bluuebunny/crossref_metadata_2025 huggingface dataset:
A context-dependent combination of Wnt receptors controls axis elongation and leg development in a short germ insect
Authors: Beermann Anke , Prühs Romy , Lutz Rebekka , Schröder Reinhard
Published: June 2011

Short germ embryos elongate their primary body axis by consecutively adding segments from a posteriorly located growth zone. Wnt signalling is required for axis elongation in short germ arthropods, including Tribolium castaneum, but the precise functions of the different Wnt receptors involved in this process are unclear. We analysed the individual and combinatorial functions of the three Wnt receptors, Frizzled-1 (Tc-Fz1), Frizzled-2 (Tc-Fz2) and Frizzled-4 (Tc-Fz4), and their co-receptor Arrow (Tc-Arr) in the beetle Tribolium. Knockdown of gene function and expression analyses revealed that Frizzled-dependent Wnt signalling occurs anteriorly in the growth zone in the presegmental region (PSR). We show that simultaneous functional knockdown of the Wnt receptors Tc-fz1 and Tc-fz2 via RNAi resulted in collapse of the growth zone and impairment of embryonic axis elongation. Although posterior cells of the growth zone were not completely abolished, Wnt signalling within the PSR controls axial elongation at the level of pair-rule patterning, Wnt5 signalling and FGF signalling. These results identify the PSR in Tribolium as an integral tissue required for the axial elongation process, reminiscent of the presomitic mesoderm in vertebrates. Knockdown of Tc-fz1 alone interfered with the formation of the proximo-distal and the dorso-ventral axes during leg development, whereas no effect was observed with single Tc-fz2 or Tc-fz4 RNAi knockdowns. We identify Tc-Arr as an obligatory Wnt co-receptor for axis elongation, leg distalisation and segmentation. We discuss how Wnt signalling is regulated at the receptor and co-receptor levels in a dose-dependent fashion.
Evidence that venous hypertension causes stasis dermatitis
Authors: Sippel K , Mayer D , Ballmer B , Dragieva G , Läuchli S , French L E , Hafner J
Published: June 2011

A clinical model to examine the hypothesis that venous hypertension of the lower leg per se can cause lower leg stasis dermatitis is described. To prove this concept, we retrospectively studied a consecutive series of 38 patients with lower leg dermatitis who underwent phlebological examination at our consultation over a period of four years. Among those patients who had an insufficiency of the superficial veins only, without insufficiency of the deep veins, 22 had undergone patch testing to common allergens in phlebology. We found 10 patients with a stasis dermatitis of the lower leg and an incompetent great saphenous vein, six of whom had no detectable contact sensitization at all and another four exclusively to phlebologically irrelevant substances, e.g. nickel, cobalt, chromate or epoxid resin. All these 10 patients showed long saphenous vein incompetence from the groin to the medial aspect of the leg. All were operated by classical flush ligation and saphenectomy. Lower leg dermatitis healed in all 10 patients within 8–12 weeks and no recurrence was observed (1 year follow-up). These results support clinical experience that venous hypertension alone indeed can cause lower leg dermatitis.
Severe diffuse hypoplasia of the aorta associated with multiple vascular abnormalities
Authors: Grebeldinger Slobodan P , Balj Svetlana S , Ađić Oto
Published: June 2011

Hypoplasia of the thoracic and abdominal aorta is an extremely rare vascular pathology. The most common clinical manifestation is severe uncontrolled hypertension in adolescents and young adults. Medical treatment alone can decrease blood pressure, but often very high doses of antihypertensive drugs are needed. When hypertension is refractory to the antihypertensive medications, surgical revascularization is considered as the treatment of choice. We report the case of a severe and diffuse hypoplasia of the aorta, beginning with the aortic isthmus, to the aortic bifurcation, associated with an aberrant celiac trunk and superior mesenteric artery, and with other multiple vascular abnormalities. Unlikely, the only manifestation of this extensive vascular malformation was medicamentously controllable hypertension. To our knowledge, this severe vascular anomaly, with such a minimal clinical manifestation, has not been previously described in the English literature.
Endovascular infrarenal aneurysm repair in patients with horseshoe kidneys: case series and literature review
Authors: Chan Y C , Qing K X , Ting A C , Cheng S W
Published: June 2011

Horseshoe kidney may cause technical and access problems during open aortic aneurysm repair. The aim of this study is to report two cases from our institution and to review the world's literature on successful endovascular infrarenal aneurysm repair in patients with horseshoe kidneys. A retrospective review of a prospectively entered departmental computerized database was performed for the two patients from our institution. Articles were searched electronically from PubMed and Medline, using the terms ‘horseshoe kidney’ and ‘aneurysm’. Endovascular cases were reviewed from the world's literature. In addition to the two patients from our institution, there were 19 patients with infrarenal aneurysms and horseshoe kidneys in published literature who underwent successful endovascular aneurysm repair. The occlusion of lower-pole or accessory renal arteries does not seem to cause significant endoleak or renal impairment in the long run. In conclusion, our experience and current literature seem to suggest that endovascular repair of infrarenal aortic aneurysms for patients with horseshoe kidneys is safe. Renal impairment will depend on the area of kidney perfused by the accessory renal arteries. The endovascular treatment option is less invasive than open repair, and circumvents the problem of difficult exposure, especially in those patients with significant co-morbidity.
Abdominal aortic endograft proximal collapse resulting in aortic aneurysm rupture
Authors: Moulakakis Konstantinos G , Dalainas Ilias , Giannakopoulos Triantafillos G , Avgerinos Efthimios , Liapis Christos D
Published: June 2011

