nonautonomous aspect, unprecedented for somatic Sxl regulation. This tra–Sxl retrograde regulatory circuit has evolutionary implications. In some Diptera, tra occupies Sxl's position as the gene that epigenetically maintains female identity through direct positive feedback on pre-mRNA splicing. The tra-mediated Sxl feedback in Drosophila may be a vestige of regulatory redundancy that facilitated the evolutionary transition from tra to Sxl as the master sex switch.
A G2-Phase Microtubule-Damage Response in Fission Yeast
Authors: Balestra Fernando R , Jimenez Juan
Published: October 2008

Microtubules assume a variety of structures throughout the different stages of the cell cycle. Ensuring the correct assembly of such structures is essential to guarantee cell division. During mitosis, it is well established that the spindle assembly checkpoint monitors the correct attachment of sister chromatids to the mitotic spindle. However, the role that microtubule cytoskeleton integrity plays for cell-cycle progression during interphase is uncertain. Here we describe the existence of a mechanism, independent of the mitotic checkpoint, that delays entry into mitosis in response to G2-phase microtubule damage. Disassembly of the G2-phase microtubule array leads to the stabilization of the universal mitotic inhibitor Wee1, thus actively delaying entry into mitosis via inhibitory Cdc2 Tyr15 phosphorylation.
Outcrossing as an Explanation of the Apparent Unconventional Genetic Behavior ofArabidopsis thaliana hthMutants
Authors: Mercier Raphael , Jolivet Sylvie , Vignard Julien , Durand Stéphanie , Drouaud Jan , Pelletier Georges , Nogué Fabien
Published: October 2008

The reappearance of HTH alleles in the offspring of homozygous Arabidopsis hth mutants is not consistent with classical Mendelian genetics. It has been suggested that stored RNA may be used to restore genetic information. However, Peng et al. reported that hth mutants tend to display outcrossing and suggested that outcrossing might provide an alternative explanation for the apparent genetic instability. We have confirmed and extended these results, corroborating that the apparent non-Mendelian behavior of hth mutants can be explained by their susceptibility to outcrossing.
RNA-Dependent RNA Polymerase Is Required for Enhancer-Mediated Transcriptional Silencing Associated With Paramutation at the Maizep1Gene
Authors: Sidorenko Lyudmila , Chandler Vicki
Published: October 2008

Paramutation is the ability of an endogenous gene or a transgene to heritably silence another closely related allele or gene. At the maize p1 (pericarp color1) gene, paramutation is associated with decreases in transcript levels and reduced pigmentation of the endogenous allele that normally specifies red seed coat (pericarp) and cob pigmentation. Herein we demonstrate that this silencing occurs at the transcriptional level and that a specific enhancer fragment from p1 is sufficient to induce all aspects of paramutation. Further, we demonstrate that a mutation in the mop1 gene (mediator of paramutation1), which encodes a RNA-dependent RNA polymerase, is absolutely required for establishing the silencing associated with p1 paramutation. In contrast to its effects on other paramutation loci, the mop1 mutation does not immediately reactivate a previously silenced allele; several generations in the presence of the mop1 mutation are required. In addition, the mop1 mutation was also able to release tissue-specific silencing of another p1 allele that does not participate in paramutation, but does contain a tandem repeated structure and is likely regulated through epigenetic mechanisms. These results demonstrate that RNA-mediated gene-silencing mechanisms play key roles in p1 paramutation and the spectrum of roles for MOP1 is broadened to include tissue-specific expression patterns.
Loss of the Histone Variant H2A.Z Restores Capping to Checkpoint-Defective Telomeres in Drosophila
Authors: Rong Yikang S
Published: October 2008

The conserved histone variant H2A.Z fulfills many functions by being an integral part of the nucleosomes placed at specific regions of the genome. Telomeres cap natural ends of chromosomes to prevent their recognition as double-strand breaks. At yeast telomeres, H2A.Z prevents the spreading of silent chromatin into proximal euchromatin. A role for H2A.Z in capping, however, has not been reported in any organism. Here, I uncover such a role for Drosophila H2A.Z. Loss of H2A.Z, through mutations in either its gene or the domino gene for the Swr1 chromatin-remodeling protein, suppressed the fusion of telomeres that lacked the protection of checkpoint proteins: ATM, ATR, and the Mre11–Rad50–NBS complex. Loss of H2A.Z partially restores the loading of the HOAP capping protein, possibly accounting for the partial restoration in capping. I propose that, in the absence of H2A.Z, checkpoint-defective telomeres adopt alternative structures, which are permissive for the loading of the capping machinery at Drosophila telomeres.
A and C Genome Distinction and Chromosome Identification inBrassica napusby Sequential Fluorescencein SituHybridization and Genomicin SituHybridization
Authors: Howell Elaine C , Kearsey Michael J , Jones Gareth H , King Graham J , Armstrong Susan J
Published: October 2008