An 82-year-old man was transferred to our emergency department due to acute abdominal pain. He had undergone an endovascular abdominal aortic aneurysm repair (EVAR) six years ago. An intravenous contrast-enhanced abdominal computed tomography revealed the rupture of the abdominal aortic aneurysm (AAA) with a large retroperitoneal hematoma. A Talent (Medtronic, Santa Rosa, CA, USA) modular bifurcated endoprosthesis had vertically collapsed approximately 7 cm after losing its infrarenal fixation. As a result, it led to the repressurization of the aneurysm sac and rupture. The patient was successfully treated by placing three Talent (Medtronic) aortic cuffs. To our knowledge, this is the first reported case of endograft collapse that has manifested with aortic aneurysm rupture. Although they are gradually declining, considerable rates of complications create the ‘Achilles’ heel' of endovascular repair of AAAs. A lifelong follow-up strategy for patients treated for AAA with EVAR is essential for the early detection and treatment of complications of the procedure.
Endoscopic type 2 endoleak repair following endovascular aortic aneurysm repair: acute results and follow-up experience
Authors: Linsen Matteus A M , Daniels Lidewine , Cuesta Miguel A , Wisselink Willem
Published: June 2011

The purpose of this study was to evaluate immediate and long-term results of endoscopic type 2 endoleak repair (EER) following endovascular abdominal aortic aneurysm repair. The basic methods include a retrospective review of electronic and paper medical records of patients admitted or referred to our institution for EER. Between July 1999 and October 2007, eight consecutive patients underwent EER. Mean operative time was 190 (104–355) min. One patient died preoperatively, due to profuse venous bleeding . One procedure was redone due to a missed pair of lumbar arteries. Mean hospital stay was five days (2–10). During mean follow-up, 50 months (29–91), one patient required additional coil embolization for a persistent type 2 endoleak. Four patients were diagnosed with a type 1 and one with a type 3 endoleak; three of these patients required an additional procedure. In conclusion, in this small series EER proved not to be beneficial.
Relationship of CYP21A2 genotype and serum 17-hydroxyprogesterone and cortisol levels in a large cohort of Italian children with premature pubarche
Authors: Ghizzoni Lucia , Cappa Marco , Vottero Alessandra , Ubertini Graziamaria , Carta Daniela , Di Iorgi Natascia , Gasco Valentina , Marchesi Maddalena , Raggi Vera , Ibba Anastasia , Napoli Flavia , Massimi Arianna , Maghnie Mohamad , Loche Sandro , Porzio Ottavia
Published: June 2011

Objective

Premature pubarche (PP) is the most frequent sign of nonclassic congenital adrenal hyperplasia (NCCAH) due to 21-hydroxylase deficiency in childhood. The aim of this study was to assess the relationship between the CYP21A2 genotype and baseline and ACTH-stimulated 17-hydroxyprogesterone (17-OHP) and cortisol serum levels in patients presenting with PP.

Patients and methods

A total of 152 Italian children with PP were studied. Baseline and ACTH-stimulated 17-OHP and cortisol serum levels were measured and CYP21A2 gene was genotyped in all subjects.

Results

Baseline and ACTH-stimulated serum 17-OHP levels were significantly higher in NCCAH patients than in both heterozygotes and children with idiopathic PP (IPP). Of the patient population, four NCCAH patients (7.3%) exhibited baseline 17-OHP values <2 ng/ml (6 nmol/l). An ACTH-stimulated 17-OHP cutoff level of 14 ng/ml (42 nmol/l) identified by the receiver-operating characteristics curves showed the best sensitivity (90.9%) and specificity (100%) in distinguishing NCCAH patients. This value, while correctly identifying all unaffected children, missed 9% of affected individuals. Cortisol response to ACTH stimulation was <18.2 μg/dl (500 nmol/l) in 14 NCCAH patients (28%) and none of the heterozygotes or IPP children. Among the 55 NCCAH patients, 54.5% were homozygous for mild CYP21A2 mutations, 41.8% were compound heterozygotes for one mild and one severe CYP21A2 gene mutations, and 3.6% had two severe CYP21A2 gene mutations.

Conclusion

In children with PP, baseline 17-OHP levels are not useful to rule out the diagnosis of NCCAH, which is accomplished by means of ACTH testing only. The different percentages of severe and mild CYP21A2 gene mutations found in PP children compared with adult NCCAH patients is an indirect evidence that the enzyme defect is under-diagnosed in childhood, and it might not lead to the development of hyperandrogenic symptoms in adulthood. Stress-dose glucocorticoids should be considered in patients with suboptimal cortisol response to ACTH stimulation.
Low prevalence of hypopituitarism after traumatic brain injury: a multicenter study
Authors: Kokshoorn N E , Smit J W A , Nieuwlaat W A , Tiemensma J , Bisschop P H , Groote Veldman R , Roelfsema F , Franken A A M , Wassenaar M J E , Biermasz N R , Romijn J A , Pereira A M
Published: June 2011

Objective

Hypopituitarism after traumatic brain injury (TBI) is considered to be a prevalent condition. However, prevalence rates differ considerably among reported studies, due to differences in definitions, endocrine assessments of hypopituitarism, and confounding factors, such as timing of evaluation and the severity of the trauma.

Aim

To evaluate the prevalence of hypopituitarism in a large cohort of TBI patients after long-term follow-up using a standardized endocrine evaluation.

Study design

Cross-sectional study.

Patients and methods

We included 112 patients with TBI, hospitalized for at least 3 days and duration of follow-up >1 year after TBI from five (neurosurgical) referral centers. Evaluation of pituitary function included fasting morning hormone measurements and insulin tolerance test (n=90) or, when contraindicated, ACTH stimulation and/or CRH stimulation tests and a GH releasing hormone–arginine test (n=22). Clinical evaluation included quality of life questionnaires.

Results

We studied 112 patients (75 males), with median age 48 years and mean body mass index (BMI) 26.7±4.8 kg/m2. Mean duration of hospitalization was 11 (3–105), and 33% of the patients had a severe trauma (Glasgow Coma Scale <9) after TBI. The mean duration of follow-up was 4 (1–12) years.

Hypopituitarism was diagnosed in 5.4% (6/112) of patients: severe GH deficiency (n=3), hypogonadism (n=1), adrenal insufficiency (n=2). Patients diagnosed with pituitary insufficiency had significantly higher BMI (P=0.002).

Conclusion

In this study, the prevalence of hypopituitarism during long-term follow-up after TBI was low. Prospective studies are urgently needed to find reliable predictive tools for the identification of patients with a significant pre-test likelihood for hypopituitarism after TBI.
Low-Dose, High-Frequency CPR Training Improves Skill Retention of In-Hospital Pediatric Providers
Authors: Sutton Robert M. , Niles Dana , Meaney Peter A. , Aplenc Richard , French Benjamin , Abella Benjamin S. , Lengetti Evelyn L. , Berg Robert A. , Helfaer Mark A. , Nadkarni Vinay
Published: June 2011

OBJECTIVE:

To investigate the effectiveness of brief bedside cardiopulmonary resuscitation (CPR) training to improve the skill retention of hospital-based pediatric providers. We hypothesized that a low-dose, high-frequency training program (booster training) would improve CPR skill retention.

PATIENTS AND METHODS:

CPR recording/feedback defibrillators were used to evaluate CPR quality during simulated arrest. Basic life support–certified, hospital-based providers were randomly assigned to 1 of 4 study arms: (1) instructor-only training; (2) automated defibrillator feedback only; (3) instructor training combined with automated feedback; and (4) control (no structured training). Each session (time: 0, 1, 3, and 6 months after training) consisted of a pretraining evaluation (60 seconds), booster training (120 seconds), and a posttraining evaluation (60 seconds). Excellent CPR was defined as chest compression (CC) depth ≥ one-third anterior-posterior chest depth, rate ≥ 90 and ≤120 CC per minute, ≤20% of CCs with incomplete release (>2500 g), and no flow fraction ≤ 0.30.

MEASUREMENTS AND MAIN RESULTS:

Eighty-nine providers were randomly assigned; 74 (83%) completed all sessions. Retention of CPR skills was 2.3 times (95% confidence interval [CI]: 1.1–4.5; P = .02) more likely after 2 trainings and 2.9 times (95% CI: 1.4–6.2; P = .005) more likely after 3 trainings. The automated defibrillator feedback only group had lower retention rates compared with the instructor-only training group (odds ratio: 0.41 [95% CI: 0.17–0.97]; P = .043).

CONCLUSIONS:

Brief bedside booster CPR training improves CPR skill retention. Our data reveal that instructor-led training improves retention compared with automated feedback training alone. Future studies should investigate whether bedside training improves CPR quality during actual pediatric arrests.
Screening for Tuberculosis at an Adult Education Center: Results of a Community-Based Participatory Process
Authors: Wieland Mark L. , Weis Jennifer A. , Olney Marilynn W. , Alemán Marty , Sullivan Susan , Millington Kendra , O'Hara Connie , Nigon Julie A. , Sia Irene G.
Published: June 2011

Objectives. We used a community-based participatory research (CBPR) approach to plan and implement free TB skin testing at an adult education center to determine the efficacy of CBPR with voluntary tuberculosis (TB) screening and the prevalence of TB infection among immigrant and refugee populations.

Methods. We formed a CBPR partnership to address TB screening at an adult education center that serves a large immigrant and refugee population in Rochester, Minnesota. We conducted focus groups involving educators, health providers, and students of the education center, and used this input to implement TB education and TB skin testing among the center's students.

Results. A total of 259 adult learners volunteered to be skin-tested in April 2009; 48 (18.5%) had positive TB skin tests.