The two genomes (A and C) of the allopolyploid Brassica napus have been clearly distinguished using genomic in situ hybridization (GISH) despite the fact that the two extant diploids, B. rapa (A, n = 10) and B. oleracea (C, n = 9), representing the progenitor genomes, are closely related. Using DNA from B. oleracea as the probe, with B. rapa DNA and the intergenic spacer of the B. oleracea 45S rDNA as the block, hybridization occurred on 9 of the 19 chromosome pairs along the majority of their length. The pattern of hybridization confirms that the two genomes have remained distinct in B. napus line DH12075, with no significant genome homogenization and no large-scale translocations between the genomes. Fluorescence in situ hybridization (FISH)—with 45S rDNA and a BAC that hybridizes to the pericentromeric heterochromatin of several chromosomes—followed by GISH allowed identification of six chromosomes and also three chromosome groups. Our procedure was used on the B. napus cultivar Westar, which has an interstitial reciprocal translocation. Two translocated segments were detected in pollen mother cells at the pachytene stage of meiosis. Using B. oleracea chromosome-specific BACs as FISH probes followed by GISH, the chromosomes involved were confirmed to be A7 and C6.
Informed Consent Revisited: A Doctrine in the Service of Cancer Care
Authors: Schachter Madeleine , Fins Joseph J.
Published: October 2008

Informed consent traditionally has been viewed as a safeguard for the protection of patients' decisional autonomy. While informed consent is a critical means for the protection of the patient's dominion over the integrity of his body, exclusive consideration of the doctrine as a safeguard for patients eclipses the doctrine's significant benefits for the therapeutic endeavor. Undertaking a thorough informed consent process helps the physician avoid the unilateral burdens of paternalism; furthers compliance with the doctor's legal obligations, ethical duties, and clinical responsibilities; and, as importantly, enhances the collaborative treatment enterprise.

When informed consent is viewed narrowly and solely as a protective device for patients' rights, the physician may be less likely to engage the patient in ongoing discussions. Important opportunities may be missed to elicit additional clinical information, assess psychosocial concerns, and reiterate the commitment to collaboration and patient autonomy.
FDA Drug Approval Summary: Lapatinib in Combination with Capecitabine for Previously Treated Metastatic Breast Cancer That Overexpresses HER-2
Authors: Ryan Qin , Ibrahim Amna , Cohen Martin H. , Johnson John , Ko Chia-wen , Sridhara Rajeshwari , Justice Robert , Pazdur Richard
Published: October 2008

Learning Objectives

After completing this course, the reader should be able to: Describe the clinical trial that led to the approval of lapatinib in combination with capecitabine for the treatment of previously treated patients with HER-2–overexpressing metastatic breast cancer.Determine appropriate patients to receive lapatinib plus capecitabine treatment.Assess and manage the toxicities of lapatinib plus capecitabine treatment.

CME This article is available for continuing medical education credit at CME.TheOncologist.com

On March 13, 2007, the U.S. Food and Drug Administration approved lapatinib (Tykerb® tablets; GlaxoSmithKline, Philadelphia), an oral, small molecule, dual tyrosine kinase inhibitor of ErbB-2 and ErbB-1, for use in combination with capecitabine for the treatment of patients with human epidermal growth factor receptor (HER)-2–overexpressing metastatic breast cancer who had received prior therapy including an anthracycline, a taxane, and trastuzumab.

One multicenter, open-label, randomized trial was submitted. Eligible patients had stage IIIb or IV breast cancer, ErbB-2 overexpression (immunohistochemistry 3+ or 2+ with fluorescence in situ hybridization confirmation), measurable disease, a 0 or 1 Eastern Cooperative Oncology Group performance status score, a cardiac ejection fraction within the institutional normal range, and adequate laboratory function.

Patients received either lapatinib (1,250 mg once daily on days 1–21) plus capecitabine (1,000 mg/m2 every 12 hours on days 1–14) every 21 days or capecitabine alone (1,250 mg/m2 every 12 hours on days 1–14) every 21 days.