Conclusions. Our results imply that TB skin testing at adult education centers that serve large foreign-born populations may be effective. Our findings also show that a participatory process may enhance the willingness of foreign-born persons to participate in TB skin-testing efforts.
Pregnant Women's and Community Health Workers' Perceptions of Root Causes of Malnutrition Among Infants and Young Children in the Slums of Dhaka, Bangladesh
Authors: Goudet Sophie M. , Faiz Sabina , Bogin Barry A. , Griffiths Paula L.
Published: June 2011

Research in Bangladesh shows that malnutrition among infants and young children is most severe in urban slums. We examined the root causes of malnutrition as perceived by pregnant women and community health workers. We conducted 10 focus group discussions in the slums of Dhaka in 2008 and 2009. Participants accurately perceived inappropriate care, inappropriate environment, inappropriate food, and flooding to be major causes. Recurrent flooding has not traditionally been identified by experts as a cause of malnutrition. We recommend further research to address the nutritional risks flooding creates for vulnerable slum populations.
Study and Application of High Density Acid in HPHT Deep Well
Authors: Cheng Xingsheng , Li Yongping , Ding Yunhong , Che Mingguang , Zhang Fuxiang , Peng Jianxin
Published: June 2011

The KKY in Tarim oilfield, Western China, is a typical HTHP deep dolomite reservoir (150C, 110Mpa and 6000m). The formation was deeply damaged with the heavy mud, and the matrix acidizing can't effectively eliminate the skin. But the acid fracturing treatment can't be carried because the surface pressure exceeds the working pressure capability of conventional 15,000psi fracturing equipment. To effectively decrease the surface treating pressure, a new high density acid system was developed. Its density is adjustable within the range of 1.25-1.55 g/cm3. Extensive laboratory test was conducted to evaluate its corrosion inhibition capacity, stability, rheological properties etc. The performance of the acid system can totally qualify for the need of high temperature, and effectively lower the surface treating pressure about 25Mpa. The new weighted acid ensured the acid fracturing successfully in KKY reservoir, with the treating pressure up to 94Mpa. And the production increased considerably after the acid fracturing with the high density acid in several wells.
Development and Evaluation of a New Environmentally Acceptable Conformance Sealant
Authors: Bøye Bjørn , Rygg Audhild , Jodal Caroline , Klungland Iselin
Published: June 2011

Water production from hydrocarbon reservoirs is a serious problem in the oil industry. High water cut reduces the economic life of producing wells and costs the industry billions of dollars each year (Curtice and Dalrymple 2004). Throughout the years, several techniques and chemicals have been developed to control undesired water production.

The industry has developed and applied a variety of chemical systems to reduce or shut off unwanted water production. However, most of these chemical systems are often quickly categorized as environmentally damaging according to the environmental laws and regulations, particularly in the North Sea area. This means that service companies must keep pushing technology development in a more environmentally acceptable direction. The recent development of a "green," environmentally acceptable colloidal silica-based sealant system is an example of this process. This sealant system is a two-component system containing a liquid silica and an activator. The system is easy to mix and easy to pump because of its low viscosity. Once it is placed into the water-bearing zone, the system forms a stiff gel to block the flow of water. Any underdisplaced gel left in the tubing can also be easily washed out using coiled tubing (CT). The system can also be viscosified or slurried with polymer or particulates, respectively, if diversion is required in longer intervals with high permeability and pressure contrast. In addition to water and gas shutoff, this new system shows potential in other areas, such as formation consolidation, temporary gel plugs, annular barrier re-establishment, as well as stopping severe losses while drilling and recompleting.

The gel-setting time can be tailored for a wide temperature range from 20 to 150°C by varying the concentration of the activator. Extensive laboratory research has been performed to develop and qualify this sealant system. Simple, static-sealed tube tests were first run to qualitatively evaluate the gel strength and gelation time. Then, gradually, the formulation was refined and rheological data was measured and collected using a Brookfield viscometer. Further, core-flooding tests were conducted both in sandpack and carbonate cores to determine the effectiveness of the system in blocking water flow.

This paper describes the development of this environmentally acceptable sealant system and the qualification process including laboratory test methods and results.
Soda Ash as Gypsum Dissolver in 8-in. Production Line Case Study Gemsa Field, Gulf of Suez, Egypt
Authors: Riad E. H.
Published: June 2011

Water flooding is the hinge pin for Gemsa Oil Field. Water injection is supplied from shallow water supply wells. Compatibility tests had indicated probable deposition of calcium sulphate scale on surface and subsurface production equipment. Calcium sulphate scale has been recognized to be a major operational problem. The bad consequences of scale formation comprised the contribution to flow restriction thus resulting in oil and gas production decrease. The nature of calcium sulphate scale is very hard and can't be dissolved with known dissolver. Sister companies that has similar problem were always going to the mechanical remover options (1).

Extensive lab and field work was conducted to determine the suitable chemicals to dissolve calcium sulphate scale.

This paper describes the development and field application of chemical treatment to remove scale in an offshore 8" production line in Gemsa oil field. Continuous precipitation of calcium sulphate scale caused partial plugging of the pipeline. This partial plugging created a back pressure on production wells which decreased the productivity. The field production has been decreased to almost one tenth of the normal field production level.

A thorough investigation was conducted to identify the composition and location of the scale, in order to recommend a suitable chemical to remove the scale, and to assess the effectiveness of the treatment method in the field.

Based on extensive lab studies, Soda Ash was tested and applied in production line to remove the scale efficiently; the program was designed taking into consideration the nature of the scale.