The primary endpoint was time to progression (TTP) determined by a blinded independent review panel. After TTP results of a prespecified interim analysis were made available, study enrollment was discontinued (399 patients enrolled).

The median TTP was 27.1 versus 18.6 weeks (hazard ratio, 0.57; p = .00013) favoring the lapatinib plus capecitabine arm. Response rates were 23.7% (lapatinib plus capecitabine) versus 13.9% (capecitabine alone). Survival data were not mature.

Although the toxicities observed in the lapatinib and capecitabine combination arm were generally similar to those in the capecitabine alone arm, a higher incidence of diarrhea and rash was noted with the combination. Grade 3 or 4 adverse reactions that occurred with a frequency of >5% in patients on the combination arm were diarrhea (13%) and palmar–plantar erythrodysesthesia (12%). There was a 2% incidence of reversible decreased left ventricular function in the combination arm.
A New Regression-Based Method for Accurate Measurement of Coal and Shale Gas Content
Authors: Shtepani E. , Noll L. A. , Elrod L. W. , Jacobs P. M.
Published: October 2008

Gas content and storage capacity are the key parameters for determination of the gas resources and reserves in unconventional reservoirs. These parameters must be obtained from laboratory experiments in the core samples such as desorption canister tests and adsorption isotherm experiments. Desorption canister testing is performed to determine the total adsorbed gas content, gas composition and the total desorption time. Adsorption isotherm experiments are conducted to determine the gas storage capacity with pressure and for CO2 sequestration purposes. Other analyses of coals include proximate analysis and bulk density measurements of all samples. Shales are commonly analyzed for total organic carbon in lieu of proximate analysis.

The gas content is estimated by placing selected freshly cut reservoir samples in air tight sealed canisters and measuring desorbed gas volume as a function of time at atmospheric conditions. Total gas content is the summation of three components: "lost gas", desorbed gas, and "residual gas". "Lost gas" is the volume of the gas that desorbs from the sample during the recovery process at wellsite, before the core sample can be sealed in a desorption canister. "Residual gas" is the gas that remains sorbed on the sample at the completion of the canister desorption test.

A disadvantage of this procedure is the estimation of "lost gas". The volume of the "lost gas" is usually estimated by extrapolation of desorbed data to time zero using linear and/or polynomial curve-fit to the plot of cumulative desorbed gas versus square root of time. The differences between both methods can become more pronounced especially in high gas content reservoirs.

In this paper a new method, which is based on nonlinear regression of measured gas content, is presented. This technique offers an accurate estimation of lost gas which coupled with sorption isotherm impacts the calculation of gas in place, the recoverable reserve and production profiles.
Improvements in Measuring Sorption-Induced Strain and Permeability in Coal
Authors: Robertson E. P.
Published: October 2008

Total worldwide CBM in-place reserves estimates are between 3500 Tcf and 9500 Tcf. Unminable coal beds have been recommended as good CO2 sequestration sites as the world prepares to sequester large amounts of greenhouse gases. In the U.S., these coal seams have the capacity to adsorb and sequester roughly 50 years of CO2 emissions from all the U.S. coal-fired power plants at today's output rates. The amount and type of gas adsorbed in coal has a strong impact on the permeability of the coal seam. An improved mixed gas adsorption isotherm model based on the extended-Langmuir theory is discussed and is applied to mixed gas sorption-induced strain based on pure gas strain data and a parameter accounting for gas-gas interactions that is independent of the coal substrate. Advantages and disadvantages of using freestanding versus constrained samples for sorption-induced strain measurements are also discussed. A permeability equation used to model laboratory was found to be very accurate when sorption-induced strain was small, but less accurate with higher strain gases.
Solving Completion Options for Underground Gas Storage Through Geomechanics
Authors: Surej Subbiah , Burgstaller C. , Fuller J. , Wielemaker E. , Jilg W.
Published: October 2008

Varition of gas demand yearly, weekly, at different tine in a day and seosonly is the main driving factor for gas storage. Ideally the gas needs to be stored at the comsumption points and the demand fluctuations need to be met by supply. Thus the underground gas strorage operators need to maximize the storage capacity and minimize the cost of storage. Furthermore the operations need to be safe during the injection and production cylces.

During underground gas storage the reservoir is exposed to large range of pressure changes i.e. injection and production cycle. The stress state acting on the reservoir rock during this cycle is very high. In addition, the rate at which gas is injected and produced can subject the reservoir rock in the near wellbore region to large stresses. Both the change in stress due to changes in the reservoir pressure and changes in stress due to injection and production rate can be sufficient to fail the rock in this near wellbore region and cause sand production. Any sand production is likely to damage wellbore and surface equipment, and ultimately may render the gas storage operation unviable.

An understanding of the state of stress in the reservoir created by these gas storage operations is critical to avoid unwanted sand production. A geomechanical review of the potential for sand production in the Haidach Underground Storage Reservoir, Austria, illustrates the steps necessary to determine the stress state that will cause formation deformation and probable sand production. The study assists the selection of stable zones for perforating wells and sets operational limits for the gas flow to and from the wells
Pore-Pressure Prediction in Overconsolidated Shales
Authors: Nygaard R. , Karimi M. , Hareland G. , Tahmeen M. , Munro H.
Published: October 2008

Several of the existing pore pressure estimation methods are based on establishing a normal compaction trend curve with depth. The rationale is that as fine grained sediments are buried with depth the increase in overburden stress compact the sediments therefrom the normal compaction curve can be developed. Common methods using a normal compaction trend as the basis is the equivalent depth method, or the Eaton ratio method which uses sonic, density or resistivity logs as inputs. When fluid overpressure develops caused by other sources than mechanical compaction, such as fluid mechanical entrapment, rock molecular transformation, migration or hydrocarbon generation, Bowers method can be applied. Bowers extended the above mentioned methods to calculate over pressure where sediments are unloaded during pore pressure build up.

However, these methods require that you establish a normal compaction curve for sediments without overpressure. In many onshore basins, such as the Mid-Alberta basin, which has thick eroded sections and therefore the sediments are over-consolidated, it is not possible to establish a normal compaction curve. To be able to predict the pore pressure in overpressured Mid-Alberta shales, we developed a pore pressure prediction method based on over-consolidation theory. We tested the method with sonic logs and the method gave promising results for establishing pore pressures in the over-consolidated Alberta basin.
Prediction of Production in Oil Reservoirs by Considering Change in Number of Production Wells
Authors: Guan Yanyan , Niu Yanliang , Han Dejin , Zhou Xisheng , Li Kewen
Published: October 2008

Decline curve analysis (DCA) is a traditional method for production prediction, which is still being used today because of its simplicity. However, DCA methods have limitations in many cases when applied to entire reservoirs. Such cases include variation in production conditions and change in the number of injection and production wells. In this study, we focused on the latter problem, change in the number of production wells. Obviously, there would be a significant oil production boost during a specific time period if more oil wells are drilled. The traditional DCA approach cannot match the increase in oil production due to the increase in the number of oil production wells. We have developed a method to match and predict the oil production of entire reservoirs by considering the change in the number of production wells. The main idea of this new approach came from the concept of effective wells. We applied this new approach in several sandstone oil reservoirs with different permeabilities. Satisfactory results were obtained. Comparison with the existing models (exponential, hyperbolic model, and harmonic models) was made and the results showed the new approach had the best fit to the production history in the cases studied.
Impact of Water-Based Drill-In Fluids on Solids Invasion and Damage Characteristics
Authors: Al-Yami A. S. , Nasr-El-Din H. A. , Al-Shafei M. , Bataweel M. A.
Published: October 2008

Drilling the U-formation (shale and sandstone) in Saudi Arabia requires high mud density (± 95 pcf) to mechanically stabilize the shale and balance the reservoir pressure. Two fluids have been used to drill this formation: KCl/ BaSO4/ CaCO3 and potassium formate/CaCO3. Barite is added in the first fluid with CaCO3 to reduce the amount of solids needed to formulate the drill-in fluid. However, BaSO4 is insoluble in acids and requires chelating agents (DTPA) to remove it from the formation. Formate drill-in fluids with low solid content can be used, but they are expensive and corrosive at pH values less than 7-8. A third drilling fluid was recently developed by Al-Yami et al (2007) to overcome some of the problems associated with these two systems.

The objective of this study is to determine solids invasion and damage characteristic for the three fluids. Core flood tests were conducted using reservoir cores at bottom hole conditions. Then the cores were examined by ESEM analysis to determine solids invasion, and characteristics of damage.