The treatment program included three - staged process:

The use of an organic solvent The main treatment (Soda Ash). The post flush stage (15 wt% HCl),

The job results were outstanding, where as

Production increased by about 2,000 BOPD Launcher pressure dropped by about 270 psi. Decrease the back pressure on our producing wells. Additional producing wells into production. Efficient cost /Bbl.
A New Fracturing Design Using Compositional Flow Simulation for Wells with Asphaltene Deposition Problems
Authors: Uetani Takaaki , Nomura Masahiko
Published: June 2011

In the Minami Kuwayama oil field located onshore in Japan, asphaltene deposition problems have been identified not only in the surface facility but also in the reservoir during production. In this study, to understand the mechanism of productivity deterioration due to asphaltene deposition, a numerical simulation study was conducted. An equation of state (EOS) based fluid model was incorporated into a compositional flow simulator, capable of predicting asphaltene deposition behavior in the reservoir. History matching was conducted for the actual production history showing a drastic decline within 6 months. Using the history matched model, several numerical investigations were conducted on the asphaltene deposition damage and productivity enhancement by hydraulic fracturing to provide a guide line for the fracturing design.
First True Tight Gas (<0.1 mD) Horizontal Multiple Fractured Well in the North Sea
Authors: Schrama Erik , Naughton-Rumbo Robin , van der Bas Fred , Norris Mark , Shaoul Josef
Published: June 2011

This paper describes the development of a tight gas reservoir in the Dutch sector of the Southern North Sea, using a horizontal well with 5 hydraulic fractures. The reservoir is tight (average permeability below 0.1 mD) and was discovered in 1986. The first development well was drilled as a long reach horizontal well in 1990, and completed with a cemented liner. The well was perforated and initial production was 0.2 mln Nm3/d after which the well quickly dropped below its liquid loading limit of 0.09 mln Nm3/d. The well was brought back into production 13 years later and produced at a stable rate of 0.07 mln Nm3/d. In 2005 the well was sidetracked using under-balanced drilling in an attempt to intersect natural fractures (Veeken, 2007). The initial production from this sidetrack was 0.1 mln Nm3/d, but this time the well was able to sustain production at 0.07 mln Nm3/d as the tubing head pressure was lower by that time.

To develop this reservoir, the well was sidetracked (overbalanced) in 2008 and completed with a cemented liner. In 2009, 5 hydraulic fractures were placed using a jackup support barge and a specially converted supply vessel. Since December 2009 the well has produced steadily at 0.3-0.4 mln Nm3/day, a (steady-state) production improvement factor of 5-6. This was the first true tight gas (<0.1 mD) development in the North Sea using a horizontal well with multiple fractures. The initial production takes place at constant rate and constant pressure, which suggests that significant cleanup is taking place, either in the fracture or the reservoir or both. An attempt has been made to model this cleanup in a 3D reservoir simulation model.

This paper describes the background of the project, fracture design methodology, operational issues and lessons learned, fracture treatment data analysis, post fracturing production analysis (with over a year of production history) and production forecast. This paper is a valuable case study for operators and contractors involved in offshore fracturing operations in low permeability gas reservoirs.
Determination of Optimum Perforating Strategy in Tight HPHT Gas Reservoirs Based on Modified RP-19B Section 2 and 3 Tests
Authors: Atwood D. , Sultan N. , Humphreys A. , Grove B. , Langseth B.
Published: June 2011

Recent laboratory and field testing enabled Total Exploration and Production Norway (TEPN) to optimize the shaped charge design and gun system used for perforating an appraisal well test in the high pressure high temperature (HPHT) Victoria field, offshore Norway.

The laboratory testing consisted of two different phases; penetration tests under downhole conditions into stressed rock, and a temperature test to evaluate any degradation in shaped charge performance.

Test shots into stressed Nugget and Crab Orchard Sandstone rock targets were used to identify which of the four charge designs being proposed would provide the best downhole penetration performance. Charge D, a 28 gram, deep penetrating, high temperature charge designed for 3.50 inch gun systems, provided the deepest penetration into the stressed rock targets.

The temperature test subjected both the charges and gun system to the high end of the reservoir temperature for the worst case expected time required to run both guns and test string into the wellbore. Results indicated that the heated charges provided penetration performance into steel bars substantially matching unheated charge penetration.

This paper discusses a recommended test methodology to qualify perforators for high temperature wells, and the importance of conducting such a test program in close collaboration with field operations.
Novel Environmentally Friendly Fluids to Remove Carbonate Minerals from Deep Sandstone Formations
Authors: Mahmoud M. A , Nasr-El-Din H. A. , De Wolf C. A.
Published: June 2011

Carbonate minerals are present in sandstone formations. These minerals are either introduced to the formation during drilling/completion operations or naturally present in the rock. There is a need to remove these carbonates to enhance well performance. This especially true if there is a need to use HF-based fluids to prevent the precipitation of calcium and magnesium fluorides.

In this study, we introduced GLDA (L-glutamic acid-N,N-diaceticacid) a new environmentally friendly chelate to remove carbonate minerals from sandstone formations. We also compared its performance with available chelates like EDTA (ethylenediaminetetraaceticacid) and HEDTA (hydroxyethylenediaminetriaceticacid). Berea (5 wt% clays) and Bandera (11 wt% clays) sandstone cores were used in the coreflood experiments. The concentration of the chelates used was 0.6M at pH values of 11 and 4. The coreflood experiments were run at a flow rate of 5 cm3/min and 300°F.

Coreflood experiments showed that at high pH values (pH =11) GLDA, HEDTA, and EDTA were almost the same in increasing the permeability of both Berea and Bandera sandstone cores. GLDA, HEDTA, and EDTA were compatible with Bandera sandstone cores. The weight loss from the core was highest in case of HEDTA and lowest in case of GLDA at pH 11. At pH 4, 0.6M-GLDA performed better than 0.6M HEDTA in the coreflood experiments. The permeability ratio (final/initial) for Bandera sandstone cores was 2 in the case of GLDA and 1.2 in the case of HEDTA at pH of 4, and 300°F. At pH 11, HEDTA, EDTA, and GLDA almost were the same in enhancing the permeability of the Bandera sandstone cores. At pH value of 4, GLDA gave the best results in Berea and Bandera sandstone cores.
Viscoelastic Evaluation of a Surfactant Gel for Hydraulic Fracturing
Authors: Gomaa A. M. , Cawiezel K. E. , Gupta D. V. , Carman P. , Nasr-El-Din H. A.
Published: June 2011

A new viscoelastic surfactant-based fluid was developed as an alternative to conventional fracturing fluids. The surfactant gel structure can be formed by adding a combination of cationic and anionic surfactants to water. This technology enables a clean fluid that can be prepared in fresh water, brines, or even produced waters without requiring biocides. Also, the cationic surfactant in the system functions as a temporary clay control agent or KCl replacement. The objective of this study is to evaluate the proppant suspension ability of the system, and its dependence on total surfactant concentration (TSC), cationic/anionic surfactant ratio (C/A), and temperature.

Elastic and viscous properties (G’ and G") of twelve different formulae were measured using an oscillatory rheometer. Static and dynamic proppant settling tests were conducted at 2- to 4-ppg concentrations. Three proppant types were selected that had the same size, but different densities and shapes.

Based on the experimental results obtained, the apparent viscosity of the surfactant gel was found to be a strong function of the TSC and temperature, while it has a weak dependence on C/A ratio. The viscous regime increased with increasing temperature and increasing TSC, while the elastic regime increased only with increasing C/A ratio. C/A ratio was found to be the primary parameter that affects proppant suspension. Only the formulae that had C/A ratio higher than 1.5 and TSC greater than 30 gpt displayed good proppant suspension properties. For these systems, proppant shape didn't affect the settling velocity. The viscous regime region was not affected by increasing the breaker concentration, but the values of G’ and G" decreased with increasing breaker concentration. Viscosity reduction profile was affected greatly by temperature and TSC, but C/A ratio did not have any significant effect. Results obtained can be used to better design hydraulic fracturing treatments.
Bridging Particle Size Distribution in Drilling Fluid and Formation Damage
Authors: He Wenwu , Stephens Mike
Published: June 2011

It is commonly understood that a reservoir drilling fluid must be compatible with the reservoir rock, both chemically and physically. One important aspect in optimizing drilling fluid is distribution of bridging particle sizes. Appropriate particle sizes can limit fluid loss to the formation and minimize solid plugging into reservoir pores. Reservoir rocks have complicated fluid-flow systems and it is important to understand pore characteristics of the rocks including pore type, size distribution and connectivity; and, secondary changes such as dissolution and fracturing. If inter-particle pores are the dominant fluid-flow channels for the sandstone and pore distribution is relatively homogeneous, a full range of particle-size distribution of bridging material may effectively bridge all pore spaces. But for many types of sandstone, natural dissolution of feldspar, rock fragments, or carbonate material has created oversized pores. Appropriately sized particles should be used to bridge them, and smaller particles should be retained in fluids to bridge smaller pores and to improve filtercake quality. For carbonate rocks, fracturing and/or dissolution may have created large pores or fluid-flow channels. They are usually inhomogeneous in space. Their sizes vary greatly and could be up to centimeter scale. The bridging particle size distribution should be comparable to the inhomogeneous pores or channels, if practical.

Differential pressure between wellbore and formation pore fluid is also a factor which influences bridging size selection. At high differential pressure, relatively large particle sizes may help limit the solids plugging into pore spaces and decrease the effect of filtercake compaction. However, a combination of pore size, fluid property, and filtercake quality considerations are needed to achieve the most effective particle size distribution.
An Innovative Offshore Fracturing Campaign for a Mature Oil Field: Case Study Offshore West Africa
Authors: LeBlanc Gilles , Muryanto Bonifasius , Ducourneau Stephane
Published: June 2011

Many of the offshore oil reservoirs along the West African coast are maturing with substantial reserves still in place; solid technical and operational solutions are required to maximize their value. The field was initially developed in the late 1960's and has since been under water injection and gas lift. The reservoir is composed of laminated sand, silt, and shale sequences, all of varying reservoir quality.

As a result of the widely ranging permeability and poor vertical permeability, hydraulic fracturing was the technology chosen to unlock the remaining reserves. Operationally, "hard rock" hydraulic fracturing is not commonplace in offshore West Africa. Therefore, procuring the proper equipment, materials, and skilled personnel was the one of the biggest challenges. To alleviate the high cost of functioning with a drilling rig, an innovative rig-less setup was devised for a 9 well campaign.