The three drilling fluids examined did damage the core plugs either through external, internal filter cake, or both. The ESEM images showed that the least damage and minimum solids invasion occurred when Mn3O4 water-based drill-in fluid use tested. The highest damage was observed when barite/CaCO3 mud was examined. This was followed by the potassium formate drill-in fluids. Kaolinite booklets were not attacked by the filtrate of the three drill-in-fluids examined. The damage noted with potassium formate mud was due to incompatibility of mud filtrate with the formation brine where potassium chloride crystals was noted in the core.
Coalbed Discontinuity Effects on the Production of Degasification Boreholes and on Emissions During Longwall Mining
Authors: Karacan C. Ö. , Goodman G. V. R.
Published: October 2008

Geological discontinues in the coalbed, such as faults, sandstone channels, permeability facies, lithotype changes, and large scale partings in the coal seam, can cause intermittent production problems or produce unexpected amounts of water or gas from degasification boreholes. These discontinuities not only can impact methane emissions into the mine workings, especially if they hinder proper and effective degasification of the coalbed but may act as conduits for methane flow from gassy strata into advancing mine workings. The effects of these discontinuities are still under debate by mining and gas production experts. This study presents a numerical investigation using reservoir simulations of the effects of partings and permeability facies and lithotype changes on the production performances of vertical and horizontal degasification boreholes, as well as the emissions during longwall operations.

In this work, the grid block was designed in a multi-layer 3-D structure which enabled spatial descriptions of the geometries and properties of the discontinuities within the coal seam. The studied coal seam discontinuities and their properties were distributed arbitrarily within the model. Production was simulated by vertical and horizontal boreholes. Degasification boreholes operated two years prior to start of the mining.

The results of this numerical study show that in coal seams with major heterogeneities and discontinuties, the geometry and location of the boreholes are important for improved gas production. These considerations are also important for controlling methane and water inflow into the working environment during longwall mining.
Water-Production Diagnosis Using Transient Test With Multiphase Flowmeter
Authors: Gasbarri S. , Basabe L. , Fariña A. , Trinidad F. , Sosa G. , Azuaje E.
Published: October 2008

Accurate determination of oil, water, and gas production rates is an important element of oilfield management and optimization. Multiphase flow meters (MPFM) are being accepted more and more for well testing, reservoir management, production allocation, production monitoring, and fiscal metering. In addition to common MPFM applications, this study shows how a multiphase flow meter may be used as a valuable tool to evaluate water production problems of the well by imposing transient flowing conditions to the well and tracking characteristic parameters such as flowrates, water cut and gas oil ratio with the equipment during the test.

Representative curves are shown in this study in order to identify some common wellbore problems associated with water conformance. The curves were obtained through numerical reservoir simulation using a number of cases related to the most important problems: water channeling in stratified formations, mechanical wellbore integrity, water conning, and oil-water contact advance.

The flowrate at the well should be shortened to a half of the current flowrate with a choke for several hours then, the dimensionless pattern curves of the water cut and gas oil ratio gathered in this study should be matched with the measurement of the MPFM on site in order to characterize the nature of the water problem.

This application represents a new tool used to identify the sources of water production. The tool is easy and quick to apply, and complements other analytical techniques being used like diagnostics plots based on production history, water-oil ratio performance and production logs. All of them are used to differentiate between the different mechanisms of water invasion, so that an appropriate treatment may be selected to control undesirable water production.
Acid Emulsified in Xylene: A Cost-Effective Treatment to Remove Asphaltene Deposition and Enhance Well Productivity
Authors: Fatah W. Abdel , Nasr-El-Din H. A.
Published: October 2008

Emulsified acid (30 vol% diesel and 70 vol% HCl acid) has been used in both matrix and acid fracturing treatments. Injection the acid in this form has several advantages including: retard the reaction of the acid with rock, reduce corrosion to well tubulars and minimize acid additives. However, using this acid to treat wells with asphaltene deposition will require removing asphaltene first using a suitable aromatic-based solvent, and then using a matrix acid treatment. This additional step will increase the cost and time needed to execute acid treatments.

To remove asphaltene deposition and enhance well productivity, hydrochloric acid was emulsified in xylene. Xylene was the external phase, and was used to dissolve asphaltenes. Then the acid, present as the dispersed phase dissolved the carbonate rock, thus enhancing well productivity. Extensive lab work was performed to ensure the stability of acid-in-xylene emulsion and measure its apparent viscosity. Acid concentration was 15 wt% HCl, the acid volume fraction was 0.7 and the balance was xylene. All tests were conducted at room temperature and 160°F.