The hydraulic fracturing method employed was conventional multi-zone fracturing using composite bridge plugs. Although very common in onshore, tight gas developments, the challenge was to properly apply it in an offshore project. Milling composite bridge plugs in under-pressured oil wells initially proved to be extremely challenging, while scale deposition made slickline well interventions very problematic.

The project has yielded numerous lessons learned and technical contributions:

▪ While the learning curve was steep, rigless "hard rock" fracturing techniques were successfully applied in offshore West Africa, thus being one of the few examples. This could have direct impacts on the future of the many offshore oil and gas fields. ▪ Consistent successful well interventions with slickline and coiled tubing proved to be the highest risk operation and often the root of most operational problems. ▪ The HSE risks using a floating barge and catenary coiled tubing system are key points which need to be considered when planning a rig-less fracturing campaign.
Effect of Residual Oil Saturation on the Propagation of Regular, Gelled, and In-Situ Gelled Acids inside Carbonate Formations
Authors: Gomaa Ahmed M. , Nasr-El-Din Hisham A.
Published: June 2011

In oil fields, serious difficulties with acid-induced sludge, a major source of well damage, can vary from a viscous, stable emulsion. A chemical analysis of sludge shows that hydrochloric acid (HCl) is present in the sludge structure. Also, Fe(III) ions in HCl formulations can cause a large amount of sludge. Even though ferric ion could not be detected in the oil phase or in the sludge, it induces sludge mainly because it works as a phase-transport catalyst for HCl. Therefore, the objective of this study is to determine the effect of residual oil saturation on the performance of regular, gelled, and in-situ gelled acids, that based on Fe(III) as crosslinker agent, inside the carbonate cores.

A core flood study was conducted using Indiana limestone cores (1.5" diameter & 6" long) at 200 °F. Propagation of the acid and crosslinker (Fe(III)) inside the long cores was examined. Analysis of the CT measurements was used to determine the locations of residual polymer inside the core. Acid injection rate was the main parameters that were investigated in this study.

Experimental results show that there was no compatibility problem between the used oil and the different acid systems. During injection of pre-flushed water, Pressure drop across the core initially increased because of creating oil bank in the zone behind the water. After reaching the maximum value, the pressure drops across the cores decreased by increasing the volume of water injection due to oil displacement. Increasing the injection rate during the pre-flush stage increases the amount of oil remained inside the core. At any injection rate, regular acid required more pore volume to breakthrough from the core that contains residual oil saturation. At 2.5 cm3/min, gelled acid took less volume to breakthrough from the core that contains residual oil saturation. However at injection rate of 10 cm3/min, gelled acid took higher volume to breakthrough from the core that contains residual oil saturation. At 2.5 cm3/min, damage due to gel was higher inside the core that contains residual oil saturation. However at injection rate of 10 cm3/min, damage due to gel was higher inside the core that contains residual oil saturation.
Investigation of Solids Flowback after Hydraulic Fracturing and Remedial Treatments
Authors: Agrawal Amit , Danait Achala , Nanda Jajati
Published: June 2011

One of the major concerns with hydraulic fracturing treatments has been the flowback of proppant and solids at various stages after the treatment. To mitigate this problem, it is necessary to understand the factors causing the proppant to flow back, which can help in the design of successful treatments.

This paper outlines the various analytical techniques used to identify the composition of solids recovered after performing a hydraulic fracturing job in the Middle East region. A laboratory test setup was designed to conduct tests by simulation of downhole conditions. Finally, a treatment was proposed to prevent flowback in future wells to be treated.

Analysis of recovered solids using X-ray diffraction (XRD), particle-size distribution, and high-resolution stereomicroscopy revealed the presence of formation sand, fibers, resin-coated proppant (RCP), non-RCP, and crushed proppant. Proppant flowback was observed in laboratory tests conducted using the same source of RCPs that was used for the job. The RCP packs exhibited poor consolidation after curing for 24 hr at 320°F. However, application of liquid-resin coating (LRC) to these RCPs resulted in well-consolidated proppant packs with high unconfined compressive strength (UCS). This in turn prevented proppant and formation-sand flowback when tested under simulated bottomhole conditions.

The results obtained further confirm the advantages of LRCs compared to conventional RCPs in hydraulic fracturing treatments.
Qualification of Scale Inhibitors for Conventional and Novel Scale Squeeze Applications to Deepwater Subsea Wells: Laboratory Testing to Field Application
Authors: Jordan Myles
Published: June 2011

Control of inorganic scale such as sulfate and carbonate has been possible via inhibitor chemical treatment or modification of the fluids types (i.e. desulfation of injection fluid). The deployment of scale inhibitor treatments via continual injection downhole and to topside process equipment is a common practice as it batch chemical treatments to production wells via the squeeze process.

The paper will outline the inhibitor selection process and field results for three oilfields (1) a conventional squeeze chemical selection study with coreflood and chemical placement evaluation for an application within two south American offshore fields and (2) non conventional batch chemical application for a West African offshore oilfield where scale inhibitor was applied within the fluids used to simulate the well prior to frac pack operation so providing initial scale inhibitor placement prior to initial water breakthrough. This non convention batch treatment eliminated a squeeze to these subsea wells and allowed uninterrupted production of oil until 850,000 bbls to 2,100,000 bbls of produced water was produced from the wells. The delay in applying the first squeeze to these wells allowed the water cut to increase above the relatively low water cut values (<10% BS&W) associated with slow clean up post an aqueous squeeze treatment.