The stability and apparent viscosity of emulsified acids were found to be a function of the type of hydrocarbon phase used to prepare emulsified acid. Emulsified acids prepared with xylene had a lower apparent viscosity and were stable for relatively shorter period of times. A matrix acid treatment was that based on xylene emulsified acid was applied in four wells without encountering operational problems. Unlike previous matrix acid treatments using regular acid, the four wells responded to the new treatment, without increasing water-cut, except in one well which was wet before the treatment.
Wettability Alteration To Increase Deliverability of Gas-Storage Wells
Authors: Xie X. , Liu Y. , Sharma M. , Weiss W. W.
Published: October 2008

More than 17,000 gas storage wells in the U.S. annually lose about 5% of their deliverability (i.e., injectivity and productivity). A common problem is believed to be water blockage around the wellbore. For strongly water-wet gas reservoirs, capillary forces promote the retention of water in pore spaces, which in turn curtails the flow of gas in and out of the storage wells. This paper reports the use of surfactants to change the water-wetness of a gas reservoir in order to increase gas deliverability. Surfactant treatment can alter the strong water-wetness of the rock around wellbore to a neutral-wet condition, thus reducing water retention and improving gas flow. The objective of this laboratory study was to demonstrate improved gas deliverability by altering the wettability of core samples with proper chemicals from strongly water-wet to neutral-wet. Seven chemicals were screened for efficacy of changing the wettability of strongly water-wet glass capillary tubes. Following the capillary rise tests two surfactants were selected for the core sample experiments. Rock samples and water from the St. Peter formation, a sandstone aquifer gas storage reservoir, have been tested. Spontaneous imbibition tests of reservoir cores were used to evaluate the wettability before and after surfactant treatment. The cores were saturated with either initial formation water or surfactant solutions were displaced with wet nitrogen gas. Gas relative permeability was measured. A decrease in the trapped water saturation caused an increase in gas permeability. This increase indicated improved gas deliverability that resulted from wettability alteration away from very strongly water-wet conditions. Laboratory results demonstrated that reducing the water-wetness increased permeability and improved the deliverability of gas from the cores. This technique provides a cost-effective method to increase gas deliverability in fields where water blocking is a major factor in decreased gas deliverability.
Evaluation of Two-Phase Flow Correlations and Mechanistic Models for Pipelines at Inclined Downward Flow
Authors: Yuan H. , Zhou D.
Published: October 2008

In this study, two-phase flow pressure prediction correlations and mechanistic models for pipelines commonly used in petroleum industry are evaluated against experimental data.

Downward two-phase flow occurs in hilly terrain pipelines, in steam injection wells, as well as in offshore oil and gas production systems. During pipeline design and simulation, experimental data are usually unavailable to calibrate against correlations and models. Sometimes it is difficult to determine which correlation or model to use in predicting pressure gradient in inclined downward flow since there are very a few correlations and models were developed specifically for downward pipe flow.

Experimental data used in this study are from a published paper (Kokal and Stanislav, 1989). Experimental data were gathered from 1-inch, 2-inch and 3-inch pipes with seven inclination angles. Oil and air were used as testing fluids. During the experiment, superficial liquid velocities range from 1.2 to 10 ft/s and superficial gas velocities range from 0.76 to 85 ft/s. The experimental results were plotted as pressure gradient vs. superficial gas velocity for each superficial liquid velocity.

Beggs-Brill, Dukler-Eaton-Flanigan, Dukler-Flanigan, Dukler, Eaton, Eaton-Flanigan correlations and Xiao mechanistic model are evaluated in this study.

The results of this study can be used as guidelines in choosing two-phase flow pressure prediction correlations and models in designing and analyzing downward two-phase flow pipelines.
An Unconventional But Definitive Analysis of a Field's Production Improvement
Authors: Schulz R. , Harms L.
Published: October 2008

Production results from capital or operational investments are often difficult to identify and quantify due to a field's decline and other factors that introduce noise in the data. This was the case with a series of operational improvements in a tight gas field of 80 mostly marginal wells located in South Texas, a mature producing area similar to Appalachia's assets.

However, approaching the problem with a set of statistical tools not commonly applied in the upstream oil and gas industry yielded a definitive answer to the success of the investments. Normal distribution analysis and hypothesis testing are well-grounded academically and have been applied in globally competitive manufacturing operations for decades, but are not common tools in the petroleum engineer's toolkit. Nevertheless, today's low-cost, easy to use statistical software facilitates an easy transition to the oil and gas industry.

The results from using the above methods eliminated uncertainty about the success of the operational changes, which was questionable using traditional production and decline curve analysis. In addition to proving the success of the investments, the model also points to the viability of improvement by reducing production variation as opposed to looking exclusively for production increases.

These statistical methods are especially significant for analyzing data, particularly in marginal, mature producing areas. Moreover, the analytical methods can yield definitive answers to a number of oil and gas engineering, operation, production and financial questions. Hence, one will be able to take the material provided and leverage it to help in a number of potential applications.
Simulation of Gel Damage on Fracture Fluid Cleanup and Long-Term Recovery in Tight Gas Reservoirs
Authors: Wang John Yilin , Holditch Stephen A. , McVay Duane A.
Published: October 2008

One major source of new natural gas supplies for the world will be gas from low permeability reservoirs. Currently, natural gas from tight sandstones, carbonates, coal seams and shales account for over 25% of the annual gas production in the United States. Global production of gas from similar reservoirs world wide will be expected in the next few decades. For such reservoirs, the wells have to be successfully fracture treated to produce at commercial gas flow rates.

In many situations, the created length was probably achieved, and maybe even the propped length was achieved. However, due to insufficient proppant concentration, or insufficient proppant transport, or the use of the wrong propping agent, or a fracture fluid that does not break to a low viscosity fluid, the effective fracture length is significantly less than the designed length and does not provide optimal production results.

It is our opinion that insufficient fracture fluid cleanup is the primary cause of poor results when the optimal effective fracture length is not achieved. Fracture fluid cleanup is affected by gel damage, which includes the static yield stress, the flowing yield stress, the amount of polymer residue in the fracture after the fracture closes, and the amount of polymer that forms a filter cake on the walls of the fracture. In addition, there are other issues such as proppant crushing and non-Darcy flow effects that also affect fracture fluid cleanup.

In this research, we have used a reservoir simulator to model how polymers in the fracture affect fracture fluid cleanup. We have incorporated mathematical expressions for static yield stress. We have included the effects of proppant crushing, gel residue plugging and the formation of a filter cake on the clean up behavior and the resulting gas flow rates. With our model, we are able to simulate many of the problems we observe in field data and problems documented in the petroleum literature. Even though real solutions to these problems still remain to be developed, we think we can explain the issues behind most fracture fluid cleanup problems and offer a few ideas on what can be done to solve them.
Hydraulic-Fracture Modeling With Bedding Plane Interfacial Slip
Authors: Gu H. , Siebrits E. , Sabourov A.
Published: October 2008

Interfacial slip is one of the mechanisms that can alter the growth of a hydraulic fracture when it encounters weak planes or natural fractures. In shallow or over-pressured formations, interfacial slip between formation bedding planes is possible when the effective normal stress on the bedding interfaces is low. Fracture height growth could be hindered or stopped by interfacial slip when a vertical hydraulic fracture propagates in such formations.

An interfacial slip model has been developed and implemented in a pseudo-three-dimensional (P3D) hydraulic fracture simulator. In the model, the width deformation of a fracture with interfacial slip is calculated using a displacement discontinuity (DD) method. An interface crossing criterion (Renshaw and Pollard, 1995) is used to determine if the hydraulic fracture crosses a particular bedding plane during height growth. Two interface properties of a coefficient of friction and a shear stiffness, required by the model, are defined, and the application of the Renshaw and Pollard criterion and the DD method is explained.

The direct effect of bedding plane interfacial slip is on fracture height growth and width deformation, but because of the coupling effects in hydraulic fracturing, the entire fracture geometry and fracture pressure will be affected. The simulation results based on the interfacial slip model are compared with the fracture height and pressure measured from a fracturing treatment with tracer logs, as well as with the fracture length inferred from post-fracturing production analysis. In this field case, a T-shaped fracture was considered likely to be generated based on the observed field measurements, and there is a good match in fracture height, length, and pressure between the simulation results using the interfacial slip model and the measured data.

A hydraulic fracturing simulator that includes an interfacial slip model can be used to better simulate fracturing in coalbed methane and other formations where slip between bedding planes is possible, and to improve fracture design and evaluation for such treatments.
Applying Science and Best Practices to Increase Production and Optimize Economics in a West Texas Gas Field—A Canyon Sand Case Study
Authors: Blackwood Kelly , Williamson Kaylene , Palisch Terry , Chapman Mark , Vincent Mike
Published: October 2008

Hydraulic fracturing is the most popular and successful stimulation treatment in the petroleum industry. Fracturing technology has opened numerous unconventional hydrocarbon frontiers that, were it not for this process, would otherwise be uneconomic to develop. However, designing the optimal hydraulic fracture is anything but an exact science. Our industry relies on many simplifying assumptions that assist in making expedient decisions, but can prevent reaching a truly optimized treatment.