This paper will present with the aid of field data from both fields how the challenges of managing scale forced innovation in terms of when to apply scale inhibitor to deepwater subsea wells within the fields. The paper will demonstrate that scale management while being complex can be controlled and treatment programs optimised with the use of varied monitoring methods and the varied skill of the scale management team members.
Measurement of Breaker Requirements for Concentrated HPG Solutions
Authors: Gdanski Rick , Bryant Jason
Published: June 2011

Fracturing treatments in tight-gas sands often suffer disappointing production results. Conductivity damage caused by immobile gel filtercakes is often cited as a probable damage mechanism. Breaker requirements for reducing the viscosity of filtercakes remain a challenge, particularly at suspected filtercake concentrations of greater than 600 lbm/1,000 gal. Previous studies measured the rheology of non-crosslinked hydroxypropyl guar (HPG) across broad ranges of molecular weight (MW), temperature, concentration, and shear rate. The reported rheology model provided a means to experimentally evaluate breaker requirements to achieve a target uncrosslinked filtercake viscosity. Experiments were conducted to determine kinetics of polymer degradation by simple hydrolysis at temperature and degradation by sodium chlorite and sodium persulfate breakers. Temperatures ranged from 85 to 280°F, while breaker concentrations ranged from 0 to 80 lbm/1,000 gal. HPG concentration was held at 1 lbm/gal of 260 kg/mole HPG. The viscosity profiles during the experiments were matched with the rheology model to infer MW decline profiles and thereby determine the rate laws for reaction with the polymer.

It was found that efficiencies of breakers on breaking backbone linkages of HPG were only 2 to 5%, with the remaining breaker consumption apparently not reducing the molecular weight of the polymer. The rate laws for the breakers were found to be first order in breaker and first order in linkage concentration. The rate laws were used to make projections on the amount of breaker required to reduce concentrated gels to an arbitrary target viscosity.
Advanced Viscoelastic Surfactant Gels for High-Density Completion Brines
Authors: van Zanten Ryan , Ezzat Dodie
Published: June 2011

Viscoelastic surfactant (VES) systems are often used as viscosifiers for solids-free, high-viscosity pills used to control brine losses in production zones after perforation, gravel packing, or frac packs due to their non-damaging characteristics. Polymer gels have relatively higher rock retention values and often damage the invaded zone, so that acidization is required for removal. The VES systems behave as "equilibrium" or "living" polymers and their viscosity can be destroyed by contact with the produced hydrocarbons or with an internal breaker. This can eliminate the need for remedial treatments, greatly reducing operating cost/time and damage to the formation.

Historically, many VES systems have demonstrated limitations in high-density brines. Electrostatic screening generally reduces the viscosity or causes phase separation. Two methods have been found to stabilize VES packages in high-density completion brines: 1) by controlling the curvature of surfactant aggregates using low molecular weight surfactant polymers, nanometer scale manipulation of the phase behavior is achieved; and 2) VES gels have been developed using a mixture of oppositely charged surfactants to create gels in these high-density brines. By varying the ratios of surfactants it is possible to control micellar growth and the gel-like behavior. The interactions between the surfactants makes it possible to control the curvature and self-assembly on a nanometer scale, allowing the creation of polymer-like VES systems. The result is a greater variety of surfactants available to create gels in high-density completion brines.

This paper details the laboratory work performed to develop VES packages for fluids ranging from freshwater to high-density completion brines. Extensive rheology experiments on several fluids show the viscoelasticity of these systems. The self-breaking nature of VES systems when in contact with hydrocarbons or exposed to a built-in breaker has also been demonstrated.
Mixing Hydrochloric Acid and Seawater for Matrix Acidizing: Is It a Good Practice?
Authors: He J. , Mohamed I. M. , Nasr-El-Din H. A.
Published: June 2011

In offshore operations where seawater is commonly used to prepare hydrochloric acid, calcium sulfate precipitation, the potential of which can greatly reduce the effectiveness of these treatments. This is because high concentreation of calcium produced in spent acid mixed with high level of sulfate in seawater. However, a few studies have provided evidence for this problem and the effect of calcium sulfate precipitation on acid treatments has not been fully examined.

In this work, core flood experiments at 0.5, 1, and 5 cm3/min flow rates were performed at 25°C to investigate formation damage due to calcium sulfate precipitation during matrix acidizing treatment. Austin Chalk cores (6 in. length and 1.5 in. diameter) with a permeability of 10 md and synthetic seawater were used. The core permeability before and after acid treatment, pressure drop response, calcium ion, sulfate ion, and pH values in the core effluent samples were measured. Solids collected in the core effluent samples were analyzed using XPS technique. Both acid prepared in seawater and in deionized water were examined.

Results showed that calcium sulfate precipitation occurred when seawater was used in any stage during matrix acidizing including preflush, post-flush, or in the main stage. Injection rate was the most important parameter that affected calcium sulfate precipitation; permeability reduction was significant at low flow rates, while at high rates wormhole breakthrough reduced the severity of the problem. This work confirms the damaging effect of preparing hydrochloric acid using seawater for acid treatments.