Additionally, the optimal hydraulic fracture treatment rests in the eye of the beholder. Given the cyclic nature of the industry, for many companies the optimization process has become synonymous with "getting the same results at lower cost." However, to successfully optimize a fracture treatment, one should also consider design modifications which increase production, evaluating the costs and benefits of each alternative. Using economic criteria appropriate for the company goals, this process can yield an economically optimized fracture design. Unfortunately, even this method typically fails to provide an industry-wide "best practices" approach. What is deemed optimal for one company may not be optimal for another, as each company may have different financial and economic goals.

This paper will outline the approach that one Canyon Sand operator used to apply sound science and best practices to meet their financial goals by altering the hydraulic fracture design. Initial well productivity has been improved over 60% with these modifications. Since the design changes required an incremental investment, the authors will present several economic analyses of the outcome. It will also be shown that depending on a company's specific evaluation criteria (NPV, Cost Target, EUR, etc.), these design changes may or may not reach individual economic hurdles and be incorporated in future work.

Readers of this paper will see how specific design changes increased production and understand the process required to truly optimize production using economic criteria.
Miscible Interaction Between Matrix and Fracture: A Visualization and Simulation Study
Authors: Er V. , Babadagli T.
Published: October 2008

CO2 injection has been commonly applied in naturally fractured reservoirs (NFR) for EOR purpose. The matrix part of those types of reservoirs could be potentially a good storage medium as well. Understanding the matrix-fracture interaction during this process and the dynamics of the flow in this dual porosity system requires visual analyses. We mimicked fully miscible CO2 injection in NFRs using 2-D models with a single fracture and oil (solute) – hydrocarbon solvent pairs. The focus was on the visual pore scale analysis of miscibility interaction, breakthrough of solvent through fracture, transfer between matrix and fracture, and the dynamics of miscible displacement inside the matrix.

First, matrix-fracture interaction was intensively studied using 2D glass bead models experimentally. The model was prepared using acrylic sheets and glass beads saturated with oil as a porous media while a narrow gap of 1 mm size containing filter paper serving as a fracture. The first contact miscible solvent (pentane) was injected into the fracture and the flow distribution was monitored using an image acquisition and processing system. The produced solvent and solute were continuously analyzed for compositional study. The effects of several parameters such as flow rate, viscosity ratio (oil/solvent), and gravity were studied. Next, the process was modeled numerically using a commercial compositional simulator and the saturation distribution in the matrix was matched to experimental data. The key parameters in the matching process were effective diffusion and longitudinal and transverse dispersion coefficients. These coefficients were assigned into grid blocks in the model according to their position to the fracture.
Relative-Permeability Modifiers Used in Conjunction With Hydraulic Fracturing Can Increase Hydrocarbon Production and Reduce Water Production
Authors: Curtice R. J. , Carlson C. , Stahl M.
Published: October 2008

The demand for hydrocarbon production increases each year as world population continues to grow and more energy is consumed. This increasing demand has caused the oil and gas industry not only to develop new technology but also to develop reservoirs that were previously overlooked. These marginal reservoirs were deemed uneconomic, primarily because they typically existed on the outer fringes of known reservoirs or the potential productive formations were subject to excessive water production.

Many of these previously-overlooked reservoirs need to be hydraulically stimulated to make them economic. When using fracture stimulation to complete a wellbore in marginal reservoirs, it is not uncommon to produce excessive amounts of water. This excessive water production can come from the producing formation, water-wet formations which bound the producing interval, or lack of sufficient barriers between the productive zone and nearby water-bearing zones.

Because wells drilled in these marginal reservoirs are economically borderline, any additional water production resulting from the completion of these wells jeopardizes the already questionable economics. Consequently, the operators run a much higher economic risk when completing wells in these marginal reservoirs.

This paper describes a case history using a relative permeability modifier (RPM) incorporated into a hydraulic fracture stimulation treatment to reduce excessive water production. By implementing this process, it gives the operator an additional tool to increase the chances of producing formations containing hydrocarbons which had been previously overlooked. Therefore, this process can help reduce the higher economic risk of completing marginal reservoirs. Incorporating this technique into a fracture stimulation treatment resulted in the best producing well in the study area.